sqlite3_mutex_enter(db->mutex);
  pRet = db->pRollbackArg;
  db->xRollbackCallback = xCallback;
  db->pRollbackArg = pArg;
  sqlite3_mutex_leave(db->mutex);
  return pRet;
}





































/*
** Register a callback to be invoked each time a transaction is written
** into the write-ahead-log by this database connection.
*/
void *sqlite3_wal_hook(
  sqlite3 *db,                    /* Attach the hook to this db handle */
  int(*xCallback)(void *, sqlite3*, const char*, int),
  void *pArg                      /* First argument passed to xCallback() */
){
#ifndef SQLITE_OMIT_WAL
  void *pRet;
  sqlite3_mutex_enter(db->mutex);
  pRet = db->pWalArg;
  db->xWalCallback = xCallback;
  db->pWalArg = pArg;
  sqlite3_mutex_leave(db->mutex);
  return pRet;















#else


















































  return 0;
#endif
}




/*
** This function returns true if main-memory should be used instead of
** a temporary file for transient pager files and statement journals.
** The value returned depends on the value of db->temp_store (runtime
** parameter) and the compile time value of SQLITE_TEMP_STORE. The
** following table describes the relationship between these two values
................................................................................
  sqlite3PagerLockingMode(sqlite3BtreePager(db->aDb[0].pBt),
                          SQLITE_DEFAULT_LOCKING_MODE);
#endif

  /* Enable the lookaside-malloc subsystem */
  setupLookaside(db, 0, sqlite3GlobalConfig.szLookaside,
                        sqlite3GlobalConfig.nLookaside);



opendb_out:
  if( db ){
    assert( db->mutex!=0 || isThreadsafe==0 || sqlite3GlobalConfig.bFullMutex==0 );
    sqlite3_mutex_leave(db->mutex);
  }
  rc = sqlite3_errcode(db);

  sqlite3_mutex_enter(db->mutex);
  pRet = db->pRollbackArg;
  db->xRollbackCallback = xCallback;
  db->pRollbackArg = pArg;
  sqlite3_mutex_leave(db->mutex);
  return pRet;
}

#ifndef SQLITE_OMIT_WAL
/*
** The sqlite3_wal_hook() callback registered by sqlite3_wal_autocheckpoint().
** Return non-zero, indicating to the caller that a checkpoint should be run,
** if the number of frames in the log file is greater than 
** sqlite3.nDefaultCheckpoint (the value configured by wal_autocheckpoint()).
*/ 
static int defaultWalHook(void *p, sqlite3 *db, const char *z, int nFrame){
  UNUSED_PARAMETER(p);
  UNUSED_PARAMETER(z);
  return ( nFrame>=db->nDefaultCheckpoint );
}

/*
** Configure an sqlite3_wal_hook() callback to automatically checkpoint
** a database after committing a transaction if there are nFrame or
** more frames in the log file. Passing zero or a negative value as the
** nFrame parameter disables automatic checkpoints entirely.
**
** The callback registered by this function replaces any existing callback
** registered using sqlite3_wal_hook(). Likewise, registering a callback
** using sqlite3_wal_hook() disables the automatic checkpoint mechanism
** configured by this function.
*/
int sqlite3_wal_autocheckpoint(sqlite3 *db, int nFrame){
  sqlite3_mutex_enter(db->mutex);
  if( nFrame>0 ){
    db->nDefaultCheckpoint = nFrame;
    sqlite3_wal_hook(db, defaultWalHook, 0);
  }else{
    sqlite3_wal_hook(db, 0, 0);
  }
  sqlite3_mutex_leave(db->mutex);
  return SQLITE_OK;
}

/*
** Register a callback to be invoked each time a transaction is written
** into the write-ahead-log by this database connection.
*/
void *sqlite3_wal_hook(
  sqlite3 *db,                    /* Attach the hook to this db handle */
  int(*xCallback)(void *, sqlite3*, const char*, int),
  void *pArg                      /* First argument passed to xCallback() */
){

  void *pRet;
  sqlite3_mutex_enter(db->mutex);
  pRet = db->pWalArg;
  db->xWalCallback = xCallback;
  db->pWalArg = pArg;
  sqlite3_mutex_leave(db->mutex);
  return pRet;
}

/*
** Checkpoint database zDb. If zDb is NULL, the main database is checkpointed.
*/
int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb){
  int rc;                         /* Return code */
  int iDb = 0;                    /* sqlite3.aDb[] index of db to checkpoint */

  sqlite3_mutex_enter(db->mutex);
  if( zDb ){
    iDb = sqlite3FindDbName(db, zDb);
  }
  if( iDb<0 ){
    rc = SQLITE_ERROR;
  }else{
    rc = sqlite3Checkpoint(db, iDb);
  }
  sqlite3_mutex_leave(db->mutex);

  return rc;
}

/*
** Run a checkpoint on database iDb. This is a no-op if database iDb is
** not currently open in WAL mode.
**
** If a transaction is open at either the database handle (db) or b-tree
** level, this function returns SQLITE_LOCKED and a checkpoint is not
** attempted. If an error occurs while running the checkpoint, an SQLite
** error code is returned (i.e. SQLITE_IOERR). Otherwise, SQLITE_OK.
**
** The mutex on database handle db should be held by the caller. The mutex
** associated with the specific b-tree being checkpointed is taken by
** this function while the checkpoint is running.
*/
int sqlite3Checkpoint(sqlite3 *db, int iDb){
  Btree *pBt;                     /* Btree handle to checkpoint */
  int rc;                         /* Return code */

  assert( sqlite3_mutex_held(db->mutex) );

  pBt = db->aDb[iDb].pBt;
  if( sqlite3BtreeIsInReadTrans(pBt) ){
    rc = SQLITE_LOCKED;
  }else{
    sqlite3BtreeEnter(pBt);
    rc = sqlite3PagerCheckpoint(sqlite3BtreePager(pBt));
    sqlite3BtreeLeave(pBt);
  }

  return rc;
}
#else /* ifndef SQLITE_OMIT_WAL */
/*
** If SQLITE_OMIT_WAL is defined, the following API functions are no-ops:
**
**   sqlite3_wal_hook()
**   sqlite3_wal_checkpoint()
**   sqlite3_wal_autocheckpoint()
*/
void *sqlite3_wal_hook(
  sqlite3 *x,
  int(*xCallback)(void *, sqlite3*, const char*, int),
  void *pArg
){
  return 0;

}
int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb){ return SQLITE_OK; }
int sqlite3_wal_autocheckpoint(sqlite3 *db, int nFrame){ return SQLITE_OK; }
#endif

/*
** This function returns true if main-memory should be used instead of
** a temporary file for transient pager files and statement journals.
** The value returned depends on the value of db->temp_store (runtime
** parameter) and the compile time value of SQLITE_TEMP_STORE. The
** following table describes the relationship between these two values
................................................................................
  sqlite3PagerLockingMode(sqlite3BtreePager(db->aDb[0].pBt),
                          SQLITE_DEFAULT_LOCKING_MODE);
#endif

  /* Enable the lookaside-malloc subsystem */
  setupLookaside(db, 0, sqlite3GlobalConfig.szLookaside,
                        sqlite3GlobalConfig.nLookaside);

  sqlite3_wal_autocheckpoint(db, SQLITE_DEFAULT_CACHE_SIZE);

opendb_out:
  if( db ){
    assert( db->mutex!=0 || isThreadsafe==0 || sqlite3GlobalConfig.bFullMutex==0 );
    sqlite3_mutex_leave(db->mutex);
  }
  rc = sqlite3_errcode(db);

#ifndef SQLITE_OMIT_WAL
  /*
  **   PRAGMA [database.]checkpoint
  **
  ** Checkpoint the database.
  */
  if( sqlite3StrICmp(zLeft, "checkpoint")==0 ){
    sqlite3VdbeUsesBtree(v, iDb);
    sqlite3VdbeAddOp3(v, OP_Checkpoint, iDb, 0, 0);
  }else
#endif

#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
  /*
  ** Report the current state of file logs for all databases

#ifndef SQLITE_OMIT_WAL
  /*
  **   PRAGMA [database.]checkpoint
  **
  ** Checkpoint the database.
  */
  if( sqlite3StrICmp(zLeft, "checkpoint")==0 ){

    sqlite3VdbeAddOp3(v, OP_Checkpoint, iDb, 0, 0);
  }else
#endif

#if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
  /*
  ** Report the current state of file logs for all databases

*/
void *sqlite3_wal_hook(
  sqlite3*, 
  int(*)(void *,sqlite3*,const char*,int),
  void*
);











/*
** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double
#endif

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif

*/
void *sqlite3_wal_hook(
  sqlite3*, 
  int(*)(void *,sqlite3*,const char*,int),
  void*
);

/*
** CAPI3REF: Configure an auto-checkpoint
*/
int sqlite3_wal_autocheckpoint(sqlite3 *db, int N);

/*
** CAPI3REF: Checkpoint a database
*/
int sqlite3_wal_checkpoint(sqlite3 *db, const char *zDb);

/*
** Undo the hack that converts floating point types to integer for
** builds on processors without floating point support.
*/
#ifdef SQLITE_OMIT_FLOATING_POINT
# undef double
#endif

#ifdef __cplusplus
}  /* End of the 'extern "C"' block */
#endif
#endif

  void *pCommitArg;                 /* Argument to xCommitCallback() */   
  int (*xCommitCallback)(void*);    /* Invoked at every commit. */
  void *pRollbackArg;               /* Argument to xRollbackCallback() */   
  void (*xRollbackCallback)(void*); /* Invoked at every commit. */
  void *pUpdateArg;
  void (*xUpdateCallback)(void*,int, const char*,const char*,sqlite_int64);
#ifndef SQLITE_OMIT_WAL

  int (*xWalCallback)(void *, sqlite3 *, const char *, int);
  void *pWalArg;
#endif
  void(*xCollNeeded)(void*,sqlite3*,int eTextRep,const char*);
  void(*xCollNeeded16)(void*,sqlite3*,int eTextRep,const void*);
  void *pCollNeededArg;
  sqlite3_value *pErr;          /* Most recent error message */
................................................................................
int sqlite3TransferBindings(sqlite3_stmt *, sqlite3_stmt *);
int sqlite3Reprepare(Vdbe*);
void sqlite3ExprListCheckLength(Parse*, ExprList*, const char*);
CollSeq *sqlite3BinaryCompareCollSeq(Parse *, Expr *, Expr *);
int sqlite3TempInMemory(const sqlite3*);
VTable *sqlite3GetVTable(sqlite3*, Table*);
const char *sqlite3JournalModename(int);


/* Declarations for functions in fkey.c. All of these are replaced by
** no-op macros if OMIT_FOREIGN_KEY is defined. In this case no foreign
** key functionality is available. If OMIT_TRIGGER is defined but
** OMIT_FOREIGN_KEY is not, only some of the functions are no-oped. In
** this case foreign keys are parsed, but no other functionality is 
** provided (enforcement of FK constraints requires the triggers sub-system).

  void *pCommitArg;                 /* Argument to xCommitCallback() */   
  int (*xCommitCallback)(void*);    /* Invoked at every commit. */
  void *pRollbackArg;               /* Argument to xRollbackCallback() */   
  void (*xRollbackCallback)(void*); /* Invoked at every commit. */
  void *pUpdateArg;
  void (*xUpdateCallback)(void*,int, const char*,const char*,sqlite_int64);
#ifndef SQLITE_OMIT_WAL
  int nDefaultCheckpoint;       /* Value configured by wal_autocheckpoint() */
  int (*xWalCallback)(void *, sqlite3 *, const char *, int);
  void *pWalArg;
#endif
  void(*xCollNeeded)(void*,sqlite3*,int eTextRep,const char*);
  void(*xCollNeeded16)(void*,sqlite3*,int eTextRep,const void*);
  void *pCollNeededArg;
  sqlite3_value *pErr;          /* Most recent error message */
................................................................................
int sqlite3TransferBindings(sqlite3_stmt *, sqlite3_stmt *);
int sqlite3Reprepare(Vdbe*);
void sqlite3ExprListCheckLength(Parse*, ExprList*, const char*);
CollSeq *sqlite3BinaryCompareCollSeq(Parse *, Expr *, Expr *);
int sqlite3TempInMemory(const sqlite3*);
VTable *sqlite3GetVTable(sqlite3*, Table*);
const char *sqlite3JournalModename(int);
int sqlite3Checkpoint(sqlite3*, int);

/* Declarations for functions in fkey.c. All of these are replaced by
** no-op macros if OMIT_FOREIGN_KEY is defined. In this case no foreign
** key functionality is available. If OMIT_TRIGGER is defined but
** OMIT_FOREIGN_KEY is not, only some of the functions are no-oped. In
** this case foreign keys are parsed, but no other functionality is 
** provided (enforcement of FK constraints requires the triggers sub-system).

#ifndef SQLITE_OMIT_WAL
/* Opcode: Checkpoint P1 * * * *
**
** Checkpoint database P1. This is a no-op if P1 is not currently in
** WAL mode.
*/
case OP_Checkpoint: {
  Btree *pBt;                     /* Btree to checkpoint */

  assert( pOp->p1>=0 && pOp->p1<db->nDb );
  assert( (p->btreeMask & (1<<pOp->p1))!=0 );
  pBt = db->aDb[pOp->p1].pBt;
  rc = sqlite3PagerCheckpoint(sqlite3BtreePager(pBt));
  break;
};  
#endif

/* Opcode: JournalMode P1 P2 P3 * *
**
** Change the journal mode of database P1 to P3. P3 must be one of the

#ifndef SQLITE_OMIT_WAL
/* Opcode: Checkpoint P1 * * * *
**
** Checkpoint database P1. This is a no-op if P1 is not currently in
** WAL mode.
*/
case OP_Checkpoint: {
  rc = sqlite3Checkpoint(db, pOp->p1);





  break;
};  
#endif

/* Opcode: JournalMode P1 P2 P3 * *
**
** Change the journal mode of database P1 to P3. P3 must be one of the

#
#   1) Backing up file-to-file. The writer writes via an external pager.
#   2) Backing up file-to-file. The writer writes via the same pager as
#      is used by the backup operation.
#   3) Backing up memory-to-file. 
#
set iTest 0

foreach {writer file} {db test.db db3 test.db db :memory:} {
  incr iTest
  catch { file delete bak.db }
  sqlite3 db2 bak.db
  catch { file delete $file }
  sqlite3 db $file
  sqlite3 db3 $file

#
#   1) Backing up file-to-file. The writer writes via an external pager.
#   2) Backing up file-to-file. The writer writes via the same pager as
#      is used by the backup operation.
#   3) Backing up memory-to-file. 
#
set iTest 0
file delete -force bak.db-wal
foreach {writer file} {db test.db db3 test.db db :memory:} {
  incr iTest
  catch { file delete bak.db }
  sqlite3 db2 bak.db
  catch { file delete $file }
  sqlite3 db $file
  sqlite3 db3 $file

# This test case attempts to provoke a deadlock condition that existed in
# the unix VFS at one point. The problem occurred only while recovering a 
# very large wal file (one that requires a wal-index larger than the 
# initial default allocation of 64KB).
#
# When recovering a log file, mutexes are usually obtained and released
# as follows:
#
#   xShmGet                         ENTER mutexBuf
#   xShmLock(RECOVER)               ENTER mutexRecov
#     <do recovery work>
#   xShmLock(READ)                  LEAVE mutexRecov
#   xShmRelease                     LEAVE mutexBuf         
#
# However, if the initial wal-index allocation needs to be enlarged during
# the recovery process, the mutex operations become:
#
#   xShmGet                         ENTER mutexBuf
#   xShmLock(RECOVER)               ENTER mutexRecov
#     <do first part of recovery work>
#     xShmRelease                   LEAVE mutexBuf
#     xShmSize
#     xShmGet                       ENTER mutexBuf
#     <do second part of recovery work>
#   xShmLock(READ)                  LEAVE mutexRecov
#   xShmRelease                     LEAVE mutexBuf         
#
# If multiple threads attempt the above simultaneously, deadlock can occur.
#
do_thread_test walthread-5 -seconds $seconds(walthread-5) -init {

  proc log_file_size {nFrame pgsz} {
    expr {12 + ($pgsz+16)*$nFrame}
  }

  execsql {

# This test case attempts to provoke a deadlock condition that existed in
# the unix VFS at one point. The problem occurred only while recovering a 
# very large wal file (one that requires a wal-index larger than the 
# initial default allocation of 64KB).
#
























do_thread_test walthread-5 -seconds $seconds(walthread-5) -init {

  proc log_file_size {nFrame pgsz} {
    expr {12 + ($pgsz+16)*$nFrame}
  }

  execsql {