AryaWu/sqlite
0
1/*2** 2007 August 283**4** The author disclaims copyright to this source code. In place of5** a legal notice, here is a blessing:6**7** May you do good and not evil.8** May you find forgiveness for yourself and forgive others.9** May you share freely, never taking more than you give.10**11*************************************************************************12** This file contains the C functions that implement mutexes for pthreads13*/14#include "sqliteInt.h"15 16/*17** The code in this file is only used if we are compiling threadsafe18** under unix with pthreads.19**20** Note that this implementation requires a version of pthreads that21** supports recursive mutexes.22*/23#ifdef SQLITE_MUTEX_PTHREADS24 25#include <pthread.h>26 27/*28** The sqlite3_mutex.id, sqlite3_mutex.nRef, and sqlite3_mutex.owner fields29** are necessary under two conditions: (1) Debug builds and (2) using30** home-grown mutexes. Encapsulate these conditions into a single #define.31*/32#if defined(SQLITE_DEBUG) || defined(SQLITE_HOMEGROWN_RECURSIVE_MUTEX)33# define SQLITE_MUTEX_NREF 134#else35# define SQLITE_MUTEX_NREF 036#endif37 38/*39** Each recursive mutex is an instance of the following structure.40*/41struct sqlite3_mutex {42 pthread_mutex_t mutex; /* Mutex controlling the lock */43#if SQLITE_MUTEX_NREF || defined(SQLITE_ENABLE_API_ARMOR)44 int id; /* Mutex type */45#endif46#if SQLITE_MUTEX_NREF47 volatile int nRef; /* Number of entrances */48 volatile pthread_t owner; /* Thread that is within this mutex */49 int trace; /* True to trace changes */50#endif51};52#if SQLITE_MUTEX_NREF53# define SQLITE3_MUTEX_INITIALIZER(id) \54 {PTHREAD_MUTEX_INITIALIZER,id,0,(pthread_t)0,0}55#elif defined(SQLITE_ENABLE_API_ARMOR)56# define SQLITE3_MUTEX_INITIALIZER(id) { PTHREAD_MUTEX_INITIALIZER, id }57#else58#define SQLITE3_MUTEX_INITIALIZER(id) { PTHREAD_MUTEX_INITIALIZER }59#endif60 61/*62** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are63** intended for use only inside assert() statements. On some platforms,64** there might be race conditions that can cause these routines to65** deliver incorrect results. In particular, if pthread_equal() is66** not an atomic operation, then these routines might delivery67** incorrect results. On most platforms, pthread_equal() is a68** comparison of two integers and is therefore atomic. But we are69** told that HPUX is not such a platform. If so, then these routines70** will not always work correctly on HPUX.71**72** On those platforms where pthread_equal() is not atomic, SQLite73** should be compiled without -DSQLITE_DEBUG and with -DNDEBUG to74** make sure no assert() statements are evaluated and hence these75** routines are never called.76*/77#if !defined(NDEBUG) || defined(SQLITE_DEBUG)78static int pthreadMutexHeld(sqlite3_mutex *p){79 return (p->nRef!=0 && pthread_equal(p->owner, pthread_self()));80}81static int pthreadMutexNotheld(sqlite3_mutex *p){82 return p->nRef==0 || pthread_equal(p->owner, pthread_self())==0;83}84#endif85 86/*87** Try to provide a memory barrier operation, needed for initialization88** and also for the implementation of xShmBarrier in the VFS in cases89** where SQLite is compiled without mutexes.90*/91void sqlite3MemoryBarrier(void){92#if defined(SQLITE_MEMORY_BARRIER)93 SQLITE_MEMORY_BARRIER;94#elif defined(__GNUC__) && GCC_VERSION>=400100095 __sync_synchronize();96#endif97}98 99/*100** Initialize and deinitialize the mutex subsystem.101*/102static int pthreadMutexInit(void){ return SQLITE_OK; }103static int pthreadMutexEnd(void){ return SQLITE_OK; }104 105/*106** The sqlite3_mutex_alloc() routine allocates a new107** mutex and returns a pointer to it. If it returns NULL108** that means that a mutex could not be allocated. SQLite109** will unwind its stack and return an error. The argument110** to sqlite3_mutex_alloc() is one of these integer constants:111**112** <ul>113** <li> SQLITE_MUTEX_FAST114** <li> SQLITE_MUTEX_RECURSIVE115** <li> SQLITE_MUTEX_STATIC_MAIN116** <li> SQLITE_MUTEX_STATIC_MEM117** <li> SQLITE_MUTEX_STATIC_OPEN118** <li> SQLITE_MUTEX_STATIC_PRNG119** <li> SQLITE_MUTEX_STATIC_LRU120** <li> SQLITE_MUTEX_STATIC_PMEM121** <li> SQLITE_MUTEX_STATIC_APP1122** <li> SQLITE_MUTEX_STATIC_APP2123** <li> SQLITE_MUTEX_STATIC_APP3124** <li> SQLITE_MUTEX_STATIC_VFS1125** <li> SQLITE_MUTEX_STATIC_VFS2126** <li> SQLITE_MUTEX_STATIC_VFS3127** </ul>128**129** The first two constants cause sqlite3_mutex_alloc() to create130** a new mutex. The new mutex is recursive when SQLITE_MUTEX_RECURSIVE131** is used but not necessarily so when SQLITE_MUTEX_FAST is used.132** The mutex implementation does not need to make a distinction133** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does134** not want to. But SQLite will only request a recursive mutex in135** cases where it really needs one. If a faster non-recursive mutex136** implementation is available on the host platform, the mutex subsystem137** might return such a mutex in response to SQLITE_MUTEX_FAST.138**139** The other allowed parameters to sqlite3_mutex_alloc() each return140** a pointer to a static preexisting mutex. Six static mutexes are141** used by the current version of SQLite. Future versions of SQLite142** may add additional static mutexes. Static mutexes are for internal143** use by SQLite only. Applications that use SQLite mutexes should144** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or145** SQLITE_MUTEX_RECURSIVE.146**147** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST148** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()149** returns a different mutex on every call. But for the static150** mutex types, the same mutex is returned on every call that has151** the same type number.152*/153static sqlite3_mutex *pthreadMutexAlloc(int iType){154 static sqlite3_mutex staticMutexes[] = {155 SQLITE3_MUTEX_INITIALIZER(2),156 SQLITE3_MUTEX_INITIALIZER(3),157 SQLITE3_MUTEX_INITIALIZER(4),158 SQLITE3_MUTEX_INITIALIZER(5),159 SQLITE3_MUTEX_INITIALIZER(6),160 SQLITE3_MUTEX_INITIALIZER(7),161 SQLITE3_MUTEX_INITIALIZER(8),162 SQLITE3_MUTEX_INITIALIZER(9),163 SQLITE3_MUTEX_INITIALIZER(10),164 SQLITE3_MUTEX_INITIALIZER(11),165 SQLITE3_MUTEX_INITIALIZER(12),166 SQLITE3_MUTEX_INITIALIZER(13)167 };168 sqlite3_mutex *p;169 switch( iType ){170 case SQLITE_MUTEX_RECURSIVE: {171 p = sqlite3MallocZero( sizeof(*p) );172 if( p ){173#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX174 /* If recursive mutexes are not available, we will have to175 ** build our own. See below. */176 pthread_mutex_init(&p->mutex, 0);177#else178 /* Use a recursive mutex if it is available */179 pthread_mutexattr_t recursiveAttr;180 pthread_mutexattr_init(&recursiveAttr);181 pthread_mutexattr_settype(&recursiveAttr, PTHREAD_MUTEX_RECURSIVE);182 pthread_mutex_init(&p->mutex, &recursiveAttr);183 pthread_mutexattr_destroy(&recursiveAttr);184#endif185#if SQLITE_MUTEX_NREF || defined(SQLITE_ENABLE_API_ARMOR)186 p->id = SQLITE_MUTEX_RECURSIVE;187#endif188 }189 break;190 }191 case SQLITE_MUTEX_FAST: {192 p = sqlite3MallocZero( sizeof(*p) );193 if( p ){194 pthread_mutex_init(&p->mutex, 0);195#if SQLITE_MUTEX_NREF || defined(SQLITE_ENABLE_API_ARMOR)196 p->id = SQLITE_MUTEX_FAST;197#endif198 }199 break;200 }201 default: {202#ifdef SQLITE_ENABLE_API_ARMOR203 if( iType-2<0 || iType-2>=ArraySize(staticMutexes) ){204 (void)SQLITE_MISUSE_BKPT;205 return 0;206 }207#endif208 p = &staticMutexes[iType-2];209 break;210 }211 }212#if SQLITE_MUTEX_NREF || defined(SQLITE_ENABLE_API_ARMOR)213 assert( p==0 || p->id==iType );214#endif215 return p;216}217 218 219/*220** This routine deallocates a previously221** allocated mutex. SQLite is careful to deallocate every222** mutex that it allocates.223*/224static void pthreadMutexFree(sqlite3_mutex *p){225 assert( p->nRef==0 );226#ifdef SQLITE_ENABLE_API_ARMOR227 if( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE )228#endif229 {230 pthread_mutex_destroy(&p->mutex);231 sqlite3_free(p);232 }233#ifdef SQLITE_ENABLE_API_ARMOR234 else{235 (void)SQLITE_MISUSE_BKPT;236 }237#endif238}239 240/*241** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt242** to enter a mutex. If another thread is already within the mutex,243** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return244** SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK245** upon successful entry. Mutexes created using SQLITE_MUTEX_RECURSIVE can246** be entered multiple times by the same thread. In such cases the,247** mutex must be exited an equal number of times before another thread248** can enter. If the same thread tries to enter any other kind of mutex249** more than once, the behavior is undefined.250*/251static void pthreadMutexEnter(sqlite3_mutex *p){252 assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );253 254#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX255 /* If recursive mutexes are not available, then we have to grow256 ** our own. This implementation assumes that pthread_equal()257 ** is atomic - that it cannot be deceived into thinking self258 ** and p->owner are equal if p->owner changes between two values259 ** that are not equal to self while the comparison is taking place.260 ** This implementation also assumes a coherent cache - that261 ** separate processes cannot read different values from the same262 ** address at the same time. If either of these two conditions263 ** are not met, then the mutexes will fail and problems will result.264 */265 {266 pthread_t self = pthread_self();267 if( p->nRef>0 && pthread_equal(p->owner, self) ){268 p->nRef++;269 }else{270 pthread_mutex_lock(&p->mutex);271 assert( p->nRef==0 );272 p->owner = self;273 p->nRef = 1;274 }275 }276#else277 /* Use the built-in recursive mutexes if they are available.278 */279 pthread_mutex_lock(&p->mutex);280#if SQLITE_MUTEX_NREF281 assert( p->nRef>0 || p->owner==0 );282 p->owner = pthread_self();283 p->nRef++;284#endif285#endif286 287#ifdef SQLITE_DEBUG288 if( p->trace ){289 printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);290 }291#endif292}293static int pthreadMutexTry(sqlite3_mutex *p){294 int rc;295 assert( p->id==SQLITE_MUTEX_RECURSIVE || pthreadMutexNotheld(p) );296 297#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX298 /* If recursive mutexes are not available, then we have to grow299 ** our own. This implementation assumes that pthread_equal()300 ** is atomic - that it cannot be deceived into thinking self301 ** and p->owner are equal if p->owner changes between two values302 ** that are not equal to self while the comparison is taking place.303 ** This implementation also assumes a coherent cache - that304 ** separate processes cannot read different values from the same305 ** address at the same time. If either of these two conditions306 ** are not met, then the mutexes will fail and problems will result.307 */308 {309 pthread_t self = pthread_self();310 if( p->nRef>0 && pthread_equal(p->owner, self) ){311 p->nRef++;312 rc = SQLITE_OK;313 }else if( pthread_mutex_trylock(&p->mutex)==0 ){314 assert( p->nRef==0 );315 p->owner = self;316 p->nRef = 1;317 rc = SQLITE_OK;318 }else{319 rc = SQLITE_BUSY;320 }321 }322#else323 /* Use the built-in recursive mutexes if they are available.324 */325 if( pthread_mutex_trylock(&p->mutex)==0 ){326#if SQLITE_MUTEX_NREF327 p->owner = pthread_self();328 p->nRef++;329#endif330 rc = SQLITE_OK;331 }else{332 rc = SQLITE_BUSY;333 }334#endif335 336#ifdef SQLITE_DEBUG337 if( rc==SQLITE_OK && p->trace ){338 printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);339 }340#endif341 return rc;342}343 344/*345** The sqlite3_mutex_leave() routine exits a mutex that was346** previously entered by the same thread. The behavior347** is undefined if the mutex is not currently entered or348** is not currently allocated. SQLite will never do either.349*/350static void pthreadMutexLeave(sqlite3_mutex *p){351 assert( pthreadMutexHeld(p) );352#if SQLITE_MUTEX_NREF353 p->nRef--;354 if( p->nRef==0 ) p->owner = 0;355#endif356 assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );357 358#ifdef SQLITE_HOMEGROWN_RECURSIVE_MUTEX359 if( p->nRef==0 ){360 pthread_mutex_unlock(&p->mutex);361 }362#else363 pthread_mutex_unlock(&p->mutex);364#endif365 366#ifdef SQLITE_DEBUG367 if( p->trace ){368 printf("leave mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);369 }370#endif371}372 373sqlite3_mutex_methods const *sqlite3DefaultMutex(void){374 static const sqlite3_mutex_methods sMutex = {375 pthreadMutexInit,376 pthreadMutexEnd,377 pthreadMutexAlloc,378 pthreadMutexFree,379 pthreadMutexEnter,380 pthreadMutexTry,381 pthreadMutexLeave,382#ifdef SQLITE_DEBUG383 pthreadMutexHeld,384 pthreadMutexNotheld385#else386 0,387 0388#endif389 };390 391 return &sMutex;392}393 394#endif /* SQLITE_MUTEX_PTHREADS */395