third_party/sqlite/sqlite-src-3070603/src/mutex_noop.c

   1 /*
   2 ** 2008 October 07
   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 implementation in this file does not provide any mutual
  15 ** exclusion and is thus suitable for use only in applications
  16 ** that use SQLite in a single thread.  The routines defined
  17 ** here are place-holders.  Applications can substitute working
  18 ** mutex routines at start-time using the
  19 **
  20 **     sqlite3_config(SQLITE_CONFIG_MUTEX,...)
  21 **
  22 ** interface.
  23 **
  24 ** If compiled with SQLITE_DEBUG, then additional logic is inserted
  25 ** that does error checking on mutexes to make sure they are being
  26 ** called correctly.
  27 */
  28 #include "sqliteInt.h"
  29
  30 #ifndef SQLITE_MUTEX_OMIT
  31
  32 #ifndef SQLITE_DEBUG
  33 /*
  34 ** Stub routines for all mutex methods.
  35 **
  36 ** This routines provide no mutual exclusion or error checking.
  37 */
  38 static int noopMutexInit(void){ return SQLITE_OK; }
  39 static int noopMutexEnd(void){ return SQLITE_OK; }
  40 static sqlite3_mutex *noopMutexAlloc(int id){
  41   UNUSED_PARAMETER(id);
  42   return (sqlite3_mutex*)8;
  43 }
  44 static void noopMutexFree(sqlite3_mutex *p){ UNUSED_PARAMETER(p); return; }
  45 static void noopMutexEnter(sqlite3_mutex *p){ UNUSED_PARAMETER(p); return; }
  46 static int noopMutexTry(sqlite3_mutex *p){
  47   UNUSED_PARAMETER(p);
  48   return SQLITE_OK;
  49 }
  50 static void noopMutexLeave(sqlite3_mutex *p){ UNUSED_PARAMETER(p); return; }
  51
  52 sqlite3_mutex_methods const *sqlite3NoopMutex(void){
  53   static const sqlite3_mutex_methods sMutex = {
  54     noopMutexInit,
  55     noopMutexEnd,
  56     noopMutexAlloc,
  57     noopMutexFree,
  58     noopMutexEnter,
  59     noopMutexTry,
  60     noopMutexLeave,
  61
  62     0,
  63     0,
  64   };
  65
  66   return &sMutex;
  67 }
  68 #endif /* !SQLITE_DEBUG */
  69
  70 #ifdef SQLITE_DEBUG
  71 /*
  72 ** In this implementation, error checking is provided for testing
  73 ** and debugging purposes.  The mutexes still do not provide any
  74 ** mutual exclusion.
  75 */
  76
  77 /*
  78 ** The mutex object
  79 */
  80 typedef struct sqlite3_debug_mutex {
  81   int id;     /* The mutex type */
  82   int cnt;    /* Number of entries without a matching leave */
  83 } sqlite3_debug_mutex;
  84
  85 /*
  86 ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
  87 ** intended for use inside assert() statements.
  88 */
  89 static int debugMutexHeld(sqlite3_mutex *pX){
  90   sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
  91   return p==0 || p->cnt>0;
  92 }
  93 static int debugMutexNotheld(sqlite3_mutex *pX){
  94   sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
  95   return p==0 || p->cnt==0;
  96 }
  97
  98 /*
  99 ** Initialize and deinitialize the mutex subsystem.
 100 */
 101 static int debugMutexInit(void){ return SQLITE_OK; }
 102 static int debugMutexEnd(void){ return SQLITE_OK; }
 103
 104 /*
 105 ** The sqlite3_mutex_alloc() routine allocates a new
 106 ** mutex and returns a pointer to it.  If it returns NULL
 107 ** that means that a mutex could not be allocated.
 108 */
 109 static sqlite3_mutex *debugMutexAlloc(int id){
 110   static sqlite3_debug_mutex aStatic[6];
 111   sqlite3_debug_mutex *pNew = 0;
 112   switch( id ){
 113     case SQLITE_MUTEX_FAST:
 114     case SQLITE_MUTEX_RECURSIVE: {
 115       pNew = sqlite3Malloc(sizeof(*pNew));
 116       if( pNew ){
 117         pNew->id = id;
 118         pNew->cnt = 0;
 119       }
 120       break;
 121     }
 122     default: {
 123       assert( id-2 >= 0 );
 124       assert( id-2 < (int)(sizeof(aStatic)/sizeof(aStatic[0])) );
 125       pNew = &aStatic[id-2];
 126       pNew->id = id;
 127       break;
 128     }
 129   }
 130   return (sqlite3_mutex*)pNew;
 131 }
 132
 133 /*
 134 ** This routine deallocates a previously allocated mutex.
 135 */
 136 static void debugMutexFree(sqlite3_mutex *pX){
 137   sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
 138   assert( p->cnt==0 );
 139   assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
 140   sqlite3_free(p);
 141 }
 142
 143 /*
 144 ** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
 145 ** to enter a mutex.  If another thread is already within the mutex,
 146 ** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
 147 ** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK
 148 ** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
 149 ** be entered multiple times by the same thread.  In such cases the,
 150 ** mutex must be exited an equal number of times before another thread
 151 ** can enter.  If the same thread tries to enter any other kind of mutex
 152 ** more than once, the behavior is undefined.
 153 */
 154 static void debugMutexEnter(sqlite3_mutex *pX){
 155   sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
 156   assert( p->id==SQLITE_MUTEX_RECURSIVE || debugMutexNotheld(pX) );
 157   p->cnt++;
 158 }
 159 static int debugMutexTry(sqlite3_mutex *pX){
 160   sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
 161   assert( p->id==SQLITE_MUTEX_RECURSIVE || debugMutexNotheld(pX) );
 162   p->cnt++;
 163   return SQLITE_OK;
 164 }
 165
 166 /*
 167 ** The sqlite3_mutex_leave() routine exits a mutex that was
 168 ** previously entered by the same thread.  The behavior
 169 ** is undefined if the mutex is not currently entered or
 170 ** is not currently allocated.  SQLite will never do either.
 171 */
 172 static void debugMutexLeave(sqlite3_mutex *pX){
 173   sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
 174   assert( debugMutexHeld(pX) );
 175   p->cnt--;
 176   assert( p->id==SQLITE_MUTEX_RECURSIVE || debugMutexNotheld(pX) );
 177 }
 178
 179 sqlite3_mutex_methods const *sqlite3NoopMutex(void){
 180   static const sqlite3_mutex_methods sMutex = {
 181     debugMutexInit,
 182     debugMutexEnd,
 183     debugMutexAlloc,
 184     debugMutexFree,
 185     debugMutexEnter,
 186     debugMutexTry,
 187     debugMutexLeave,
 188
 189     debugMutexHeld,
 190     debugMutexNotheld
 191   };
 192
 193   return &sMutex;
 194 }
 195 #endif /* SQLITE_DEBUG */
 196
 197 /*
 198 ** If compiled with SQLITE_MUTEX_NOOP, then the no-op mutex implementation
 199 ** is used regardless of the run-time threadsafety setting.
 200 */
 201 #ifdef SQLITE_MUTEX_NOOP
 202 sqlite3_mutex_methods const *sqlite3DefaultMutex(void){
 203   return sqlite3NoopMutex();
 204 }
 205 #endif /* SQLITE_MUTEX_NOOP */
 206 #endif /* SQLITE_MUTEX_OMIT */