src/mutex.c

   1 /*
   2 ** 2007 August 14
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** 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.
  13 **
  14 ** This file contains code that is common across all mutex implementations.
  15 */
  16 #include "sqliteInt.h"
  17
  18 #if defined(SQLITE_DEBUG) && !defined(SQLITE_MUTEX_OMIT)
  19 /*
  20 ** For debugging purposes, record when the mutex subsystem is initialized
  21 ** and uninitialized so that we can assert() if there is an attempt to
  22 ** allocate a mutex while the system is uninitialized.
  23 */
  24 static SQLITE_WSD int mutexIsInit = 0;
  25 #endif /* SQLITE_DEBUG */
  26
  27
  28 #ifndef SQLITE_MUTEX_OMIT
  29 /*
  30 ** Initialize the mutex system.
  31 */
  32 int sqlite3MutexInit(void){
  33   int rc = SQLITE_OK;
  34   if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
  35     /* If the xMutexAlloc method has not been set, then the user did not
  36     ** install a mutex implementation via sqlite3_config() prior to
  37     ** sqlite3_initialize() being called. This block copies pointers to
  38     ** the default implementation into the sqlite3GlobalConfig structure.
  39     */
  40     sqlite3_mutex_methods const *pFrom;
  41     sqlite3_mutex_methods *pTo = &sqlite3GlobalConfig.mutex;
  42
  43     if( sqlite3GlobalConfig.bCoreMutex ){
  44       pFrom = sqlite3DefaultMutex();
  45     }else{
  46       pFrom = sqlite3NoopMutex();
  47     }
  48     memcpy(pTo, pFrom, offsetof(sqlite3_mutex_methods, xMutexAlloc));
  49     memcpy(&pTo->xMutexFree, &pFrom->xMutexFree,
  50            sizeof(*pTo) - offsetof(sqlite3_mutex_methods, xMutexFree));
  51     pTo->xMutexAlloc = pFrom->xMutexAlloc;
  52   }
  53   rc = sqlite3GlobalConfig.mutex.xMutexInit();
  54
  55 #ifdef SQLITE_DEBUG
  56   GLOBAL(int, mutexIsInit) = 1;
  57 #endif
  58
  59   return rc;
  60 }
  61
  62 /*
  63 ** Shutdown the mutex system. This call frees resources allocated by
  64 ** sqlite3MutexInit().
  65 */
  66 int sqlite3MutexEnd(void){
  67   int rc = SQLITE_OK;
  68   if( sqlite3GlobalConfig.mutex.xMutexEnd ){
  69     rc = sqlite3GlobalConfig.mutex.xMutexEnd();
  70   }
  71
  72 #ifdef SQLITE_DEBUG
  73   GLOBAL(int, mutexIsInit) = 0;
  74 #endif
  75
  76   return rc;
  77 }
  78
  79 /*
  80 ** Retrieve a pointer to a static mutex or allocate a new dynamic one.
  81 */
  82 sqlite3_mutex *sqlite3_mutex_alloc(int id){
  83 #ifndef SQLITE_OMIT_AUTOINIT
  84   if( sqlite3_initialize() ) return 0;
  85 #endif
  86   return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
  87 }
  88
  89 sqlite3_mutex *sqlite3MutexAlloc(int id){
  90   if( !sqlite3GlobalConfig.bCoreMutex ){
  91     return 0;
  92   }
  93   assert( GLOBAL(int, mutexIsInit) );
  94   return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
  95 }
  96
  97 /*
  98 ** Free a dynamic mutex.
  99 */
 100 void sqlite3_mutex_free(sqlite3_mutex *p){
 101   if( p ){
 102     sqlite3GlobalConfig.mutex.xMutexFree(p);
 103   }
 104 }
 105
 106 /*
 107 ** Obtain the mutex p. If some other thread already has the mutex, block
 108 ** until it can be obtained.
 109 */
 110 void sqlite3_mutex_enter(sqlite3_mutex *p){
 111   if( p ){
 112     sqlite3GlobalConfig.mutex.xMutexEnter(p);
 113   }
 114 }
 115
 116 /*
 117 ** Obtain the mutex p. If successful, return SQLITE_OK. Otherwise, if another
 118 ** thread holds the mutex and it cannot be obtained, return SQLITE_BUSY.
 119 */
 120 int sqlite3_mutex_try(sqlite3_mutex *p){
 121   int rc = SQLITE_OK;
 122   if( p ){
 123     return sqlite3GlobalConfig.mutex.xMutexTry(p);
 124   }
 125   return rc;
 126 }
 127
 128 /*
 129 ** The sqlite3_mutex_leave() routine exits a mutex that was previously
 130 ** entered by the same thread.  The behavior is undefined if the mutex
 131 ** is not currently entered. If a NULL pointer is passed as an argument
 132 ** this function is a no-op.
 133 */
 134 void sqlite3_mutex_leave(sqlite3_mutex *p){
 135   if( p ){
 136     sqlite3GlobalConfig.mutex.xMutexLeave(p);
 137   }
 138 }
 139
 140 #ifndef NDEBUG
 141 /*
 142 ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
 143 ** intended for use inside assert() statements.
 144 */
 145 int sqlite3_mutex_held(sqlite3_mutex *p){
 146   return p==0 || sqlite3GlobalConfig.mutex.xMutexHeld(p);
 147 }
 148 int sqlite3_mutex_notheld(sqlite3_mutex *p){
 149   return p==0 || sqlite3GlobalConfig.mutex.xMutexNotheld(p);
 150 }
 151 #endif
 152
 153 #endif /* SQLITE_MUTEX_OMIT */