** 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 unixShmPage(
  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;
................................................................................
}

#else
# define unixShmOpen    0
# define unixShmLock    0
# define unixShmBarrier 0
# define unixShmClose   0
# define unixShmPage    0
#endif /* #ifndef SQLITE_OMIT_WAL */

/*
** Here ends the implementation of all sqlite3_file methods.
**
********************** End sqlite3_file Methods *******************************
******************************************************************************/
................................................................................
   unixFileControl,            /* xFileControl */                            \
   unixSectorSize,             /* xSectorSize */                             \
   unixDeviceCharacteristics,  /* xDeviceCapabilities */                     \
   unixShmOpen,                /* xShmOpen */                                \
   unixShmLock,                /* xShmLock */                                \
   unixShmBarrier,             /* xShmBarrier */                             \
   unixShmClose,               /* xShmClose */                               \
   unixShmPage                 /* xShmPage */                                \
};                                                                           \
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;

** 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;
................................................................................
}

#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 *******************************
******************************************************************************/
................................................................................
   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;

** 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.
****************************************************************************/

** 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.
****************************************************************************/