--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/persistentstorage/sqlite3api/SQLite/mutex_unix.c Fri Jan 22 11:06:30 2010 +0200
@@ -0,0 +1,325 @@
+/*
+** 2007 August 28
+**
+** 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 pthreads
+**
+** $Id: mutex_unix.c,v 1.13 2008/07/16 12:33:24 drh Exp $
+*/
+#include "sqliteInt.h"
+
+/*
+** The code in this file is only used if we are compiling threadsafe
+** under unix with pthreads.
+**
+** Note that this implementation requires a version of pthreads that
+** supports recursive mutexes.
+*/
+#ifdef SQLITE_MUTEX_PTHREADS
+
+#include <pthread.h>
+
+
+/*
+** Each recursive mutex is an instance of the following structure.
+*/
+struct sqlite3_mutex {
+ pthread_mutex_t mutex; /* Mutex controlling the lock */
+ int id; /* Mutex type */
+ int nRef; /* Number of entrances */
+ pthread_t owner; /* Thread that is within this mutex */
+#ifdef SQLITE_DEBUG
+ int trace; /* True to trace changes */
+#endif
+};
+#ifdef SQLITE_DEBUG
+#define SQLITE3_MUTEX_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, 0, 0, (pthread_t)0, 0 }
+#else
+#define SQLITE3_MUTEX_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, 0, 0, (pthread_t)0 }
+#endif
+
+/*
+** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
+** intended for use only inside assert() statements. On some platforms,
+** there might be race conditions that can cause these routines to
+** deliver incorrect results. In particular, if pthread_equal() is
+** not an atomic operation, then these routines might delivery
+** incorrect results. On most platforms, pthread_equal() is a
+** comparison of two integers and is therefore atomic. But we are
+** told that HPUX is not such a platform. If so, then these routines
+** will not always work correctly on HPUX.
+**
+** On those platforms where pthread_equal() is not atomic, SQLite
+** should be compiled without -DSQLITE_DEBUG and with -DNDEBUG to
+** make sure no assert() statements are evaluated and hence these
+** routines are never called.
+*/
+#ifndef NDEBUG
+static int pthreadMutexHeld(sqlite3_mutex *p){
+ return (p->nRef!=0 && pthread_equal(p->owner, pthread_self()));
+}
+static int pthreadMutexNotheld(sqlite3_mutex *p){
+ return p->nRef==0 || pthread_equal(p->owner, pthread_self())==0;
+}
+#endif
+
+/*
+** Initialize and deinitialize the mutex subsystem.
+*/
+static int pthreadMutexInit(void){ return SQLITE_OK; }
+static int pthreadMutexEnd(void){ return SQLITE_OK; }
+
+/*
+** 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 one of these integer constants:
+**
+** <ul>
+** <li> SQLITE_MUTEX_FAST
+** <li> SQLITE_MUTEX_RECURSIVE
+** <li> SQLITE_MUTEX_STATIC_MASTER
+** <li> SQLITE_MUTEX_STATIC_MEM
+** <li> SQLITE_MUTEX_STATIC_MEM2
+** <li> SQLITE_MUTEX_STATIC_PRNG
+** <li> SQLITE_MUTEX_STATIC_LRU
+** </ul>
+**
+** The first two constants cause sqlite3_mutex_alloc() to create
+** a new mutex. The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
+** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
+** The mutex implementation does not need to make a distinction
+** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
+** not want to. But SQLite will only request a recursive mutex in
+** cases where it really needs one. If a faster non-recursive mutex
+** implementation is available on the host platform, the mutex subsystem
+** might return such a mutex in response to SQLITE_MUTEX_FAST.
+**
+** The other allowed parameters to sqlite3_mutex_alloc() each return
+** a pointer to a static preexisting mutex. Three static mutexes are
+** used by the current version of SQLite. Future versions of SQLite
+** may add additional static mutexes. Static mutexes are for internal
+** use by SQLite only. Applications that use SQLite mutexes should
+** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
+** SQLITE_MUTEX_RECURSIVE.
+**
+** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
+** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
+** returns a different mutex on every call. But for the static
+** mutex types, the same mutex is returned on every call that has
+** the same type number.
+*/
+static sqlite3_mutex *pthreadMutexAlloc(int iType){
+ static sqlite3_mutex staticMutexes[] = {
+ SQLITE3_MUTEX_INITIALIZER,
+ SQLITE3_MUTEX_INITIALIZER,
+ SQLITE3_MUTEX_INITIALIZER,
+ SQLITE3_MUTEX_INITIALIZER,
+ SQLITE3_MUTEX_INITIALIZER,
+ SQLITE3_MUTEX_INITIALIZER
+ };
+ sqlite3_mutex *p;
+ switch( iType ){
+ case SQLITE_MUTEX_RECURSIVE: {
+ p = sqlite3MallocZero( sizeof(*p) );
+ if( p ){
+#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
+ /* If recursive mutexes are not available, we will have to
+ ** build our own. See below. */
+ pthread_mutex_init(&p->mutex, 0);
+#else
+ /* Use a recursive mutex if it is available */
+ pthread_mutexattr_t recursiveAttr;
+ pthread_mutexattr_init(&recursiveAttr);
+ pthread_mutexattr_settype(&recursiveAttr, PTHREAD_MUTEX_RECURSIVE);
+ pthread_mutex_init(&p->mutex, &recursiveAttr);
+ pthread_mutexattr_destroy(&recursiveAttr);
+#endif
+ p->id = iType;
+ }
+ break;
+ }
+ case SQLITE_MUTEX_FAST: {
+ p = sqlite3MallocZero( sizeof(*p) );
+ if( p ){
+ p->id = iType;
+ pthread_mutex_init(&p->mutex, 0);
+ }
+ break;
+ }
+ default: {
+ assert( iType-2 >= 0 );
+ assert( iType-2 < sizeof(staticMutexes)/sizeof(staticMutexes[0]) );
+ p = &staticMutexes[iType-2];
+ p->id = iType;
+ break;
+ }
+ }
+ return p;
+}
+
+
+/*
+** This routine deallocates a previously
+** allocated mutex. SQLite is careful to deallocate every
+** mutex that it allocates.
+*/
+static void pthreadMutexFree(sqlite3_mutex *p){
+ assert( p->nRef==0 );
+ assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
+ pthread_mutex_destroy(&p->mutex);
+ sqlite3_free(p);
+}
+
+/*
+** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
+** to enter a mutex. If another thread is already within the mutex,
+** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
+** SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK
+** upon successful entry. Mutexes created using SQLITE_MUTEX_RECURSIVE can
+** be entered multiple times by the same thread. In such cases the,
+** mutex must be exited an equal number of times before another thread
+** can enter. If the same thread tries to enter any other kind of mutex
+** more than once, the behavior is undefined.
+*/
+static void pthreadMutexEnter(sqlite3_mutex *p){
+ assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );
+
+#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
+ /* If recursive mutexes are not available, then we have to grow
+ ** our own. This implementation assumes that pthread_equal()
+ ** is atomic - that it cannot be deceived into thinking self
+ ** and p->owner are equal if p->owner changes between two values
+ ** that are not equal to self while the comparison is taking place.
+ ** This implementation also assumes a coherent cache - that
+ ** separate processes cannot read different values from the same
+ ** address at the same time. If either of these two conditions
+ ** are not met, then the mutexes will fail and problems will result.
+ */
+ {
+ pthread_t self = pthread_self();
+ if( p->nRef>0 && pthread_equal(p->owner, self) ){
+ p->nRef++;
+ }else{
+ pthread_mutex_lock(&p->mutex);
+ assert( p->nRef==0 );
+ p->owner = self;
+ p->nRef = 1;
+ }
+ }
+#else
+ /* Use the built-in recursive mutexes if they are available.
+ */
+ pthread_mutex_lock(&p->mutex);
+ p->owner = pthread_self();
+ p->nRef++;
+#endif
+
+#ifdef SQLITE_DEBUG
+ if( p->trace ){
+ printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
+ }
+#endif
+}
+static int pthreadMutexTry(sqlite3_mutex *p){
+ int rc;
+ assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );
+
+#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
+ /* If recursive mutexes are not available, then we have to grow
+ ** our own. This implementation assumes that pthread_equal()
+ ** is atomic - that it cannot be deceived into thinking self
+ ** and p->owner are equal if p->owner changes between two values
+ ** that are not equal to self while the comparison is taking place.
+ ** This implementation also assumes a coherent cache - that
+ ** separate processes cannot read different values from the same
+ ** address at the same time. If either of these two conditions
+ ** are not met, then the mutexes will fail and problems will result.
+ */
+ {
+ pthread_t self = pthread_self();
+ if( p->nRef>0 && pthread_equal(p->owner, self) ){
+ p->nRef++;
+ rc = SQLITE_OK;
+ }else if( pthread_mutex_trylock(&p->mutex)==0 ){
+ assert( p->nRef==0 );
+ p->owner = self;
+ p->nRef = 1;
+ rc = SQLITE_OK;
+ }else{
+ rc = SQLITE_BUSY;
+ }
+ }
+#else
+ /* Use the built-in recursive mutexes if they are available.
+ */
+ if( pthread_mutex_trylock(&p->mutex)==0 ){
+ p->owner = pthread_self();
+ p->nRef++;
+ rc = SQLITE_OK;
+ }else{
+ rc = SQLITE_BUSY;
+ }
+#endif
+
+#ifdef SQLITE_DEBUG
+ if( rc==SQLITE_OK && p->trace ){
+ printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
+ }
+#endif
+ return rc;
+}
+
+/*
+** The sqlite3_mutex_leave() 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.
+*/
+static void pthreadMutexLeave(sqlite3_mutex *p){
+ assert( pthreadMutexHeld(p) );
+ p->nRef--;
+ assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
+
+#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX
+ if( p->nRef==0 ){
+ pthread_mutex_unlock(&p->mutex);
+ }
+#else
+ pthread_mutex_unlock(&p->mutex);
+#endif
+
+#ifdef SQLITE_DEBUG
+ if( p->trace ){
+ printf("leave mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
+ }
+#endif
+}
+
+sqlite3_mutex_methods *sqlite3DefaultMutex(void){
+ static sqlite3_mutex_methods sMutex = {
+ pthreadMutexInit,
+ pthreadMutexEnd,
+ pthreadMutexAlloc,
+ pthreadMutexFree,
+ pthreadMutexEnter,
+ pthreadMutexTry,
+ pthreadMutexLeave,
+#ifdef SQLITE_DEBUG
+ pthreadMutexHeld,
+ pthreadMutexNotheld
+#endif
+ };
+
+ return &sMutex;
+}
+
+#endif /* SQLITE_MUTEX_PTHREAD */