SQLite

  sqlite3_mutex_leave(db->mutex);
  return pRet;
}

#ifndef SQLITE_OMIT_WAL
/*
** The sqlite3_wal_hook() callback registered by sqlite3_wal_autocheckpoint().

** Invoke sqlite3_wal_checkpoint if the number of frames in the log file
** is greater than sqlite3.pWalArg cast to an integer (the value configured by
** wal_autocheckpoint()).
*/ 
int sqlite3WalDefaultHook(
  void *pClientData,     /* Argument */
  sqlite3 *db,           /* Connection */
  const char *zDb,       /* Database */
  int nFrame             /* Size of WAL */
){

  if( nFrame>=SQLITE_PTR_TO_INT(pClientData) ){
    sqlite3_wal_checkpoint(db, zDb);
  }
  return SQLITE_OK;
}
#endif /* SQLITE_OMIT_WAL */

/*
** 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){
#ifndef SQLITE_OMIT_WAL

  if( nFrame>0 ){
    sqlite3_wal_hook(db, sqlite3WalDefaultHook, SQLITE_INT_TO_PTR(nFrame));
  }else{
    sqlite3_wal_hook(db, 0, 0);
  }

#endif
  return SQLITE_OK;
}

/*
** Register a callback to be invoked each time a transaction is written
** into the write-ahead-log by this database connection.

** is a copy of the third parameter passed to sqlite3_wal_hook() when
** registering the callback. The second is a copy of the database handle.
** The third parameter is the name of the database that was written to -
** either "main" or the name of an ATTACHed database. The fourth parameter
** is the number of pages currently in the log file, including those that
** were just committed.
**
** The callback function should normally return SQLITE_OK.  If an error
** code is returned, that error will propagate back up through the
** SQLite code base to cause the statement that provoked the callback
** to fail.
**
** A single database handle may have at most a single log callback 
** registered at one time. Calling [sqlite3_wal_hook()] replaces any
** previously registered log callback. 
*/
void *sqlite3_wal_hook(
  sqlite3*, 

  char *zProgress;           /* The progress callback routine */
  char *zAuth;               /* The authorization callback routine */
  int disableAuth;           /* Disable the authorizer if it exists */
  char *zNull;               /* Text to substitute for an SQL NULL value */
  SqlFunc *pFunc;            /* List of SQL functions */
  Tcl_Obj *pUpdateHook;      /* Update hook script (if any) */
  Tcl_Obj *pRollbackHook;    /* Rollback hook script (if any) */
  Tcl_Obj *pWalHook;         /* WAL hook script (if any) */
  Tcl_Obj *pUnlockNotify;    /* Unlock notify script (if any) */
  SqlCollate *pCollate;      /* List of SQL collation functions */
  int rc;                    /* Return code of most recent sqlite3_exec() */
  Tcl_Obj *pCollateNeeded;   /* Collation needed script */
  SqlPreparedStmt *stmtList; /* List of prepared statements*/
  SqlPreparedStmt *stmtLast; /* Last statement in the list */
  int maxStmt;               /* The next maximum number of stmtList */

  }
  if( pDb->pUpdateHook ){
    Tcl_DecrRefCount(pDb->pUpdateHook);
  }
  if( pDb->pRollbackHook ){
    Tcl_DecrRefCount(pDb->pRollbackHook);
  }
  if( pDb->pWalHook ){
    Tcl_DecrRefCount(pDb->pWalHook);
  }
  if( pDb->pCollateNeeded ){
    Tcl_DecrRefCount(pDb->pCollateNeeded);
  }
  Tcl_Free((char*)pDb);
}

  SqliteDb *pDb = (SqliteDb*)clientData;
  assert(pDb->pRollbackHook);
  if( TCL_OK!=Tcl_EvalObjEx(pDb->interp, pDb->pRollbackHook, 0) ){
    Tcl_BackgroundError(pDb->interp);
  }
}

/*
** This procedure handles wal_hook callbacks.
*/
static int DbWalHandler(
  void *clientData, 
  sqlite3 *db, 
  const char *zDb, 
  int nEntry
){
  int ret = SQLITE_OK;
  Tcl_Obj *p;
  SqliteDb *pDb = (SqliteDb*)clientData;
  Tcl_Interp *interp = pDb->interp;
  assert(pDb->pWalHook);

  p = Tcl_DuplicateObj(pDb->pWalHook);
  Tcl_IncrRefCount(p);
  Tcl_ListObjAppendElement(interp, p, Tcl_NewStringObj(zDb, -1));
  Tcl_ListObjAppendElement(interp, p, Tcl_NewIntObj(nEntry));
  if( TCL_OK!=Tcl_EvalObjEx(interp, p, 0) 
   || TCL_OK!=Tcl_GetIntFromObj(interp, Tcl_GetObjResult(interp), &ret)
  ){
    Tcl_BackgroundError(interp);

    /* set ppHook to point at pUpdateHook or pRollbackHook, depending on 
    ** whether [$db update_hook] or [$db rollback_hook] was invoked.
    */
    Tcl_Obj **ppHook; 
    if( choice==DB_UPDATE_HOOK ){
      ppHook = &pDb->pUpdateHook;
    }else if( choice==DB_WAL_HOOK ){
      ppHook = &pDb->pWalHook;
    }else{
      ppHook = &pDb->pRollbackHook;
    }

    if( objc!=2 && objc!=3 ){
       Tcl_WrongNumArgs(interp, 2, objv, "?SCRIPT?");
       return TCL_ERROR;

        *ppHook = objv[2];
        Tcl_IncrRefCount(*ppHook);
      }
    }

    sqlite3_update_hook(pDb->db, (pDb->pUpdateHook?DbUpdateHandler:0), pDb);
    sqlite3_rollback_hook(pDb->db,(pDb->pRollbackHook?DbRollbackHandler:0),pDb);
    sqlite3_wal_hook(pDb->db,(pDb->pWalHook?DbWalHandler:0),pDb);

    break;
  }

  /*    $db version
  **
  ** Return the version string for this database.

  int rc = SQLITE_OK;
#ifndef SQLITE_OMIT_WAL
  int i;
  for(i=0; i<db->nDb; i++){
    Btree *pBt = db->aDb[i].pBt;
    if( pBt ){
      int nEntry = sqlite3PagerWalCallback(sqlite3BtreePager(pBt));
      if( db->xWalCallback && nEntry>0 && rc==SQLITE_OK ){
        rc = db->xWalCallback(db->pWalArg, db, db->aDb[i].zName, nEntry);


      }
    }
  }
#endif
  return rc;
}

do_test walhook-1.2 {
  set ::wal_hook [list]
  execsql { INSERT INTO t1 VALUES(1, 'one') }
  set ::wal_hook
} {main 5}
do_test walhook-1.3 {
  proc wal_hook {args} { db eval {PRAGMA wal_checkpoint}; return 0 }
  execsql { INSERT INTO t1 VALUES(2, 'two') }
  file size test.db
} [expr 3*1024]
do_test walhook-1.4 {
  proc wal_hook {zDb nEntry} { 
    execsql { PRAGMA wal_checkpoint }
    return 0

    INSERT INTO t1 VALUES(0, 0, 0);
  }
} -thread t 10 {

  set nextwrite $E(pid)

  proc wal_hook {zDb nEntry} {
    if {$nEntry>10} {db eval {PRAGMA wal_checkpoint}}
    return 0
  }
  db wal_hook wal_hook

  while {[tt_continue]} {
    set max 0
    while { $max != ($nextwrite-1) && [tt_continue] } {

  # busy-handler is not required. Disable it to check that this is true.
  db busy {}
  while {[tt_continue]} integrity_check
  set {} ok
} -thread w 1 {

  proc wal_hook {zDb nEntry} {
    if {$nEntry>15} {db eval {PRAGMA wal_checkpoint}}
    return 0
  }
  db wal_hook wal_hook
  set row 1
  while {[tt_continue]} {
    db eval { REPLACE INTO t1 VALUES($row, randomblob(300)) }
    incr row