SQLite

**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This header file defines the interface that the SQLite library
** presents to client programs.
**
** @(#) $Id: sqlite.h.in,v 1.196 2007/01/10 12:54:51 drh Exp $
*/
#ifndef _SQLITE3_H_
#define _SQLITE3_H_
#include <stdarg.h>     /* Needed for the definition of va_list */

/*
** Make sure we can call this stuff from C++.

/*
** This routine identifies a callback function that is invoked
** whenever an attempt is made to open a database table that is
** currently locked by another process or thread.  If the busy callback
** is NULL, then sqlite3_exec() returns SQLITE_BUSY immediately if
** it finds a locked table.  If the busy callback is not NULL, then
** sqlite3_exec() invokes the callback with two arguments.  The
** first argument to the handler is a copy of the void* pointer which
** is the third argument to this routine.  The second argument to
** the handler is the number of times that the busy handler has
** been invoked for this locking event.  If the
** busy callback returns 0, then sqlite3_exec() immediately returns
** SQLITE_BUSY.  If the callback returns non-zero, then sqlite3_exec()
** tries to open the table again and the cycle repeats.
**
** The presence of a busy handler does not guarantee that
** it will be invoked when there is lock contention.
** If SQLite determines that invoking the busy handler could result in
** a deadlock, it will return SQLITE_BUSY instead.
** Consider a scenario where one process is holding a read lock that
** it is trying to promote to a reserved lock and
** a second process is holding a reserved lock that it is trying
** to promote to an exclusive lock.  The first process cannot proceed
** because it is blocked by the second and the second process cannot
** proceed because it is blocked by the first.  If both processes
** invoke the busy handlers, neither will make any progress.  Therefore,
** SQLite returns SQLITE_BUSY for the first process, hoping that this
** will induce the first process to release its read lock and allow
** the second process to proceed.
**
** The default busy callback is NULL.
**
** Sqlite is re-entrant, so the busy handler may start a new query. 
** (It is not clear why anyone would every want to do this, but it
** is allowed, in theory.)  But the busy handler may not close the
** database.  Closing the database from a busy handler will delete 

set rcsid {$Id: capi3ref.tcl,v 1.50 2007/01/10 12:54:52 drh Exp $}
source common.tcl
header {C/C++ Interface For SQLite Version 3}
puts {
<h2>C/C++ Interface For SQLite Version 3</h2>
}

proc api {name prototype desc {notused x}} {

 This routine identifies a callback function that might be invoked
 whenever an attempt is made to open a database table 
 that another thread or process has locked.
 If the busy callback is NULL, then SQLITE_BUSY is returned immediately
 upon encountering the lock.
 If the busy callback is not NULL, then the
 callback will be invoked with two arguments.  The
 first argument to the handler is a copy of the void* pointer which
 is the third argument to this routine.  The second argument to
 the handler is the number of times that the busy handler has
 been invoked for this locking event. If the
 busy callback returns 0, then no additional attempts are made to
 access the database and SQLITE_BUSY is returned.
 If the callback returns non-zero, then another attempt is made to open the
 database for reading and the cycle repeats.

 The presence of a busy handler does not guarantee that
 it will be invoked when there is lock contention.