src/mutex_w32.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 for Win32.
  13 */
  14 #include "sqliteInt.h"
  15
  16 #if SQLITE_OS_WIN
  17 /*
  18 ** Include code that is common to all os_*.c files
  19 */
  20 #include "os_common.h"
  21
  22 /*
  23 ** Include the header file for the Windows VFS.
  24 */
  25 #include "os_win.h"
  26 #endif
  27
  28 /*
  29 ** The code in this file is only used if we are compiling multithreaded
  30 ** on a Win32 system.
  31 */
  32 #ifdef SQLITE_MUTEX_W32
  33
  34 /*
  35 ** Each recursive mutex is an instance of the following structure.
  36 */
  37 struct sqlite3_mutex {
  38   CRITICAL_SECTION mutex;    /* Mutex controlling the lock */
  39   int id;                    /* Mutex type */
  40 #ifdef SQLITE_DEBUG
  41   volatile int nRef;         /* Number of enterances */
  42   volatile DWORD owner;      /* Thread holding this mutex */
  43   volatile int trace;        /* True to trace changes */
  44 #endif
  45 };
  46
  47 /*
  48 ** These are the initializer values used when declaring a "static" mutex
  49 ** on Win32.  It should be noted that all mutexes require initialization
  50 ** on the Win32 platform.
  51 */
  52 #define SQLITE_W32_MUTEX_INITIALIZER { 0 }
  53
  54 #ifdef SQLITE_DEBUG
  55 #define SQLITE3_MUTEX_INITIALIZER { SQLITE_W32_MUTEX_INITIALIZER, 0, \
  56                                     0L, (DWORD)0, 0 }
  57 #else
  58 #define SQLITE3_MUTEX_INITIALIZER { SQLITE_W32_MUTEX_INITIALIZER, 0 }
  59 #endif
  60
  61 #ifdef SQLITE_DEBUG
  62 /*
  63 ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
  64 ** intended for use only inside assert() statements.
  65 */
  66 static int winMutexHeld(sqlite3_mutex *p){
  67   return p->nRef!=0 && p->owner==GetCurrentThreadId();
  68 }
  69
  70 static int winMutexNotheld2(sqlite3_mutex *p, DWORD tid){
  71   return p->nRef==0 || p->owner!=tid;
  72 }
  73
  74 static int winMutexNotheld(sqlite3_mutex *p){
  75   DWORD tid = GetCurrentThreadId();
  76   return winMutexNotheld2(p, tid);
  77 }
  78 #endif
  79
  80 /*
  81 ** Try to provide a memory barrier operation, needed for initialization
  82 ** and also for the xShmBarrier method of the VFS in cases when SQLite is
  83 ** compiled without mutexes (SQLITE_THREADSAFE=0).
  84 */
  85 void sqlite3MemoryBarrier(void){
  86 #if defined(SQLITE_MEMORY_BARRIER)
  87   SQLITE_MEMORY_BARRIER;
  88 #elif defined(__GNUC__)
  89   __sync_synchronize();
  90 #elif !defined(SQLITE_DISABLE_INTRINSIC) && \
  91       defined(_MSC_VER) && _MSC_VER>=1300
  92   _ReadWriteBarrier();
  93 #elif defined(MemoryBarrier)
  94   MemoryBarrier();
  95 #endif
  96 }
  97
  98 /*
  99 ** Initialize and deinitialize the mutex subsystem.
 100 */
 101 static sqlite3_mutex winMutex_staticMutexes[] = {
 102   SQLITE3_MUTEX_INITIALIZER,
 103   SQLITE3_MUTEX_INITIALIZER,
 104   SQLITE3_MUTEX_INITIALIZER,
 105   SQLITE3_MUTEX_INITIALIZER,
 106   SQLITE3_MUTEX_INITIALIZER,
 107   SQLITE3_MUTEX_INITIALIZER,
 108   SQLITE3_MUTEX_INITIALIZER,
 109   SQLITE3_MUTEX_INITIALIZER,
 110   SQLITE3_MUTEX_INITIALIZER,
 111   SQLITE3_MUTEX_INITIALIZER,
 112   SQLITE3_MUTEX_INITIALIZER,
 113   SQLITE3_MUTEX_INITIALIZER
 114 };
 115
 116 static int winMutex_isInit = 0;
 117 static int winMutex_isNt = -1; /* <0 means "need to query" */
 118
 119 /* As the winMutexInit() and winMutexEnd() functions are called as part
 120 ** of the sqlite3_initialize() and sqlite3_shutdown() processing, the
 121 ** "interlocked" magic used here is probably not strictly necessary.
 122 */
 123 static LONG SQLITE_WIN32_VOLATILE winMutex_lock = 0;
 124
 125 int sqlite3_win32_is_nt(void); /* os_win.c */
 126 void sqlite3_win32_sleep(DWORD milliseconds); /* os_win.c */
 127
 128 static int winMutexInit(void){
 129   /* The first to increment to 1 does actual initialization */
 130   if( InterlockedCompareExchange(&winMutex_lock, 1, 0)==0 ){
 131     int i;
 132     for(i=0; i<ArraySize(winMutex_staticMutexes); i++){
 133 #if SQLITE_OS_WINRT
 134       InitializeCriticalSectionEx(&winMutex_staticMutexes[i].mutex, 0, 0);
 135 #else
 136       InitializeCriticalSection(&winMutex_staticMutexes[i].mutex);
 137 #endif
 138     }
 139     winMutex_isInit = 1;
 140   }else{
 141     /* Another thread is (in the process of) initializing the static
 142     ** mutexes */
 143     while( !winMutex_isInit ){
 144       sqlite3_win32_sleep(1);
 145     }
 146   }
 147   return SQLITE_OK;
 148 }
 149
 150 static int winMutexEnd(void){
 151   /* The first to decrement to 0 does actual shutdown
 152   ** (which should be the last to shutdown.) */
 153   if( InterlockedCompareExchange(&winMutex_lock, 0, 1)==1 ){
 154     if( winMutex_isInit==1 ){
 155       int i;
 156       for(i=0; i<ArraySize(winMutex_staticMutexes); i++){
 157         DeleteCriticalSection(&winMutex_staticMutexes[i].mutex);
 158       }
 159       winMutex_isInit = 0;
 160     }
 161   }
 162   return SQLITE_OK;
 163 }
 164
 165 /*
 166 ** The sqlite3_mutex_alloc() routine allocates a new
 167 ** mutex and returns a pointer to it.  If it returns NULL
 168 ** that means that a mutex could not be allocated.  SQLite
 169 ** will unwind its stack and return an error.  The argument
 170 ** to sqlite3_mutex_alloc() is one of these integer constants:
 171 **
 172 ** <ul>
 173 ** <li>  SQLITE_MUTEX_FAST
 174 ** <li>  SQLITE_MUTEX_RECURSIVE
 175 ** <li>  SQLITE_MUTEX_STATIC_MASTER
 176 ** <li>  SQLITE_MUTEX_STATIC_MEM
 177 ** <li>  SQLITE_MUTEX_STATIC_OPEN
 178 ** <li>  SQLITE_MUTEX_STATIC_PRNG
 179 ** <li>  SQLITE_MUTEX_STATIC_LRU
 180 ** <li>  SQLITE_MUTEX_STATIC_PMEM
 181 ** <li>  SQLITE_MUTEX_STATIC_APP1
 182 ** <li>  SQLITE_MUTEX_STATIC_APP2
 183 ** <li>  SQLITE_MUTEX_STATIC_APP3
 184 ** <li>  SQLITE_MUTEX_STATIC_VFS1
 185 ** <li>  SQLITE_MUTEX_STATIC_VFS2
 186 ** <li>  SQLITE_MUTEX_STATIC_VFS3
 187 ** </ul>
 188 **
 189 ** The first two constants cause sqlite3_mutex_alloc() to create
 190 ** a new mutex.  The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
 191 ** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
 192 ** The mutex implementation does not need to make a distinction
 193 ** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
 194 ** not want to.  But SQLite will only request a recursive mutex in
 195 ** cases where it really needs one.  If a faster non-recursive mutex
 196 ** implementation is available on the host platform, the mutex subsystem
 197 ** might return such a mutex in response to SQLITE_MUTEX_FAST.
 198 **
 199 ** The other allowed parameters to sqlite3_mutex_alloc() each return
 200 ** a pointer to a static preexisting mutex.  Six static mutexes are
 201 ** used by the current version of SQLite.  Future versions of SQLite
 202 ** may add additional static mutexes.  Static mutexes are for internal
 203 ** use by SQLite only.  Applications that use SQLite mutexes should
 204 ** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
 205 ** SQLITE_MUTEX_RECURSIVE.
 206 **
 207 ** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
 208 ** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
 209 ** returns a different mutex on every call.  But for the static
 210 ** mutex types, the same mutex is returned on every call that has
 211 ** the same type number.
 212 */
 213 static sqlite3_mutex *winMutexAlloc(int iType){
 214   sqlite3_mutex *p;
 215
 216   switch( iType ){
 217     case SQLITE_MUTEX_FAST:
 218     case SQLITE_MUTEX_RECURSIVE: {
 219       p = sqlite3MallocZero( sizeof(*p) );
 220       if( p ){
 221         p->id = iType;
 222 #ifdef SQLITE_DEBUG
 223 #ifdef SQLITE_WIN32_MUTEX_TRACE_DYNAMIC
 224         p->trace = 1;
 225 #endif
 226 #endif
 227 #if SQLITE_OS_WINRT
 228         InitializeCriticalSectionEx(&p->mutex, 0, 0);
 229 #else
 230         InitializeCriticalSection(&p->mutex);
 231 #endif
 232       }
 233       break;
 234     }
 235     default: {
 236 #ifdef SQLITE_ENABLE_API_ARMOR
 237       if( iType-2<0 || iType-2>=ArraySize(winMutex_staticMutexes) ){
 238         (void)SQLITE_MISUSE_BKPT;
 239         return 0;
 240       }
 241 #endif
 242       p = &winMutex_staticMutexes[iType-2];
 243       p->id = iType;
 244 #ifdef SQLITE_DEBUG
 245 #ifdef SQLITE_WIN32_MUTEX_TRACE_STATIC
 246       p->trace = 1;
 247 #endif
 248 #endif
 249       break;
 250     }
 251   }
 252   return p;
 253 }
 254
 255
 256 /*
 257 ** This routine deallocates a previously
 258 ** allocated mutex.  SQLite is careful to deallocate every
 259 ** mutex that it allocates.
 260 */
 261 static void winMutexFree(sqlite3_mutex *p){
 262   assert( p );
 263   assert( p->nRef==0 && p->owner==0 );
 264   if( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE ){
 265     DeleteCriticalSection(&p->mutex);
 266     sqlite3_free(p);
 267   }else{
 268 #ifdef SQLITE_ENABLE_API_ARMOR
 269     (void)SQLITE_MISUSE_BKPT;
 270 #endif
 271   }
 272 }
 273
 274 /*
 275 ** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
 276 ** to enter a mutex.  If another thread is already within the mutex,
 277 ** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
 278 ** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK
 279 ** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
 280 ** be entered multiple times by the same thread.  In such cases the,
 281 ** mutex must be exited an equal number of times before another thread
 282 ** can enter.  If the same thread tries to enter any other kind of mutex
 283 ** more than once, the behavior is undefined.
 284 */
 285 static void winMutexEnter(sqlite3_mutex *p){
 286 #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
 287   DWORD tid = GetCurrentThreadId();
 288 #endif
 289 #ifdef SQLITE_DEBUG
 290   assert( p );
 291   assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld2(p, tid) );
 292 #else
 293   assert( p );
 294 #endif
 295   assert( winMutex_isInit==1 );
 296   EnterCriticalSection(&p->mutex);
 297 #ifdef SQLITE_DEBUG
 298   assert( p->nRef>0 || p->owner==0 );
 299   p->owner = tid;
 300   p->nRef++;
 301   if( p->trace ){
 302     OSTRACE(("ENTER-MUTEX tid=%lu, mutex=%p (%d), nRef=%d\n",
 303              tid, p, p->trace, p->nRef));
 304   }
 305 #endif
 306 }
 307
 308 static int winMutexTry(sqlite3_mutex *p){
 309 #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
 310   DWORD tid = GetCurrentThreadId();
 311 #endif
 312   int rc = SQLITE_BUSY;
 313   assert( p );
 314   assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld2(p, tid) );
 315   /*
 316   ** The sqlite3_mutex_try() routine is very rarely used, and when it
 317   ** is used it is merely an optimization.  So it is OK for it to always
 318   ** fail.
 319   **
 320   ** The TryEnterCriticalSection() interface is only available on WinNT.
 321   ** And some windows compilers complain if you try to use it without
 322   ** first doing some #defines that prevent SQLite from building on Win98.
 323   ** For that reason, we will omit this optimization for now.  See
 324   ** ticket #2685.
 325   */
 326 #if defined(_WIN32_WINNT) && _WIN32_WINNT >= 0x0400
 327   assert( winMutex_isInit==1 );
 328   assert( winMutex_isNt>=-1 && winMutex_isNt<=1 );
 329   if( winMutex_isNt<0 ){
 330     winMutex_isNt = sqlite3_win32_is_nt();
 331   }
 332   assert( winMutex_isNt==0 || winMutex_isNt==1 );
 333   if( winMutex_isNt && TryEnterCriticalSection(&p->mutex) ){
 334 #ifdef SQLITE_DEBUG
 335     p->owner = tid;
 336     p->nRef++;
 337 #endif
 338     rc = SQLITE_OK;
 339   }
 340 #else
 341   UNUSED_PARAMETER(p);
 342 #endif
 343 #ifdef SQLITE_DEBUG
 344   if( p->trace ){
 345     OSTRACE(("TRY-MUTEX tid=%lu, mutex=%p (%d), owner=%lu, nRef=%d, rc=%s\n",
 346              tid, p, p->trace, p->owner, p->nRef, sqlite3ErrName(rc)));
 347   }
 348 #endif
 349   return rc;
 350 }
 351
 352 /*
 353 ** The sqlite3_mutex_leave() routine exits a mutex that was
 354 ** previously entered by the same thread.  The behavior
 355 ** is undefined if the mutex is not currently entered or
 356 ** is not currently allocated.  SQLite will never do either.
 357 */
 358 static void winMutexLeave(sqlite3_mutex *p){
 359 #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
 360   DWORD tid = GetCurrentThreadId();
 361 #endif
 362   assert( p );
 363 #ifdef SQLITE_DEBUG
 364   assert( p->nRef>0 );
 365   assert( p->owner==tid );
 366   p->nRef--;
 367   if( p->nRef==0 ) p->owner = 0;
 368   assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
 369 #endif
 370   assert( winMutex_isInit==1 );
 371   LeaveCriticalSection(&p->mutex);
 372 #ifdef SQLITE_DEBUG
 373   if( p->trace ){
 374     OSTRACE(("LEAVE-MUTEX tid=%lu, mutex=%p (%d), nRef=%d\n",
 375              tid, p, p->trace, p->nRef));
 376   }
 377 #endif
 378 }
 379
 380 sqlite3_mutex_methods const *sqlite3DefaultMutex(void){
 381   static const sqlite3_mutex_methods sMutex = {
 382     winMutexInit,
 383     winMutexEnd,
 384     winMutexAlloc,
 385     winMutexFree,
 386     winMutexEnter,
 387     winMutexTry,
 388     winMutexLeave,
 389 #ifdef SQLITE_DEBUG
 390     winMutexHeld,
 391     winMutexNotheld
 392 #else
 393     0,
 394     0
 395 #endif
 396   };
 397   return &sMutex;
 398 }
 399
 400 #endif /* SQLITE_MUTEX_W32 */