| /* |
| ** 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 |
| */ |
| #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> |
| |
| /* |
| ** The sqlite3_mutex.id, sqlite3_mutex.nRef, and sqlite3_mutex.owner fields |
| ** are necessary under two condidtions: (1) Debug builds and (2) using |
| ** home-grown mutexes. Encapsulate these conditions into a single #define. |
| */ |
| #if defined(SQLITE_DEBUG) || defined(SQLITE_HOMEGROWN_RECURSIVE_MUTEX) |
| # define SQLITE_MUTEX_NREF 1 |
| #else |
| # define SQLITE_MUTEX_NREF 0 |
| #endif |
| |
| /* |
| ** Each recursive mutex is an instance of the following structure. |
| */ |
| struct sqlite3_mutex { |
| pthread_mutex_t mutex; /* Mutex controlling the lock */ |
| #if SQLITE_MUTEX_NREF |
| int id; /* Mutex type */ |
| volatile int nRef; /* Number of entrances */ |
| volatile pthread_t owner; /* Thread that is within this mutex */ |
| int trace; /* True to trace changes */ |
| #endif |
| }; |
| #if SQLITE_MUTEX_NREF |
| #define SQLITE3_MUTEX_INITIALIZER { PTHREAD_MUTEX_INITIALIZER, 0, 0, (pthread_t)0, 0 } |
| #else |
| #define SQLITE3_MUTEX_INITIALIZER { PTHREAD_MUTEX_INITIALIZER } |
| #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. |
| */ |
| #if !defined(NDEBUG) || defined(SQLITE_DEBUG) |
| 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 |
| ** <li> SQLITE_MUTEX_STATIC_PMEM |
| ** </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. Six 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 |
| #if SQLITE_MUTEX_NREF |
| p->id = iType; |
| #endif |
| } |
| break; |
| } |
| case SQLITE_MUTEX_FAST: { |
| p = sqlite3MallocZero( sizeof(*p) ); |
| if( p ){ |
| #if SQLITE_MUTEX_NREF |
| p->id = iType; |
| #endif |
| pthread_mutex_init(&p->mutex, 0); |
| } |
| break; |
| } |
| default: { |
| assert( iType-2 >= 0 ); |
| assert( iType-2 < ArraySize(staticMutexes) ); |
| p = &staticMutexes[iType-2]; |
| #if SQLITE_MUTEX_NREF |
| p->id = iType; |
| #endif |
| 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); |
| #if SQLITE_MUTEX_NREF |
| assert( p->nRef>0 || p->owner==0 ); |
| p->owner = pthread_self(); |
| p->nRef++; |
| #endif |
| #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 ){ |
| #if SQLITE_MUTEX_NREF |
| p->owner = pthread_self(); |
| p->nRef++; |
| #endif |
| 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) ); |
| #if SQLITE_MUTEX_NREF |
| p->nRef--; |
| if( p->nRef==0 ) p->owner = 0; |
| #endif |
| 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 const *sqlite3DefaultMutex(void){ |
| static const sqlite3_mutex_methods sMutex = { |
| pthreadMutexInit, |
| pthreadMutexEnd, |
| pthreadMutexAlloc, |
| pthreadMutexFree, |
| pthreadMutexEnter, |
| pthreadMutexTry, |
| pthreadMutexLeave, |
| #ifdef SQLITE_DEBUG |
| pthreadMutexHeld, |
| pthreadMutexNotheld |
| #else |
| 0, |
| 0 |
| #endif |
| }; |
| |
| return &sMutex; |
| } |
| |
| #endif /* SQLITE_MUTEX_PTHREAD */ |