SQLite

**    May you share freely, never taking more than you give.
**
*************************************************************************
**
** This file contains the implementation of the sqlite3_unlock_notify()
** API method and its associated functionality.
**
** $Id: notify.c,v 1.4 2009/04/07 22:06:57 drh Exp $
*/
#include "sqliteInt.h"
#include "btreeInt.h"

/* Omit this entire file if SQLITE_ENABLE_UNLOCK_NOTIFY is not defined. */
#ifdef SQLITE_ENABLE_UNLOCK_NOTIFY

  assertMutexHeld();
  checkListProperties(0);
  sqlite3_mutex_leave(sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_MASTER));
}

/*
** Register an unlock-notify callback.
**
** This is called after connection "db" has attempted some operation
** but has received an SQLITE_LOCKED error because another connection
** (call it pOther) in the same process was busy using the same shared
** cache.  pOther is found by looking at db->pBlockingConnection.
**
** If there is no blocking connection, the callback is invoked immediately,
** before this routine returns.
**
** If pOther is already blocked on db, then report SQLITE_LOCKED, to indicate
** a deadlock.
**
** Otherwise, make arrangements to invoke xNotify when pOther drops
** its locks.
**
** Each call to this routine overrides any prior callbacks registered
** on the same "db".  If xNotify==0 then any prior callbacks are immediately
** cancelled.
*/
int sqlite3_unlock_notify(
  sqlite3 *db,
  void (*xNotify)(void **, int),
  void *pArg
){
  int rc = SQLITE_OK;

  sqlite3_mutex_enter(db->mutex);
  enterMutex();

  if( xNotify==0 ){
    removeFromBlockedList(db);
    db->pUnlockConnection = 0;
    db->xUnlockNotify = 0;
    db->pUnlockArg = 0;
  }else if( 0==db->pBlockingConnection ){
    /* The blocking transaction has been concluded. Or there never was a 
    ** blocking transaction. In either case, invoke the notify callback
    ** immediately. 
    */
    xNotify(&pArg, 1);
  }else{
    sqlite3 *p;

    for(p=db->pBlockingConnection; p && p!=db; p=p->pUnlockConnection){}
    if( p ){
      rc = SQLITE_LOCKED;              /* Deadlock detected. */
    }else{
      db->pUnlockConnection = db->pBlockingConnection;
      db->xUnlockNotify = xNotify;
      db->pUnlockArg = pArg;
      removeFromBlockedList(db);

    addToBlockedList(db);
  }
  db->pBlockingConnection = pBlocker;
  leaveMutex();
}

/*
** This function is called when
** the transaction opened by database db has just finished. Locks held 
** by database connection db have been released.
**
** This function loops through each entry in the blocked connections
** list and does the following:
**
**   1) If the sqlite3.pBlockingConnection member of a list entry is
**      set to db, then set pBlockingConnection=0.
**
**   2) If the sqlite3.pUnlockConnection member of a list entry is
**      set to db, then invoke the configured unlock-notify callback and
**      set pUnlockConnection=0.
**
**   3) If the two steps above mean that pBlockingConnection==0 and
**      pUnlockConnection==0, remove the entry from the blocked connections
**      list.
*/
void sqlite3ConnectionUnlocked(sqlite3 *db){
  void (*xUnlockNotify)(void **, int) = 0; /* Unlock-notify cb to invoke */
  int nArg = 0;                            /* Number of entries in aArg[] */
  sqlite3 **pp;                            /* Iterator variable */
  void **aArg;               /* Arguments to the unlock callback */


  void **aDyn = 0;           /* Dynamically allocated space for aArg[] */
  void *aStatic[16];         /* Starter space for aArg[].  No malloc required */

  aArg = aStatic;
  enterMutex();         /* Enter STATIC_MASTER mutex */

  /* This loop runs once for each entry in the blocked-connections list. */
  for(pp=&sqlite3BlockedList; *pp; /* no-op */ ){
    sqlite3 *p = *pp;

    /* Step 1. */

/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.853 2009/04/07 22:06:57 drh Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/*
** Include the configuration header output by 'configure' if we're using the
** autoconf-based build

  int nSavepoint;               /* Number of non-transaction savepoints */
  int nStatement;               /* Number of nested statement-transactions  */
  u8 isTransactionSavepoint;    /* True if the outermost savepoint is a TS */

#ifdef SQLITE_ENABLE_UNLOCK_NOTIFY
  /* The following variables are all protected by the STATIC_MASTER 
  ** mutex, not by sqlite3.mutex. They are used by code in notify.c. 
  **
  ** When X.pUnlockConnection==Y, that means that X is waiting for Y to
  ** unlock so that it can proceed.
  **
  ** When X.pBlockingConnection==Y, that means that something that X tried
  ** tried to do recently failed with an SQLITE_LOCKED error due to locks
  ** held by Y.
  */
  sqlite3 *pBlockingConnection; /* Connection that caused SQLITE_LOCKED */
  sqlite3 *pUnlockConnection;           /* Connection to watch for unlock */
  void *pUnlockArg;                     /* Argument to xUnlockNotify */
  void (*xUnlockNotify)(void **, int);  /* Unlock notify callback */
  sqlite3 *pNextBlocked;        /* Next in list of all blocked connections */
#endif

# 2009 March 04
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing the sqlite3_unlock_notify() API.
#
# $Id: notify1.test,v 1.3 2009/04/07 22:06:57 drh Exp $

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

ifcapable !unlock_notify||!shared_cache {
  finish_test
  return

  set zScript
} {}
do_test notify1-1.5 {
  execsql { COMMIT }
  eval $zScript
  execsql { SELECT * FROM t1 }
} {1 2 3 4}

#-------------------------------------------------------------------------
# Verify that invoking the "unlock_notify" method with no arguments
# (which is the equivalent of invoking sqlite3_unlock_notify() with
# a NULL xNotify argument) cancels a pending notify callback.
#
do_test notify1-1.11 {
  execsql { DROP TABLE t1; CREATE TABLE t1(a, b) }
} {}
do_test notify1-1.12 {
  execsql {
    BEGIN;
    INSERT INTO t1 VALUES(1, 2);
  }
  catchsql { INSERT INTO t1 VALUES(3, 4) } db2
} {1 {database table is locked}}
do_test notify1-1.13 {
  set zScript ""
  db2 unlock_notify {
    set zScript "db2 eval { INSERT INTO t1 VALUES(3, 4) }"
  }
  execsql { SELECT * FROM t1 }
} {1 2}
do_test notify1-1.14 {
  set zScript
} {}
do_test notify1-1.15 {
  db2 unlock_notify
  execsql { COMMIT }
  eval $zScript
  execsql { SELECT * FROM t1 }
} {1 2}

#-------------------------------------------------------------------------
# The following tests, notify1-2.*, test that deadlock is detected 
# correctly.
# 
do_test notify1-2.1 {
  execsql {