/*
** 2007 August 14
**
** 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 contains the C functions that implement mutexes for
** use by the SQLite core.
**
** $Id: mutex.c,v 1.1 2007/08/15 13:04:54 drh Exp $
*/
/*
** If SQLITE_MUTEX_APPDEF is defined, then this whole module is
** omitted and equivalent functionality just be provided by the
** application that links against the SQLite library.
*/
#ifndef SQLITE_MUTEX_APPDEF
/*
** The start of real code
*/
#include "sqliteInt.h"
/************************ No-op Mutex Implementation **********************
**
** This first implementation of mutexes is really a no-op. In other words,
** no real locking occurs. This implementation is appropriate for use
** in single threaded applications which do not want the extra overhead
** of thread locking primitives.
*/
/*
** The sqlite3_mutex_alloc() routine allocates a new
** mutex and returns a pointer to it. If it returns NULL
** that means that a mutex could not be allocated. SQLite
** will unwind its stack and return an error. The argument
** to sqlite3_mutex_alloc() is usually zero, which causes
** any space required for the mutex to be obtained from
** sqlite3_malloc(). However if the argument is a positive
** integer less than SQLITE_NUM_STATIC_MUTEX, then a pointer
** to a static mutex is returned. There are a finite number
** of static mutexes. Static mutexes should not be passed
** to sqlite3_mutex_free(). The allocation of a static
** mutex cannot fail.
*/
sqlite3_mutex *sqlite3_mutex_alloc(int idNotUsed){
return (sqlite3_mutex*)sqlite3_mutex_alloc;
}
/*
** This routine deallocates a previously
** allocated mutex. SQLite is careful to deallocate every
** mutex that it allocates.
*/
void sqlite3_mutex_free(sqlite3_mutex *pNotUsed){}
/*
** The sqlite3_mutex_enter() routine attempts to enter a
** mutex. If another thread is already within the mutex,
** sqlite3_mutex_enter() will return SQLITE_BUSY if blockFlag
** is zero, or it will block and wait for the other thread to
** exit if blockFlag is non-zero. Mutexes are recursive. The
** same thread can enter a single mutex multiple times. Each
** entrance must be matched with a corresponding exit before
** another thread is able to enter the mutex.
*/
int sqlite3_mutex_enter(sqlite3_mutex *pNotUsed, int blockFlag){
return SQLITE_OK;
}
/*
** The sqlite3_mutex_exit() routine exits a mutex that was
** previously entered by the same thread. The behavior
** is undefined if the mutex is not currently entered or
** is not currently allocated. SQLite will never do either.
*/
void sqlite3_mutex_leave(sqlite3_mutex *pNotUsed){
return;
}
/*
** The sqlite3_mutex_serialize() routine is used to serialize
** execution of a subroutine. The subroutine given in the argument
** is invoked. But only one thread at a time is allowed to be
** running a subroutine using sqlite3_mutex_serialize().
*/
int sqlite3_mutex_serialize(void (*xCallback)(void*), void *pArg){
xCallback(pArg);
}
#if 0
/**************** Non-recursive Pthread Mutex Implementation *****************
**
** This implementation of mutexes is built using a version of pthreads that
** does not have native support for recursive mutexes.
*/
/*
** Each recursive mutex is an instance of the following structure.
*/
struct RMutex {
int nRef; /* Number of entrances */
pthread_mutex_t auxMutex; /* Mutex controlling access to nRef and owner */
pthread_mutex_t mainMutex; /* Mutex controlling the lock */
pthread_t owner; /* Thread that is within this mutex */
};
/*
** Static mutexes
*/
static struct RMutex rmutexes[] = {
{ 0, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, },
{ 0, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, },
{ 0, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, },
};
/*
** A mutex used for serialization.
*/
static RMutex serialMutex =
{0, PTHREAD_MUTEX_INITIALIZER, PTHREAD_MUTEX_INITIALIZER, };
/*
** The sqlite3_mutex_alloc() routine allocates a new
** mutex and returns a pointer to it. If it returns NULL
** that means that a mutex could not be allocated. SQLite
** will unwind its stack and return an error. The argument
** to sqlite3_mutex_alloc() is usually zero, which causes
** any space required for the mutex to be obtained from
** sqlite3_malloc(). However if the argument is a positive
** integer less than SQLITE_NUM_STATIC_MUTEX, then a pointer
** to a static mutex is returned. There are a finite number
** of static mutexes. Static mutexes should not be passed
** to sqlite3_mutex_free(). The allocation of a static
** mutex cannot fail.
*/
sqlite3_mutex *sqlite3_mutex_alloc(int id){
struct RMutex *p;
if( id>0 ){
if( id>sizeof(rmutexes)/sizeof(rmutexes[0]) ){
p = 0;
}else{
p = &rmutexes[id-1];
}
}else{
p = sqlite3_malloc( sizeof(*p) );
if( p ){
p->nRef = 0;
pthread_mutex_init(&p->mutex, 0);
}
}
return (sqlite3_mutex*)p;
}
/*
** This routine deallocates a previously
** allocated mutex. SQLite is careful to deallocate every
** mutex that it allocates.
*/
void sqlite3_mutex_free(sqlite3_mutex *pMutex){
struct RMutex *p = (struct RMutex*)pMutex;
assert( p->nRef==0 );
pthread_mutex_destroy(&p->mutex);
sqlite3_free(p);
}
/*
** The sqlite3_mutex_enter() routine attempts to enter a
** mutex. If another thread is already within the mutex,
** sqlite3_mutex_enter() will return SQLITE_BUSY if blockFlag
** is zero, or it will block and wait for the other thread to
** exit if blockFlag is non-zero. Mutexes are recursive. The
** same thread can enter a single mutex multiple times. Each
** entrance must be matched with a corresponding exit before
** another thread is able to enter the mutex.
*/
int sqlite3_mutex_enter(sqlite3_mutex *pMutex, int blockFlag){
struct RMutex *p = (struct RMutex*)pMutex;
while(1){
pthread_mutex_lock(&p->auxMutex);
if( p->nRef==0 ){
p->nRef++;
p->owner = pthread_self();
pthread_mutex_lock(&p->mainMutex);
pthread_mutex_unlock(&p->auxMutex);
return SQLITE_OK;
}else if( pthread_equal(p->owner, pthread_self()) ){
p->nRef++;
pthread_mutex_unlock(&p->auxMutex);
return SQLITE_OK;
}else if( !blockFlag ){
pthread_mutex_unlock(&p->auxMutex);
return SQLITE_BUSY;
}else{
pthread_mutex_unlock(&p->auxMutex);
pthread_mutex_lock(&p->mainMutex);
pthread_mutex_unlock(&p->mainMutex);
}
}
/* NOTREACHED */
}
/*
** The sqlite3_mutex_exit() routine exits a mutex that was
** previously entered by the same thread. The behavior
** is undefined if the mutex is not currently entered or
** is not currently allocated. SQLite will never do either.
*/
void sqlite3_mutex_leave(sqlite3_mutex *pMutex){
struct RMutex *p = (struct RMutex*)pMutex;
pthread_mutex_lock(&p->auxMutex);
p->nRef--;
if( p->nRef<=0 ){
pthread_mutex_unlock(&p->mainMutex);
}
pthread_mutex_unlock(&p->auxMutex);
}
/*
** The sqlite3_mutex_serialize() routine is used to serialize
** execution of a subroutine. The subroutine given in the argument
** is invoked. But only one thread at a time is allowed to be
** running a subroutine using sqlite3_mutex_serialize().
*/
int sqlite3_mutex_serialize(void (*xCallback)(void*), void *pArg){
sqlite3_mutex_enter(&serialMutex, 1);
xCallback(pArg);
sqlite3_mutex_leave(&serialMutex);
}
#endif /* non-recursive pthreads */
#endif /* !defined(SQLITE_MUTEX_APPDEF) */