/ Check-in [f295e7ed]
Login

Many hyperlinks are disabled.
Use anonymous login to enable hyperlinks.

Overview
Comment:Merge the experimental shared-memory mmap-by-chunk changes into the trunk.
Downloads: Tarball | ZIP archive | SQL archive
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: f295e7ed5f04f6b8bffdaff8b565be3836ce4e80
User & Date: drh 2010-06-14 17:09:53
Context
2010-06-14
18:01
Move the xShmMap method to in between xShmLock and xShmBarrier, since it seems to fit in there logically. check-in: 58dfd83d user: drh tags: trunk
17:09
Merge the experimental shared-memory mmap-by-chunk changes into the trunk. check-in: f295e7ed user: drh tags: trunk
16:16
Add the new xShmMap (formerly xShmPage) to os_win.c. check-in: 13e7a824 user: dan tags: experimental
2010-06-11
17:01
Refactor and simplify the logic used to change journalmode. check-in: 95cc3f6f user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/os.c.

97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121









122
123
124
125
126
127
128
}
int sqlite3OsDeviceCharacteristics(sqlite3_file *id){
  return id->pMethods->xDeviceCharacteristics(id);
}
int sqlite3OsShmOpen(sqlite3_file *id){
  return id->pMethods->xShmOpen(id);
}
int sqlite3OsShmSize(sqlite3_file *id, int reqSize, int *pNewSize){
  return id->pMethods->xShmSize(id, reqSize, pNewSize);
}
int sqlite3OsShmGet(sqlite3_file *id,int reqSize,int *pSize,void volatile **pp){
  return id->pMethods->xShmGet(id, reqSize, pSize, pp);
}
int sqlite3OsShmRelease(sqlite3_file *id){
  return id->pMethods->xShmRelease(id);
}
int sqlite3OsShmLock(sqlite3_file *id, int offset, int n, int flags){
  return id->pMethods->xShmLock(id, offset, n, flags);
}
void sqlite3OsShmBarrier(sqlite3_file *id){
  id->pMethods->xShmBarrier(id);
}
int sqlite3OsShmClose(sqlite3_file *id, int deleteFlag){
  return id->pMethods->xShmClose(id, deleteFlag);
}










/*
** The next group of routines are convenience wrappers around the
** VFS methods.
*/
int sqlite3OsOpen(
  sqlite3_vfs *pVfs, 







<
<
<
<
<
<
<
<
<









>
>
>
>
>
>
>
>
>







97
98
99
100
101
102
103









104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
}
int sqlite3OsDeviceCharacteristics(sqlite3_file *id){
  return id->pMethods->xDeviceCharacteristics(id);
}
int sqlite3OsShmOpen(sqlite3_file *id){
  return id->pMethods->xShmOpen(id);
}









int sqlite3OsShmLock(sqlite3_file *id, int offset, int n, int flags){
  return id->pMethods->xShmLock(id, offset, n, flags);
}
void sqlite3OsShmBarrier(sqlite3_file *id){
  id->pMethods->xShmBarrier(id);
}
int sqlite3OsShmClose(sqlite3_file *id, int deleteFlag){
  return id->pMethods->xShmClose(id, deleteFlag);
}
int sqlite3OsShmMap(
  sqlite3_file *id, 
  int iPage, 
  int pgsz, 
  int isWrite, 
  void volatile **pp
){
  return id->pMethods->xShmMap(id, iPage, pgsz, isWrite, pp);
}

/*
** The next group of routines are convenience wrappers around the
** VFS methods.
*/
int sqlite3OsOpen(
  sqlite3_vfs *pVfs, 

Changes to src/os.h.

244
245
246
247
248
249
250
251
252
253
254
255
256

257
258
259
260
261
262
263
int sqlite3OsUnlock(sqlite3_file*, int);
int sqlite3OsCheckReservedLock(sqlite3_file *id, int *pResOut);
int sqlite3OsFileControl(sqlite3_file*,int,void*);
#define SQLITE_FCNTL_DB_UNCHANGED 0xca093fa0
int sqlite3OsSectorSize(sqlite3_file *id);
int sqlite3OsDeviceCharacteristics(sqlite3_file *id);
int sqlite3OsShmOpen(sqlite3_file *id);
int sqlite3OsShmSize(sqlite3_file *id, int, int*);
int sqlite3OsShmGet(sqlite3_file *id, int, int*, void volatile**);
int sqlite3OsShmRelease(sqlite3_file *id);
int sqlite3OsShmLock(sqlite3_file *id, int, int, int);
void sqlite3OsShmBarrier(sqlite3_file *id);
int sqlite3OsShmClose(sqlite3_file *id, int);


/* 
** Functions for accessing sqlite3_vfs methods 
*/
int sqlite3OsOpen(sqlite3_vfs *, const char *, sqlite3_file*, int, int *);
int sqlite3OsDelete(sqlite3_vfs *, const char *, int);
int sqlite3OsAccess(sqlite3_vfs *, const char *, int, int *pResOut);







<
<
<



>







244
245
246
247
248
249
250



251
252
253
254
255
256
257
258
259
260
261
int sqlite3OsUnlock(sqlite3_file*, int);
int sqlite3OsCheckReservedLock(sqlite3_file *id, int *pResOut);
int sqlite3OsFileControl(sqlite3_file*,int,void*);
#define SQLITE_FCNTL_DB_UNCHANGED 0xca093fa0
int sqlite3OsSectorSize(sqlite3_file *id);
int sqlite3OsDeviceCharacteristics(sqlite3_file *id);
int sqlite3OsShmOpen(sqlite3_file *id);



int sqlite3OsShmLock(sqlite3_file *id, int, int, int);
void sqlite3OsShmBarrier(sqlite3_file *id);
int sqlite3OsShmClose(sqlite3_file *id, int);
int sqlite3OsShmMap(sqlite3_file *,int,int,int,void volatile **);

/* 
** Functions for accessing sqlite3_vfs methods 
*/
int sqlite3OsOpen(sqlite3_vfs *, const char *, sqlite3_file*, int, int *);
int sqlite3OsDelete(sqlite3_vfs *, const char *, int);
int sqlite3OsAccess(sqlite3_vfs *, const char *, int, int *pResOut);

Changes to src/os_unix.c.

3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143

3144
3145
3146
3147
3148
3149
3150
3151
3152
....
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
....
3262
3263
3264
3265
3266
3267
3268

3269
3270
3271
3272



3273
3274
3275
3276
3277
3278
3279
....
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
....
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
....
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
....
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708






























3709

































































3710
3711
3712
3713
3714
3715
3716
3717

3718
3719
3720
3721
3722
3723
3724
....
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781

3782
3783
3784
3785
3786
3787
3788
** 
**      fid
**      zFilename
**
** Either unixShmNode.mutex must be held or unixShmNode.nRef==0 and
** unixMutexHeld() is true when reading or writing any other field
** in this structure.
**
** To avoid deadlocks, mutex and mutexBuf are always released in the
** reverse order that they are acquired.  mutexBuf is always acquired
** first and released last.  This invariant is check by asserting
** sqlite3_mutex_notheld() on mutex whenever mutexBuf is acquired or
** released.
*/
struct unixShmNode {
  unixInodeInfo *pInode;     /* unixInodeInfo that owns this SHM node */
  sqlite3_mutex *mutex;      /* Mutex to access this object */
  sqlite3_mutex *mutexBuf;   /* Mutex to access zBuf[] */
  char *zFilename;           /* Name of the mmapped file */
  int h;                     /* Open file descriptor */

  int szMap;                 /* Size of the mapping into memory */
  char *pMMapBuf;            /* Where currently mmapped().  NULL if unmapped */
  int nRef;                  /* Number of unixShm objects pointing to this */
  unixShm *pFirst;           /* All unixShm objects pointing to this */
#ifdef SQLITE_DEBUG
  u8 exclMask;               /* Mask of exclusive locks held */
  u8 sharedMask;             /* Mask of shared locks held */
  u8 nextShmId;              /* Next available unixShm.id value */
#endif
................................................................................
** All other fields are read/write.  The unixShm.pFile->mutex must be held
** while accessing any read/write fields.
*/
struct unixShm {
  unixShmNode *pShmNode;     /* The underlying unixShmNode object */
  unixShm *pNext;            /* Next unixShm with the same unixShmNode */
  u8 hasMutex;               /* True if holding the unixShmNode mutex */
  u8 hasMutexBuf;            /* True if holding pFile->mutexBuf */
  u16 sharedMask;            /* Mask of shared locks held */
  u16 exclMask;              /* Mask of exclusive locks held */
#ifdef SQLITE_DEBUG
  u8 id;                     /* Id of this connection within its unixShmNode */
#endif
};

................................................................................
** This is not a VFS shared-memory method; it is a utility function called
** by VFS shared-memory methods.
*/
static void unixShmPurge(unixFile *pFd){
  unixShmNode *p = pFd->pInode->pShmNode;
  assert( unixMutexHeld() );
  if( p && p->nRef==0 ){

    assert( p->pInode==pFd->pInode );
    if( p->mutex ) sqlite3_mutex_free(p->mutex);
    if( p->mutexBuf ) sqlite3_mutex_free(p->mutexBuf);
    if( p->pMMapBuf ) munmap(p->pMMapBuf, p->szMap);



    if( p->h>=0 ) close(p->h);
    p->pInode->pShmNode = 0;
    sqlite3_free(p);
  }
}

/* Forward reference */
................................................................................
    pDbFd->pInode->pShmNode = pShmNode;
    pShmNode->pInode = pDbFd->pInode;
    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }
    pShmNode->mutexBuf = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutexBuf==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }

    pShmNode->h = open(pShmNode->zFilename, O_RDWR|O_CREAT, 0664);
    if( pShmNode->h<0 ){
      rc = SQLITE_CANTOPEN_BKPT;
      goto shm_open_err;
    }

................................................................................
  /* Remove connection p from the set of connections associated
  ** with pShmNode */
  sqlite3_mutex_enter(pShmNode->mutex);
  for(pp=&pShmNode->pFirst; (*pp)!=p; pp = &(*pp)->pNext){}
  *pp = p->pNext;

  /* Free the connection p */
  assert( p->hasMutexBuf==0 );
  sqlite3_free(p);
  pDbFd->pShm = 0;
  sqlite3_mutex_leave(pShmNode->mutex);

  /* If pShmNode->nRef has reached 0, then close the underlying
  ** shared-memory file, too */
  unixEnterMutex();
................................................................................
    if( deleteFlag ) unlink(pShmNode->zFilename);
    unixShmPurge(pDbFd);
  }
  unixLeaveMutex();

  return SQLITE_OK;
}

/*
** Changes the size of the underlying storage for  a shared-memory segment.
**
** The reqSize parameter is the new requested size of the shared memory.
** This implementation is free to increase the shared memory size to
** any amount greater than or equal to reqSize.  If the shared memory is
** already as big or bigger as reqSize, this routine is a no-op.
**
** The reqSize parameter is the minimum size requested.  The implementation
** is free to expand the storage to some larger amount if it chooses.
*/
static int unixShmSize(
  sqlite3_file *fd,         /* The open database file holding SHM */
  int reqSize,              /* Requested size.  -1 for query only */
  int *pNewSize             /* Write new size here */
){
  unixFile *pDbFd = (unixFile*)fd;
  unixShm *p = pDbFd->pShm;
  unixShmNode *pShmNode = p->pShmNode;
  int rc = SQLITE_OK;
  struct stat sStat;

  assert( pShmNode==pDbFd->pInode->pShmNode );
  assert( pShmNode->pInode==pDbFd->pInode );

  while( 1 ){
    if( fstat(pShmNode->h, &sStat)==0 ){
      *pNewSize = (int)sStat.st_size;
      if( reqSize<=(int)sStat.st_size ) break;
    }else{
      *pNewSize = 0;
      rc = SQLITE_IOERR_SHMSIZE;
      break;
    }
    rc = ftruncate(pShmNode->h, reqSize);
    reqSize = -1;
  }
  return rc;
}

/*
** Release the lock held on the shared memory segment to that other
** threads are free to resize it if necessary.
**
** If the lock is not currently held, this routine is a harmless no-op.
**
** If the shared-memory object is in lock state RECOVER, then we do not
** really want to release the lock, so in that case too, this routine
** is a no-op.
*/
static int unixShmRelease(sqlite3_file *fd){
  unixFile *pDbFd = (unixFile*)fd;
  unixShm *p = pDbFd->pShm;

  if( p->hasMutexBuf ){
    assert( sqlite3_mutex_notheld(p->pShmNode->mutex) );
    sqlite3_mutex_leave(p->pShmNode->mutexBuf);
    p->hasMutexBuf = 0;
  }
  return SQLITE_OK;
}

/*
** Map the shared storage into memory. 
**
** If reqMapSize is positive, then an attempt is made to make the
** mapping at least reqMapSize bytes in size.  However, the mapping
** will never be larger than the size of the underlying shared memory
** as set by prior calls to xShmSize().  
**
** *ppBuf is made to point to the memory which is a mapping of the
** underlying storage.  A mutex is acquired to prevent other threads
** from running while *ppBuf is in use in order to prevent other threads
** remapping *ppBuf out from under this thread.  The unixShmRelease()
** call will release the mutex.  However, if the lock state is CHECKPOINT,
** the mutex is not acquired because CHECKPOINT will never remap the
** buffer.  RECOVER might remap, though, so CHECKPOINT will acquire
** the mutex if and when it promotes to RECOVER.
**
** RECOVER needs to be atomic.  The same mutex that prevents *ppBuf from
** being remapped also prevents more than one thread from being in
** RECOVER at a time.  But, RECOVER sometimes wants to remap itself.
** To prevent RECOVER from losing its lock while remapping, the
** mutex is not released by unixShmRelease() when in RECOVER.
**
** *pNewMapSize is set to the size of the mapping.  Usually *pNewMapSize
** will be reqMapSize or larger, though it could be smaller if the
** underlying shared memory has never been enlarged to reqMapSize bytes
** by prior calls to xShmSize().
**
** *ppBuf might be NULL and zero if no space has
** yet been allocated to the underlying storage.
*/
static int unixShmGet(
  sqlite3_file *fd,        /* Database file holding shared memory */
  int reqMapSize,          /* Requested size of mapping. -1 means don't care */
  int *pNewMapSize,        /* Write new size of mapping here */
  void volatile **ppBuf    /* Write mapping buffer origin here */
){
  unixFile *pDbFd = (unixFile*)fd;
  unixShm *p = pDbFd->pShm;
  unixShmNode *pShmNode = p->pShmNode;
  int rc = SQLITE_OK;

  assert( pShmNode==pDbFd->pInode->pShmNode );
  assert( pShmNode->pInode==pDbFd->pInode );

  if( p->hasMutexBuf==0 ){
    assert( sqlite3_mutex_notheld(pShmNode->mutex) );
    sqlite3_mutex_enter(pShmNode->mutexBuf);
    p->hasMutexBuf = 1;
  }
  sqlite3_mutex_enter(pShmNode->mutex);
  if( pShmNode->szMap==0 || reqMapSize>pShmNode->szMap ){
    int actualSize;
    if( unixShmSize(fd, -1, &actualSize)!=SQLITE_OK ){
      actualSize = 0;
    }
    reqMapSize = actualSize;
    if( pShmNode->pMMapBuf || reqMapSize<=0 ){
      munmap(pShmNode->pMMapBuf, pShmNode->szMap);
    }
    if( reqMapSize>0 ){
      pShmNode->pMMapBuf = mmap(0, reqMapSize, PROT_READ|PROT_WRITE, MAP_SHARED,
                             pShmNode->h, 0);
      pShmNode->szMap = pShmNode->pMMapBuf ? reqMapSize : 0;
    }else{
      pShmNode->pMMapBuf = 0;
      pShmNode->szMap = 0;
    }
  }
  *pNewMapSize = pShmNode->szMap;
  *ppBuf = pShmNode->pMMapBuf;
  sqlite3_mutex_leave(pShmNode->mutex);
  if( *ppBuf==0 ){
    /* Do not hold the mutex if a NULL pointer is being returned. */
    unixShmRelease(fd);
  }
  return rc;
}


/*
** Change the lock state for a shared-memory segment.
**
** Note that the relationship between SHAREd and EXCLUSIVE locks is a little
** different here than in posix.  In xShmLock(), one can go from unlocked
** to shared and back or from unlocked to exclusive and back.  But one may
................................................................................
/*
** Implement a memory barrier or memory fence on shared memory.  
**
** All loads and stores begun before the barrier must complete before
** any load or store begun after the barrier.
*/
static void unixShmBarrier(
  sqlite3_file *fd           /* Database file holding the shared memory */
){
  unixEnterMutex();
  unixLeaveMutex();
}

































































































#else
# define unixShmOpen    0
# define unixShmSize    0
# define unixShmGet     0
# define unixShmRelease 0
# define unixShmLock    0
# define unixShmBarrier 0
# define unixShmClose   0

#endif /* #ifndef SQLITE_OMIT_WAL */

/*
** Here ends the implementation of all sqlite3_file methods.
**
********************** End sqlite3_file Methods *******************************
******************************************************************************/
................................................................................
   LOCK,                       /* xLock */                                   \
   UNLOCK,                     /* xUnlock */                                 \
   CKLOCK,                     /* xCheckReservedLock */                      \
   unixFileControl,            /* xFileControl */                            \
   unixSectorSize,             /* xSectorSize */                             \
   unixDeviceCharacteristics,  /* xDeviceCapabilities */                     \
   unixShmOpen,                /* xShmOpen */                                \
   unixShmSize,                /* xShmSize */                                \
   unixShmGet,                 /* xShmGet */                                 \
   unixShmRelease,             /* xShmRelease */                             \
   unixShmLock,                /* xShmLock */                                \
   unixShmBarrier,             /* xShmBarrier */                             \
   unixShmClose                /* xShmClose */                               \

};                                                                           \
static const sqlite3_io_methods *FINDER##Impl(const char *z, unixFile *p){   \
  UNUSED_PARAMETER(z); UNUSED_PARAMETER(p);                                  \
  return &METHOD;                                                            \
}                                                                            \
static const sqlite3_io_methods *(*const FINDER)(const char*,unixFile *p)    \
    = FINDER##Impl;







<
<
<
<
<
<




<


>
|
|







 







<







 







>


<
|
>
>
>







 







<
<
<
<
<







 







<







 







<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<







 







|





>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>

>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>


<
<
<



>







 







<
<
<


|
>







3124
3125
3126
3127
3128
3129
3130






3131
3132
3133
3134

3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
....
3159
3160
3161
3162
3163
3164
3165

3166
3167
3168
3169
3170
3171
3172
....
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264

3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
....
3337
3338
3339
3340
3341
3342
3343





3344
3345
3346
3347
3348
3349
3350
....
3407
3408
3409
3410
3411
3412
3413

3414
3415
3416
3417
3418
3419
3420
....
3424
3425
3426
3427
3428
3429
3430














































































































































3431
3432
3433
3434
3435
3436
3437
....
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654



3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
....
3710
3711
3712
3713
3714
3715
3716



3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
** 
**      fid
**      zFilename
**
** Either unixShmNode.mutex must be held or unixShmNode.nRef==0 and
** unixMutexHeld() is true when reading or writing any other field
** in this structure.






*/
struct unixShmNode {
  unixInodeInfo *pInode;     /* unixInodeInfo that owns this SHM node */
  sqlite3_mutex *mutex;      /* Mutex to access this object */

  char *zFilename;           /* Name of the mmapped file */
  int h;                     /* Open file descriptor */
  int szRegion;              /* Size of shared-memory regions */
  int nRegion;               /* Size of array apRegion */
  char **apRegion;           /* Array of mapped shared-memory regions */
  int nRef;                  /* Number of unixShm objects pointing to this */
  unixShm *pFirst;           /* All unixShm objects pointing to this */
#ifdef SQLITE_DEBUG
  u8 exclMask;               /* Mask of exclusive locks held */
  u8 sharedMask;             /* Mask of shared locks held */
  u8 nextShmId;              /* Next available unixShm.id value */
#endif
................................................................................
** All other fields are read/write.  The unixShm.pFile->mutex must be held
** while accessing any read/write fields.
*/
struct unixShm {
  unixShmNode *pShmNode;     /* The underlying unixShmNode object */
  unixShm *pNext;            /* Next unixShm with the same unixShmNode */
  u8 hasMutex;               /* True if holding the unixShmNode mutex */

  u16 sharedMask;            /* Mask of shared locks held */
  u16 exclMask;              /* Mask of exclusive locks held */
#ifdef SQLITE_DEBUG
  u8 id;                     /* Id of this connection within its unixShmNode */
#endif
};

................................................................................
** This is not a VFS shared-memory method; it is a utility function called
** by VFS shared-memory methods.
*/
static void unixShmPurge(unixFile *pFd){
  unixShmNode *p = pFd->pInode->pShmNode;
  assert( unixMutexHeld() );
  if( p && p->nRef==0 ){
    int i;
    assert( p->pInode==pFd->pInode );
    if( p->mutex ) sqlite3_mutex_free(p->mutex);

    for(i=0; i<p->nRegion; i++){
      munmap(p->apRegion[i], p->szRegion);
    }
    sqlite3_free(p->apRegion);
    if( p->h>=0 ) close(p->h);
    p->pInode->pShmNode = 0;
    sqlite3_free(p);
  }
}

/* Forward reference */
................................................................................
    pDbFd->pInode->pShmNode = pShmNode;
    pShmNode->pInode = pDbFd->pInode;
    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }






    pShmNode->h = open(pShmNode->zFilename, O_RDWR|O_CREAT, 0664);
    if( pShmNode->h<0 ){
      rc = SQLITE_CANTOPEN_BKPT;
      goto shm_open_err;
    }

................................................................................
  /* Remove connection p from the set of connections associated
  ** with pShmNode */
  sqlite3_mutex_enter(pShmNode->mutex);
  for(pp=&pShmNode->pFirst; (*pp)!=p; pp = &(*pp)->pNext){}
  *pp = p->pNext;

  /* Free the connection p */

  sqlite3_free(p);
  pDbFd->pShm = 0;
  sqlite3_mutex_leave(pShmNode->mutex);

  /* If pShmNode->nRef has reached 0, then close the underlying
  ** shared-memory file, too */
  unixEnterMutex();
................................................................................
    if( deleteFlag ) unlink(pShmNode->zFilename);
    unixShmPurge(pDbFd);
  }
  unixLeaveMutex();

  return SQLITE_OK;
}















































































































































/*
** Change the lock state for a shared-memory segment.
**
** Note that the relationship between SHAREd and EXCLUSIVE locks is a little
** different here than in posix.  In xShmLock(), one can go from unlocked
** to shared and back or from unlocked to exclusive and back.  But one may
................................................................................
/*
** Implement a memory barrier or memory fence on shared memory.  
**
** All loads and stores begun before the barrier must complete before
** any load or store begun after the barrier.
*/
static void unixShmBarrier(
  sqlite3_file *fd                /* Database file holding the shared memory */
){
  unixEnterMutex();
  unixLeaveMutex();
}

/*
** This function is called to obtain a pointer to region iRegion of the 
** shared-memory associated with the database file fd. Shared-memory regions 
** are numbered starting from zero. Each shared-memory region is szRegion 
** bytes in size.
**
** If an error occurs, an error code is returned and *pp is set to NULL.
**
** Otherwise, if the isWrite parameter is 0 and the requested shared-memory
** region has not been allocated (by any client, including one running in a
** separate process), then *pp is set to NULL and SQLITE_OK returned. If 
** isWrite is non-zero and the requested shared-memory region has not yet 
** been allocated, it is allocated by this function.
**
** If the shared-memory region has already been allocated or is allocated by
** this call as described above, then it is mapped into this processes 
** address space (if it is not already), *pp is set to point to the mapped 
** memory and SQLITE_OK returned.
*/
static int unixShmMap(
  sqlite3_file *fd,               /* Handle open on database file */
  int iRegion,                    /* Region to retrieve */
  int szRegion,                   /* Size of regions */
  int isWrite,                    /* True to extend file if necessary */
  void volatile **pp              /* OUT: Mapped memory */
){
  unixFile *pDbFd = (unixFile*)fd;
  unixShm *p = pDbFd->pShm;
  unixShmNode *pShmNode = p->pShmNode;
  int rc = SQLITE_OK;

  sqlite3_mutex_enter(pShmNode->mutex);
  assert( szRegion==pShmNode->szRegion || pShmNode->nRegion==0 );

  if( pShmNode->nRegion<=iRegion ){
    char **apNew;                      /* New apRegion[] array */
    int nByte = (iRegion+1)*szRegion;  /* Minimum required file size */
    struct stat sStat;                 /* Used by fstat() */

    pShmNode->szRegion = szRegion;

    /* The requested region is not mapped into this processes address space.
    ** Check to see if it has been allocated (i.e. if the wal-index file is
    ** large enough to contain the requested region).
    */
    if( fstat(pShmNode->h, &sStat) ){
      rc = SQLITE_IOERR_SHMSIZE;
      goto shmpage_out;
    }

    if( sStat.st_size<nByte ){
      /* The requested memory region does not exist. If isWrite is set to
      ** zero, exit early. *pp will be set to NULL and SQLITE_OK returned.
      **
      ** Alternatively, if isWrite is non-zero, use ftruncate() to allocate
      ** the requested memory region.
      */
      if( !isWrite ) goto shmpage_out;
      if( ftruncate(pShmNode->h, nByte) ){
        rc = SQLITE_IOERR_SHMSIZE;
        goto shmpage_out;
      }  
    }

    /* Map the requested memory region into this processes address space. */
    apNew = (char **)sqlite3_realloc(
        pShmNode->apRegion, (iRegion+1)*sizeof(char *)
    );
    if( !apNew ){
      rc = SQLITE_IOERR_NOMEM;
      goto shmpage_out;
    }
    pShmNode->apRegion = apNew;
    while(pShmNode->nRegion<=iRegion){
      void *pMem = mmap(0, szRegion, PROT_READ|PROT_WRITE, 
          MAP_SHARED, pShmNode->h, iRegion*szRegion
      );
      if( pMem==MAP_FAILED ){
        rc = SQLITE_IOERR;
        goto shmpage_out;
      }
      pShmNode->apRegion[pShmNode->nRegion] = pMem;
      pShmNode->nRegion++;
    }
  }

shmpage_out:
  if( pShmNode->nRegion>iRegion ){
    *pp = pShmNode->apRegion[iRegion];
  }else{
    *pp = 0;
  }
  sqlite3_mutex_leave(pShmNode->mutex);
  return rc;
}

#else
# define unixShmOpen    0



# define unixShmLock    0
# define unixShmBarrier 0
# define unixShmClose   0
# define unixShmMap     0
#endif /* #ifndef SQLITE_OMIT_WAL */

/*
** Here ends the implementation of all sqlite3_file methods.
**
********************** End sqlite3_file Methods *******************************
******************************************************************************/
................................................................................
   LOCK,                       /* xLock */                                   \
   UNLOCK,                     /* xUnlock */                                 \
   CKLOCK,                     /* xCheckReservedLock */                      \
   unixFileControl,            /* xFileControl */                            \
   unixSectorSize,             /* xSectorSize */                             \
   unixDeviceCharacteristics,  /* xDeviceCapabilities */                     \
   unixShmOpen,                /* xShmOpen */                                \



   unixShmLock,                /* xShmLock */                                \
   unixShmBarrier,             /* xShmBarrier */                             \
   unixShmClose,               /* xShmClose */                               \
   unixShmMap                  /* xShmMap */                                 \
};                                                                           \
static const sqlite3_io_methods *FINDER##Impl(const char *z, unixFile *p){   \
  UNUSED_PARAMETER(z); UNUSED_PARAMETER(p);                                  \
  return &METHOD;                                                            \
}                                                                            \
static const sqlite3_io_methods *(*const FINDER)(const char*,unixFile *p)    \
    = FINDER##Impl;

Changes to src/os_win.c.

1212
1213
1214
1215
1216
1217
1218
1219
1220
1221




1222


1223
1224
1225

1226
1227
1228
1229
1230
1231
1232
....
1321
1322
1323
1324
1325
1326
1327

1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340

1341
1342
1343
1344
1345
1346
1347
....
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
....
1503
1504
1505
1506
1507
1508
1509
1510



1511
1512
1513
1514
1515
1516
1517
1518








1519
1520
1521
1522
1523




1524
1525
1526
1527
1528
1529
1530
1531






1532
1533
1534
1535
1536

1537
1538
1539




1540
1541
1542
1543
1544

1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555



1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585


1586

1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603





1604

1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619




1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638




1639
1640
1641
1642
1643


1644
1645



1646
1647
1648
1649

1650
1651
1652




1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
....
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764

1765
1766
1767
1768
1769
1770
1771
** reverse order that they are acquired.  mutexBuf is always acquired
** first and released last.  This invariant is check by asserting
** sqlite3_mutex_notheld() on mutex whenever mutexBuf is acquired or
** released.
*/
struct winShmNode {
  sqlite3_mutex *mutex;      /* Mutex to access this object */
  sqlite3_mutex *mutexBuf;   /* Mutex to access zBuf[] */
  char *zFilename;           /* Name of the file */
  winFile hFile;             /* File handle from winOpen */




  HANDLE hMap;               /* File handle from CreateFileMapping */


  DWORD lastErrno;           /* The Windows errno from the last I/O error */
  int szMap;                 /* Size of the mapping of file into memory */
  char *pMMapBuf;            /* Where currently mmapped().  NULL if unmapped */

  int nRef;                  /* Number of winShm objects pointing to this */
  winShm *pFirst;            /* All winShm objects pointing to this */
  winShmNode *pNext;         /* Next in list of all winShmNode objects */
#ifdef SQLITE_DEBUG
  u8 nextShmId;              /* Next available winShm.id value */
#endif
};
................................................................................
static void winShmPurge(sqlite3_vfs *pVfs, int deleteFlag){
  winShmNode **pp;
  winShmNode *p;
  assert( winShmMutexHeld() );
  pp = &winShmNodeList;
  while( (p = *pp)!=0 ){
    if( p->nRef==0 ){

      if( p->mutex ) sqlite3_mutex_free(p->mutex);
      if( p->mutexBuf ) sqlite3_mutex_free(p->mutexBuf);
      if( p->pMMapBuf ){
        UnmapViewOfFile(p->pMMapBuf);
      }
      if( INVALID_HANDLE_VALUE != p->hMap ){
        CloseHandle(p->hMap);
      }
      if( p->hFile.h != INVALID_HANDLE_VALUE ) {
        winClose((sqlite3_file *)&p->hFile);
      }
      if( deleteFlag ) winDelete(pVfs, p->zFilename, 0);
      *pp = p->pNext;

      sqlite3_free(p);
    }else{
      pp = &p->pNext;
    }
  }
}

................................................................................
    if( sqlite3StrICmp(pShmNode->zFilename, pNew->zFilename)==0 ) break;
  }
  if( pShmNode ){
    sqlite3_free(pNew);
  }else{
    pShmNode = pNew;
    pNew = 0;
    pShmNode->pMMapBuf = NULL;
    pShmNode->hMap = INVALID_HANDLE_VALUE;
    ((winFile*)(&pShmNode->hFile))->h = INVALID_HANDLE_VALUE;
    pShmNode->pNext = winShmNodeList;
    winShmNodeList = pShmNode;

    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }
    pShmNode->mutexBuf = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutexBuf==0 ){
      rc = SQLITE_NOMEM;
      goto shm_open_err;
    }
    rc = winOpen(pDbFd->pVfs,
                 pShmNode->zFilename,             /* Name of the file (UTF-8) */
                 (sqlite3_file*)&pShmNode->hFile,  /* File handle here */
                 SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, /* Mode flags */
                 0);
................................................................................
  }
  winShmLeaveMutex();

  return SQLITE_OK;
}

/*
** Increase the size of the underlying storage for a shared-memory segment.



**
** The reqSize parameter is the new requested minimum size of the underlying
** shared memory.  This routine may choose to make the shared memory larger
** than this value (for example to round the shared memory size up to an
** operating-system dependent page size.)
**
** This routine will only grow the size of shared memory.  A request for
** a smaller size is a no-op.








*/
static int winShmSize(
  sqlite3_file *fd,         /* Database holding the shared memory */
  int reqSize,              /* Requested size.  -1 for query only */
  int *pNewSize             /* Write new size here */




){
  winFile *pDbFd = (winFile*)fd;
  winShm *p = pDbFd->pShm;
  winShmNode *pShmNode = p->pShmNode;
  int rc = SQLITE_OK;

  *pNewSize = 0;
  if( reqSize>=0 ){






    sqlite3_int64 sz;
    rc = winFileSize((sqlite3_file *)&pShmNode->hFile, &sz);
    if( SQLITE_OK==rc && reqSize>sz ){
      rc = winTruncate((sqlite3_file *)&pShmNode->hFile, reqSize);
    }

  }
  if( SQLITE_OK==rc ){
    sqlite3_int64 sz;




    rc = winFileSize((sqlite3_file *)&pShmNode->hFile, &sz);
    if( SQLITE_OK==rc ){
      *pNewSize = (int)sz;
    }else{
      rc = SQLITE_IOERR;

    }
  }
  return rc;
}


/*
** Map the shared storage into memory.  The minimum size of the
** mapping should be reqMapSize if reqMapSize is positive.  If
** reqMapSize is zero or negative, the implementation can choose
** whatever mapping size is convenient.



**
** *ppBuf is made to point to the memory which is a mapping of the
** underlying storage.  A mutex is acquired to prevent other threads
** from running while *ppBuf is in use in order to prevent other threads
** remapping *ppBuf out from under this thread.  The winShmRelease()
** call will release the mutex.  However, if the lock state is CHECKPOINT,
** the mutex is not acquired because CHECKPOINT will never remap the
** buffer.  RECOVER might remap, though, so CHECKPOINT will acquire
** the mutex if and when it promotes to RECOVER.
**
** RECOVER needs to be atomic.  The same mutex that prevents *ppBuf from
** being remapped also prevents more than one thread from being in
** RECOVER at a time.  But, RECOVER sometimes wants to remap itself.
** To prevent RECOVER from losing its lock while remapping, the
** mutex is not released by winShmRelease() when in RECOVER.
**
** *pNewMapSize is set to the size of the mapping.
**
** *ppBuf and *pNewMapSize might be NULL and zero if no space has
** yet been allocated to the underlying storage.
*/
static int winShmGet(
  sqlite3_file *fd,        /* The database file holding the shared memory */
  int reqMapSize,          /* Requested size of mapping. -1 means don't care */
  int *pNewMapSize,        /* Write new size of mapping here */
  void volatile **ppBuf    /* Write mapping buffer origin here */
){
  winFile *pDbFd = (winFile*)fd;
  winShm *p = pDbFd->pShm;
  winShmNode *pShmNode = p->pShmNode;


  int rc = SQLITE_OK;


  if( p->hasMutexBuf==0 ){
    assert( sqlite3_mutex_notheld(pShmNode->mutex) );
    sqlite3_mutex_enter(pShmNode->mutexBuf);
    p->hasMutexBuf = 1;
  }
  sqlite3_mutex_enter(pShmNode->mutex);
  if( pShmNode->szMap==0 || reqMapSize>pShmNode->szMap ){
    int actualSize;
    if( winShmSize(fd, -1, &actualSize)==SQLITE_OK
     && reqMapSize<actualSize
    ){
      reqMapSize = actualSize;
    }
    if( pShmNode->pMMapBuf ){
      if( !UnmapViewOfFile(pShmNode->pMMapBuf) ){
        pShmNode->lastErrno = GetLastError();





        rc = SQLITE_IOERR;

      }
      CloseHandle(pShmNode->hMap);
      pShmNode->hMap = INVALID_HANDLE_VALUE;
    }
    if( SQLITE_OK == rc ){
      pShmNode->pMMapBuf = 0;
      if( reqMapSize == 0 ){
        /* can't create 0 byte file mapping in Windows */
        pShmNode->szMap = 0;
      }else{
        /* create the file mapping object */
        if( INVALID_HANDLE_VALUE == pShmNode->hMap ){
          /* TBD provide an object name to each file
          ** mapping so it can be re-used across processes.
          */




          pShmNode->hMap = CreateFileMapping(pShmNode->hFile.h,
                                          NULL,
                                          PAGE_READWRITE,
                                          0,
                                          reqMapSize,
                                          NULL);
        }
        if( NULL==pShmNode->hMap ){
          pShmNode->lastErrno = GetLastError();
          rc = SQLITE_IOERR;
          pShmNode->szMap = 0;
          pShmNode->hMap = INVALID_HANDLE_VALUE;
        }else{
          pShmNode->pMMapBuf = MapViewOfFile(pShmNode->hMap,
                                          FILE_MAP_WRITE | FILE_MAP_READ,
                                          0,
                                          0,
                                          reqMapSize);
          if( !pShmNode->pMMapBuf ){




            pShmNode->lastErrno = GetLastError();
            rc = SQLITE_IOERR;
            pShmNode->szMap = 0;
          }else{
            pShmNode->szMap = reqMapSize;


          }
        }



      }
    }
  }
  *pNewMapSize = pShmNode->szMap;

  *ppBuf = pShmNode->pMMapBuf;
  sqlite3_mutex_leave(pShmNode->mutex);
  return rc;




}

/*
** Release the lock held on the shared memory segment so that other
** threads are free to resize it if necessary.
**
** If the lock is not currently held, this routine is a harmless no-op.
**
** If the shared-memory object is in lock state RECOVER, then we do not
** really want to release the lock, so in that case too, this routine
** is a no-op.
*/
static int winShmRelease(sqlite3_file *fd){
  winFile *pDbFd = (winFile*)fd;
  winShm *p = pDbFd->pShm;
  if( p->hasMutexBuf ){
    winShmNode *pShmNode = p->pShmNode;
    assert( sqlite3_mutex_notheld(pShmNode->mutex) );
    sqlite3_mutex_leave(pShmNode->mutexBuf);
    p->hasMutexBuf = 0;
  }
  return SQLITE_OK;
}

/*
** Change the lock state for a shared-memory segment.
*/
static int winShmLock(
  sqlite3_file *fd,          /* Database file holding the shared memory */
  int ofst,                  /* First lock to acquire or release */
  int n,                     /* Number of locks to acquire or release */
................................................................................
  winLock,
  winUnlock,
  winCheckReservedLock,
  winFileControl,
  winSectorSize,
  winDeviceCharacteristics,
  winShmOpen,              /* xShmOpen */
  winShmSize,              /* xShmSize */
  winShmGet,               /* xShmGet */
  winShmRelease,           /* xShmRelease */
  winShmLock,              /* xShmLock */
  winShmBarrier,           /* xShmBarrier */
  winShmClose              /* xShmClose */

};

/***************************************************************************
** Here ends the I/O methods that form the sqlite3_io_methods object.
**
** The next block of code implements the VFS methods.
****************************************************************************/







<


>
>
>
>
|
>
>

<
<
>







 







>

<
|
|
<
<
|






>







 







<
<







<
<
<
<
<







 







|
>
>
>

<
<
<
|

|
|
>
>
>
>
>
>
>
>

|
|
<
<
>
>
>
>






<
<
>
>
>
>
>
>
|
<
<
<
|
>
|
<
<
>
>
>
>

|
<
<
<
>

|
<
<
<
<
<
<
<
<
<
>
>
>
|
<
<
<
<
<
<
|
|
<
<
<
<
<
<
<
<
<
<
<
|
<
<
<
<
<
<
<
<
<
>
>
|
>
|
<
<
<
<
|
<
<
<
<
<
<
<
|
<
<
<
>
>
>
>
>
|
>
|
|
<
|
<
<
<
<
<
<
<
<
<
<
<
>
>
>
>
|
<
|
<
<
|
<
|
<
<
<
<
<
<
|
<
<
<
<
>
>
>
>
|
|
<
<
<
>
>
|
|
>
>
>
|
|
|
<
>
|
<
<
>
>
>
>
|
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
|
<
<
|









 







<
<
<


|
>







1212
1213
1214
1215
1216
1217
1218

1219
1220
1221
1222
1223
1224
1225
1226
1227
1228


1229
1230
1231
1232
1233
1234
1235
1236
....
1325
1326
1327
1328
1329
1330
1331
1332
1333

1334
1335


1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
....
1403
1404
1405
1406
1407
1408
1409


1410
1411
1412
1413
1414
1415
1416





1417
1418
1419
1420
1421
1422
1423
....
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510



1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525


1526
1527
1528
1529
1530
1531
1532
1533
1534
1535


1536
1537
1538
1539
1540
1541
1542



1543
1544
1545


1546
1547
1548
1549
1550
1551



1552
1553
1554









1555
1556
1557
1558






1559
1560











1561









1562
1563
1564
1565
1566




1567







1568



1569
1570
1571
1572
1573
1574
1575
1576
1577

1578











1579
1580
1581
1582
1583

1584


1585

1586






1587




1588
1589
1590
1591
1592
1593



1594
1595
1596
1597
1598
1599
1600
1601
1602
1603

1604
1605


1606
1607
1608
1609
1610

















1611


1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
....
1690
1691
1692
1693
1694
1695
1696



1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
** reverse order that they are acquired.  mutexBuf is always acquired
** first and released last.  This invariant is check by asserting
** sqlite3_mutex_notheld() on mutex whenever mutexBuf is acquired or
** released.
*/
struct winShmNode {
  sqlite3_mutex *mutex;      /* Mutex to access this object */

  char *zFilename;           /* Name of the file */
  winFile hFile;             /* File handle from winOpen */

  int szRegion;              /* Size of shared-memory regions */
  int nRegion;               /* Size of array apRegion */
  struct ShmRegion {
    HANDLE hMap;             /* File handle from CreateFileMapping */
    void *pMap;
  } *aRegion;
  DWORD lastErrno;           /* The Windows errno from the last I/O error */



  int nRef;                  /* Number of winShm objects pointing to this */
  winShm *pFirst;            /* All winShm objects pointing to this */
  winShmNode *pNext;         /* Next in list of all winShmNode objects */
#ifdef SQLITE_DEBUG
  u8 nextShmId;              /* Next available winShm.id value */
#endif
};
................................................................................
static void winShmPurge(sqlite3_vfs *pVfs, int deleteFlag){
  winShmNode **pp;
  winShmNode *p;
  assert( winShmMutexHeld() );
  pp = &winShmNodeList;
  while( (p = *pp)!=0 ){
    if( p->nRef==0 ){
      int i;
      if( p->mutex ) sqlite3_mutex_free(p->mutex);

      for(i=0; i<p->nRegion; i++){
        UnmapViewOfFile(p->aRegion[i].pMap);


        CloseHandle(p->aRegion[i].hMap);
      }
      if( p->hFile.h != INVALID_HANDLE_VALUE ) {
        winClose((sqlite3_file *)&p->hFile);
      }
      if( deleteFlag ) winDelete(pVfs, p->zFilename, 0);
      *pp = p->pNext;
      sqlite3_free(p->aRegion);
      sqlite3_free(p);
    }else{
      pp = &p->pNext;
    }
  }
}

................................................................................
    if( sqlite3StrICmp(pShmNode->zFilename, pNew->zFilename)==0 ) break;
  }
  if( pShmNode ){
    sqlite3_free(pNew);
  }else{
    pShmNode = pNew;
    pNew = 0;


    ((winFile*)(&pShmNode->hFile))->h = INVALID_HANDLE_VALUE;
    pShmNode->pNext = winShmNodeList;
    winShmNodeList = pShmNode;

    pShmNode->mutex = sqlite3_mutex_alloc(SQLITE_MUTEX_FAST);
    if( pShmNode->mutex==0 ){
      rc = SQLITE_NOMEM;





      goto shm_open_err;
    }
    rc = winOpen(pDbFd->pVfs,
                 pShmNode->zFilename,             /* Name of the file (UTF-8) */
                 (sqlite3_file*)&pShmNode->hFile,  /* File handle here */
                 SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE, /* Mode flags */
                 0);
................................................................................
  }
  winShmLeaveMutex();

  return SQLITE_OK;
}

/*
** This function is called to obtain a pointer to region iRegion of the 
** shared-memory associated with the database file fd. Shared-memory regions 
** are numbered starting from zero. Each shared-memory region is szRegion 
** bytes in size.
**



** If an error occurs, an error code is returned and *pp is set to NULL.
**
** Otherwise, if the isWrite parameter is 0 and the requested shared-memory
** region has not been allocated (by any client, including one running in a
** separate process), then *pp is set to NULL and SQLITE_OK returned. If 
** isWrite is non-zero and the requested shared-memory region has not yet 
** been allocated, it is allocated by this function.
**
** If the shared-memory region has already been allocated or is allocated by
** this call as described above, then it is mapped into this processes 
** address space (if it is not already), *pp is set to point to the mapped 
** memory and SQLITE_OK returned.
*/
static int winShmMap(
  sqlite3_file *fd,               /* Handle open on database file */


  int iRegion,                    /* Region to retrieve */
  int szRegion,                   /* Size of regions */
  int isWrite,                    /* True to extend file if necessary */
  void volatile **pp              /* OUT: Mapped memory */
){
  winFile *pDbFd = (winFile*)fd;
  winShm *p = pDbFd->pShm;
  winShmNode *pShmNode = p->pShmNode;
  int rc = SQLITE_OK;



  sqlite3_mutex_enter(pShmNode->mutex);
  assert( szRegion==pShmNode->szRegion || pShmNode->nRegion==0 );

  if( pShmNode->nRegion<=iRegion ){
    struct ShmRegion *apNew;           /* New aRegion[] array */
    int nByte = (iRegion+1)*szRegion;  /* Minimum required file size */
    sqlite3_int64 sz;                  /* Current size of wal-index file */




    pShmNode->szRegion = szRegion;



    /* The requested region is not mapped into this processes address space.
    ** Check to see if it has been allocated (i.e. if the wal-index file is
    ** large enough to contain the requested region).
    */
    rc = winFileSize((sqlite3_file *)&pShmNode->hFile, &sz);
    if( rc!=SQLITE_OK ){



      goto shmpage_out;
    }










    if( sz<nByte ){
      /* The requested memory region does not exist. If isWrite is set to
      ** zero, exit early. *pp will be set to NULL and SQLITE_OK returned.
      **






      ** Alternatively, if isWrite is non-zero, use ftruncate() to allocate
      ** the requested memory region.











      */









      if( !isWrite ) goto shmpage_out;
      rc = winTruncate((sqlite3_file *)&pShmNode->hFile, nByte);
      if( rc!=SQLITE_OK ){
        goto shmpage_out;
      }




    }











    /* Map the requested memory region into this processes address space. */
    apNew = (struct ShmRegion *)sqlite3_realloc(
        pShmNode->aRegion, (iRegion+1)*sizeof(apNew[0])
    );
    if( !apNew ){
      rc = SQLITE_IOERR_NOMEM;
      goto shmpage_out;
    }
    pShmNode->aRegion = apNew;













    while( pShmNode->nRegion<=iRegion ){
      HANDLE hMap;                /* file-mapping handle */
      void *pMap = 0;             /* Mapped memory region */
     
      hMap = CreateFileMapping(pShmNode->hFile.h, 

          NULL, PAGE_READWRITE, 0, nByte, NULL


      );

      if( hMap ){






        pMap = MapViewOfFile(hMap, FILE_MAP_WRITE | FILE_MAP_READ,




            0, 0, nByte
        );
      }
      if( !pMap ){
        pShmNode->lastErrno = GetLastError();
        rc = SQLITE_IOERR;



        if( hMap ) CloseHandle(hMap);
        goto shmpage_out;
      }

      pShmNode->aRegion[pShmNode->nRegion].pMap = pMap;
      pShmNode->aRegion[pShmNode->nRegion].hMap = hMap;
      pShmNode->nRegion++;
    }
  }


shmpage_out:
  if( pShmNode->nRegion>iRegion ){


    char *p = (char *)pShmNode->aRegion[iRegion].pMap;
    *pp = (void *)&p[iRegion*szRegion];
  }else{
    *pp = 0;
  }

















  sqlite3_mutex_leave(pShmNode->mutex);


  return rc;
}

/*
** Change the lock state for a shared-memory segment.
*/
static int winShmLock(
  sqlite3_file *fd,          /* Database file holding the shared memory */
  int ofst,                  /* First lock to acquire or release */
  int n,                     /* Number of locks to acquire or release */
................................................................................
  winLock,
  winUnlock,
  winCheckReservedLock,
  winFileControl,
  winSectorSize,
  winDeviceCharacteristics,
  winShmOpen,              /* xShmOpen */



  winShmLock,              /* xShmLock */
  winShmBarrier,           /* xShmBarrier */
  winShmClose,             /* xShmClose */
  winShmMap                /* xShmMap */
};

/***************************************************************************
** Here ends the I/O methods that form the sqlite3_io_methods object.
**
** The next block of code implements the VFS methods.
****************************************************************************/

Changes to src/sqlite.h.in.

656
657
658
659
660
661
662
663
664
665
666
667
668

669
670
671
672
673
674
675
  int (*xUnlock)(sqlite3_file*, int);
  int (*xCheckReservedLock)(sqlite3_file*, int *pResOut);
  int (*xFileControl)(sqlite3_file*, int op, void *pArg);
  int (*xSectorSize)(sqlite3_file*);
  int (*xDeviceCharacteristics)(sqlite3_file*);
  /* Methods above are valid for version 1 */
  int (*xShmOpen)(sqlite3_file*);
  int (*xShmSize)(sqlite3_file*, int reqSize, int *pNewSize);
  int (*xShmGet)(sqlite3_file*, int reqSize, int *pSize, void volatile**);
  int (*xShmRelease)(sqlite3_file*);
  int (*xShmLock)(sqlite3_file*, int offset, int n, int flags);
  void (*xShmBarrier)(sqlite3_file*);
  int (*xShmClose)(sqlite3_file*, int deleteFlag);

  /* Methods above are valid for version 2 */
  /* Additional methods may be added in future releases */
};

/*
** CAPI3REF: Standard File Control Opcodes
**







<
<
<



>







656
657
658
659
660
661
662



663
664
665
666
667
668
669
670
671
672
673
  int (*xUnlock)(sqlite3_file*, int);
  int (*xCheckReservedLock)(sqlite3_file*, int *pResOut);
  int (*xFileControl)(sqlite3_file*, int op, void *pArg);
  int (*xSectorSize)(sqlite3_file*);
  int (*xDeviceCharacteristics)(sqlite3_file*);
  /* Methods above are valid for version 1 */
  int (*xShmOpen)(sqlite3_file*);



  int (*xShmLock)(sqlite3_file*, int offset, int n, int flags);
  void (*xShmBarrier)(sqlite3_file*);
  int (*xShmClose)(sqlite3_file*, int deleteFlag);
  int (*xShmMap)(sqlite3_file*, int iPage, int pgsz, int, void volatile**);
  /* Methods above are valid for version 2 */
  /* Additional methods may be added in future releases */
};

/*
** CAPI3REF: Standard File Control Opcodes
**

Changes to src/test6.c.

522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551








552
553
554
555
556
557
558
559
...
562
563
564
565
566
567
568
569
570
571
572
573
574

575
576
577
578
579
580
581

/*
** Pass-throughs for WAL support.
*/
static int cfShmOpen(sqlite3_file *pFile){
  return sqlite3OsShmOpen(((CrashFile*)pFile)->pRealFile);
}
static int cfShmSize(sqlite3_file *pFile, int reqSize, int *pNew){
  return sqlite3OsShmSize(((CrashFile*)pFile)->pRealFile, reqSize, pNew);
}
static int cfShmGet(
  sqlite3_file *pFile,
  int reqSize,
  int *pSize,
  void volatile **pp
){
  return sqlite3OsShmGet(((CrashFile*)pFile)->pRealFile, reqSize, pSize, pp);
}
static int cfShmRelease(sqlite3_file *pFile){
  return sqlite3OsShmRelease(((CrashFile*)pFile)->pRealFile);
}
static int cfShmLock(sqlite3_file *pFile, int ofst, int n, int flags){
  return sqlite3OsShmLock(((CrashFile*)pFile)->pRealFile, ofst, n, flags);
}
static void cfShmBarrier(sqlite3_file *pFile){
  sqlite3OsShmBarrier(((CrashFile*)pFile)->pRealFile);
}
static int cfShmClose(sqlite3_file *pFile, int delFlag){
  return sqlite3OsShmClose(((CrashFile*)pFile)->pRealFile, delFlag);
}










static const sqlite3_io_methods CrashFileVtab = {
  2,                            /* iVersion */
  cfClose,                      /* xClose */
  cfRead,                       /* xRead */
  cfWrite,                      /* xWrite */
  cfTruncate,                   /* xTruncate */
................................................................................
  cfLock,                       /* xLock */
  cfUnlock,                     /* xUnlock */
  cfCheckReservedLock,          /* xCheckReservedLock */
  cfFileControl,                /* xFileControl */
  cfSectorSize,                 /* xSectorSize */
  cfDeviceCharacteristics,      /* xDeviceCharacteristics */
  cfShmOpen,                    /* xShmOpen */
  cfShmSize,                    /* xShmSize */
  cfShmGet,                     /* xShmGet */
  cfShmRelease,                 /* xShmRelease */
  cfShmLock,                    /* xShmLock */
  cfShmBarrier,                 /* xShmBarrier */
  cfShmClose                    /* xShmClose */

};

/*
** Application data for the crash VFS
*/
struct crashAppData {
  sqlite3_vfs *pOrig;                   /* Wrapped vfs structure */







<
<
<
<
<
<
<
<
<
<
<
<
<
<









>
>
>
>
>
>
>
>
|







 







<
<
<


|
>







522
523
524
525
526
527
528














529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
...
556
557
558
559
560
561
562



563
564
565
566
567
568
569
570
571
572
573

/*
** Pass-throughs for WAL support.
*/
static int cfShmOpen(sqlite3_file *pFile){
  return sqlite3OsShmOpen(((CrashFile*)pFile)->pRealFile);
}














static int cfShmLock(sqlite3_file *pFile, int ofst, int n, int flags){
  return sqlite3OsShmLock(((CrashFile*)pFile)->pRealFile, ofst, n, flags);
}
static void cfShmBarrier(sqlite3_file *pFile){
  sqlite3OsShmBarrier(((CrashFile*)pFile)->pRealFile);
}
static int cfShmClose(sqlite3_file *pFile, int delFlag){
  return sqlite3OsShmClose(((CrashFile*)pFile)->pRealFile, delFlag);
}
static int cfShmMap(
  sqlite3_file *pFile,            /* Handle open on database file */
  int iRegion,                    /* Region to retrieve */
  int sz,                         /* Size of regions */
  int w,                          /* True to extend file if necessary */
  void volatile **pp              /* OUT: Mapped memory */
){
  return sqlite3OsShmMap(((CrashFile*)pFile)->pRealFile, iRegion, sz, w, pp);
}

static const sqlite3_io_methods CrashFileVtab = {
  2,                            /* iVersion */
  cfClose,                      /* xClose */
  cfRead,                       /* xRead */
  cfWrite,                      /* xWrite */
  cfTruncate,                   /* xTruncate */
................................................................................
  cfLock,                       /* xLock */
  cfUnlock,                     /* xUnlock */
  cfCheckReservedLock,          /* xCheckReservedLock */
  cfFileControl,                /* xFileControl */
  cfSectorSize,                 /* xSectorSize */
  cfDeviceCharacteristics,      /* xDeviceCharacteristics */
  cfShmOpen,                    /* xShmOpen */



  cfShmLock,                    /* xShmLock */
  cfShmBarrier,                 /* xShmBarrier */
  cfShmClose,                   /* xShmClose */
  cfShmMap                      /* xShmMap */
};

/*
** Application data for the crash VFS
*/
struct crashAppData {
  sqlite3_vfs *pOrig;                   /* Wrapped vfs structure */

Changes to src/test_devsym.c.

47
48
49
50
51
52
53
54
55
56
57
58
59

60
61
62
63
64
65
66
...
116
117
118
119
120
121
122
123
124
125
126
127
128

129
130
131
132
133
134
135
...
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277










278
279
280
281
282
283
284
static int devsymLock(sqlite3_file*, int);
static int devsymUnlock(sqlite3_file*, int);
static int devsymCheckReservedLock(sqlite3_file*, int *);
static int devsymFileControl(sqlite3_file*, int op, void *pArg);
static int devsymSectorSize(sqlite3_file*);
static int devsymDeviceCharacteristics(sqlite3_file*);
static int devsymShmOpen(sqlite3_file*);
static int devsymShmSize(sqlite3_file*,int,int*);
static int devsymShmGet(sqlite3_file*,int,int*,volatile void**);
static int devsymShmRelease(sqlite3_file*);
static int devsymShmLock(sqlite3_file*,int,int,int);
static void devsymShmBarrier(sqlite3_file*);
static int devsymShmClose(sqlite3_file*,int);


/*
** Method declarations for devsym_vfs.
*/
static int devsymOpen(sqlite3_vfs*, const char *, sqlite3_file*, int , int *);
static int devsymDelete(sqlite3_vfs*, const char *zName, int syncDir);
static int devsymAccess(sqlite3_vfs*, const char *zName, int flags, int *);
................................................................................
  devsymLock,                       /* xLock */
  devsymUnlock,                     /* xUnlock */
  devsymCheckReservedLock,          /* xCheckReservedLock */
  devsymFileControl,                /* xFileControl */
  devsymSectorSize,                 /* xSectorSize */
  devsymDeviceCharacteristics,      /* xDeviceCharacteristics */
  devsymShmOpen,                    /* xShmOpen */
  devsymShmSize,                    /* xShmSize */
  devsymShmGet,                     /* xShmGet */
  devsymShmRelease,                 /* xShmRelease */
  devsymShmLock,                    /* xShmLock */
  devsymShmBarrier,                 /* xShmBarrier */
  devsymShmClose                    /* xShmClose */

};

struct DevsymGlobal {
  sqlite3_vfs *pVfs;
  int iDeviceChar;
  int iSectorSize;
};
................................................................................
/*
** Shared-memory methods are all pass-thrus.
*/
static int devsymShmOpen(sqlite3_file *pFile){
  devsym_file *p = (devsym_file *)pFile;
  return sqlite3OsShmOpen(p->pReal);
}
static int devsymShmSize(sqlite3_file *pFile, int reqSize, int *pSize){
  devsym_file *p = (devsym_file *)pFile;
  return sqlite3OsShmSize(p->pReal, reqSize, pSize);
}
static int devsymShmGet(
  sqlite3_file *pFile,
  int reqSz,
  int *pSize,
  void volatile **pp
){
  devsym_file *p = (devsym_file *)pFile;
  return sqlite3OsShmGet(p->pReal, reqSz, pSize, pp);
}
static int devsymShmRelease(sqlite3_file *pFile){
  devsym_file *p = (devsym_file *)pFile;
  return sqlite3OsShmRelease(p->pReal);
}
static int devsymShmLock(sqlite3_file *pFile, int ofst, int n, int flags){
  devsym_file *p = (devsym_file *)pFile;
  return sqlite3OsShmLock(p->pReal, ofst, n, flags);
}
static void devsymShmBarrier(sqlite3_file *pFile){
  devsym_file *p = (devsym_file *)pFile;
  sqlite3OsShmBarrier(p->pReal);
}
static int devsymShmClose(sqlite3_file *pFile, int delFlag){
  devsym_file *p = (devsym_file *)pFile;
  return sqlite3OsShmClose(p->pReal, delFlag);
}













/*
** Open an devsym file handle.
*/
static int devsymOpen(







<
<
<



>







 







<
<
<


|
>







 







<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<












>
>
>
>
>
>
>
>
>
>







47
48
49
50
51
52
53



54
55
56
57
58
59
60
61
62
63
64
...
114
115
116
117
118
119
120



121
122
123
124
125
126
127
128
129
130
131
...
238
239
240
241
242
243
244

















245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
static int devsymLock(sqlite3_file*, int);
static int devsymUnlock(sqlite3_file*, int);
static int devsymCheckReservedLock(sqlite3_file*, int *);
static int devsymFileControl(sqlite3_file*, int op, void *pArg);
static int devsymSectorSize(sqlite3_file*);
static int devsymDeviceCharacteristics(sqlite3_file*);
static int devsymShmOpen(sqlite3_file*);



static int devsymShmLock(sqlite3_file*,int,int,int);
static void devsymShmBarrier(sqlite3_file*);
static int devsymShmClose(sqlite3_file*,int);
static int devsymShmMap(sqlite3_file*,int,int,int, void volatile **);

/*
** Method declarations for devsym_vfs.
*/
static int devsymOpen(sqlite3_vfs*, const char *, sqlite3_file*, int , int *);
static int devsymDelete(sqlite3_vfs*, const char *zName, int syncDir);
static int devsymAccess(sqlite3_vfs*, const char *zName, int flags, int *);
................................................................................
  devsymLock,                       /* xLock */
  devsymUnlock,                     /* xUnlock */
  devsymCheckReservedLock,          /* xCheckReservedLock */
  devsymFileControl,                /* xFileControl */
  devsymSectorSize,                 /* xSectorSize */
  devsymDeviceCharacteristics,      /* xDeviceCharacteristics */
  devsymShmOpen,                    /* xShmOpen */



  devsymShmLock,                    /* xShmLock */
  devsymShmBarrier,                 /* xShmBarrier */
  devsymShmClose,                   /* xShmClose */
  devsymShmMap                     /* xShmMap */
};

struct DevsymGlobal {
  sqlite3_vfs *pVfs;
  int iDeviceChar;
  int iSectorSize;
};
................................................................................
/*
** Shared-memory methods are all pass-thrus.
*/
static int devsymShmOpen(sqlite3_file *pFile){
  devsym_file *p = (devsym_file *)pFile;
  return sqlite3OsShmOpen(p->pReal);
}

















static int devsymShmLock(sqlite3_file *pFile, int ofst, int n, int flags){
  devsym_file *p = (devsym_file *)pFile;
  return sqlite3OsShmLock(p->pReal, ofst, n, flags);
}
static void devsymShmBarrier(sqlite3_file *pFile){
  devsym_file *p = (devsym_file *)pFile;
  sqlite3OsShmBarrier(p->pReal);
}
static int devsymShmClose(sqlite3_file *pFile, int delFlag){
  devsym_file *p = (devsym_file *)pFile;
  return sqlite3OsShmClose(p->pReal, delFlag);
}
static int devsymShmMap(
  sqlite3_file *pFile, 
  int iRegion, 
  int szRegion, 
  int isWrite, 
  void volatile **pp
){
  devsym_file *p = (devsym_file *)pFile;
  return sqlite3OsShmMap(p->pReal, iRegion, szRegion, isWrite, pp);
}



/*
** Open an devsym file handle.
*/
static int devsymOpen(

Changes to src/test_osinst.c.

96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
...
148
149
150
151
152
153
154
155
156
157
158
159
160

161
162
163
164
165
166
167
...
212
213
214
215
216
217
218
219
220
221
222
223
224

225
226
227
228
229
230
231
...
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
...
499
500
501
502
503
504
505
















506
507
508
509
510
511
512
...
822
823
824
825
826
827
828
829
830
831
832
833

834
835
836
837
838
839
840
#define OS_SLEEP             16
#define OS_SYNC              17
#define OS_TRUNCATE          18
#define OS_UNLOCK            19
#define OS_WRITE             20
#define OS_SHMOPEN           21
#define OS_SHMCLOSE          22
#define OS_SHMGET            23
#define OS_SHMRELEASE        24
#define OS_SHMLOCK           25
#define OS_SHMBARRIER        26
#define OS_SHMSIZE           27
#define OS_ANNOTATE          28

#define OS_NUMEVENTS         29

#define VFSLOG_BUFFERSIZE 8192

typedef struct VfslogVfs VfslogVfs;
................................................................................
static int vfslogUnlock(sqlite3_file*, int);
static int vfslogCheckReservedLock(sqlite3_file*, int *pResOut);
static int vfslogFileControl(sqlite3_file*, int op, void *pArg);
static int vfslogSectorSize(sqlite3_file*);
static int vfslogDeviceCharacteristics(sqlite3_file*);

static int vfslogShmOpen(sqlite3_file *pFile);
static int vfslogShmSize(sqlite3_file *pFile, int reqSize, int *pNewSize);
static int vfslogShmGet(sqlite3_file *pFile, int,int*,volatile void **);
static int vfslogShmRelease(sqlite3_file *pFile);
static int vfslogShmLock(sqlite3_file *pFile, int ofst, int n, int flags);
static void vfslogShmBarrier(sqlite3_file*);
static int vfslogShmClose(sqlite3_file *pFile, int deleteFlag);


/*
** Method declarations for vfslog_vfs.
*/
static int vfslogOpen(sqlite3_vfs*, const char *, sqlite3_file*, int , int *);
static int vfslogDelete(sqlite3_vfs*, const char *zName, int syncDir);
static int vfslogAccess(sqlite3_vfs*, const char *zName, int flags, int *);
................................................................................
  vfslogLock,                     /* xLock */
  vfslogUnlock,                   /* xUnlock */
  vfslogCheckReservedLock,        /* xCheckReservedLock */
  vfslogFileControl,              /* xFileControl */
  vfslogSectorSize,               /* xSectorSize */
  vfslogDeviceCharacteristics,    /* xDeviceCharacteristics */
  vfslogShmOpen,                  /* xShmOpen */
  vfslogShmSize,                  /* xShmSize */
  vfslogShmGet,                   /* xShmGet */
  vfslogShmRelease,               /* xShmRelease */
  vfslogShmLock,                  /* xShmLock */
  vfslogShmBarrier,               /* xShmBarrier */
  vfslogShmClose                  /* xShmClose */

};

#if defined(SQLITE_OS_UNIX) && !defined(NO_GETTOD)
#include <sys/time.h>
static sqlite3_uint64 vfslog_time(){
  struct timeval sTime;
  gettimeofday(&sTime, 0);
................................................................................
  VfslogFile *p = (VfslogFile *)pFile;
  t = vfslog_time();
  rc = p->pReal->pMethods->xShmOpen(p->pReal);
  t = vfslog_time() - t;
  vfslog_call(p->pVfslog, OS_SHMOPEN, p->iFileId, t, rc, 0, 0);
  return rc;
}
static int vfslogShmSize(sqlite3_file *pFile, int reqSize, int *pNewSize){
  int rc;
  sqlite3_uint64 t;
  VfslogFile *p = (VfslogFile *)pFile;
  t = vfslog_time();
  rc = p->pReal->pMethods->xShmSize(p->pReal, reqSize, pNewSize);
  t = vfslog_time() - t;
  vfslog_call(p->pVfslog, OS_SHMSIZE, p->iFileId, t, rc, 0, 0);
  return rc;
}
static int vfslogShmGet(
  sqlite3_file *pFile,
  int req,
  int *pSize,
  volatile void **pp
){
  int rc;
  sqlite3_uint64 t;
  VfslogFile *p = (VfslogFile *)pFile;
  t = vfslog_time();
  rc = p->pReal->pMethods->xShmGet(p->pReal, req, pSize, pp);
  t = vfslog_time() - t;
  vfslog_call(p->pVfslog, OS_SHMGET, p->iFileId, t, rc, 0, 0);
  return rc;
}
static int vfslogShmRelease(sqlite3_file *pFile){
  int rc;
  sqlite3_uint64 t;
  VfslogFile *p = (VfslogFile *)pFile;
  t = vfslog_time();
  rc = p->pReal->pMethods->xShmRelease(p->pReal);
  t = vfslog_time() - t;
  vfslog_call(p->pVfslog, OS_SHMRELEASE, p->iFileId, t, rc, 0, 0);
  return rc;
}
static int vfslogShmLock(sqlite3_file *pFile, int ofst, int n, int flags){
  int rc;
  sqlite3_uint64 t;
  VfslogFile *p = (VfslogFile *)pFile;
  t = vfslog_time();
  rc = p->pReal->pMethods->xShmLock(p->pReal, ofst, n, flags);
  t = vfslog_time() - t;
................................................................................
  sqlite3_uint64 t;
  VfslogFile *p = (VfslogFile *)pFile;
  t = vfslog_time();
  rc = p->pReal->pMethods->xShmClose(p->pReal, deleteFlag);
  t = vfslog_time() - t;
  vfslog_call(p->pVfslog, OS_SHMCLOSE, p->iFileId, t, rc, 0, 0);
  return rc;
















}


/*
** Open an vfslog file handle.
*/
static int vfslogOpen(
................................................................................
    case OS_FULLPATHNAME:      zEvent = "xFullPathname"; break;
    case OS_RANDOMNESS:        zEvent = "xRandomness"; break;
    case OS_SLEEP:             zEvent = "xSleep"; break;
    case OS_CURRENTTIME:       zEvent = "xCurrentTime"; break;

    case OS_SHMCLOSE:          zEvent = "xShmClose"; break;
    case OS_SHMOPEN:           zEvent = "xShmOpen"; break;
    case OS_SHMGET:            zEvent = "xShmGet"; break;
    case OS_SHMSIZE:           zEvent = "xShmSize"; break;
    case OS_SHMRELEASE:        zEvent = "xShmRelease"; break;
    case OS_SHMLOCK:           zEvent = "xShmLock"; break;
    case OS_SHMBARRIER:        zEvent = "xShmBarrier"; break;


    case OS_ANNOTATE:          zEvent = "annotation"; break;
  }

  return zEvent;
}








|
<


<







 







<
<
<



>







 







<
<
<


|
>







 







<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<







 







>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>







 







<
<
<


>







96
97
98
99
100
101
102
103

104
105

106
107
108
109
110
111
112
...
146
147
148
149
150
151
152



153
154
155
156
157
158
159
160
161
162
163
...
208
209
210
211
212
213
214



215
216
217
218
219
220
221
222
223
224
225
...
431
432
433
434
435
436
437



































438
439
440
441
442
443
444
...
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
...
797
798
799
800
801
802
803



804
805
806
807
808
809
810
811
812
813
#define OS_SLEEP             16
#define OS_SYNC              17
#define OS_TRUNCATE          18
#define OS_UNLOCK            19
#define OS_WRITE             20
#define OS_SHMOPEN           21
#define OS_SHMCLOSE          22
#define OS_SHMMAP            23

#define OS_SHMLOCK           25
#define OS_SHMBARRIER        26

#define OS_ANNOTATE          28

#define OS_NUMEVENTS         29

#define VFSLOG_BUFFERSIZE 8192

typedef struct VfslogVfs VfslogVfs;
................................................................................
static int vfslogUnlock(sqlite3_file*, int);
static int vfslogCheckReservedLock(sqlite3_file*, int *pResOut);
static int vfslogFileControl(sqlite3_file*, int op, void *pArg);
static int vfslogSectorSize(sqlite3_file*);
static int vfslogDeviceCharacteristics(sqlite3_file*);

static int vfslogShmOpen(sqlite3_file *pFile);



static int vfslogShmLock(sqlite3_file *pFile, int ofst, int n, int flags);
static void vfslogShmBarrier(sqlite3_file*);
static int vfslogShmClose(sqlite3_file *pFile, int deleteFlag);
static int vfslogShmMap(sqlite3_file *pFile,int,int,int,volatile void **);

/*
** Method declarations for vfslog_vfs.
*/
static int vfslogOpen(sqlite3_vfs*, const char *, sqlite3_file*, int , int *);
static int vfslogDelete(sqlite3_vfs*, const char *zName, int syncDir);
static int vfslogAccess(sqlite3_vfs*, const char *zName, int flags, int *);
................................................................................
  vfslogLock,                     /* xLock */
  vfslogUnlock,                   /* xUnlock */
  vfslogCheckReservedLock,        /* xCheckReservedLock */
  vfslogFileControl,              /* xFileControl */
  vfslogSectorSize,               /* xSectorSize */
  vfslogDeviceCharacteristics,    /* xDeviceCharacteristics */
  vfslogShmOpen,                  /* xShmOpen */



  vfslogShmLock,                  /* xShmLock */
  vfslogShmBarrier,               /* xShmBarrier */
  vfslogShmClose,                 /* xShmClose */
  vfslogShmMap                    /* xShmMap */
};

#if defined(SQLITE_OS_UNIX) && !defined(NO_GETTOD)
#include <sys/time.h>
static sqlite3_uint64 vfslog_time(){
  struct timeval sTime;
  gettimeofday(&sTime, 0);
................................................................................
  VfslogFile *p = (VfslogFile *)pFile;
  t = vfslog_time();
  rc = p->pReal->pMethods->xShmOpen(p->pReal);
  t = vfslog_time() - t;
  vfslog_call(p->pVfslog, OS_SHMOPEN, p->iFileId, t, rc, 0, 0);
  return rc;
}



































static int vfslogShmLock(sqlite3_file *pFile, int ofst, int n, int flags){
  int rc;
  sqlite3_uint64 t;
  VfslogFile *p = (VfslogFile *)pFile;
  t = vfslog_time();
  rc = p->pReal->pMethods->xShmLock(p->pReal, ofst, n, flags);
  t = vfslog_time() - t;
................................................................................
  sqlite3_uint64 t;
  VfslogFile *p = (VfslogFile *)pFile;
  t = vfslog_time();
  rc = p->pReal->pMethods->xShmClose(p->pReal, deleteFlag);
  t = vfslog_time() - t;
  vfslog_call(p->pVfslog, OS_SHMCLOSE, p->iFileId, t, rc, 0, 0);
  return rc;
}
static int vfslogShmMap(
  sqlite3_file *pFile, 
  int iRegion, 
  int szRegion, 
  int isWrite, 
  volatile void **pp
){
  int rc;
  sqlite3_uint64 t;
  VfslogFile *p = (VfslogFile *)pFile;
  t = vfslog_time();
  rc = p->pReal->pMethods->xShmMap(p->pReal, iRegion, szRegion, isWrite, pp);
  t = vfslog_time() - t;
  vfslog_call(p->pVfslog, OS_SHMMAP, p->iFileId, t, rc, 0, 0);
  return rc;
}


/*
** Open an vfslog file handle.
*/
static int vfslogOpen(
................................................................................
    case OS_FULLPATHNAME:      zEvent = "xFullPathname"; break;
    case OS_RANDOMNESS:        zEvent = "xRandomness"; break;
    case OS_SLEEP:             zEvent = "xSleep"; break;
    case OS_CURRENTTIME:       zEvent = "xCurrentTime"; break;

    case OS_SHMCLOSE:          zEvent = "xShmClose"; break;
    case OS_SHMOPEN:           zEvent = "xShmOpen"; break;



    case OS_SHMLOCK:           zEvent = "xShmLock"; break;
    case OS_SHMBARRIER:        zEvent = "xShmBarrier"; break;
    case OS_SHMMAP:            zEvent = "xShmMap"; break;

    case OS_ANNOTATE:          zEvent = "annotation"; break;
  }

  return zEvent;
}

Changes to src/test_vfs.c.

65
66
67
68
69
70
71
72
73
74
75
76
77

78
79
80
81



82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
...
129
130
131
132
133
134
135
136
137
138
139
140
141

142
143
144
145
146
147
148
...
151
152
153
154
155
156
157
158
159
160
161
162
163

164
165
166
167
168
169
170
...
439
440
441
442
443
444
445
446
447
448
449
450
451

452
453
454
455
456
457
458
...
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
...
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650




651
652
653
654
655
656





657
658
659
660
661

662
663
664
665
666
667
668



669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
...
778
779
780
781
782
783
784

785
786
787

788

789
790
791
792
793
794
795
...
817
818
819
820
821
822
823


824
825
826
827
828
829


830


831
832
833

834
835
836
837
838
839
840
841




842

843
844






845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860

861
862
863
864
865
866
867
...
895
896
897
898
899
900
901

902
903
904
905
906
907
908
....
1067
1068
1069
1070
1071
1072
1073







1074
1075
1076
1077
1078
1079
1080
....
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
** If a bit is clear in Testvfs.mask, then calls made by SQLite to the 
** corresponding VFS method is ignored for purposes of:
**
**   + Simulating IO errors, and
**   + Invoking the Tcl callback script.
*/
#define TESTVFS_SHMOPEN_MASK    0x00000001
#define TESTVFS_SHMSIZE_MASK    0x00000002
#define TESTVFS_SHMGET_MASK     0x00000004
#define TESTVFS_SHMRELEASE_MASK 0x00000008
#define TESTVFS_SHMLOCK_MASK    0x00000010
#define TESTVFS_SHMBARRIER_MASK 0x00000020
#define TESTVFS_SHMCLOSE_MASK   0x00000040


#define TESTVFS_OPEN_MASK       0x00000080
#define TESTVFS_SYNC_MASK       0x00000100
#define TESTVFS_ALL_MASK        0x000001FF




/*
** A shared-memory buffer. There is one of these objects for each shared
** memory region opened by clients. If two clients open the same file,
** there are two TestvfsFile structures but only one TestvfsBuffer structure.
*/
struct TestvfsBuffer {
  char *zFile;                    /* Associated file name */
  int n;                          /* Size of allocated buffer in bytes */
  u8 *a;                          /* Buffer allocated using ckalloc() */
  TestvfsFile *pFile;             /* List of open handles */
  TestvfsBuffer *pNext;           /* Next in linked list of all buffers */
};


#define PARENTVFS(x) (((Testvfs *)((x)->pAppData))->pParent)

................................................................................
static void tvfsDlClose(sqlite3_vfs*, void*);
#endif /* SQLITE_OMIT_LOAD_EXTENSION */
static int tvfsRandomness(sqlite3_vfs*, int nByte, char *zOut);
static int tvfsSleep(sqlite3_vfs*, int microseconds);
static int tvfsCurrentTime(sqlite3_vfs*, double*);

static int tvfsShmOpen(sqlite3_file*);
static int tvfsShmSize(sqlite3_file*, int , int *);
static int tvfsShmGet(sqlite3_file*, int , int *, volatile void **);
static int tvfsShmRelease(sqlite3_file*);
static int tvfsShmLock(sqlite3_file*, int , int, int);
static void tvfsShmBarrier(sqlite3_file*);
static int tvfsShmClose(sqlite3_file*, int);


static sqlite3_io_methods tvfs_io_methods = {
  2,                            /* iVersion */
  tvfsClose,                      /* xClose */
  tvfsRead,                       /* xRead */
  tvfsWrite,                      /* xWrite */
  tvfsTruncate,                   /* xTruncate */
................................................................................
  tvfsLock,                       /* xLock */
  tvfsUnlock,                     /* xUnlock */
  tvfsCheckReservedLock,          /* xCheckReservedLock */
  tvfsFileControl,                /* xFileControl */
  tvfsSectorSize,                 /* xSectorSize */
  tvfsDeviceCharacteristics,      /* xDeviceCharacteristics */
  tvfsShmOpen,                    /* xShmOpen */
  tvfsShmSize,                    /* xShmSize */
  tvfsShmGet,                     /* xShmGet */
  tvfsShmRelease,                 /* xShmRelease */
  tvfsShmLock,                    /* xShmLock */
  tvfsShmBarrier,                 /* xShmBarrier */
  tvfsShmClose                    /* xShmClose */

};

static int tvfsResultCode(Testvfs *p, int *pRc){
  struct errcode {
    int eCode;
    const char *zCode;
  } aCode[] = {
................................................................................
  rc = sqlite3OsOpen(PARENTVFS(pVfs), zName, pFd->pReal, flags, pOutFlags);
  if( pFd->pReal->pMethods ){
    sqlite3_io_methods *pMethods;
    pMethods = (sqlite3_io_methods *)ckalloc(sizeof(sqlite3_io_methods));
    memcpy(pMethods, &tvfs_io_methods, sizeof(sqlite3_io_methods));
    if( ((Testvfs *)pVfs->pAppData)->isNoshm ){
      pMethods->xShmOpen = 0;
      pMethods->xShmGet = 0;
      pMethods->xShmSize = 0;
      pMethods->xShmRelease = 0;
      pMethods->xShmClose = 0;
      pMethods->xShmLock = 0;
      pMethods->xShmBarrier = 0;

    }
    pFile->pMethods = pMethods;
  }

  return rc;
}

................................................................................
/*
** Return the current time as a Julian Day number in *pTimeOut.
*/
static int tvfsCurrentTime(sqlite3_vfs *pVfs, double *pTimeOut){
  return PARENTVFS(pVfs)->xCurrentTime(PARENTVFS(pVfs), pTimeOut);
}

static void tvfsGrowBuffer(TestvfsFile *pFd, int reqSize, int *pNewSize){
  TestvfsBuffer *pBuffer = pFd->pShm;
  if( reqSize>pBuffer->n ){
    pBuffer->a = (u8 *)ckrealloc((char *)pBuffer->a, reqSize);
    memset(&pBuffer->a[pBuffer->n], 0x55, reqSize-pBuffer->n);
    pBuffer->n = reqSize;
  }
  *pNewSize = pBuffer->n;
}

static int tvfsInjectIoerr(Testvfs *p){
  int ret = 0;
  if( p->ioerr ){
    p->iIoerrCnt--;
    if( p->iIoerrCnt==0 || (p->iIoerrCnt<0 && p->ioerr==2) ){
      ret = 1;
      p->nIoerrFail++;
................................................................................
  /* Connect the TestvfsBuffer to the new TestvfsShm handle and return. */
  pFd->pNext = pBuffer->pFile;
  pBuffer->pFile = pFd;
  pFd->pShm = pBuffer;
  return SQLITE_OK;
}

static int tvfsShmSize(
  sqlite3_file *pFile,
  int reqSize,
  int *pNewSize
){
  int rc = SQLITE_OK;
  TestvfsFile *pFd = (TestvfsFile *)pFile;
  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);

  if( p->pScript && p->mask&TESTVFS_SHMSIZE_MASK ){
    tvfsExecTcl(p, "xShmSize", 
        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 0
    );
    tvfsResultCode(p, &rc);
  }
  if( rc==SQLITE_OK && p->mask&TESTVFS_SHMSIZE_MASK && tvfsInjectIoerr(p) ){
    rc = SQLITE_IOERR;
  }
  if( rc==SQLITE_OK ){
    tvfsGrowBuffer(pFd, reqSize, pNewSize);
  }
  return rc;
}

static int tvfsShmGet(
  sqlite3_file *pFile, 
  int reqMapSize, 
  int *pMapSize, 
  volatile void **pp




){
  int rc = SQLITE_OK;
  TestvfsFile *pFd = (TestvfsFile *)pFile;
  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);

  if( p->pScript && p->mask&TESTVFS_SHMGET_MASK ){





    tvfsExecTcl(p, "xShmGet", 
        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 
        Tcl_NewIntObj(reqMapSize)
    );
    tvfsResultCode(p, &rc);

  }
  if( rc==SQLITE_OK && p->mask&TESTVFS_SHMGET_MASK && tvfsInjectIoerr(p) ){
    rc = SQLITE_IOERR;
  }

  *pMapSize = pFd->pShm->n;
  *pp = pFd->pShm->a;



  return rc;
}

static int tvfsShmRelease(sqlite3_file *pFile){
  int rc = SQLITE_OK;
  TestvfsFile *pFd = (TestvfsFile *)pFile;
  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);

  if( p->pScript && p->mask&TESTVFS_SHMRELEASE_MASK ){
    tvfsExecTcl(p, "xShmRelease", 
        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, 0
    );
    tvfsResultCode(p, &rc);
  }

  return rc;
}

static int tvfsShmLock(
  sqlite3_file *pFile,
  int ofst,
  int n,
  int flags
){
................................................................................
  }

  for(ppFd=&pBuffer->pFile; *ppFd!=pFd; ppFd=&((*ppFd)->pNext));
  assert( (*ppFd)==pFd );
  *ppFd = pFd->pNext;

  if( pBuffer->pFile==0 ){

    TestvfsBuffer **pp;
    for(pp=&p->pBuffer; *pp!=pBuffer; pp=&((*pp)->pNext));
    *pp = (*pp)->pNext;

    ckfree((char *)pBuffer->a);

    ckfree((char *)pBuffer);
  }
  pFd->pShm = 0;

  return rc;
}

................................................................................
  if( Tcl_GetIndexFromObj(interp, objv[1], CMD_strs, "subcommand", 0, &i) ){
    return TCL_ERROR;
  }
  Tcl_ResetResult(interp);

  switch( (enum DB_enum)i ){
    case CMD_SHM: {


      TestvfsBuffer *pBuffer;
      char *zName;
      if( objc!=3 && objc!=4 ){
        Tcl_WrongNumArgs(interp, 2, objv, "FILE ?VALUE?");
        return TCL_ERROR;
      }


      zName = Tcl_GetString(objv[2]);


      for(pBuffer=p->pBuffer; pBuffer; pBuffer=pBuffer->pNext){
        if( 0==strcmp(pBuffer->zFile, zName) ) break;
      }

      if( !pBuffer ){
        Tcl_AppendResult(interp, "no such file: ", zName, 0);
        return TCL_ERROR;
      }
      if( objc==4 ){
        int n;
        u8 *a = Tcl_GetByteArrayFromObj(objv[3], &n);
        pBuffer->a = (u8 *)ckrealloc((char *)pBuffer->a, n);




        pBuffer->n = n;

        memcpy(pBuffer->a, a, n);
      }






      Tcl_SetObjResult(interp, Tcl_NewByteArrayObj(pBuffer->a, pBuffer->n));
      break;
    }

    case CMD_FILTER: {
      static struct VfsMethod {
        char *zName;
        int mask;
      } vfsmethod [] = {
        { "xShmOpen",    TESTVFS_SHMOPEN_MASK },
        { "xShmSize",    TESTVFS_SHMSIZE_MASK },
        { "xShmGet",     TESTVFS_SHMGET_MASK },
        { "xShmRelease", TESTVFS_SHMRELEASE_MASK },
        { "xShmLock",    TESTVFS_SHMLOCK_MASK },
        { "xShmBarrier", TESTVFS_SHMBARRIER_MASK },
        { "xShmClose",   TESTVFS_SHMCLOSE_MASK },

        { "xSync",       TESTVFS_SYNC_MASK },
        { "xOpen",       TESTVFS_OPEN_MASK },
      };
      Tcl_Obj **apElem = 0;
      int nElem = 0;
      int i;
      int mask = 0;
................................................................................
      if( objc==3 ){
        int nByte;
        if( p->pScript ){
          Tcl_DecrRefCount(p->pScript);
          ckfree((char *)p->apScript);
          p->apScript = 0;
          p->nScript = 0;

        }
        Tcl_GetStringFromObj(objv[2], &nByte);
        if( nByte>0 ){
          p->pScript = Tcl_DuplicateObj(objv[2]);
          Tcl_IncrRefCount(p->pScript);
        }
      }else if( objc!=2 ){
................................................................................
  }

  zVfs = Tcl_GetString(objv[1]);
  nByte = sizeof(Testvfs) + strlen(zVfs)+1;
  p = (Testvfs *)ckalloc(nByte);
  memset(p, 0, nByte);








  p->pParent = sqlite3_vfs_find(0);
  p->interp = interp;

  p->zName = (char *)&p[1];
  memcpy(p->zName, zVfs, strlen(zVfs)+1);

  pVfs = (sqlite3_vfs *)ckalloc(sizeof(sqlite3_vfs));
................................................................................
  pVfs->zName = p->zName;
  pVfs->mxPathname = p->pParent->mxPathname;
  pVfs->szOsFile += p->pParent->szOsFile;
  p->pVfs = pVfs;
  p->isNoshm = isNoshm;
  p->mask = TESTVFS_ALL_MASK;

  Tcl_CreateObjCommand(interp, zVfs, testvfs_obj_cmd, p, testvfs_obj_del);
  sqlite3_vfs_register(pVfs, isDefault);

  return TCL_OK;

 bad_args:
  Tcl_WrongNumArgs(interp, 1, objv, "VFSNAME ?-noshm BOOL? ?-default BOOL?");
  return TCL_ERROR;







<
<
<



>

|
|
|
>
>
>








|
|







 







<
<
<



>







 







<
<
<


|
>







 







<
<
<



>







 







<
<
<
<
<
<
<
<
<
<







 







|
|
|
|
|
|
<
<
|
<
<
<
<
<
|
<
<
|
<
<
<
<
<
<
|
|
<
<
<
>
>
>
>





|
>
>
>
>
>
|
|
<


>

|



|
|
>
>
>



<
<
<
<
<
<
<
<
<
<
<
<
<
<







 







>



>
|
>







 







>
>






>
>
|
>
>



>

|





|
>
>
>
>
|
>
|
|
>
>
>
>
>
>
|









<
<
<



>







 







>







 







>
>
>
>
>
>
>







 







<







65
66
67
68
69
70
71



72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
...
130
131
132
133
134
135
136



137
138
139
140
141
142
143
144
145
146
147
...
150
151
152
153
154
155
156



157
158
159
160
161
162
163
164
165
166
167
...
436
437
438
439
440
441
442



443
444
445
446
447
448
449
450
451
452
453
...
538
539
540
541
542
543
544










545
546
547
548
549
550
551
...
600
601
602
603
604
605
606
607
608
609
610
611
612


613





614


615






616
617



618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634

635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650














651
652
653
654
655
656
657
...
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
...
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840



841
842
843
844
845
846
847
848
849
850
851
...
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
....
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
....
1075
1076
1077
1078
1079
1080
1081

1082
1083
1084
1085
1086
1087
1088
** If a bit is clear in Testvfs.mask, then calls made by SQLite to the 
** corresponding VFS method is ignored for purposes of:
**
**   + Simulating IO errors, and
**   + Invoking the Tcl callback script.
*/
#define TESTVFS_SHMOPEN_MASK    0x00000001



#define TESTVFS_SHMLOCK_MASK    0x00000010
#define TESTVFS_SHMBARRIER_MASK 0x00000020
#define TESTVFS_SHMCLOSE_MASK   0x00000040
#define TESTVFS_SHMPAGE_MASK    0x00000080

#define TESTVFS_OPEN_MASK       0x00000100
#define TESTVFS_SYNC_MASK       0x00000200
#define TESTVFS_ALL_MASK        0x000003FF


#define TESTVFS_MAX_PAGES 256

/*
** A shared-memory buffer. There is one of these objects for each shared
** memory region opened by clients. If two clients open the same file,
** there are two TestvfsFile structures but only one TestvfsBuffer structure.
*/
struct TestvfsBuffer {
  char *zFile;                    /* Associated file name */
  int pgsz;                       /* Page size */
  u8 *aPage[TESTVFS_MAX_PAGES];   /* Array of ckalloc'd pages */
  TestvfsFile *pFile;             /* List of open handles */
  TestvfsBuffer *pNext;           /* Next in linked list of all buffers */
};


#define PARENTVFS(x) (((Testvfs *)((x)->pAppData))->pParent)

................................................................................
static void tvfsDlClose(sqlite3_vfs*, void*);
#endif /* SQLITE_OMIT_LOAD_EXTENSION */
static int tvfsRandomness(sqlite3_vfs*, int nByte, char *zOut);
static int tvfsSleep(sqlite3_vfs*, int microseconds);
static int tvfsCurrentTime(sqlite3_vfs*, double*);

static int tvfsShmOpen(sqlite3_file*);



static int tvfsShmLock(sqlite3_file*, int , int, int);
static void tvfsShmBarrier(sqlite3_file*);
static int tvfsShmClose(sqlite3_file*, int);
static int tvfsShmPage(sqlite3_file*,int,int,int, void volatile **);

static sqlite3_io_methods tvfs_io_methods = {
  2,                            /* iVersion */
  tvfsClose,                      /* xClose */
  tvfsRead,                       /* xRead */
  tvfsWrite,                      /* xWrite */
  tvfsTruncate,                   /* xTruncate */
................................................................................
  tvfsLock,                       /* xLock */
  tvfsUnlock,                     /* xUnlock */
  tvfsCheckReservedLock,          /* xCheckReservedLock */
  tvfsFileControl,                /* xFileControl */
  tvfsSectorSize,                 /* xSectorSize */
  tvfsDeviceCharacteristics,      /* xDeviceCharacteristics */
  tvfsShmOpen,                    /* xShmOpen */



  tvfsShmLock,                    /* xShmLock */
  tvfsShmBarrier,                 /* xShmBarrier */
  tvfsShmClose,                   /* xShmClose */
  tvfsShmPage                     /* xShmPage */
};

static int tvfsResultCode(Testvfs *p, int *pRc){
  struct errcode {
    int eCode;
    const char *zCode;
  } aCode[] = {
................................................................................
  rc = sqlite3OsOpen(PARENTVFS(pVfs), zName, pFd->pReal, flags, pOutFlags);
  if( pFd->pReal->pMethods ){
    sqlite3_io_methods *pMethods;
    pMethods = (sqlite3_io_methods *)ckalloc(sizeof(sqlite3_io_methods));
    memcpy(pMethods, &tvfs_io_methods, sizeof(sqlite3_io_methods));
    if( ((Testvfs *)pVfs->pAppData)->isNoshm ){
      pMethods->xShmOpen = 0;



      pMethods->xShmClose = 0;
      pMethods->xShmLock = 0;
      pMethods->xShmBarrier = 0;
      pMethods->xShmMap = 0;
    }
    pFile->pMethods = pMethods;
  }

  return rc;
}

................................................................................
/*
** Return the current time as a Julian Day number in *pTimeOut.
*/
static int tvfsCurrentTime(sqlite3_vfs *pVfs, double *pTimeOut){
  return PARENTVFS(pVfs)->xCurrentTime(PARENTVFS(pVfs), pTimeOut);
}











static int tvfsInjectIoerr(Testvfs *p){
  int ret = 0;
  if( p->ioerr ){
    p->iIoerrCnt--;
    if( p->iIoerrCnt==0 || (p->iIoerrCnt<0 && p->ioerr==2) ){
      ret = 1;
      p->nIoerrFail++;
................................................................................
  /* Connect the TestvfsBuffer to the new TestvfsShm handle and return. */
  pFd->pNext = pBuffer->pFile;
  pBuffer->pFile = pFd;
  pFd->pShm = pBuffer;
  return SQLITE_OK;
}

static void tvfsAllocPage(TestvfsBuffer *p, int iPage, int pgsz){
  assert( iPage<TESTVFS_MAX_PAGES );
  if( p->aPage[iPage]==0 ){
    p->aPage[iPage] = (u8 *)ckalloc(pgsz);
    memset(p->aPage[iPage], 0, pgsz);
    p->pgsz = pgsz;


  }





}









static int tvfsShmPage(
  sqlite3_file *pFile,            /* Handle open on database file */



  int iPage,                      /* Page to retrieve */
  int pgsz,                       /* Size of pages */
  int isWrite,                    /* True to extend file if necessary */
  void volatile **pp              /* OUT: Mapped memory */
){
  int rc = SQLITE_OK;
  TestvfsFile *pFd = (TestvfsFile *)pFile;
  Testvfs *p = (Testvfs *)(pFd->pVfs->pAppData);

  if( p->pScript && p->mask&TESTVFS_SHMPAGE_MASK ){
    Tcl_Obj *pArg = Tcl_NewObj();
    Tcl_IncrRefCount(pArg);
    Tcl_ListObjAppendElement(p->interp, pArg, Tcl_NewIntObj(iPage));
    Tcl_ListObjAppendElement(p->interp, pArg, Tcl_NewIntObj(pgsz));
    Tcl_ListObjAppendElement(p->interp, pArg, Tcl_NewIntObj(isWrite));
    tvfsExecTcl(p, "xShmPage", 
        Tcl_NewStringObj(pFd->pShm->zFile, -1), pFd->pShmId, pArg

    );
    tvfsResultCode(p, &rc);
    Tcl_DecrRefCount(pArg);
  }
  if( rc==SQLITE_OK && p->mask&TESTVFS_SHMPAGE_MASK && tvfsInjectIoerr(p) ){
    rc = SQLITE_IOERR;
  }

  if( rc==SQLITE_OK && isWrite && !pFd->pShm->aPage[iPage] ){
    tvfsAllocPage(pFd->pShm, iPage, pgsz);
  }
  *pp = (void volatile *)pFd->pShm->aPage[iPage];

  return rc;
}
















static int tvfsShmLock(
  sqlite3_file *pFile,
  int ofst,
  int n,
  int flags
){
................................................................................
  }

  for(ppFd=&pBuffer->pFile; *ppFd!=pFd; ppFd=&((*ppFd)->pNext));
  assert( (*ppFd)==pFd );
  *ppFd = pFd->pNext;

  if( pBuffer->pFile==0 ){
    int i;
    TestvfsBuffer **pp;
    for(pp=&p->pBuffer; *pp!=pBuffer; pp=&((*pp)->pNext));
    *pp = (*pp)->pNext;
    for(i=0; pBuffer->aPage[i]; i++){
      ckfree((char *)pBuffer->aPage[i]);
    }
    ckfree((char *)pBuffer);
  }
  pFd->pShm = 0;

  return rc;
}

................................................................................
  if( Tcl_GetIndexFromObj(interp, objv[1], CMD_strs, "subcommand", 0, &i) ){
    return TCL_ERROR;
  }
  Tcl_ResetResult(interp);

  switch( (enum DB_enum)i ){
    case CMD_SHM: {
      Tcl_Obj *pObj;
      int i;
      TestvfsBuffer *pBuffer;
      char *zName;
      if( objc!=3 && objc!=4 ){
        Tcl_WrongNumArgs(interp, 2, objv, "FILE ?VALUE?");
        return TCL_ERROR;
      }
      zName = ckalloc(p->pParent->mxPathname);
      p->pParent->xFullPathname(
          p->pParent, Tcl_GetString(objv[2]), 
          p->pParent->mxPathname, zName
      );
      for(pBuffer=p->pBuffer; pBuffer; pBuffer=pBuffer->pNext){
        if( 0==strcmp(pBuffer->zFile, zName) ) break;
      }
      ckfree(zName);
      if( !pBuffer ){
        Tcl_AppendResult(interp, "no such file: ", Tcl_GetString(objv[2]), 0);
        return TCL_ERROR;
      }
      if( objc==4 ){
        int n;
        u8 *a = Tcl_GetByteArrayFromObj(objv[3], &n);
        assert( pBuffer->pgsz==0 || pBuffer->pgsz==32768 );
        for(i=0; i*32768<n; i++){
          int nByte = 32768;
          tvfsAllocPage(pBuffer, i, 32768);
          if( n-i*32768<32768 ){
            nByte = n;
          }
          memcpy(pBuffer->aPage[i], &a[i*32768], nByte);
        }
      }

      pObj = Tcl_NewObj();
      for(i=0; pBuffer->aPage[i]; i++){
        Tcl_AppendObjToObj(pObj, Tcl_NewByteArrayObj(pBuffer->aPage[i], 32768));
      }
      Tcl_SetObjResult(interp, pObj);
      break;
    }

    case CMD_FILTER: {
      static struct VfsMethod {
        char *zName;
        int mask;
      } vfsmethod [] = {
        { "xShmOpen",    TESTVFS_SHMOPEN_MASK },



        { "xShmLock",    TESTVFS_SHMLOCK_MASK },
        { "xShmBarrier", TESTVFS_SHMBARRIER_MASK },
        { "xShmClose",   TESTVFS_SHMCLOSE_MASK },
        { "xShmPage",    TESTVFS_SHMPAGE_MASK },
        { "xSync",       TESTVFS_SYNC_MASK },
        { "xOpen",       TESTVFS_OPEN_MASK },
      };
      Tcl_Obj **apElem = 0;
      int nElem = 0;
      int i;
      int mask = 0;
................................................................................
      if( objc==3 ){
        int nByte;
        if( p->pScript ){
          Tcl_DecrRefCount(p->pScript);
          ckfree((char *)p->apScript);
          p->apScript = 0;
          p->nScript = 0;
          p->pScript = 0;
        }
        Tcl_GetStringFromObj(objv[2], &nByte);
        if( nByte>0 ){
          p->pScript = Tcl_DuplicateObj(objv[2]);
          Tcl_IncrRefCount(p->pScript);
        }
      }else if( objc!=2 ){
................................................................................
  }

  zVfs = Tcl_GetString(objv[1]);
  nByte = sizeof(Testvfs) + strlen(zVfs)+1;
  p = (Testvfs *)ckalloc(nByte);
  memset(p, 0, nByte);

  /* Create the new object command before querying SQLite for a default VFS
  ** to use for 'real' IO operations. This is because creating the new VFS
  ** may delete an existing [testvfs] VFS of the same name. If such a VFS
  ** is currently the default, the new [testvfs] may end up calling the 
  ** methods of a deleted object.
  */
  Tcl_CreateObjCommand(interp, zVfs, testvfs_obj_cmd, p, testvfs_obj_del);
  p->pParent = sqlite3_vfs_find(0);
  p->interp = interp;

  p->zName = (char *)&p[1];
  memcpy(p->zName, zVfs, strlen(zVfs)+1);

  pVfs = (sqlite3_vfs *)ckalloc(sizeof(sqlite3_vfs));
................................................................................
  pVfs->zName = p->zName;
  pVfs->mxPathname = p->pParent->mxPathname;
  pVfs->szOsFile += p->pParent->szOsFile;
  p->pVfs = pVfs;
  p->isNoshm = isNoshm;
  p->mask = TESTVFS_ALL_MASK;


  sqlite3_vfs_register(pVfs, isDefault);

  return TCL_OK;

 bad_args:
  Tcl_WrongNumArgs(interp, 1, objv, "VFSNAME ?-noshm BOOL? ?-default BOOL?");
  return TCL_ERROR;

Changes to src/wal.c.

137
138
139
140
141
142
143
144


145
146
147
148
149
150
151
152
153













154
155
156
157
158
159
160
161
162
163
164
165
...
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
...
383
384
385
386
387
388
389
390

391
392
393
394
395
396
397
398
399
400
401
402
403
...
407
408
409
410
411
412
413
414
415
416
417
418
419
420

421

422














































































423
424
425
426
427
428
429
...
482
483
484
485
486
487
488
489

490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
...
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
...
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
...
763
764
765
766
767
768
769
770
771

772
773
774
775
776
777
778
779
780
781
782
783
784
785

786
787

788
789
790
791
792
793
794
795

796
797
798
799


800
801

802
803

804
805
806

807
808
809


810
811
812






























813
814
815
816
817
818
819
...
821
822
823
824
825
826
827
828
829
830
831


832
833
834
835
836

837
838
839
840









841

842
843
844
845
846
847
848
849
850
851
852
853

854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
...
875
876
877
878
879
880
881
882


883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905





906

907
908
909
910
911
912
913
914
915
916
917
918

919
920
921
922


923
924
925

926
927
928
929
930
931
932
...
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
....
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
....
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
....
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249


1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
....
1280
1281
1282
1283
1284
1285
1286







1287
1288
1289
1290
1291
1292
1293
....
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314

1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328

1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342

1343


1344
1345
1346










1347
1348
1349




1350
1351
1352
1353
1354

1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
....
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
....
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
....
1457
1458
1459
1460
1461
1462
1463

1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
....
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536

1537
1538
1539
1540
1541
1542
1543
....
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
....
1621
1622
1623
1624
1625
1626
1627

1628



1629
1630

1631
1632
1633

1634
1635
1636




1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647

1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667


1668
1669
1670
1671
1672
1673
1674
....
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
....
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
....
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
....
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
....
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
....
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
....
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975

1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
....
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
....
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104

2105
2106

2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127

2128
2129
2130
2131
2132
2133

2134
2135
2136
2137
2138
2139
2140
....
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
....
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
....
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
....
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
....
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
....
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
....
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
....
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
** a page number P, return the index of the last frame for page P in the WAL,
** or return NULL if there are no frames for page P in the WAL.
**
** The wal-index consists of a header region, followed by an one or
** more index blocks.  
**
** The wal-index header contains the total number of frames within the WAL
** in the the mxFrame field.  Each index block contains information on


** HASHTABLE_NPAGE frames.  Each index block contains two sections, a
** mapping which is a database page number for each frame, and a hash
** table used to look up frames by page number.  The mapping section is
** an array of HASHTABLE_NPAGE 32-bit page numbers.  The first entry on the
** array is the page number for the first frame; the second entry is the
** page number for the second frame; and so forth.  The last index block
** holds a total of (mxFrame%HASHTABLE_NPAGE) page numbers.  All index
** blocks other than the last are completely full with HASHTABLE_NPAGE
** page numbers.  All index blocks are the same size; the mapping section













** of the last index block merely contains unused entries if mxFrame is
** not an even multiple of HASHTABLE_NPAGE.
**
** Even without using the hash table, the last frame for page P
** can be found by scanning the mapping sections of each index block
** starting with the last index block and moving toward the first, and
** within each index block, starting at the end and moving toward the
** beginning.  The first entry that equals P corresponds to the frame
** holding the content for that page.
**
** The hash table consists of HASHTABLE_NSLOT 16-bit unsigned integers.
** HASHTABLE_NSLOT = 2*HASHTABLE_NPAGE, and there is one entry in the
................................................................................
** following object.
*/
struct Wal {
  sqlite3_vfs *pVfs;         /* The VFS used to create pDbFd */
  sqlite3_file *pDbFd;       /* File handle for the database file */
  sqlite3_file *pWalFd;      /* File handle for WAL file */
  u32 iCallback;             /* Value to pass to log callback (or 0) */
  int szWIndex;              /* Size of the wal-index that is mapped in mem */
  volatile u32 *pWiData;     /* Pointer to wal-index content in memory */
  u16 szPage;                /* Database page size */
  i16 readLock;              /* Which read lock is being held.  -1 for none */
  u8 exclusiveMode;          /* Non-zero if connection is in exclusive mode */
  u8 isWIndexOpen;           /* True if ShmOpen() called on pDbFd */
  u8 writeLock;              /* True if in a write transaction */
  u8 ckptLock;               /* True if holding a checkpoint lock */
  WalIndexHdr hdr;           /* Wal-index header for current transaction */
................................................................................
  u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
  u8 lockError;              /* True if a locking error has occurred */
#endif
};

/*
** Return a pointer to the WalCkptInfo structure in the wal-index.

*/
static volatile WalCkptInfo *walCkptInfo(Wal *pWal){
  assert( pWal->pWiData!=0 );
  return (volatile WalCkptInfo*)&pWal->pWiData[sizeof(WalIndexHdr)/2];
}


/*
** This structure is used to implement an iterator that loops through
** all frames in the WAL in database page order. Where two or more frames
** correspond to the same database page, the iterator visits only the 
** frame most recently written to the WAL (in other words, the frame with
** the largest index).
................................................................................
**   walIteratorInit() - Create a new iterator,
**   walIteratorNext() - Step an iterator,
**   walIteratorFree() - Free an iterator.
**
** This functionality is used by the checkpoint code (see walCheckpoint()).
*/
struct WalIterator {
  int iPrior;           /* Last result returned from the iterator */
  int nSegment;         /* Size of the aSegment[] array */
  int nFinal;           /* Elements in aSegment[nSegment-1]  */
  struct WalSegment {
    int iNext;              /* Next slot in aIndex[] not previously returned */
    u8 *aIndex;             /* i0, i1, i2... such that aPgno[iN] ascending */
    u32 *aPgno;             /* 256 page numbers.  Pointer to Wal.pWiData */

  } aSegment[1];        /* One for every 256 entries in the WAL */

};















































































/*
** The argument to this macro must be of type u32. On a little-endian
** architecture, it returns the u32 value that results from interpreting
** the 4 bytes as a big-endian value. On a big-endian architecture, it
** returns the value that would be produced by intepreting the 4 bytes
** of the input value as a little-endian integer.
................................................................................

/*
** Write the header information in pWal->hdr into the wal-index.
**
** The checksum on pWal->hdr is updated before it is written.
*/
static void walIndexWriteHdr(Wal *pWal){
  WalIndexHdr *aHdr;


  assert( pWal->writeLock );
  pWal->hdr.isInit = 1;
  walChecksumBytes(1, (u8*)&pWal->hdr, offsetof(WalIndexHdr, aCksum),
                   0, pWal->hdr.aCksum);
  aHdr = (WalIndexHdr*)pWal->pWiData;
  memcpy(&aHdr[1], &pWal->hdr, sizeof(WalIndexHdr));
  sqlite3OsShmBarrier(pWal->pDbFd);
  memcpy(&aHdr[0], &pWal->hdr, sizeof(WalIndexHdr));
}

/*
** This function encodes a single frame header and writes it to a buffer
** supplied by the caller. A frame-header is made up of a series of 
** 4-byte big-endian integers, as follows:
**
................................................................................
  ** and the new database size.
  */
  *piPage = pgno;
  *pnTruncate = sqlite3Get4byte(&aFrame[4]);
  return 1;
}

/*
** Define the parameters of the hash tables in the wal-index file. There
** is a hash-table following every HASHTABLE_NPAGE page numbers in the
** wal-index.
**
** Changing any of these constants will alter the wal-index format and
** create incompatibilities.
*/
#define HASHTABLE_NPAGE      4096  /* Must be power of 2 and multiple of 256 */
#define HASHTABLE_DATATYPE   u16
#define HASHTABLE_HASH_1     383                  /* Should be prime */
#define HASHTABLE_NSLOT      (HASHTABLE_NPAGE*2)  /* Must be a power of 2 */
#define HASHTABLE_NBYTE      (sizeof(HASHTABLE_DATATYPE)*HASHTABLE_NSLOT)

#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
/*
** Names of locks.  This routine is used to provide debugging output and is not
** a part of an ordinary build.
*/
static const char *walLockName(int lockIdx){
................................................................................
  if( pWal->exclusiveMode ) return;
  (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, n,
                         SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE);
  WALTRACE(("WAL%p: release EXCLUSIVE-%s cnt=%d\n", pWal,
             walLockName(lockIdx), n));
}

/*
** Return the index in the Wal.pWiData array that corresponds to 
** frame iFrame.
**
** Wal.pWiData is an array of u32 elements that is the wal-index.
** The array begins with a header and is then followed by alternating
** "map" and "hash-table" blocks.  Each "map" block consists of
** HASHTABLE_NPAGE u32 elements which are page numbers corresponding
** to frames in the WAL file.  
**
** This routine returns an index X such that Wal.pWiData[X] is part
** of a "map" block that contains the page number of the iFrame-th
** frame in the WAL file.
*/
static int walIndexEntry(u32 iFrame){
  return (
      (WALINDEX_LOCK_OFFSET+WALINDEX_LOCK_RESERVED)/sizeof(u32)
    + (((iFrame-1)/HASHTABLE_NPAGE) * HASHTABLE_NBYTE)/sizeof(u32)
    + (iFrame-1)
  );
}

/*
** Return the minimum size of the shared-memory, in bytes, that is needed
** to support a wal-index containing frame iFrame.  The value returned
** includes the wal-index header and the complete "block" containing iFrame,
** including the hash table segment that follows the block.
*/
static int walMappingSize(u32 iFrame){
  const int nByte = (sizeof(u32)*HASHTABLE_NPAGE + HASHTABLE_NBYTE) ;
  return ( WALINDEX_LOCK_OFFSET 
         + WALINDEX_LOCK_RESERVED 
         + nByte * ((iFrame + HASHTABLE_NPAGE - 1)/HASHTABLE_NPAGE)
  );
}

/*
** Release our reference to the wal-index memory map, if we are holding
** it.
*/
static void walIndexUnmap(Wal *pWal){
  if( pWal->pWiData ){
    sqlite3OsShmRelease(pWal->pDbFd);
  }
  pWal->pWiData = 0;
  pWal->szWIndex = -1;
}

/*
** Map the wal-index file into memory if it isn't already. 
**
** The reqSize parameter is the requested size of the mapping.  The
** mapping will be at least this big if the underlying storage is
** that big.  But the mapping will never grow larger than the underlying
** storage.  Use the walIndexRemap() to enlarget the storage space.
*/
static int walIndexMap(Wal *pWal, int reqSize){
  int rc = SQLITE_OK;
  if( pWal->pWiData==0 || reqSize>pWal->szWIndex ){
    walIndexUnmap(pWal);
    rc = sqlite3OsShmGet(pWal->pDbFd, reqSize, &pWal->szWIndex,
                             (void volatile**)(char volatile*)&pWal->pWiData);
    if( rc!=SQLITE_OK ){
      walIndexUnmap(pWal);
    }
  }
  return rc;
}

/*
** Enlarge the wal-index to be at least enlargeTo bytes in size and
** Remap the wal-index so that the mapping covers the full size
** of the underlying file.
**
** If enlargeTo is non-negative, then increase the size of the underlying
** storage to be at least as big as enlargeTo before remapping.
*/
static int walIndexRemap(Wal *pWal, int enlargeTo){
  int rc;
  int sz;
  assert( pWal->writeLock );
  rc = sqlite3OsShmSize(pWal->pDbFd, enlargeTo, &sz);
  if( rc==SQLITE_OK && sz>pWal->szWIndex ){
    walIndexUnmap(pWal);
    rc = walIndexMap(pWal, sz);
  }
  assert( pWal->szWIndex>=enlargeTo || rc!=SQLITE_OK );
  return rc;
}

/*
** Compute a hash on a page number.  The resulting hash value must land
** between 0 and (HASHTABLE_NSLOT-1).  The walHashNext() function advances
** the hash to the next value in the event of a collision.
*/
static int walHash(u32 iPage){
  assert( iPage>0 );
................................................................................
  assert( (HASHTABLE_NSLOT & (HASHTABLE_NSLOT-1))==0 );
  return (iPage*HASHTABLE_HASH_1) & (HASHTABLE_NSLOT-1);
}
static int walNextHash(int iPriorHash){
  return (iPriorHash+1)&(HASHTABLE_NSLOT-1);
}


/* 

** Find the hash table and (section of the) page number array used to
** store data for WAL frame iFrame.
**
** Set output variable *paHash to point to the start of the hash table
** in the wal-index file. Set *piZero to one less than the frame 
** number of the first frame indexed by this hash table. If a
** slot in the hash table is set to N, it refers to frame number 
** (*piZero+N) in the log.
**
** Finally, set *paPgno such that for all frames F between (*piZero+1) and 
** (*piZero+HASHTABLE_NPAGE), (*paPgno)[F] is the database page number 
** associated with frame F.
*/
static void walHashFind(

  Wal *pWal,                      /* WAL handle */
  u32 iFrame,                     /* Find the hash table indexing this frame */

  volatile HASHTABLE_DATATYPE **paHash,    /* OUT: Pointer to hash index */
  volatile u32 **paPgno,          /* OUT: Pointer to page number array */
  u32 *piZero                     /* OUT: Frame associated with *paPgno[0] */
){
  u32 iZero;
  volatile u32 *aPgno;
  volatile HASHTABLE_DATATYPE *aHash;


  iZero = ((iFrame-1)/HASHTABLE_NPAGE) * HASHTABLE_NPAGE;
  aPgno = &pWal->pWiData[walIndexEntry(iZero+1)-iZero-1];
  aHash = (HASHTABLE_DATATYPE *)&aPgno[iZero+HASHTABLE_NPAGE+1];



  /* Assert that:
  **

  **   + the mapping is large enough for this hash-table, and
  **

  **   + that aPgno[iZero+1] really is the database page number associated
  **     with the first frame indexed by this hash table.
  */

  assert( (u32*)(&aHash[HASHTABLE_NSLOT])<=&pWal->pWiData[pWal->szWIndex/4] );
  assert( walIndexEntry(iZero+1)==(&aPgno[iZero+1] - pWal->pWiData) );



  *paHash = aHash;
  *paPgno = aPgno;
  *piZero = iZero;






























}

/*
** Remove entries from the hash table that point to WAL slots greater
** than pWal->hdr.mxFrame.
**
** This function is called whenever pWal->hdr.mxFrame is decreased due
................................................................................
**
** At most only the hash table containing pWal->hdr.mxFrame needs to be
** updated.  Any later hash tables will be automatically cleared when
** pWal->hdr.mxFrame advances to the point where those hash tables are
** actually needed.
*/
static void walCleanupHash(Wal *pWal){
  volatile HASHTABLE_DATATYPE *aHash;  /* Pointer to hash table to clear */
  volatile u32 *aPgno;                 /* Unused return from walHashFind() */
  u32 iZero;                           /* frame == (aHash[x]+iZero) */
  int iLimit = 0;                      /* Zero values greater than this */



  assert( pWal->writeLock );
  testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE-1 );
  testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE );
  testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE+1 );

  if( (pWal->hdr.mxFrame % HASHTABLE_NPAGE)>0 ){
    int nByte;                    /* Number of bytes to zero in aPgno[] */
    int i;                        /* Used to iterate through aHash[] */










    walHashFind(pWal, pWal->hdr.mxFrame+1, &aHash, &aPgno, &iZero);

    iLimit = pWal->hdr.mxFrame - iZero;
    assert( iLimit>0 );
    for(i=0; i<HASHTABLE_NSLOT; i++){
      if( aHash[i]>iLimit ){
        aHash[i] = 0;
      }
    }

    /* Zero the entries in the aPgno array that correspond to frames with
    ** frame numbers greater than pWal->hdr.mxFrame. 
    */
    nByte = sizeof(u32) * (HASHTABLE_NPAGE-iLimit);

    memset((void *)&aPgno[iZero+iLimit+1], 0, nByte);
    assert( &((u8 *)&aPgno[iZero+iLimit+1])[nByte]==(u8 *)aHash );
  }

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* Verify that the every entry in the mapping region is still reachable
  ** via the hash table even after the cleanup.
  */
  if( iLimit ){
    int i;           /* Loop counter */
    int iKey;        /* Hash key */
    for(i=1; i<=iLimit; i++){
      for(iKey=walHash(aPgno[i+iZero]); aHash[iKey]; iKey=walNextHash(iKey)){
        if( aHash[iKey]==i ) break;
      }
      assert( aHash[iKey]==i );
    }
  }
#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
}
................................................................................

/*
** Set an entry in the wal-index that will map database page number
** pPage into WAL frame iFrame.
*/
static int walIndexAppend(Wal *pWal, u32 iFrame, u32 iPage){
  int rc;                         /* Return code */
  int nMapping;                   /* Required mapping size in bytes */


  
  /* Make sure the wal-index is mapped. Enlarge the mapping if required. */
  nMapping = walMappingSize(iFrame);
  rc = walIndexMap(pWal, nMapping);
  while( rc==SQLITE_OK && nMapping>pWal->szWIndex ){
    rc = walIndexRemap(pWal, nMapping);
  }

  /* Assuming the wal-index file was successfully mapped, find the hash 
  ** table and section of of the page number array that pertain to frame 
  ** iFrame of the WAL. Then populate the page number array and the hash 
  ** table entry.
  */
  if( rc==SQLITE_OK ){
    int iKey;                     /* Hash table key */
    u32 iZero;                    /* One less than frame number of aPgno[1] */
    volatile u32 *aPgno;                 /* Page number array */
    volatile HASHTABLE_DATATYPE *aHash;  /* Hash table */
    int idx;                             /* Value to write to hash-table slot */
    TESTONLY( int nCollide = 0;          /* Number of hash collisions */ )

    walHashFind(pWal, iFrame, &aHash, &aPgno, &iZero);
    idx = iFrame - iZero;





    if( idx==1 ){

      memset((void*)&aPgno[iZero+1], 0, HASHTABLE_NPAGE*sizeof(u32));
      memset((void*)aHash, 0, HASHTABLE_NBYTE);
    }
    assert( idx <= HASHTABLE_NSLOT/2 + 1 );

    if( aPgno[iFrame] ){
      /* If the entry in aPgno[] is already set, then the previous writer
      ** must have exited unexpectedly in the middle of a transaction (after
      ** writing one or more dirty pages to the WAL to free up memory). 
      ** Remove the remnants of that writers uncommitted transaction from 
      ** the hash-table before writing any new entries.
      */

      walCleanupHash(pWal);
      assert( !aPgno[iFrame] );
    }
    aPgno[iFrame] = iPage;


    for(iKey=walHash(iPage); aHash[iKey]; iKey=walNextHash(iKey)){
      assert( nCollide++ < idx );
    }

    aHash[iKey] = idx;

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
    /* Verify that the number of entries in the hash table exactly equals
    ** the number of entries in the mapping region.
    */
    {
................................................................................
    ** via the hash table.  This turns out to be a really, really expensive
    ** thing to check, so only do this occasionally - not on every
    ** iteration.
    */
    if( (idx&0x3ff)==0 ){
      int i;           /* Loop counter */
      for(i=1; i<=idx; i++){
        for(iKey=walHash(aPgno[i+iZero]); aHash[iKey]; iKey=walNextHash(iKey)){
          if( aHash[iKey]==i ) break;
        }
        assert( aHash[iKey]==i );
      }
    }
#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
  }
................................................................................
      }
    }

    sqlite3_free(aFrame);
  }

finished:
  if( rc==SQLITE_OK && pWal->hdr.mxFrame==0 ){
    rc = walIndexRemap(pWal, walMappingSize(1));
  }
  if( rc==SQLITE_OK ){
    volatile WalCkptInfo *pInfo;
    int i;
    pWal->hdr.aFrameCksum[0] = aFrameCksum[0];
    pWal->hdr.aFrameCksum[1] = aFrameCksum[1];
    walIndexWriteHdr(pWal);

................................................................................
  if( !pRet ){
    return SQLITE_NOMEM;
  }

  pRet->pVfs = pVfs;
  pRet->pWalFd = (sqlite3_file *)&pRet[1];
  pRet->pDbFd = pDbFd;
  pRet->szWIndex = -1;
  pRet->readLock = -1;
  sqlite3_randomness(8, &pRet->hdr.aSalt);
  pRet->zWalName = zWal = pVfs->szOsFile + (char*)pRet->pWalFd;
  sqlite3_snprintf(nWal, zWal, "%s-wal", zDbName);
  rc = sqlite3OsShmOpen(pDbFd);

  /* Open file handle on the write-ahead log file. */
................................................................................
  WalIterator *p,               /* Iterator */
  u32 *piPage,                  /* OUT: The page number of the next page */
  u32 *piFrame                  /* OUT: Wal frame index of next page */
){
  u32 iMin;                     /* Result pgno must be greater than iMin */
  u32 iRet = 0xFFFFFFFF;        /* 0xffffffff is never a valid page number */
  int i;                        /* For looping through segments */
  int nBlock = p->nFinal;       /* Number of entries in current segment */

  iMin = p->iPrior;
  assert( iMin<0xffffffff );
  for(i=p->nSegment-1; i>=0; i--){
    struct WalSegment *pSegment = &p->aSegment[i];
    while( pSegment->iNext<nBlock ){
      u32 iPg = pSegment->aPgno[pSegment->aIndex[pSegment->iNext]];
      if( iPg>iMin ){
        if( iPg<iRet ){
          iRet = iPg;
          *piFrame = i*256 + 1 + pSegment->aIndex[pSegment->iNext];
        }
        break;
      }
      pSegment->iNext++;
    }
    nBlock = 256;
  }

  *piPage = p->iPrior = iRet;
  return (iRet==0xFFFFFFFF);
}


static void walMergesort8(
  Pgno *aContent,                 /* Pages in wal */
  u8 *aBuffer,                    /* Buffer of at least *pnList items to use */
  u8 *aList,                      /* IN/OUT: List to sort */
  int *pnList                     /* IN/OUT: Number of elements in aList[] */
){
  int nList = *pnList;
  if( nList>1 ){
    int nLeft = nList / 2;        /* Elements in left list */
    int nRight = nList - nLeft;   /* Elements in right list */
    u8 *aLeft = aList;            /* Left list */
    u8 *aRight = &aList[nLeft];   /* Right list */
    int iLeft = 0;                /* Current index in aLeft */
    int iRight = 0;               /* Current index in aright */
    int iOut = 0;                 /* Current index in output buffer */



    /* TODO: Change to non-recursive version. */
    walMergesort8(aContent, aBuffer, aLeft, &nLeft);
    walMergesort8(aContent, aBuffer, aRight, &nRight);

    while( iRight<nRight || iLeft<nLeft ){
      u8 logpage;
      Pgno dbpage;

      if( (iLeft<nLeft) 
       && (iRight>=nRight || aContent[aLeft[iLeft]]<aContent[aRight[iRight]])
      ){
        logpage = aLeft[iLeft++];
      }else{
................................................................................
    int i;
    for(i=1; i<*pnList; i++){
      assert( aContent[aList[i]] > aContent[aList[i-1]] );
    }
  }
#endif
}








/*
** Map the wal-index into memory owned by this thread, if it is not
** mapped already.  Then construct a WalInterator object that can be
** used to loop over all pages in the WAL in ascending order.  
**
** On success, make *pp point to the newly allocated WalInterator object
................................................................................
**
** The calling routine should invoke walIteratorFree() to destroy the
** WalIterator object when it has finished with it.  The caller must
** also unmap the wal-index.  But the wal-index must not be unmapped
** prior to the WalIterator object being destroyed.
*/
static int walIteratorInit(Wal *pWal, WalIterator **pp){
  u32 *aData;           /* Content of the wal-index file */
  WalIterator *p;       /* Return value */
  int nSegment;         /* Number of segments to merge */
  u32 iLast;            /* Last frame in log */
  int nByte;            /* Number of bytes to allocate */
  int i;                /* Iterator variable */
  int nFinal;           /* Number of unindexed entries */
  u8 *aTmp;             /* Temp space used by merge-sort */
  u8 *aSpace;           /* Surplus space on the end of the allocation */

  /* Make sure the wal-index is mapped into local memory */
  assert( pWal->pWiData && pWal->szWIndex>=walMappingSize(pWal->hdr.mxFrame) );


  /* This routine only runs while holding SQLITE_SHM_CHECKPOINT.  No other
  ** thread is able to write to shared memory while this routine is
  ** running (or, indeed, while the WalIterator object exists).  Hence,
  ** we can cast off the volatile qualifacation from shared memory
  */
  assert( pWal->ckptLock );
  aData = (u32*)pWal->pWiData;

  /* Allocate space for the WalIterator object */
  iLast = pWal->hdr.mxFrame;
  nSegment = (iLast >> 8) + 1;
  nFinal = (iLast & 0x000000FF);
  nByte = sizeof(WalIterator) + (nSegment+1)*(sizeof(struct WalSegment)+256);

  p = (WalIterator *)sqlite3_malloc(nByte);
  if( !p ){
    return SQLITE_NOMEM;
  }
  memset(p, 0, nByte);

  /* Initialize the WalIterator object.  Each 256-entry segment is
  ** presorted in order to make iterating through all entries much
  ** faster.
  */
  p->nSegment = nSegment;
  aSpace = (u8 *)&p->aSegment[nSegment];
  aTmp = &aSpace[nSegment*256];
  for(i=0; i<nSegment; i++){

    int j;


    int nIndex = (i==nSegment-1) ? nFinal : 256;
    p->aSegment[i].aPgno = &aData[walIndexEntry(i*256+1)];
    p->aSegment[i].aIndex = aSpace;










    for(j=0; j<nIndex; j++){
      aSpace[j] = j;
    }




    walMergesort8(p->aSegment[i].aPgno, aTmp, aSpace, &nIndex);
    memset(&aSpace[nIndex], aSpace[nIndex-1], 256-nIndex);
    aSpace += 256;
    p->nFinal = nIndex;
  }


  /* Return the fully initializd WalIterator object */
  *pp = p;
  return SQLITE_OK ;
}

/* 
** Free an iterator allocated by walIteratorInit().
*/
static void walIteratorFree(WalIterator *p){
  sqlite3_free(p);
}

/*
** Copy as much content as we can from the WAL back into the database file
** in response to an sqlite3_wal_checkpoint() request or the equivalent.
**
** The amount of information copies from WAL to database might be limited
** by active readers.  This routine will never overwrite a database page
** that a concurrent reader might be using.
................................................................................
  int rc;                         /* Return code */
  int szPage = pWal->hdr.szPage;  /* Database page-size */
  WalIterator *pIter = 0;         /* Wal iterator context */
  u32 iDbpage = 0;                /* Next database page to write */
  u32 iFrame = 0;                 /* Wal frame containing data for iDbpage */
  u32 mxSafeFrame;                /* Max frame that can be backfilled */
  int i;                          /* Loop counter */
  volatile WalIndexHdr *pHdr;     /* The actual wal-index header in SHM */
  volatile WalCkptInfo *pInfo;    /* The checkpoint status information */

  /* Allocate the iterator */
  rc = walIteratorInit(pWal, &pIter);
  if( rc!=SQLITE_OK || pWal->hdr.mxFrame==0 ){
    goto walcheckpoint_out;
  }
................................................................................

  /* Compute in mxSafeFrame the index of the last frame of the WAL that is
  ** safe to write into the database.  Frames beyond mxSafeFrame might
  ** overwrite database pages that are in use by active readers and thus
  ** cannot be backfilled from the WAL.
  */
  mxSafeFrame = pWal->hdr.mxFrame;
  pHdr = (volatile WalIndexHdr*)pWal->pWiData;
  pInfo = (volatile WalCkptInfo*)&pHdr[2];
  assert( pInfo==walCkptInfo(pWal) );
  for(i=1; i<WAL_NREADER; i++){
    u32 y = pInfo->aReadMark[i];
    if( mxSafeFrame>=y ){
      assert( y<=pWal->hdr.mxFrame );
      rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
      if( rc==SQLITE_OK ){
        pInfo->aReadMark[i] = READMARK_NOT_USED;
................................................................................
    /* Sync the WAL to disk */
    if( sync_flags ){
      rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
    }

    /* Iterate through the contents of the WAL, copying data to the db file. */
    while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){

      if( iFrame<=nBackfill || iFrame>mxSafeFrame ) continue;
      rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, 
          walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE
      );
      if( rc!=SQLITE_OK ) break;
      rc = sqlite3OsWrite(pWal->pDbFd, zBuf, szPage, (iDbpage-1)*szPage);
      if( rc!=SQLITE_OK ) break;
    }

    /* If work was actually accomplished... */
    if( rc==SQLITE_OK ){
      if( mxSafeFrame==pHdr[0].mxFrame ){
        rc = sqlite3OsTruncate(pWal->pDbFd, ((i64)pWal->hdr.nPage*(i64)szPage));
        if( rc==SQLITE_OK && sync_flags ){
          rc = sqlite3OsSync(pWal->pDbFd, sync_flags);
        }
      }
      if( rc==SQLITE_OK ){
        pInfo->nBackfill = mxSafeFrame;
................................................................................
    rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){
      pWal->exclusiveMode = 1;
      rc = sqlite3WalCheckpoint(pWal, sync_flags, nBuf, zBuf);
      if( rc==SQLITE_OK ){
        isDelete = 1;
      }
      walIndexUnmap(pWal);
    }

    walIndexClose(pWal, isDelete);
    sqlite3OsClose(pWal->pWalFd);
    if( isDelete ){
      sqlite3OsDelete(pWal->pVfs, pWal->zWalName, 0);
    }
    WALTRACE(("WAL%p: closed\n", pWal));

    sqlite3_free(pWal);
  }
  return rc;
}

/*
** Try to read the wal-index header.  Return 0 on success and 1 if
................................................................................
** pWal->hdr, then pWal->hdr is updated to the content of the new header
** and *pChanged is set to 1.
**
** If the checksum cannot be verified return non-zero. If the header
** is read successfully and the checksum verified, return zero.
*/
int walIndexTryHdr(Wal *pWal, int *pChanged){
  u32 aCksum[2];               /* Checksum on the header content */
  WalIndexHdr h1, h2;          /* Two copies of the header content */
  WalIndexHdr *aHdr;           /* Header in shared memory */

  if( pWal->szWIndex < WALINDEX_HDR_SIZE ){
    /* The wal-index is not large enough to hold the header, then assume
    ** header is invalid. */
    return 1;
  }
  assert( pWal->pWiData );

  /* Read the header. This might happen currently with a write to the
  ** same area of shared memory on a different CPU in a SMP,
  ** meaning it is possible that an inconsistent snapshot is read
  ** from the file. If this happens, return non-zero.
  **
  ** There are two copies of the header at the beginning of the wal-index.
  ** When reading, read [0] first then [1].  Writes are in the reverse order.
  ** Memory barriers are used to prevent the compiler or the hardware from
  ** reordering the reads and writes.
  */
  aHdr = (WalIndexHdr*)pWal->pWiData;
  memcpy(&h1, &aHdr[0], sizeof(h1));
  sqlite3OsShmBarrier(pWal->pDbFd);
  memcpy(&h2, &aHdr[1], sizeof(h2));

  if( memcmp(&h1, &h2, sizeof(h1))!=0 ){
    return 1;   /* Dirty read */
  }  
  if( h1.isInit==0 ){
    return 1;   /* Malformed header - probably all zeros */
  }
................................................................................
**
** If the wal-index header is successfully read, return SQLITE_OK. 
** Otherwise an SQLite error code.
*/
static int walIndexReadHdr(Wal *pWal, int *pChanged){
  int rc;                         /* Return code */
  int badHdr;                     /* True if a header read failed */





  assert( pChanged );
  rc = walIndexMap(pWal, walMappingSize(1));

  if( rc!=SQLITE_OK ){
    return rc;
  }


  /* Try once to read the header straight out.  This works most of the
  ** time.




  */
  badHdr = walIndexTryHdr(pWal, pChanged);

  /* If the first attempt failed, it might have been due to a race
  ** with a writer.  So get a WRITE lock and try again.
  */
  assert( badHdr==0 || pWal->writeLock==0 );
  if( badHdr ){
    rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1);
    if( rc==SQLITE_OK ){
      pWal->writeLock = 1;

      badHdr = walIndexTryHdr(pWal, pChanged);
      if( badHdr ){
        /* If the wal-index header is still malformed even while holding
        ** a WRITE lock, it can only mean that the header is corrupted and
        ** needs to be reconstructed.  So run recovery to do exactly that.
        */
        rc = walIndexRecover(pWal);
        *pChanged = 1;
      }
      walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
      pWal->writeLock = 0;
    }
  }

  /* Make sure the mapping is large enough to cover the entire wal-index */
  if( rc==SQLITE_OK ){
    int szWanted = walMappingSize(pWal->hdr.mxFrame);
    if( pWal->szWIndex<szWanted ){
      rc = walIndexMap(pWal, szWanted);
    }


  }

  return rc;
}

/*
** This is the value that walTryBeginRead returns when it needs to
................................................................................
** to select a particular WAL_READ_LOCK() that strives to let the
** checkpoint process do as much work as possible.  This routine might
** update values of the aReadMark[] array in the header, but if it does
** so it takes care to hold an exclusive lock on the corresponding
** WAL_READ_LOCK() while changing values.
*/
static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
  volatile WalIndexHdr *pHdr;     /* Header of the wal-index */
  volatile WalCkptInfo *pInfo;    /* Checkpoint information in wal-index */
  u32 mxReadMark;                 /* Largest aReadMark[] value */
  int mxI;                        /* Index of largest aReadMark[] value */
  int i;                          /* Loop counter */
  int rc;                         /* Return code  */

  assert( pWal->readLock<0 );     /* Not currently locked */

  /* Take steps to avoid spinning forever if there is a protocol error. */
  if( cnt>5 ){
    if( cnt>100 ) return SQLITE_PROTOCOL;
    sqlite3OsSleep(pWal->pVfs, 1);
................................................................................
      if( rc==SQLITE_OK ){
        walUnlockShared(pWal, WAL_RECOVER_LOCK);
        rc = WAL_RETRY;
      }else if( rc==SQLITE_BUSY ){
        rc = SQLITE_BUSY_RECOVERY;
      }
    }
  }else{
    rc = walIndexMap(pWal, walMappingSize(pWal->hdr.mxFrame));
  }
  if( rc!=SQLITE_OK ){
    return rc;
  }

  pHdr = (volatile WalIndexHdr*)pWal->pWiData;
  pInfo = (volatile WalCkptInfo*)&pHdr[2];
  assert( pInfo==walCkptInfo(pWal) );
  if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame ){
    /* The WAL has been completely backfilled (or it is empty).
    ** and can be safely ignored.
    */
    rc = walLockShared(pWal, WAL_READ_LOCK(0));
    sqlite3OsShmBarrier(pWal->pDbFd);
    if( rc==SQLITE_OK ){
      if( memcmp((void *)pHdr, &pWal->hdr, sizeof(WalIndexHdr)) ){
        /* It is not safe to allow the reader to continue here if frames
        ** may have been appended to the log before READ_LOCK(0) was obtained.
        ** When holding READ_LOCK(0), the reader ignores the entire log file,
        ** which implies that the database file contains a trustworthy
        ** snapshoT. Since holding READ_LOCK(0) prevents a checkpoint from
        ** happening, this is usually correct.
        **
................................................................................
    ** date before proceeding. That would not be possible without somehow
    ** blocking writers. It only guarantees that a dangerous checkpoint or 
    ** log-wrap (either of which would require an exclusive lock on
    ** WAL_READ_LOCK(mxI)) has not occurred since the snapshot was valid.
    */
    sqlite3OsShmBarrier(pWal->pDbFd);
    if( pInfo->aReadMark[mxI]!=mxReadMark
     || memcmp((void *)pHdr, &pWal->hdr, sizeof(WalIndexHdr))
    ){
      walUnlockShared(pWal, WAL_READ_LOCK(mxI));
      return WAL_RETRY;
    }else{
      assert( mxReadMark<=pWal->hdr.mxFrame );
      pWal->readLock = mxI;
    }
................................................................................
int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
  int rc;                         /* Return code */
  int cnt = 0;                    /* Number of TryBeginRead attempts */

  do{
    rc = walTryBeginRead(pWal, pChanged, 0, ++cnt);
  }while( rc==WAL_RETRY );
  walIndexUnmap(pWal);
  return rc;
}

/*
** Finish with a read transaction.  All this does is release the
** read-lock.
*/
................................................................................
int sqlite3WalRead(
  Wal *pWal,                      /* WAL handle */
  Pgno pgno,                      /* Database page number to read data for */
  int *pInWal,                    /* OUT: True if data is read from WAL */
  int nOut,                       /* Size of buffer pOut in bytes */
  u8 *pOut                        /* Buffer to write page data to */
){
  int rc;                         /* Return code */
  u32 iRead = 0;                  /* If !=0, WAL frame to return data from */
  u32 iLast = pWal->hdr.mxFrame;  /* Last page in WAL for this reader */
  int iHash;                      /* Used to loop through N hash tables */

  /* This routine is only be called from within a read transaction. */
  assert( pWal->readLock>=0 || pWal->lockError );

................................................................................
  ** return early, as if the WAL were empty.
  */
  if( iLast==0 || pWal->readLock==0 ){
    *pInWal = 0;
    return SQLITE_OK;
  }

  /* Ensure the wal-index is mapped. */
  rc = walIndexMap(pWal, walMappingSize(iLast));
  if( rc!=SQLITE_OK ){
    return rc;
  }

  /* Search the hash table or tables for an entry matching page number
  ** pgno. Each iteration of the following for() loop searches one
  ** hash table (each hash table indexes up to HASHTABLE_NPAGE frames).
  **
  ** This code may run concurrently to the code in walIndexAppend()
  ** that adds entries to the wal-index (and possibly to this hash 
  ** table). This means the value just read from the hash 
................................................................................
  **   (aPgno[iFrame]==pgno): 
  **     This condition filters out normal hash-table collisions.
  **
  **   (iFrame<=iLast): 
  **     This condition filters out entries that were added to the hash
  **     table after the current read-transaction had started.
  */
  for(iHash=iLast; iHash>0 && iRead==0; iHash-=HASHTABLE_NPAGE){
    volatile HASHTABLE_DATATYPE *aHash;  /* Pointer to hash table */
    volatile u32 *aPgno;                 /* Pointer to array of page numbers */
    u32 iZero;                    /* Frame number corresponding to aPgno[0] */
    int iKey;                     /* Hash slot index */
    int mxHash;                   /* upper bound on aHash[] values */

    walHashFind(pWal, iHash, &aHash, &aPgno, &iZero);
    mxHash = iLast - iZero;
    if( mxHash > HASHTABLE_NPAGE )  mxHash = HASHTABLE_NPAGE;

    for(iKey=walHash(pgno); aHash[iKey]; iKey=walNextHash(iKey)){
      u32 iFrame = aHash[iKey] + iZero;
      if( iFrame<=iLast && aPgno[iFrame]==pgno ){
        assert( iFrame>iRead );
        iRead = iFrame;
      }
    }
  }
  assert( iRead==0 || pWal->pWiData[walIndexEntry(iRead)]==pgno );

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* If expensive assert() statements are available, do a linear search
  ** of the wal-index file content. Make sure the results agree with the
  ** result obtained using the hash indexes above.  */
  {
    u32 iRead2 = 0;
    u32 iTest;
    for(iTest=iLast; iTest>0; iTest--){
      if( pWal->pWiData[walIndexEntry(iTest)]==pgno ){
        iRead2 = iTest;
        break;
      }
    }
    assert( iRead==iRead2 );
  }
#endif

  /* If iRead is non-zero, then it is the log frame number that contains the
  ** required page. Read and return data from the log file.
  */
  walIndexUnmap(pWal);
  if( iRead ){
    i64 iOffset = walFrameOffset(iRead, pWal->hdr.szPage) + WAL_FRAME_HDRSIZE;
    *pInWal = 1;
    return sqlite3OsRead(pWal->pWalFd, pOut, nOut, iOffset);
  }

  *pInWal = 0;
................................................................................
  }
  pWal->writeLock = 1;

  /* If another connection has written to the database file since the
  ** time the read transaction on this connection was started, then
  ** the write is disallowed.
  */
  rc = walIndexMap(pWal, walMappingSize(pWal->hdr.mxFrame));
  if( rc ){
    walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
    pWal->writeLock = 0;
    return rc;
  }
  if( memcmp(&pWal->hdr, (void*)pWal->pWiData, sizeof(WalIndexHdr))!=0 ){
    walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
    pWal->writeLock = 0;
    rc = SQLITE_BUSY;
  }

  walIndexUnmap(pWal);
  return rc;
}

/*
** End a write transaction.  The commit has already been done.  This
** routine merely releases the lock.
*/
................................................................................
**
** Otherwise, if the callback function does not return an error, this
** function returns SQLITE_OK.
*/
int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){
  int rc = SQLITE_OK;
  if( pWal->writeLock ){
    int unused;
    Pgno iMax = pWal->hdr.mxFrame;
    Pgno iFrame;
  

    assert( pWal->pWiData==0 );
    rc = walIndexReadHdr(pWal, &unused);

    if( rc==SQLITE_OK ){
      rc = walIndexMap(pWal, walMappingSize(iMax));
    }
    if( rc==SQLITE_OK ){
      for(iFrame=pWal->hdr.mxFrame+1; 
          ALWAYS(rc==SQLITE_OK) && iFrame<=iMax; 
          iFrame++
      ){
        /* This call cannot fail. Unless the page for which the page number
        ** is passed as the second argument is (a) in the cache and 
        ** (b) has an outstanding reference, then xUndo is either a no-op
        ** (if (a) is false) or simply expels the page from the cache (if (b)
        ** is false).
        **
        ** If the upper layer is doing a rollback, it is guaranteed that there
        ** are no outstanding references to any page other than page 1. And
        ** page 1 is never written to the log until the transaction is
        ** committed. As a result, the call to xUndo may not fail.
        */
        assert( pWal->writeLock );
        assert( pWal->pWiData[walIndexEntry(iFrame)]!=1 );

        rc = xUndo(pUndoCtx, pWal->pWiData[walIndexEntry(iFrame)]);
      }
      walCleanupHash(pWal);
    }
    walIndexUnmap(pWal);
  }

  return rc;
}

/* 
** Argument aWalData must point to an array of WAL_SAVEPOINT_NDATA u32 
** values. This function populates the array with values required to 
** "rollback" the write position of the WAL handle back to the current 
................................................................................
    ** to the start of the log. Update the savepoint values to match.
    */
    aWalData[0] = 0;
    aWalData[3] = pWal->nCkpt;
  }

  if( aWalData[0]<pWal->hdr.mxFrame ){
    rc = walIndexMap(pWal, walMappingSize(pWal->hdr.mxFrame));
    pWal->hdr.mxFrame = aWalData[0];
    pWal->hdr.aFrameCksum[0] = aWalData[1];
    pWal->hdr.aFrameCksum[1] = aWalData[2];
    if( rc==SQLITE_OK ){
      walCleanupHash(pWal);
    }
  }

  walIndexUnmap(pWal);
  return rc;
}

/*
** This function is called just before writing a set of frames to the log
** file (see sqlite3WalFrames()). It checks to see if, instead of appending
** to the current log file, it is possible to overwrite the start of the
................................................................................
** or not pWal->hdr.mxFrame is modified). An SQLite error code is returned
** if some error 
*/
static int walRestartLog(Wal *pWal){
  int rc = SQLITE_OK;
  int cnt;

  if( pWal->readLock==0 
   && SQLITE_OK==(rc = walIndexMap(pWal, walMappingSize(pWal->hdr.mxFrame)))
  ){
    volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
    assert( pInfo->nBackfill==pWal->hdr.mxFrame );
    if( pInfo->nBackfill>0 ){
      rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
      if( rc==SQLITE_OK ){
        /* If all readers are using WAL_READ_LOCK(0) (in other words if no
        ** readers are currently using the WAL), then the transactions
................................................................................
    walUnlockShared(pWal, WAL_READ_LOCK(0));
    pWal->readLock = -1;
    cnt = 0;
    do{
      int notUsed;
      rc = walTryBeginRead(pWal, &notUsed, 1, ++cnt);
    }while( rc==WAL_RETRY );

    /* Unmap the wal-index before returning. Otherwise the VFS layer may
    ** hold a mutex for the duration of the IO performed by WalFrames().
    */
    walIndexUnmap(pWal);
  }
  return rc;
}

/* 
** Write a set of frames to the log. The caller must hold the write-lock
** on the log file (obtained using sqlite3WalBeginWriteTransaction()).
................................................................................
  u8 aFrame[WAL_FRAME_HDRSIZE];   /* Buffer to assemble frame-header in */
  PgHdr *p;                       /* Iterator to run through pList with. */
  PgHdr *pLast = 0;               /* Last frame in list */
  int nLast = 0;                  /* Number of extra copies of last page */

  assert( pList );
  assert( pWal->writeLock );
  assert( pWal->pWiData==0 );

#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
  { int cnt; for(cnt=0, p=pList; p; p=p->pDirty, cnt++){}
    WALTRACE(("WAL%p: frame write begin. %d frames. mxFrame=%d. %s\n",
              pWal, cnt, pWal->hdr.mxFrame, isCommit ? "Commit" : "Spill"));
  }
#endif

  /* See if it is possible to write these frames into the start of the
  ** log file, instead of appending to it at pWal->hdr.mxFrame.
  */
  if( SQLITE_OK!=(rc = walRestartLog(pWal)) ){
    assert( pWal->pWiData==0 );
    return rc;
  }
  assert( pWal->pWiData==0 && pWal->readLock>0 );

  /* If this is the first frame written into the log, write the WAL
  ** header to the start of the WAL file. See comments at the top of
  ** this source file for a description of the WAL header format.
  */
  iFrame = pWal->hdr.mxFrame;
  if( iFrame==0 ){
................................................................................
      }
      nLast++;
      iOffset += szPage;
    }

    rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
  }
  assert( pWal->pWiData==0 );

  /* Append data to the wal-index. It is not necessary to lock the 
  ** wal-index to do this as the SQLITE_SHM_WRITE lock held on the wal-index
  ** guarantees that there are no other writers, and no data that may
  ** be in use by existing readers is being overwritten.
  */
  iFrame = pWal->hdr.mxFrame;
................................................................................
    /* If this is a commit, update the wal-index header too. */
    if( isCommit ){
      walIndexWriteHdr(pWal);
      pWal->iCallback = iFrame;
    }
  }

  walIndexUnmap(pWal);
  WALTRACE(("WAL%p: frame write %s\n", pWal, rc ? "failed" : "ok"));
  return rc;
}

/* 
** This routine is called to implement sqlite3_wal_checkpoint() and
** related interfaces.
................................................................................
  int sync_flags,                 /* Flags to sync db file with (or 0) */
  int nBuf,                       /* Size of temporary buffer */
  u8 *zBuf                        /* Temporary buffer to use */
){
  int rc;                         /* Return code */
  int isChanged = 0;              /* True if a new wal-index header is loaded */

  assert( pWal->pWiData==0 );
  assert( pWal->ckptLock==0 );

  WALTRACE(("WAL%p: checkpoint begins\n", pWal));
  rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
  if( rc ){
    /* Usually this is SQLITE_BUSY meaning that another thread or process
    ** is already running a checkpoint, or maybe a recovery.  But it might
................................................................................
    ** next time the pager opens a snapshot on this database it knows that
    ** the cache needs to be reset.
    */
    memset(&pWal->hdr, 0, sizeof(WalIndexHdr));
  }

  /* Release the locks. */
  walIndexUnmap(pWal);
  walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
  pWal->ckptLock = 0;
  WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok"));
  return rc;
}

/* Return the value to pass to a sqlite3_wal_hook callback, the







|
>
>
|
<
<
|
|
|
|
|
|
>
>
>
>
>
>
>
>
>
>
>
>
>
|
<


|







 







|
|







 







|
>

<
|
<
<
<







 







|
|
<

|
|
|
>
|
>

>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>







 







|
>



|
<
<
|

|







 







<
<
<
<
<
<
<
<
<
<
<
<
<







 







<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<







 







<

>
|
|







|
|
<

<
>

<
>
|



|

<

>
|
<
<

>
>
|
<
>
|
<
>
|
|
<
>
|
<
|
>
>
|
<
|
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>







 







|
|
|
|
>
>





>
|
<
<

>
>
>
>
>
>
>
>
>
|
>
|
|
|
|
|
|
|
|
|
|
|
<
>
|
<
<









|







 







|
>
>
|
<
<
|
<
<
|
<
|
<
<
|



<
<
<
|
|

<

>
>
>
>
>

>
|
<

<

<
|
|
|
|
|
|
>

|

<
>
>



>







 







|







 







<
<
<







 







<







 







<





|




|





<







|
|
|
|






<
<



>
>


|
|


|







 







>
>
>
>
>
>
>







 







<
|
|
|
|
|
<
|
<
<
<
<
>




|


|


|
|
<
|
>






|
<
<
<

|
|

>

>
>
|
|
<
>
>
>
>
>
>
>
>
>
>
|


>
>
>
>
|
<
|
<

>

|




<
<
<
<
<
<
<







 







<







 







<
<
|







 







>











|







 







<








>







 







|
|
|

|
<
<
<
<
|











|
|

|







 







>

>
>
>

<
>


|
>

<
<
>
>
>
>

|





<
|
<
|
>









<
<

<
<
<
<
<
<
<
<
>
>







 







<




|







 







<
<





<
<
|







|







 







|







 







<







 







<







 







<
<
<
<
<
<







 







|
|
|


|

|
|
|
>


|





<









|











<







 







<
<
<
<
<
<
|





<







 







<



>
|
<
>
|
<
|
<
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<
<
>
|
|
|
|
<
<
>







 







<



<
|
|
|
<
<







 







|
<
<







 







<
<
<
<
<







 







<












<


<







 







<







 







<







 







<







 







<







137
138
139
140
141
142
143
144
145
146
147


148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167

168
169
170
171
172
173
174
175
176
177
...
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
...
395
396
397
398
399
400
401
402
403
404

405



406
407
408
409
410
411
412
...
416
417
418
419
420
421
422
423
424

425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
...
570
571
572
573
574
575
576
577
578
579
580
581
582


583
584
585
586
587
588
589
590
591
592
...
669
670
671
672
673
674
675













676
677
678
679
680
681
682
...
733
734
735
736
737
738
739


























































































740
741
742
743
744
745
746
...
747
748
749
750
751
752
753

754
755
756
757
758
759
760
761
762
763
764
765
766

767

768
769

770
771
772
773
774
775
776

777
778
779


780
781
782
783

784
785

786
787
788

789
790

791
792
793
794

795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
...
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853


854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876

877
878


879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
...
897
898
899
900
901
902
903
904
905
906
907


908


909

910


911
912
913
914



915
916
917

918
919
920
921
922
923
924
925
926

927

928

929
930
931
932
933
934
935
936
937
938

939
940
941
942
943
944
945
946
947
948
949
950
951
...
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
....
1091
1092
1093
1094
1095
1096
1097



1098
1099
1100
1101
1102
1103
1104
....
1176
1177
1178
1179
1180
1181
1182

1183
1184
1185
1186
1187
1188
1189
....
1218
1219
1220
1221
1222
1223
1224

1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240

1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257


1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
....
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
....
1316
1317
1318
1319
1320
1321
1322

1323
1324
1325
1326
1327

1328




1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341

1342
1343
1344
1345
1346
1347
1348
1349
1350



1351
1352
1353
1354
1355
1356
1357
1358
1359
1360

1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378

1379

1380
1381
1382
1383
1384
1385
1386
1387







1388
1389
1390
1391
1392
1393
1394
....
1425
1426
1427
1428
1429
1430
1431

1432
1433
1434
1435
1436
1437
1438
....
1445
1446
1447
1448
1449
1450
1451


1452
1453
1454
1455
1456
1457
1458
1459
....
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
....
1539
1540
1541
1542
1543
1544
1545

1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
....
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582




1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
....
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647

1648
1649
1650
1651
1652
1653


1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664

1665

1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676


1677








1678
1679
1680
1681
1682
1683
1684
1685
1686
....
1713
1714
1715
1716
1717
1718
1719

1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
....
1746
1747
1748
1749
1750
1751
1752


1753
1754
1755
1756
1757


1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
....
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
....
1886
1887
1888
1889
1890
1891
1892

1893
1894
1895
1896
1897
1898
1899
....
1915
1916
1917
1918
1919
1920
1921

1922
1923
1924
1925
1926
1927
1928
....
1933
1934
1935
1936
1937
1938
1939






1940
1941
1942
1943
1944
1945
1946
....
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983

1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004

2005
2006
2007
2008
2009
2010
2011
....
2051
2052
2053
2054
2055
2056
2057






2058
2059
2060
2061
2062
2063

2064
2065
2066
2067
2068
2069
2070
....
2085
2086
2087
2088
2089
2090
2091

2092
2093
2094
2095
2096

2097
2098

2099

2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114


2115
2116
2117
2118
2119


2120
2121
2122
2123
2124
2125
2126
2127
....
2153
2154
2155
2156
2157
2158
2159

2160
2161
2162

2163
2164
2165


2166
2167
2168
2169
2170
2171
2172
....
2178
2179
2180
2181
2182
2183
2184
2185


2186
2187
2188
2189
2190
2191
2192
....
2214
2215
2216
2217
2218
2219
2220





2221
2222
2223
2224
2225
2226
2227
....
2239
2240
2241
2242
2243
2244
2245

2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257

2258
2259

2260
2261
2262
2263
2264
2265
2266
....
2327
2328
2329
2330
2331
2332
2333

2334
2335
2336
2337
2338
2339
2340
....
2359
2360
2361
2362
2363
2364
2365

2366
2367
2368
2369
2370
2371
2372
....
2379
2380
2381
2382
2383
2384
2385

2386
2387
2388
2389
2390
2391
2392
....
2407
2408
2409
2410
2411
2412
2413

2414
2415
2416
2417
2418
2419
2420
** a page number P, return the index of the last frame for page P in the WAL,
** or return NULL if there are no frames for page P in the WAL.
**
** The wal-index consists of a header region, followed by an one or
** more index blocks.  
**
** The wal-index header contains the total number of frames within the WAL
** in the the mxFrame field.  
**
** Each index block except for the first contains information on 
** HASHTABLE_NPAGE frames. The first index block contains information on


** HASHTABLE_NPAGE_ONE frames. The values of HASHTABLE_NPAGE_ONE and 
** HASHTABLE_NPAGE are selected so that together the wal-index header and
** first index block are the same size as all other index blocks in the
** wal-index.
**
** Each index block contains two sections, a page-mapping that contains the
** database page number associated with each wal frame, and a hash-table 
** that allows users to query an index block for a specific page number.
** The page-mapping is an array of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE
** for the first index block) 32-bit page numbers. The first entry in the 
** first index-block contains the database page number corresponding to the
** first frame in the WAL file. The first entry in the second index block
** in the WAL file corresponds to the (HASHTABLE_NPAGE_ONE+1)th frame in
** the log, and so on.
**
** The last index block in a wal-index usually contains less than the full
** complement of HASHTABLE_NPAGE (or HASHTABLE_NPAGE_ONE) page-numbers,
** depending on the contents of the WAL file. This does not change the
** allocated size of the page-mapping array - the page-mapping array merely
** contains unused entries.

**
** Even without using the hash table, the last frame for page P
** can be found by scanning the page-mapping sections of each index block
** starting with the last index block and moving toward the first, and
** within each index block, starting at the end and moving toward the
** beginning.  The first entry that equals P corresponds to the frame
** holding the content for that page.
**
** The hash table consists of HASHTABLE_NSLOT 16-bit unsigned integers.
** HASHTABLE_NSLOT = 2*HASHTABLE_NPAGE, and there is one entry in the
................................................................................
** following object.
*/
struct Wal {
  sqlite3_vfs *pVfs;         /* The VFS used to create pDbFd */
  sqlite3_file *pDbFd;       /* File handle for the database file */
  sqlite3_file *pWalFd;      /* File handle for WAL file */
  u32 iCallback;             /* Value to pass to log callback (or 0) */
  int nWiData;               /* Size of array apWiData */
  volatile u32 **apWiData;   /* Pointer to wal-index content in memory */
  u16 szPage;                /* Database page size */
  i16 readLock;              /* Which read lock is being held.  -1 for none */
  u8 exclusiveMode;          /* Non-zero if connection is in exclusive mode */
  u8 isWIndexOpen;           /* True if ShmOpen() called on pDbFd */
  u8 writeLock;              /* True if in a write transaction */
  u8 ckptLock;               /* True if holding a checkpoint lock */
  WalIndexHdr hdr;           /* Wal-index header for current transaction */
................................................................................
  u32 nCkpt;                 /* Checkpoint sequence counter in the wal-header */
#ifdef SQLITE_DEBUG
  u8 lockError;              /* True if a locking error has occurred */
#endif
};

/*
** Each page of the wal-index mapping contains a hash-table made up of
** an array of HASHTABLE_NSLOT elements of the following type.
*/

typedef u16 ht_slot;




/*
** This structure is used to implement an iterator that loops through
** all frames in the WAL in database page order. Where two or more frames
** correspond to the same database page, the iterator visits only the 
** frame most recently written to the WAL (in other words, the frame with
** the largest index).
................................................................................
**   walIteratorInit() - Create a new iterator,
**   walIteratorNext() - Step an iterator,
**   walIteratorFree() - Free an iterator.
**
** This functionality is used by the checkpoint code (see walCheckpoint()).
*/
struct WalIterator {
  int iPrior;                     /* Last result returned from the iterator */
  int nSegment;                   /* Size of the aSegment[] array */

  struct WalSegment {
    int iNext;                    /* Next slot in aIndex[] not yet returned */
    ht_slot *aIndex;              /* i0, i1, i2... such that aPgno[iN] ascend */
    u32 *aPgno;                   /* Array of page numbers. */
    int nEntry;                   /* Max size of aPgno[] and aIndex[] arrays */
    int iZero;                    /* Frame number associated with aPgno[0] */
  } aSegment[1];                  /* One for every 32KB page in the WAL */
};

/*
** Define the parameters of the hash tables in the wal-index file. There
** is a hash-table following every HASHTABLE_NPAGE page numbers in the
** wal-index.
**
** Changing any of these constants will alter the wal-index format and
** create incompatibilities.
*/
#define HASHTABLE_NPAGE      4096                 /* Must be power of 2 */
#define HASHTABLE_HASH_1     383                  /* Should be prime */
#define HASHTABLE_NSLOT      (HASHTABLE_NPAGE*2)  /* Must be a power of 2 */

/* 
** The block of page numbers associated with the first hash-table in a
** wal-index is smaller than usual. This is so that there is a complete
** hash-table on each aligned 32KB page of the wal-index.
*/
#define HASHTABLE_NPAGE_ONE  (HASHTABLE_NPAGE - (WALINDEX_HDR_SIZE/sizeof(u32)))

/* The wal-index is divided into pages of WALINDEX_PGSZ bytes each. */
#define WALINDEX_PGSZ   (                                         \
    sizeof(ht_slot)*HASHTABLE_NSLOT + HASHTABLE_NPAGE*sizeof(u32) \
)

/*
** Obtain a pointer to the iPage'th page of the wal-index. The wal-index
** is broken into pages of WALINDEX_PGSZ bytes. Wal-index pages are
** numbered from zero.
**
** If this call is successful, *ppPage is set to point to the wal-index
** page and SQLITE_OK is returned. If an error (an OOM or VFS error) occurs,
** then an SQLite error code is returned and *ppPage is set to 0.
*/
static int walIndexPage(Wal *pWal, int iPage, volatile u32 **ppPage){
  int rc = SQLITE_OK;

  /* Enlarge the pWal->apWiData[] array if required */
  if( pWal->nWiData<=iPage ){
    int nByte = sizeof(u32 *)*(iPage+1);
    volatile u32 **apNew;
    apNew = (volatile u32 **)sqlite3_realloc(pWal->apWiData, nByte);
    if( !apNew ){
      *ppPage = 0;
      return SQLITE_NOMEM;
    }
    memset(&apNew[pWal->nWiData], 0, sizeof(u32 *)*(iPage+1-pWal->nWiData));
    pWal->apWiData = apNew;
    pWal->nWiData = iPage+1;
  }

  /* Request a pointer to the required page from the VFS */
  if( pWal->apWiData[iPage]==0 ){
    rc = sqlite3OsShmMap(pWal->pDbFd, iPage, WALINDEX_PGSZ, 
        pWal->writeLock, (void volatile **)&pWal->apWiData[iPage]
    );
  }

  *ppPage = pWal->apWiData[iPage];
  assert( iPage==0 || *ppPage || rc!=SQLITE_OK );
  return rc;
}

/*
** Return a pointer to the WalCkptInfo structure in the wal-index.
*/
static volatile WalCkptInfo *walCkptInfo(Wal *pWal){
  assert( pWal->nWiData>0 && pWal->apWiData[0] );
  return (volatile WalCkptInfo*)&(pWal->apWiData[0][sizeof(WalIndexHdr)/2]);
}

/*
** Return a pointer to the WalIndexHdr structure in the wal-index.
*/
static volatile WalIndexHdr *walIndexHdr(Wal *pWal){
  assert( pWal->nWiData>0 && pWal->apWiData[0] );
  return (volatile WalIndexHdr*)pWal->apWiData[0];
}

/*
** The argument to this macro must be of type u32. On a little-endian
** architecture, it returns the u32 value that results from interpreting
** the 4 bytes as a big-endian value. On a big-endian architecture, it
** returns the value that would be produced by intepreting the 4 bytes
** of the input value as a little-endian integer.
................................................................................

/*
** Write the header information in pWal->hdr into the wal-index.
**
** The checksum on pWal->hdr is updated before it is written.
*/
static void walIndexWriteHdr(Wal *pWal){
  volatile WalIndexHdr *aHdr = walIndexHdr(pWal);
  const int nCksum = offsetof(WalIndexHdr, aCksum);

  assert( pWal->writeLock );
  pWal->hdr.isInit = 1;
  walChecksumBytes(1, (u8*)&pWal->hdr, nCksum, 0, pWal->hdr.aCksum);


  memcpy((void *)&aHdr[1], (void *)&pWal->hdr, sizeof(WalIndexHdr));
  sqlite3OsShmBarrier(pWal->pDbFd);
  memcpy((void *)&aHdr[0], (void *)&pWal->hdr, sizeof(WalIndexHdr));
}

/*
** This function encodes a single frame header and writes it to a buffer
** supplied by the caller. A frame-header is made up of a series of 
** 4-byte big-endian integers, as follows:
**
................................................................................
  ** and the new database size.
  */
  *piPage = pgno;
  *pnTruncate = sqlite3Get4byte(&aFrame[4]);
  return 1;
}















#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
/*
** Names of locks.  This routine is used to provide debugging output and is not
** a part of an ordinary build.
*/
static const char *walLockName(int lockIdx){
................................................................................
  if( pWal->exclusiveMode ) return;
  (void)sqlite3OsShmLock(pWal->pDbFd, lockIdx, n,
                         SQLITE_SHM_UNLOCK | SQLITE_SHM_EXCLUSIVE);
  WALTRACE(("WAL%p: release EXCLUSIVE-%s cnt=%d\n", pWal,
             walLockName(lockIdx), n));
}



























































































/*
** Compute a hash on a page number.  The resulting hash value must land
** between 0 and (HASHTABLE_NSLOT-1).  The walHashNext() function advances
** the hash to the next value in the event of a collision.
*/
static int walHash(u32 iPage){
  assert( iPage>0 );
................................................................................
  assert( (HASHTABLE_NSLOT & (HASHTABLE_NSLOT-1))==0 );
  return (iPage*HASHTABLE_HASH_1) & (HASHTABLE_NSLOT-1);
}
static int walNextHash(int iPriorHash){
  return (iPriorHash+1)&(HASHTABLE_NSLOT-1);
}


/* 
** Return pointers to the hash table and page number array stored on
** page iHash of the wal-index. The wal-index is broken into 32KB pages
** numbered starting from 0.
**
** Set output variable *paHash to point to the start of the hash table
** in the wal-index file. Set *piZero to one less than the frame 
** number of the first frame indexed by this hash table. If a
** slot in the hash table is set to N, it refers to frame number 
** (*piZero+N) in the log.
**
** Finally, set *paPgno so that *paPgno[1] is the page number of the
** first frame indexed by the hash table, frame (*piZero+1).

*/

static int walHashGet(
  Wal *pWal,                      /* WAL handle */

  int iHash,                      /* Find the iHash'th table */
  volatile ht_slot **paHash,      /* OUT: Pointer to hash index */
  volatile u32 **paPgno,          /* OUT: Pointer to page number array */
  u32 *piZero                     /* OUT: Frame associated with *paPgno[0] */
){
  int rc;                         /* Return code */
  volatile u32 *aPgno;


  rc = walIndexPage(pWal, iHash, &aPgno);
  assert( rc==SQLITE_OK || iHash>0 );



  if( rc==SQLITE_OK ){
    u32 iZero;
    volatile ht_slot *aHash;


    aHash = (volatile ht_slot *)&aPgno[HASHTABLE_NPAGE];

    if( iHash==0 ){
      aPgno = &aPgno[WALINDEX_HDR_SIZE/sizeof(u32)];
      iZero = 0;

    }else{
      iZero = HASHTABLE_NPAGE_ONE + (iHash-1)*HASHTABLE_NPAGE;

    }
  
    *paPgno = &aPgno[-1];
    *paHash = aHash;

    *piZero = iZero;
  }
  return rc;
}

/*
** Return the number of the wal-index page that contains the hash-table
** and page-number array that contain entries corresponding to WAL frame
** iFrame. The wal-index is broken up into 32KB pages. Wal-index pages 
** are numbered starting from 0.
*/
static int walFramePage(u32 iFrame){
  int iHash = (iFrame+HASHTABLE_NPAGE-HASHTABLE_NPAGE_ONE-1) / HASHTABLE_NPAGE;
  assert( (iHash==0 || iFrame>HASHTABLE_NPAGE_ONE)
       && (iHash>=1 || iFrame<=HASHTABLE_NPAGE_ONE)
       && (iHash<=1 || iFrame>(HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE))
       && (iHash>=2 || iFrame<=HASHTABLE_NPAGE_ONE+HASHTABLE_NPAGE)
       && (iHash<=2 || iFrame>(HASHTABLE_NPAGE_ONE+2*HASHTABLE_NPAGE))
  );
  return iHash;
}

/*
** Return the page number associated with frame iFrame in this WAL.
*/
static u32 walFramePgno(Wal *pWal, u32 iFrame){
  int iHash = walFramePage(iFrame);
  if( iHash==0 ){
    return pWal->apWiData[0][WALINDEX_HDR_SIZE/sizeof(u32) + iFrame - 1];
  }
  return pWal->apWiData[iHash][(iFrame-1-HASHTABLE_NPAGE_ONE)%HASHTABLE_NPAGE];
}

/*
** Remove entries from the hash table that point to WAL slots greater
** than pWal->hdr.mxFrame.
**
** This function is called whenever pWal->hdr.mxFrame is decreased due
................................................................................
**
** At most only the hash table containing pWal->hdr.mxFrame needs to be
** updated.  Any later hash tables will be automatically cleared when
** pWal->hdr.mxFrame advances to the point where those hash tables are
** actually needed.
*/
static void walCleanupHash(Wal *pWal){
  volatile ht_slot *aHash;        /* Pointer to hash table to clear */
  volatile u32 *aPgno;            /* Page number array for hash table */
  u32 iZero;                      /* frame == (aHash[x]+iZero) */
  int iLimit = 0;                 /* Zero values greater than this */
  int nByte;                      /* Number of bytes to zero in aPgno[] */
  int i;                          /* Used to iterate through aHash[] */

  assert( pWal->writeLock );
  testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE-1 );
  testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE );
  testcase( pWal->hdr.mxFrame==HASHTABLE_NPAGE+1 );

  if( pWal->hdr.mxFrame==0 ) return;



  /* Obtain pointers to the hash-table and page-number array containing 
  ** the entry that corresponds to frame pWal->hdr.mxFrame. It is guaranteed
  ** that the page said hash-table and array reside on is already mapped.
  */
  assert( pWal->nWiData>walFramePage(pWal->hdr.mxFrame) );
  assert( pWal->apWiData[walFramePage(pWal->hdr.mxFrame)] );
  walHashGet(pWal, walFramePage(pWal->hdr.mxFrame), &aHash, &aPgno, &iZero);

  /* Zero all hash-table entries that correspond to frame numbers greater
  ** than pWal->hdr.mxFrame.
  */
  iLimit = pWal->hdr.mxFrame - iZero;
  assert( iLimit>0 );
  for(i=0; i<HASHTABLE_NSLOT; i++){
    if( aHash[i]>iLimit ){
      aHash[i] = 0;
    }
  }
  
  /* Zero the entries in the aPgno array that correspond to frames with
  ** frame numbers greater than pWal->hdr.mxFrame. 
  */

  nByte = ((char *)aHash - (char *)&aPgno[iLimit+1]);
  memset((void *)&aPgno[iLimit+1], 0, nByte);



#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* Verify that the every entry in the mapping region is still reachable
  ** via the hash table even after the cleanup.
  */
  if( iLimit ){
    int i;           /* Loop counter */
    int iKey;        /* Hash key */
    for(i=1; i<=iLimit; i++){
      for(iKey=walHash(aPgno[i]); aHash[iKey]; iKey=walNextHash(iKey)){
        if( aHash[iKey]==i ) break;
      }
      assert( aHash[iKey]==i );
    }
  }
#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
}
................................................................................

/*
** Set an entry in the wal-index that will map database page number
** pPage into WAL frame iFrame.
*/
static int walIndexAppend(Wal *pWal, u32 iFrame, u32 iPage){
  int rc;                         /* Return code */
  u32 iZero;                      /* One less than frame number of aPgno[1] */
  volatile u32 *aPgno;            /* Page number array */
  volatile ht_slot *aHash;        /* Hash table */



  rc = walHashGet(pWal, walFramePage(iFrame), &aHash, &aPgno, &iZero);




  /* Assuming the wal-index file was successfully mapped, populate the


  ** page number array and hash table entry.
  */
  if( rc==SQLITE_OK ){
    int iKey;                     /* Hash table key */



    int idx;                      /* Value to write to hash-table slot */
    TESTONLY( int nCollide = 0;   /* Number of hash collisions */ )


    idx = iFrame - iZero;
    assert( idx <= HASHTABLE_NSLOT/2 + 1 );
    
    /* If this is the first entry to be added to this hash-table, zero the
    ** entire hash table and aPgno[] array before proceding. 
    */
    if( idx==1 ){
      int nByte = (u8 *)&aHash[HASHTABLE_NSLOT] - (u8 *)&aPgno[1];
      memset((void*)&aPgno[1], 0, nByte);

    }



    /* If the entry in aPgno[] is already set, then the previous writer
    ** must have exited unexpectedly in the middle of a transaction (after
    ** writing one or more dirty pages to the WAL to free up memory). 
    ** Remove the remnants of that writers uncommitted transaction from 
    ** the hash-table before writing any new entries.
    */
    if( aPgno[idx] ){
      walCleanupHash(pWal);
      assert( !aPgno[idx] );
    }


    /* Write the aPgno[] array entry and the hash-table slot. */
    for(iKey=walHash(iPage); aHash[iKey]; iKey=walNextHash(iKey)){
      assert( nCollide++ < idx );
    }
    aPgno[idx] = iPage;
    aHash[iKey] = idx;

#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
    /* Verify that the number of entries in the hash table exactly equals
    ** the number of entries in the mapping region.
    */
    {
................................................................................
    ** via the hash table.  This turns out to be a really, really expensive
    ** thing to check, so only do this occasionally - not on every
    ** iteration.
    */
    if( (idx&0x3ff)==0 ){
      int i;           /* Loop counter */
      for(i=1; i<=idx; i++){
        for(iKey=walHash(aPgno[i]); aHash[iKey]; iKey=walNextHash(iKey)){
          if( aHash[iKey]==i ) break;
        }
        assert( aHash[iKey]==i );
      }
    }
#endif /* SQLITE_ENABLE_EXPENSIVE_ASSERT */
  }
................................................................................
      }
    }

    sqlite3_free(aFrame);
  }

finished:



  if( rc==SQLITE_OK ){
    volatile WalCkptInfo *pInfo;
    int i;
    pWal->hdr.aFrameCksum[0] = aFrameCksum[0];
    pWal->hdr.aFrameCksum[1] = aFrameCksum[1];
    walIndexWriteHdr(pWal);

................................................................................
  if( !pRet ){
    return SQLITE_NOMEM;
  }

  pRet->pVfs = pVfs;
  pRet->pWalFd = (sqlite3_file *)&pRet[1];
  pRet->pDbFd = pDbFd;

  pRet->readLock = -1;
  sqlite3_randomness(8, &pRet->hdr.aSalt);
  pRet->zWalName = zWal = pVfs->szOsFile + (char*)pRet->pWalFd;
  sqlite3_snprintf(nWal, zWal, "%s-wal", zDbName);
  rc = sqlite3OsShmOpen(pDbFd);

  /* Open file handle on the write-ahead log file. */
................................................................................
  WalIterator *p,               /* Iterator */
  u32 *piPage,                  /* OUT: The page number of the next page */
  u32 *piFrame                  /* OUT: Wal frame index of next page */
){
  u32 iMin;                     /* Result pgno must be greater than iMin */
  u32 iRet = 0xFFFFFFFF;        /* 0xffffffff is never a valid page number */
  int i;                        /* For looping through segments */


  iMin = p->iPrior;
  assert( iMin<0xffffffff );
  for(i=p->nSegment-1; i>=0; i--){
    struct WalSegment *pSegment = &p->aSegment[i];
    while( pSegment->iNext<pSegment->nEntry ){
      u32 iPg = pSegment->aPgno[pSegment->aIndex[pSegment->iNext]];
      if( iPg>iMin ){
        if( iPg<iRet ){
          iRet = iPg;
          *piFrame = pSegment->iZero + pSegment->aIndex[pSegment->iNext];
        }
        break;
      }
      pSegment->iNext++;
    }

  }

  *piPage = p->iPrior = iRet;
  return (iRet==0xFFFFFFFF);
}


static void walMergesort(
  u32 *aContent,                  /* Pages in wal */
  ht_slot *aBuffer,               /* Buffer of at least *pnList items to use */
  ht_slot *aList,                 /* IN/OUT: List to sort */
  int *pnList                     /* IN/OUT: Number of elements in aList[] */
){
  int nList = *pnList;
  if( nList>1 ){
    int nLeft = nList / 2;        /* Elements in left list */
    int nRight = nList - nLeft;   /* Elements in right list */


    int iLeft = 0;                /* Current index in aLeft */
    int iRight = 0;               /* Current index in aright */
    int iOut = 0;                 /* Current index in output buffer */
    ht_slot *aLeft = aList;       /* Left list */
    ht_slot *aRight = aList+nLeft;/* Right list */

    /* TODO: Change to non-recursive version. */
    walMergesort(aContent, aBuffer, aLeft, &nLeft);
    walMergesort(aContent, aBuffer, aRight, &nRight);

    while( iRight<nRight || iLeft<nLeft ){
      ht_slot logpage;
      Pgno dbpage;

      if( (iLeft<nLeft) 
       && (iRight>=nRight || aContent[aLeft[iLeft]]<aContent[aRight[iRight]])
      ){
        logpage = aLeft[iLeft++];
      }else{
................................................................................
    int i;
    for(i=1; i<*pnList; i++){
      assert( aContent[aList[i]] > aContent[aList[i-1]] );
    }
  }
#endif
}

/* 
** Free an iterator allocated by walIteratorInit().
*/
static void walIteratorFree(WalIterator *p){
  sqlite3_free(p);
}

/*
** Map the wal-index into memory owned by this thread, if it is not
** mapped already.  Then construct a WalInterator object that can be
** used to loop over all pages in the WAL in ascending order.  
**
** On success, make *pp point to the newly allocated WalInterator object
................................................................................
**
** The calling routine should invoke walIteratorFree() to destroy the
** WalIterator object when it has finished with it.  The caller must
** also unmap the wal-index.  But the wal-index must not be unmapped
** prior to the WalIterator object being destroyed.
*/
static int walIteratorInit(Wal *pWal, WalIterator **pp){

  WalIterator *p;                 /* Return value */
  int nSegment;                   /* Number of segments to merge */
  u32 iLast;                      /* Last frame in log */
  int nByte;                      /* Number of bytes to allocate */
  int i;                          /* Iterator variable */

  ht_slot *aTmp;                  /* Temp space used by merge-sort */




  ht_slot *aSpace;                /* Space at the end of the allocation */

  /* This routine only runs while holding SQLITE_SHM_CHECKPOINT.  No other
  ** thread is able to write to shared memory while this routine is
  ** running (or, indeed, while the WalIterator object exists).  Hence,
  ** we can cast off the volatile qualification from shared memory
  */
  assert( pWal->ckptLock );
  iLast = pWal->hdr.mxFrame;

  /* Allocate space for the WalIterator object */
  nSegment = walFramePage(iLast) + 1;
  nByte = sizeof(WalIterator) 

        + nSegment*(sizeof(struct WalSegment))
        + (nSegment+1)*(HASHTABLE_NPAGE * sizeof(ht_slot));
  p = (WalIterator *)sqlite3_malloc(nByte);
  if( !p ){
    return SQLITE_NOMEM;
  }
  memset(p, 0, nByte);

  /* Allocate space for the WalIterator object */



  p->nSegment = nSegment;
  aSpace = (ht_slot *)&p->aSegment[nSegment];
  aTmp = &aSpace[HASHTABLE_NPAGE*nSegment];
  for(i=0; i<nSegment; i++){
    volatile ht_slot *aHash;
    int j;
    u32 iZero;
    int nEntry;
    volatile u32 *aPgno;
    int rc;


    rc = walHashGet(pWal, i, &aHash, &aPgno, &iZero);
    if( rc!=SQLITE_OK ){
      walIteratorFree(p);
      return rc;
    }
    aPgno++;
    nEntry = ((i+1)==nSegment)?iLast-iZero:(u32 *)aHash-(u32 *)aPgno;
    iZero++;

    for(j=0; j<nEntry; j++){
      aSpace[j] = j;
    }
    walMergesort((u32 *)aPgno, aTmp, aSpace, &nEntry);
    p->aSegment[i].iZero = iZero;
    p->aSegment[i].nEntry = nEntry;
    p->aSegment[i].aIndex = aSpace;
    p->aSegment[i].aPgno = (u32 *)aPgno;

    aSpace += HASHTABLE_NPAGE;

  }
  assert( aSpace==aTmp );

  /* Return the fully initialized WalIterator object */
  *pp = p;
  return SQLITE_OK ;
}








/*
** Copy as much content as we can from the WAL back into the database file
** in response to an sqlite3_wal_checkpoint() request or the equivalent.
**
** The amount of information copies from WAL to database might be limited
** by active readers.  This routine will never overwrite a database page
** that a concurrent reader might be using.
................................................................................
  int rc;                         /* Return code */
  int szPage = pWal->hdr.szPage;  /* Database page-size */
  WalIterator *pIter = 0;         /* Wal iterator context */
  u32 iDbpage = 0;                /* Next database page to write */
  u32 iFrame = 0;                 /* Wal frame containing data for iDbpage */
  u32 mxSafeFrame;                /* Max frame that can be backfilled */
  int i;                          /* Loop counter */

  volatile WalCkptInfo *pInfo;    /* The checkpoint status information */

  /* Allocate the iterator */
  rc = walIteratorInit(pWal, &pIter);
  if( rc!=SQLITE_OK || pWal->hdr.mxFrame==0 ){
    goto walcheckpoint_out;
  }
................................................................................

  /* Compute in mxSafeFrame the index of the last frame of the WAL that is
  ** safe to write into the database.  Frames beyond mxSafeFrame might
  ** overwrite database pages that are in use by active readers and thus
  ** cannot be backfilled from the WAL.
  */
  mxSafeFrame = pWal->hdr.mxFrame;


  pInfo = walCkptInfo(pWal);
  for(i=1; i<WAL_NREADER; i++){
    u32 y = pInfo->aReadMark[i];
    if( mxSafeFrame>=y ){
      assert( y<=pWal->hdr.mxFrame );
      rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
      if( rc==SQLITE_OK ){
        pInfo->aReadMark[i] = READMARK_NOT_USED;
................................................................................
    /* Sync the WAL to disk */
    if( sync_flags ){
      rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
    }

    /* Iterate through the contents of the WAL, copying data to the db file. */
    while( rc==SQLITE_OK && 0==walIteratorNext(pIter, &iDbpage, &iFrame) ){
      assert( walFramePgno(pWal, iFrame)==iDbpage );
      if( iFrame<=nBackfill || iFrame>mxSafeFrame ) continue;
      rc = sqlite3OsRead(pWal->pWalFd, zBuf, szPage, 
          walFrameOffset(iFrame, szPage) + WAL_FRAME_HDRSIZE
      );
      if( rc!=SQLITE_OK ) break;
      rc = sqlite3OsWrite(pWal->pDbFd, zBuf, szPage, (iDbpage-1)*szPage);
      if( rc!=SQLITE_OK ) break;
    }

    /* If work was actually accomplished... */
    if( rc==SQLITE_OK ){
      if( mxSafeFrame==walIndexHdr(pWal)->mxFrame ){
        rc = sqlite3OsTruncate(pWal->pDbFd, ((i64)pWal->hdr.nPage*(i64)szPage));
        if( rc==SQLITE_OK && sync_flags ){
          rc = sqlite3OsSync(pWal->pDbFd, sync_flags);
        }
      }
      if( rc==SQLITE_OK ){
        pInfo->nBackfill = mxSafeFrame;
................................................................................
    rc = sqlite3OsLock(pWal->pDbFd, SQLITE_LOCK_EXCLUSIVE);
    if( rc==SQLITE_OK ){
      pWal->exclusiveMode = 1;
      rc = sqlite3WalCheckpoint(pWal, sync_flags, nBuf, zBuf);
      if( rc==SQLITE_OK ){
        isDelete = 1;
      }

    }

    walIndexClose(pWal, isDelete);
    sqlite3OsClose(pWal->pWalFd);
    if( isDelete ){
      sqlite3OsDelete(pWal->pVfs, pWal->zWalName, 0);
    }
    WALTRACE(("WAL%p: closed\n", pWal));
    sqlite3_free(pWal->apWiData);
    sqlite3_free(pWal);
  }
  return rc;
}

/*
** Try to read the wal-index header.  Return 0 on success and 1 if
................................................................................
** pWal->hdr, then pWal->hdr is updated to the content of the new header
** and *pChanged is set to 1.
**
** If the checksum cannot be verified return non-zero. If the header
** is read successfully and the checksum verified, return zero.
*/
int walIndexTryHdr(Wal *pWal, int *pChanged){
  u32 aCksum[2];                  /* Checksum on the header content */
  WalIndexHdr h1, h2;             /* Two copies of the header content */
  WalIndexHdr volatile *aHdr;     /* Header in shared memory */

  /* The first page of the wal-index must be mapped at this point. */




  assert( pWal->nWiData>0 && pWal->apWiData[0] );

  /* Read the header. This might happen currently with a write to the
  ** same area of shared memory on a different CPU in a SMP,
  ** meaning it is possible that an inconsistent snapshot is read
  ** from the file. If this happens, return non-zero.
  **
  ** There are two copies of the header at the beginning of the wal-index.
  ** When reading, read [0] first then [1].  Writes are in the reverse order.
  ** Memory barriers are used to prevent the compiler or the hardware from
  ** reordering the reads and writes.
  */
  aHdr = walIndexHdr(pWal);
  memcpy(&h1, (void *)&aHdr[0], sizeof(h1));
  sqlite3OsShmBarrier(pWal->pDbFd);
  memcpy(&h2, (void *)&aHdr[1], sizeof(h2));

  if( memcmp(&h1, &h2, sizeof(h1))!=0 ){
    return 1;   /* Dirty read */
  }  
  if( h1.isInit==0 ){
    return 1;   /* Malformed header - probably all zeros */
  }
................................................................................
**
** If the wal-index header is successfully read, return SQLITE_OK. 
** Otherwise an SQLite error code.
*/
static int walIndexReadHdr(Wal *pWal, int *pChanged){
  int rc;                         /* Return code */
  int badHdr;                     /* True if a header read failed */
  volatile u32 *page0;

  /* Ensure that page 0 of the wal-index (the page that contains the 
  ** wal-index header) is mapped. Return early if an error occurs here.
  */
  assert( pChanged );

  rc = walIndexPage(pWal, 0, &page0);
  if( rc!=SQLITE_OK ){
    return rc;
  };
  assert( page0 || pWal->writeLock==0 );



  /* If the first page of the wal-index has been mapped, try to read the
  ** wal-index header immediately, without holding any lock. This usually
  ** works, but may fail if the wal-index header is corrupt or currently 
  ** being modified by another user.
  */
  badHdr = (page0 ? walIndexTryHdr(pWal, pChanged) : 1);

  /* If the first attempt failed, it might have been due to a race
  ** with a writer.  So get a WRITE lock and try again.
  */
  assert( badHdr==0 || pWal->writeLock==0 );

  if( badHdr && SQLITE_OK==(rc = walLockExclusive(pWal, WAL_WRITE_LOCK, 1)) ){

    pWal->writeLock = 1;
    if( SQLITE_OK==(rc = walIndexPage(pWal, 0, &page0)) ){
      badHdr = walIndexTryHdr(pWal, pChanged);
      if( badHdr ){
        /* If the wal-index header is still malformed even while holding
        ** a WRITE lock, it can only mean that the header is corrupted and
        ** needs to be reconstructed.  So run recovery to do exactly that.
        */
        rc = walIndexRecover(pWal);
        *pChanged = 1;
      }


    }








    pWal->writeLock = 0;
    walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
  }

  return rc;
}

/*
** This is the value that walTryBeginRead returns when it needs to
................................................................................
** to select a particular WAL_READ_LOCK() that strives to let the
** checkpoint process do as much work as possible.  This routine might
** update values of the aReadMark[] array in the header, but if it does
** so it takes care to hold an exclusive lock on the corresponding
** WAL_READ_LOCK() while changing values.
*/
static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){

  volatile WalCkptInfo *pInfo;    /* Checkpoint information in wal-index */
  u32 mxReadMark;                 /* Largest aReadMark[] value */
  int mxI;                        /* Index of largest aReadMark[] value */
  int i;                          /* Loop counter */
  int rc = SQLITE_OK;             /* Return code  */

  assert( pWal->readLock<0 );     /* Not currently locked */

  /* Take steps to avoid spinning forever if there is a protocol error. */
  if( cnt>5 ){
    if( cnt>100 ) return SQLITE_PROTOCOL;
    sqlite3OsSleep(pWal->pVfs, 1);
................................................................................
      if( rc==SQLITE_OK ){
        walUnlockShared(pWal, WAL_RECOVER_LOCK);
        rc = WAL_RETRY;
      }else if( rc==SQLITE_BUSY ){
        rc = SQLITE_BUSY_RECOVERY;
      }
    }


  }
  if( rc!=SQLITE_OK ){
    return rc;
  }



  pInfo = walCkptInfo(pWal);
  if( !useWal && pInfo->nBackfill==pWal->hdr.mxFrame ){
    /* The WAL has been completely backfilled (or it is empty).
    ** and can be safely ignored.
    */
    rc = walLockShared(pWal, WAL_READ_LOCK(0));
    sqlite3OsShmBarrier(pWal->pDbFd);
    if( rc==SQLITE_OK ){
      if( memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr)) ){
        /* It is not safe to allow the reader to continue here if frames
        ** may have been appended to the log before READ_LOCK(0) was obtained.
        ** When holding READ_LOCK(0), the reader ignores the entire log file,
        ** which implies that the database file contains a trustworthy
        ** snapshoT. Since holding READ_LOCK(0) prevents a checkpoint from
        ** happening, this is usually correct.
        **
................................................................................
    ** date before proceeding. That would not be possible without somehow
    ** blocking writers. It only guarantees that a dangerous checkpoint or 
    ** log-wrap (either of which would require an exclusive lock on
    ** WAL_READ_LOCK(mxI)) has not occurred since the snapshot was valid.
    */
    sqlite3OsShmBarrier(pWal->pDbFd);
    if( pInfo->aReadMark[mxI]!=mxReadMark
     || memcmp((void *)walIndexHdr(pWal), &pWal->hdr, sizeof(WalIndexHdr))
    ){
      walUnlockShared(pWal, WAL_READ_LOCK(mxI));
      return WAL_RETRY;
    }else{
      assert( mxReadMark<=pWal->hdr.mxFrame );
      pWal->readLock = mxI;
    }
................................................................................
int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
  int rc;                         /* Return code */
  int cnt = 0;                    /* Number of TryBeginRead attempts */

  do{
    rc = walTryBeginRead(pWal, pChanged, 0, ++cnt);
  }while( rc==WAL_RETRY );

  return rc;
}

/*
** Finish with a read transaction.  All this does is release the
** read-lock.
*/
................................................................................
int sqlite3WalRead(
  Wal *pWal,                      /* WAL handle */
  Pgno pgno,                      /* Database page number to read data for */
  int *pInWal,                    /* OUT: True if data is read from WAL */
  int nOut,                       /* Size of buffer pOut in bytes */
  u8 *pOut                        /* Buffer to write page data to */
){

  u32 iRead = 0;                  /* If !=0, WAL frame to return data from */
  u32 iLast = pWal->hdr.mxFrame;  /* Last page in WAL for this reader */
  int iHash;                      /* Used to loop through N hash tables */

  /* This routine is only be called from within a read transaction. */
  assert( pWal->readLock>=0 || pWal->lockError );

................................................................................
  ** return early, as if the WAL were empty.
  */
  if( iLast==0 || pWal->readLock==0 ){
    *pInWal = 0;
    return SQLITE_OK;
  }







  /* Search the hash table or tables for an entry matching page number
  ** pgno. Each iteration of the following for() loop searches one
  ** hash table (each hash table indexes up to HASHTABLE_NPAGE frames).
  **
  ** This code may run concurrently to the code in walIndexAppend()
  ** that adds entries to the wal-index (and possibly to this hash 
  ** table). This means the value just read from the hash 
................................................................................
  **   (aPgno[iFrame]==pgno): 
  **     This condition filters out normal hash-table collisions.
  **
  **   (iFrame<=iLast): 
  **     This condition filters out entries that were added to the hash
  **     table after the current read-transaction had started.
  */
  for(iHash=walFramePage(iLast); iHash>=0 && iRead==0; iHash--){
    volatile ht_slot *aHash;      /* Pointer to hash table */
    volatile u32 *aPgno;          /* Pointer to array of page numbers */
    u32 iZero;                    /* Frame number corresponding to aPgno[0] */
    int iKey;                     /* Hash slot index */
    int rc;

    rc = walHashGet(pWal, iHash, &aHash, &aPgno, &iZero);
    if( rc!=SQLITE_OK ){
      return rc;
    }
    for(iKey=walHash(pgno); aHash[iKey]; iKey=walNextHash(iKey)){
      u32 iFrame = aHash[iKey] + iZero;
      if( iFrame<=iLast && aPgno[aHash[iKey]]==pgno ){
        assert( iFrame>iRead );
        iRead = iFrame;
      }
    }
  }


#ifdef SQLITE_ENABLE_EXPENSIVE_ASSERT
  /* If expensive assert() statements are available, do a linear search
  ** of the wal-index file content. Make sure the results agree with the
  ** result obtained using the hash indexes above.  */
  {
    u32 iRead2 = 0;
    u32 iTest;
    for(iTest=iLast; iTest>0; iTest--){
      if( walFramePgno(pWal, iTest)==pgno ){
        iRead2 = iTest;
        break;
      }
    }
    assert( iRead==iRead2 );
  }
#endif

  /* If iRead is non-zero, then it is the log frame number that contains the
  ** required page. Read and return data from the log file.
  */

  if( iRead ){
    i64 iOffset = walFrameOffset(iRead, pWal->hdr.szPage) + WAL_FRAME_HDRSIZE;
    *pInWal = 1;
    return sqlite3OsRead(pWal->pWalFd, pOut, nOut, iOffset);
  }

  *pInWal = 0;
................................................................................
  }
  pWal->writeLock = 1;

  /* If another connection has written to the database file since the
  ** time the read transaction on this connection was started, then
  ** the write is disallowed.
  */






  if( memcmp(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr))!=0 ){
    walUnlockExclusive(pWal, WAL_WRITE_LOCK, 1);
    pWal->writeLock = 0;
    rc = SQLITE_BUSY;
  }


  return rc;
}

/*
** End a write transaction.  The commit has already been done.  This
** routine merely releases the lock.
*/
................................................................................
**
** Otherwise, if the callback function does not return an error, this
** function returns SQLITE_OK.
*/
int sqlite3WalUndo(Wal *pWal, int (*xUndo)(void *, Pgno), void *pUndoCtx){
  int rc = SQLITE_OK;
  if( pWal->writeLock ){

    Pgno iMax = pWal->hdr.mxFrame;
    Pgno iFrame;
  
    /* Restore the clients cache of the wal-index header to the state it
    ** was in before the client began writing to the database. 

    */
    memcpy(&pWal->hdr, (void *)walIndexHdr(pWal), sizeof(WalIndexHdr));



    for(iFrame=pWal->hdr.mxFrame+1; 
        ALWAYS(rc==SQLITE_OK) && iFrame<=iMax; 
        iFrame++
    ){
      /* This call cannot fail. Unless the page for which the page number
      ** is passed as the second argument is (a) in the cache and 
      ** (b) has an outstanding reference, then xUndo is either a no-op
      ** (if (a) is false) or simply expels the page from the cache (if (b)
      ** is false).
      **
      ** If the upper layer is doing a rollback, it is guaranteed that there
      ** are no outstanding references to any page other than page 1. And
      ** page 1 is never written to the log until the transaction is
      ** committed. As a result, the call to xUndo may not fail.
      */


      assert( walFramePgno(pWal, iFrame)!=1 );
      rc = xUndo(pUndoCtx, walFramePgno(pWal, iFrame));
    }
    walCleanupHash(pWal);
  }


  assert( rc==SQLITE_OK );
  return rc;
}

/* 
** Argument aWalData must point to an array of WAL_SAVEPOINT_NDATA u32 
** values. This function populates the array with values required to 
** "rollback" the write position of the WAL handle back to the current 
................................................................................
    ** to the start of the log. Update the savepoint values to match.
    */
    aWalData[0] = 0;
    aWalData[3] = pWal->nCkpt;
  }

  if( aWalData[0]<pWal->hdr.mxFrame ){

    pWal->hdr.mxFrame = aWalData[0];
    pWal->hdr.aFrameCksum[0] = aWalData[1];
    pWal->hdr.aFrameCksum[1] = aWalData[2];

    walCleanupHash(pWal);
  }



  return rc;
}

/*
** This function is called just before writing a set of frames to the log
** file (see sqlite3WalFrames()). It checks to see if, instead of appending
** to the current log file, it is possible to overwrite the start of the
................................................................................
** or not pWal->hdr.mxFrame is modified). An SQLite error code is returned
** if some error 
*/
static int walRestartLog(Wal *pWal){
  int rc = SQLITE_OK;
  int cnt;

  if( pWal->readLock==0 ){


    volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
    assert( pInfo->nBackfill==pWal->hdr.mxFrame );
    if( pInfo->nBackfill>0 ){
      rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
      if( rc==SQLITE_OK ){
        /* If all readers are using WAL_READ_LOCK(0) (in other words if no
        ** readers are currently using the WAL), then the transactions
................................................................................
    walUnlockShared(pWal, WAL_READ_LOCK(0));
    pWal->readLock = -1;
    cnt = 0;
    do{
      int notUsed;
      rc = walTryBeginRead(pWal, &notUsed, 1, ++cnt);
    }while( rc==WAL_RETRY );





  }
  return rc;
}

/* 
** Write a set of frames to the log. The caller must hold the write-lock
** on the log file (obtained using sqlite3WalBeginWriteTransaction()).
................................................................................
  u8 aFrame[WAL_FRAME_HDRSIZE];   /* Buffer to assemble frame-header in */
  PgHdr *p;                       /* Iterator to run through pList with. */
  PgHdr *pLast = 0;               /* Last frame in list */
  int nLast = 0;                  /* Number of extra copies of last page */

  assert( pList );
  assert( pWal->writeLock );


#if defined(SQLITE_TEST) && defined(SQLITE_DEBUG)
  { int cnt; for(cnt=0, p=pList; p; p=p->pDirty, cnt++){}
    WALTRACE(("WAL%p: frame write begin. %d frames. mxFrame=%d. %s\n",
              pWal, cnt, pWal->hdr.mxFrame, isCommit ? "Commit" : "Spill"));
  }
#endif

  /* See if it is possible to write these frames into the start of the
  ** log file, instead of appending to it at pWal->hdr.mxFrame.
  */
  if( SQLITE_OK!=(rc = walRestartLog(pWal)) ){

    return rc;
  }


  /* If this is the first frame written into the log, write the WAL
  ** header to the start of the WAL file. See comments at the top of
  ** this source file for a description of the WAL header format.
  */
  iFrame = pWal->hdr.mxFrame;
  if( iFrame==0 ){
................................................................................
      }
      nLast++;
      iOffset += szPage;
    }

    rc = sqlite3OsSync(pWal->pWalFd, sync_flags);
  }


  /* Append data to the wal-index. It is not necessary to lock the 
  ** wal-index to do this as the SQLITE_SHM_WRITE lock held on the wal-index
  ** guarantees that there are no other writers, and no data that may
  ** be in use by existing readers is being overwritten.
  */
  iFrame = pWal->hdr.mxFrame;
................................................................................
    /* If this is a commit, update the wal-index header too. */
    if( isCommit ){
      walIndexWriteHdr(pWal);
      pWal->iCallback = iFrame;
    }
  }


  WALTRACE(("WAL%p: frame write %s\n", pWal, rc ? "failed" : "ok"));
  return rc;
}

/* 
** This routine is called to implement sqlite3_wal_checkpoint() and
** related interfaces.
................................................................................
  int sync_flags,                 /* Flags to sync db file with (or 0) */
  int nBuf,                       /* Size of temporary buffer */
  u8 *zBuf                        /* Temporary buffer to use */
){
  int rc;                         /* Return code */
  int isChanged = 0;              /* True if a new wal-index header is loaded */


  assert( pWal->ckptLock==0 );

  WALTRACE(("WAL%p: checkpoint begins\n", pWal));
  rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
  if( rc ){
    /* Usually this is SQLITE_BUSY meaning that another thread or process
    ** is already running a checkpoint, or maybe a recovery.  But it might
................................................................................
    ** next time the pager opens a snapshot on this database it knows that
    ** the cache needs to be reset.
    */
    memset(&pWal->hdr, 0, sizeof(WalIndexHdr));
  }

  /* Release the locks. */

  walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
  pWal->ckptLock = 0;
  WALTRACE(("WAL%p: checkpoint %s\n", pWal, rc ? "failed" : "ok"));
  return rc;
}

/* Return the value to pass to a sqlite3_wal_hook callback, the

Changes to test/permutations.test.

9
10
11
12
13
14
15

16
17
18
19
20
21
22
#
#***********************************************************************
#
# $Id: permutations.test,v 1.51 2009/07/01 18:09:02 danielk1977 Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl


# Argument processing.
#
#puts "PERM-DEBUG: argv=$argv"
namespace eval ::perm {
  variable testmode [lindex $::argv 0]
  variable testfile [lindex $::argv 1]







>







9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
#
#***********************************************************************
#
# $Id: permutations.test,v 1.51 2009/07/01 18:09:02 danielk1977 Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl
db close

# Argument processing.
#
#puts "PERM-DEBUG: argv=$argv"
namespace eval ::perm {
  variable testmode [lindex $::argv 0]
  variable testfile [lindex $::argv 1]

Changes to test/wal2.test.

71
72
73
74
75
76
77


78


79
80

81
82
83
84
85
86
87
...
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139



140
141
142
143
144
145
146
147
...
170
171
172
173
174
175
176

177
178

179
180
181
182
183
184
185
...
204
205
206
207
208
209
210


211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236



237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260



261
262
263
264
265
266
267
#      of the the integer fields (so that the reader ends up with a corrupted
#      header).
#
#   3. Check that the reader recovers the wal-index and reads the correct
#      database content.
#
do_test wal2-1.0 {


  proc tvfs_cb {method args} { return SQLITE_OK }


  testvfs tvfs
  tvfs script tvfs_cb


  sqlite3 db  test.db -vfs tvfs
  sqlite3 db2 test.db -vfs tvfs

  execsql {
    PRAGMA journal_mode = WAL;
    CREATE TABLE t1(a);
................................................................................
        10   13   {13 91}   8             {$RECOVER $READ}
        11   14   {14 105}  9             {$RECOVER $READ}
        12   15   {15 120}  -1            {$READ}
" {

  do_test wal2-1.$tn.1 {
    execsql { INSERT INTO t1 VALUES($iInsert) }

    set ::locks [list]
    set ::cb_done 0

    proc tvfs_cb {method args} {
      if {$::cb_done == 0 && $method == "xShmGet"} {
        set ::cb_done 1
        if {$::wal_index_hdr_mod >= 0} {
          incr_tvfs_hdr [lindex $args 0] $::wal_index_hdr_mod 1
        }
      }
      if {$method == "xShmLock"} { lappend ::locks [lindex $args 2] }
      return SQLITE_OK
    }




    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res

  do_test wal2-1.$tn.2 {
    set ::locks
  } $wal_locks
}
................................................................................
  {4 1 lock exclusive} {4 1 unlock exclusive} \
  {4 1 lock shared}    {4 1 unlock shared}    \
]
do_test wal2-2.0 {

  testvfs tvfs
  tvfs script tvfs_cb

  proc tvfs_cb {method args} {
    if {$method == "xShmOpen"} { set ::shm_file [lindex $args 0] }

    return SQLITE_OK
  }

  sqlite3 db  test.db -vfs tvfs
  sqlite3 db2 test.db -vfs tvfs

  execsql {
................................................................................
         4    7   {6 21}   {7 28}    2
         5    8   {7 28}   {8 36}    3
         6    9   {8 36}   {9 45}    4
         7   10   {9 45}   {10 55}   5
         8   11   {10 55}  {11 66}   6
         9   12   {11 66}  {12 78}   7
} {


  do_test wal2-2.$tn.1 {
    set oldhdr [set_tvfs_hdr $::shm_file]
    execsql { INSERT INTO t1 VALUES($iInsert) }
    execsql { SELECT count(a), sum(a) FROM t1 }
  } $res1

  do_test wal2-2.$tn.2 {
    set ::locks [list]
    set ::cb_done 0
    proc tvfs_cb {method args} {
      if {$::cb_done == 0 && $method == "xShmGet"} {
        set ::cb_done 1
        if {$::wal_index_hdr_mod >= 0} {
          incr_tvfs_hdr $::shm_file $::wal_index_hdr_mod 1
        }
      }
      if {$method == "xShmLock"} {
        set lock [lindex $args 2]
        lappend ::locks $lock
        if {$lock == $::WRITER} {
          set_tvfs_hdr $::shm_file $::oldhdr
        }
      }
      return SQLITE_OK
    }




    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res0

  do_test wal2-2.$tn.3 {
    set ::locks
  } $LOCKS

  do_test wal2-2.$tn.4 {
    set ::locks [list]
    set ::cb_done 0
    proc tvfs_cb {method args} {
      if {$::cb_done == 0 && $method == "xShmGet"} {
        set ::cb_done 1
        if {$::wal_index_hdr_mod >= 0} {
          incr_tvfs_hdr $::shm_file $::wal_index_hdr_mod 1
        }
      }
      if {$method == "xShmLock"} {
        set lock [lindex $args 2]
        lappend ::locks $lock
      }
      return SQLITE_OK
    }




    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res1
}
db close
db2 close
tvfs delete
file delete -force test.db test.db-wal test.db-journal







>
>
|
>
>


>







 







<

<
<

<
<
<
<
<
<
|


>
>
>
|







 







>

<
>







 







>
>

|






<

<
<
<
<
<
<
<
|
|
|
|
<




>
>
>









<

<
<
<
<
<
<
<
|
|
<



>
>
>







71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
...
124
125
126
127
128
129
130

131


132






133
134
135
136
137
138
139
140
141
142
143
144
145
146
...
169
170
171
172
173
174
175
176
177

178
179
180
181
182
183
184
185
...
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220

221







222
223
224
225

226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241

242







243
244

245
246
247
248
249
250
251
252
253
254
255
256
257
#      of the the integer fields (so that the reader ends up with a corrupted
#      header).
#
#   3. Check that the reader recovers the wal-index and reads the correct
#      database content.
#
do_test wal2-1.0 {
  proc tvfs_cb {method filename args} { 
    set ::filename $filename
    return SQLITE_OK 
  }

  testvfs tvfs
  tvfs script tvfs_cb
  tvfs filter xShmOpen

  sqlite3 db  test.db -vfs tvfs
  sqlite3 db2 test.db -vfs tvfs

  execsql {
    PRAGMA journal_mode = WAL;
    CREATE TABLE t1(a);
................................................................................
        10   13   {13 91}   8             {$RECOVER $READ}
        11   14   {14 105}  9             {$RECOVER $READ}
        12   15   {15 120}  -1            {$READ}
" {

  do_test wal2-1.$tn.1 {
    execsql { INSERT INTO t1 VALUES($iInsert) }

    set ::locks [list]


    proc tvfs_cb {method args} {






      lappend ::locks [lindex $args 2]
      return SQLITE_OK
    }
    tvfs filter xShmLock
    if {$::wal_index_hdr_mod >= 0} {
      incr_tvfs_hdr $::filename $::wal_index_hdr_mod 1
    }
    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res

  do_test wal2-1.$tn.2 {
    set ::locks
  } $wal_locks
}
................................................................................
  {4 1 lock exclusive} {4 1 unlock exclusive} \
  {4 1 lock shared}    {4 1 unlock shared}    \
]
do_test wal2-2.0 {

  testvfs tvfs
  tvfs script tvfs_cb
  tvfs filter xShmOpen
  proc tvfs_cb {method args} {

    set ::filename [lindex $args 0]
    return SQLITE_OK
  }

  sqlite3 db  test.db -vfs tvfs
  sqlite3 db2 test.db -vfs tvfs

  execsql {
................................................................................
         4    7   {6 21}   {7 28}    2
         5    8   {7 28}   {8 36}    3
         6    9   {8 36}   {9 45}    4
         7   10   {9 45}   {10 55}   5
         8   11   {10 55}  {11 66}   6
         9   12   {11 66}  {12 78}   7
} {
  tvfs filter xShmLock

  do_test wal2-2.$tn.1 {
    set oldhdr [set_tvfs_hdr $::filename]
    execsql { INSERT INTO t1 VALUES($iInsert) }
    execsql { SELECT count(a), sum(a) FROM t1 }
  } $res1

  do_test wal2-2.$tn.2 {
    set ::locks [list]

    proc tvfs_cb {method args} {







      set lock [lindex $args 2]
      lappend ::locks $lock
      if {$lock == $::WRITER} {
        set_tvfs_hdr $::filename $::oldhdr

      }
      return SQLITE_OK
    }

    if {$::wal_index_hdr_mod >= 0} {
      incr_tvfs_hdr $::filename $::wal_index_hdr_mod 1
    }
    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res0

  do_test wal2-2.$tn.3 {
    set ::locks
  } $LOCKS

  do_test wal2-2.$tn.4 {
    set ::locks [list]

    proc tvfs_cb {method args} {







      set lock [lindex $args 2]
      lappend ::locks $lock

      return SQLITE_OK
    }

    if {$::wal_index_hdr_mod >= 0} {
      incr_tvfs_hdr $::filename $::wal_index_hdr_mod 1
    }
    execsql { SELECT count(a), sum(a) FROM t1 } db2
  } $res1
}
db close
db2 close
tvfs delete
file delete -force test.db test.db-wal test.db-journal

Changes to test/wal3.test.

349
350
351
352
353
354
355
356
357
358
359
360
361
362
363

testvfs T -default 1
T script method_callback

proc method_callback {method args} {
  if {$method == "xShmBarrier"} {
    incr ::barrier_count
    if {$::barrier_count == 1} {
      # This code is executed within the xShmBarrier() callback invoked
      # by the client running recovery as part of writing the recovered
      # wal-index header. If a second client attempts to access the 
      # database now, it reads a corrupt (partially written) wal-index
      # header. But it cannot even get that far, as the first client
      # is still holding all the locks (recovery takes an exclusive lock
      # on *all* db locks, preventing access by any other client).







|







349
350
351
352
353
354
355
356
357
358
359
360
361
362
363

testvfs T -default 1
T script method_callback

proc method_callback {method args} {
  if {$method == "xShmBarrier"} {
    incr ::barrier_count
    if {$::barrier_count == 2} {
      # This code is executed within the xShmBarrier() callback invoked
      # by the client running recovery as part of writing the recovered
      # wal-index header. If a second client attempts to access the 
      # database now, it reads a corrupt (partially written) wal-index
      # header. But it cannot even get that far, as the first client
      # is still holding all the locks (recovery takes an exclusive lock
      # on *all* db locks, preventing access by any other client).

Changes to test/walfault.test.

115
116
117
118
119
120
121

122
123
124
125
126
127
128
...
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
...
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
...
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
...
358
359
360
361
362
363
364
365















































































366
367
  db eval {
    DELETE FROM abc;
    PRAGMA wal_checkpoint;
  }
} -test {
  faultsim_test_result {0 {}}
}


#--------------------------------------------------------------------------
#
faultsim_delete_and_reopen
faultsim_save_and_close
do_faultsim_test walfault-4 -prep {
  faultsim_restore_and_reopen
................................................................................
    PRAGMA journal_mode = WAL;
  }
  faultsim_save_and_close
} {}
do_faultsim_test walfault-5 -faults shmerr* -prep {
  faultsim_restore_and_reopen
  execsql { PRAGMA wal_autocheckpoint = 0 }
  shmfault filter xShmSize
} -body {
  execsql {
    CREATE TABLE t1(x);
    BEGIN;
      INSERT INTO t1 VALUES(randomblob(400));           /* 1 */
      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 2 */
      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 4 */
................................................................................
      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 16384 */
    COMMIT;
  }
  faultsim_save_and_close
} {}
do_faultsim_test walfault-6 -faults shmerr* -prep {
  faultsim_restore_and_reopen
  shmfault filter xShmSize
} -body {
  execsql { SELECT count(*) FROM t1 }
} -test {
  faultsim_test_result {0 16384}
  faultsim_integrity_check
  set n [db one {SELECT count(*) FROM t1}]
  if {$n != 16384 && $n != 0} { error "Incorrect number of rows: $n" }
................................................................................
  if {$n != 1 && $n != 2} { error "Incorrect number of rows: $n" }
}

do_test walfault-10-pre1 {
  faultsim_delete_and_reopen
  execsql {
    PRAGMA journal_mode = WAL;
    PRAGMA wal_checkpoint = 0;
    CREATE TABLE z(zz INTEGER PRIMARY KEY, zzz BLOB);
    CREATE INDEX zzzz ON z(zzz);
    INSERT INTO z VALUES(NULL, randomblob(800));
    INSERT INTO z VALUES(NULL, randomblob(800));
    INSERT INTO z SELECT NULL, randomblob(800) FROM z;
    INSERT INTO z SELECT NULL, randomblob(800) FROM z;
    INSERT INTO z SELECT NULL, randomblob(800) FROM z;
................................................................................
  faultsim_test_result {0 {}}
  catch { db eval { ROLLBACK } }
  faultsim_integrity_check

  set n [db eval {SELECT count(*), sum(length(zzz)) FROM z}]
  if {$n != "64 51200"} { error "Incorrect data: $n" }
}
















































































finish_test








>







 







|







 







|







 







|







 








>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>


115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
...
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
...
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
...
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
...
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
  db eval {
    DELETE FROM abc;
    PRAGMA wal_checkpoint;
  }
} -test {
  faultsim_test_result {0 {}}
}


#--------------------------------------------------------------------------
#
faultsim_delete_and_reopen
faultsim_save_and_close
do_faultsim_test walfault-4 -prep {
  faultsim_restore_and_reopen
................................................................................
    PRAGMA journal_mode = WAL;
  }
  faultsim_save_and_close
} {}
do_faultsim_test walfault-5 -faults shmerr* -prep {
  faultsim_restore_and_reopen
  execsql { PRAGMA wal_autocheckpoint = 0 }
  shmfault filter xShmPage
} -body {
  execsql {
    CREATE TABLE t1(x);
    BEGIN;
      INSERT INTO t1 VALUES(randomblob(400));           /* 1 */
      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 2 */
      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 4 */
................................................................................
      INSERT INTO t1 SELECT randomblob(400) FROM t1;    /* 16384 */
    COMMIT;
  }
  faultsim_save_and_close
} {}
do_faultsim_test walfault-6 -faults shmerr* -prep {
  faultsim_restore_and_reopen
  shmfault filter xShmPage
} -body {
  execsql { SELECT count(*) FROM t1 }
} -test {
  faultsim_test_result {0 16384}
  faultsim_integrity_check
  set n [db one {SELECT count(*) FROM t1}]
  if {$n != 16384 && $n != 0} { error "Incorrect number of rows: $n" }
................................................................................
  if {$n != 1 && $n != 2} { error "Incorrect number of rows: $n" }
}

do_test walfault-10-pre1 {
  faultsim_delete_and_reopen
  execsql {
    PRAGMA journal_mode = WAL;
    PRAGMA wal_autocheckpoint = 0;
    CREATE TABLE z(zz INTEGER PRIMARY KEY, zzz BLOB);
    CREATE INDEX zzzz ON z(zzz);
    INSERT INTO z VALUES(NULL, randomblob(800));
    INSERT INTO z VALUES(NULL, randomblob(800));
    INSERT INTO z SELECT NULL, randomblob(800) FROM z;
    INSERT INTO z SELECT NULL, randomblob(800) FROM z;
    INSERT INTO z SELECT NULL, randomblob(800) FROM z;
................................................................................
  faultsim_test_result {0 {}}
  catch { db eval { ROLLBACK } }
  faultsim_integrity_check

  set n [db eval {SELECT count(*), sum(length(zzz)) FROM z}]
  if {$n != "64 51200"} { error "Incorrect data: $n" }
}

#--------------------------------------------------------------------------
# Test fault injection while checkpointing a large WAL file, if the 
# checkpoint is the first operation run after opening the database.
# This means that some of the required wal-index pages are mapped as part of
# the checkpoint process, which means there are a few more opportunities
# for IO errors.
#
# To speed this up, IO errors are only simulated within xShmPage() calls.
#
do_test walfault-11-pre-1 {
  sqlite3 db test.db
  execsql {
    PRAGMA journal_mode = WAL;
    PRAGMA wal_autocheckpoint = 0;
    BEGIN;
      CREATE TABLE abc(a PRIMARY KEY);
      INSERT INTO abc VALUES(randomblob(1500));
      INSERT INTO abc VALUES(randomblob(1500));
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   --    4
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   --    8
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   --   16
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   --   32
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   --   64
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   --  128
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   --  256
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   --  512
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   -- 1024
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   -- 2048
      INSERT INTO abc SELECT randomblob(1500) FROM abc;   -- 4096
    COMMIT;
  }
  faultsim_save_and_close
} {}
do_faultsim_test walfault-11 -faults shmerr* -prep {
  catch { db2 close }
  faultsim_restore_and_reopen
  shmfault filter xShmPage
} -body {
  db eval { SELECT count(*) FROM abc }
  sqlite3 db2 test.db -vfs shmfault
  db2 eval { PRAGMA wal_checkpoint }
} -test {
  faultsim_test_result {0 {}}
}

#-------------------------------------------------------------------------
# Test the handling of the various IO/OOM/SHM errors that may occur during 
# a log recovery operation undertaken as part of a call to 
# sqlite3_wal_checkpoint().
# 
do_test walfault-12-pre-1 {
  faultsim_delete_and_reopen
  execsql {
    PRAGMA journal_mode = WAL;
    PRAGMA wal_autocheckpoint = 0;
    BEGIN;
      CREATE TABLE abc(a PRIMARY KEY);
      INSERT INTO abc VALUES(randomblob(1500));
      INSERT INTO abc VALUES(randomblob(1500));
    COMMIT;
  }
  faultsim_save_and_close
} {}
do_faultsim_test walfault-12 -prep {
  if {[info commands shmfault] == ""} {
    testvfs shmfault -default true
  }
  faultsim_restore_and_reopen
  db eval { SELECT * FROM sqlite_master }
  shmfault shm test.db [string repeat "\000" 40]
} -body {
  set rc [sqlite3_wal_checkpoint db]
  if {$rc != "SQLITE_OK"} { error [sqlite3_errmsg db] }
} -test {
  db close
  faultsim_test_result {0 {}}
}


finish_test