224 lines
7.4 KiB
C
Executable File
224 lines
7.4 KiB
C
Executable File
/*
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** 2007 August 28
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**
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** The author disclaims copyright to this source code. In place of
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** a legal notice, here is a blessing:
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**
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** May you do good and not evil.
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** May you find forgiveness for yourself and forgive others.
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** May you share freely, never taking more than you give.
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**
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*************************************************************************
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** This file contains the C functions that implement mutexes for pthreads
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**
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** $Id: mutex_unix.c,v 1.2 2007/08/28 22:24:35 drh Exp $
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*/
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#include "sqliteInt.h"
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/*
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** The code in this file is only used if we are compiling threadsafe
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** under unix with pthreads.
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**
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** Note that this implementation requires a version of pthreads that
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** supports recursive mutexes.
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*/
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#ifdef SQLITE_MUTEX_PTHREADS
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#include <pthread.h>
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/*
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** Each recursive mutex is an instance of the following structure.
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*/
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struct sqlite3_mutex {
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pthread_mutex_t mutex; /* Mutex controlling the lock */
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int id; /* Mutex type */
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int nRef; /* Number of entrances */
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pthread_t owner; /* Thread that is within this mutex */
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#ifdef SQLITE_DEBUG
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int trace; /* True to trace changes */
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#endif
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};
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/*
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** The sqlite3_mutex_alloc() routine allocates a new
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** mutex and returns a pointer to it. If it returns NULL
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** that means that a mutex could not be allocated. SQLite
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** will unwind its stack and return an error. The argument
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** to sqlite3_mutex_alloc() is one of these integer constants:
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**
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** <ul>
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** <li> SQLITE_MUTEX_FAST
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** <li> SQLITE_MUTEX_RECURSIVE
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** <li> SQLITE_MUTEX_STATIC_MASTER
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** <li> SQLITE_MUTEX_STATIC_MEM
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** <li> SQLITE_MUTEX_STATIC_MEM2
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** <li> SQLITE_MUTEX_STATIC_PRNG
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** <li> SQLITE_MUTEX_STATIC_LRU
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** </ul>
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**
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** The first two constants cause sqlite3_mutex_alloc() to create
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** a new mutex. The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
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** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
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** The mutex implementation does not need to make a distinction
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** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
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** not want to. But SQLite will only request a recursive mutex in
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** cases where it really needs one. If a faster non-recursive mutex
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** implementation is available on the host platform, the mutex subsystem
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** might return such a mutex in response to SQLITE_MUTEX_FAST.
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**
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** The other allowed parameters to sqlite3_mutex_alloc() each return
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** a pointer to a static preexisting mutex. Three static mutexes are
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** used by the current version of SQLite. Future versions of SQLite
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** may add additional static mutexes. Static mutexes are for internal
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** use by SQLite only. Applications that use SQLite mutexes should
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** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
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** SQLITE_MUTEX_RECURSIVE.
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**
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** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
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** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
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** returns a different mutex on every call. But for the static
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** mutex types, the same mutex is returned on every call that has
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** the same type number.
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*/
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sqlite3_mutex *sqlite3_mutex_alloc(int iType){
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static sqlite3_mutex staticMutexes[] = {
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{ PTHREAD_MUTEX_INITIALIZER, },
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{ PTHREAD_MUTEX_INITIALIZER, },
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{ PTHREAD_MUTEX_INITIALIZER, },
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{ PTHREAD_MUTEX_INITIALIZER, },
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{ PTHREAD_MUTEX_INITIALIZER, },
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};
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sqlite3_mutex *p;
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switch( iType ){
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case SQLITE_MUTEX_RECURSIVE: {
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p = sqlite3MallocZero( sizeof(*p) );
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if( p ){
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pthread_mutexattr_t recursiveAttr;
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pthread_mutexattr_init(&recursiveAttr);
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pthread_mutexattr_settype(&recursiveAttr, PTHREAD_MUTEX_RECURSIVE);
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pthread_mutex_init(&p->mutex, &recursiveAttr);
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pthread_mutexattr_destroy(&recursiveAttr);
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p->id = iType;
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}
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break;
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}
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case SQLITE_MUTEX_FAST: {
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p = sqlite3MallocZero( sizeof(*p) );
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if( p ){
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p->id = iType;
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pthread_mutex_init(&p->mutex, 0);
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}
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break;
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}
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default: {
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assert( iType-2 >= 0 );
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assert( iType-2 < sizeof(staticMutexes)/sizeof(staticMutexes[0]) );
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p = &staticMutexes[iType-2];
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p->id = iType;
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break;
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}
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}
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return p;
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}
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/*
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** This routine deallocates a previously
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** allocated mutex. SQLite is careful to deallocate every
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** mutex that it allocates.
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*/
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void sqlite3_mutex_free(sqlite3_mutex *p){
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assert( p );
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assert( p->nRef==0 );
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assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
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pthread_mutex_destroy(&p->mutex);
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sqlite3_free(p);
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}
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/*
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** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
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** to enter a mutex. If another thread is already within the mutex,
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** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
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** SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK
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** upon successful entry. Mutexes created using SQLITE_MUTEX_RECURSIVE can
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** be entered multiple times by the same thread. In such cases the,
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** mutex must be exited an equal number of times before another thread
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** can enter. If the same thread tries to enter any other kind of mutex
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** more than once, the behavior is undefined.
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*/
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void sqlite3_mutex_enter(sqlite3_mutex *p){
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assert( p );
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assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
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pthread_mutex_lock(&p->mutex);
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p->owner = pthread_self();
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p->nRef++;
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#ifdef SQLITE_DEBUG
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if( p->trace ){
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printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
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}
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#endif
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}
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int sqlite3_mutex_try(sqlite3_mutex *p){
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int rc;
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assert( p );
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assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
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if( pthread_mutex_trylock(&p->mutex)==0 ){
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p->owner = pthread_self();
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p->nRef++;
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rc = SQLITE_OK;
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#ifdef SQLITE_DEBUG
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if( p->trace ){
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printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
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}
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#endif
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}else{
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rc = SQLITE_BUSY;
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}
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return rc;
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}
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/*
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** The sqlite3_mutex_leave() routine exits a mutex that was
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** previously entered by the same thread. The behavior
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** is undefined if the mutex is not currently entered or
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** is not currently allocated. SQLite will never do either.
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*/
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void sqlite3_mutex_leave(sqlite3_mutex *p){
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assert( p );
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assert( sqlite3_mutex_held(p) );
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p->nRef--;
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assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
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#ifdef SQLITE_DEBUG
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if( p->trace ){
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printf("leave mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
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}
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#endif
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pthread_mutex_unlock(&p->mutex);
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}
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/*
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** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
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** intended for use only inside assert() statements. On some platforms,
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** there might be race conditions that can cause these routines to
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** deliver incorrect results. In particular, if pthread_equal() is
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** not an atomic operation, then these routines might delivery
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** incorrect results. On most platforms, pthread_equal() is a
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** comparison of two integers and is therefore atomic. But we are
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** told that HPUX is not such a platform. If so, then these routines
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** will not always work correctly on HPUX.
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**
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** On those platforms where pthread_equal() is not atomic, SQLite
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** should be compiled without -DSQLITE_DEBUG and with -DNDEBUG to
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** make sure no assert() statements are evaluated and hence these
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** routines are never called.
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*/
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#ifndef NDEBUG
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int sqlite3_mutex_held(sqlite3_mutex *p){
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return p==0 || (p->nRef!=0 && pthread_equal(p->owner, pthread_self()));
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}
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int sqlite3_mutex_notheld(sqlite3_mutex *p){
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return p==0 || p->nRef==0 || pthread_equal(p->owner, pthread_self())==0;
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}
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#endif
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#endif /* SQLITE_MUTEX_PTHREAD */
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