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 MSVC_VERSION>=1300
  91   _ReadWriteBarrier();
  92 #elif defined(MemoryBarrier)
  93   MemoryBarrier();
  94 #endif
  95 }
  96
  97 /*
  98 ** Initialize and deinitialize the mutex subsystem.
  99 */
 100 static sqlite3_mutex winMutex_staticMutexes[] = {
 101   SQLITE3_MUTEX_INITIALIZER,
 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 };
 114
 115 static int winMutex_isInit = 0;
 116 static int winMutex_isNt = -1; /* <0 means "need to query" */
 117
 118 /* As the winMutexInit() and winMutexEnd() functions are called as part
 119 ** of the sqlite3_initialize() and sqlite3_shutdown() processing, the
 120 ** "interlocked" magic used here is probably not strictly necessary.
 121 */
 122 static LONG SQLITE_WIN32_VOLATILE winMutex_lock = 0;
 123
 124 int sqlite3_win32_is_nt(void); /* os_win.c */
 125 void sqlite3_win32_sleep(DWORD milliseconds); /* os_win.c */
 126
 127 static int winMutexInit(void){
 128   /* The first to increment to 1 does actual initialization */
 129   if( InterlockedCompareExchange(&winMutex_lock, 1, 0)==0 ){
 130     int i;
 131     for(i=0; i<ArraySize(winMutex_staticMutexes); i++){
 132 #if SQLITE_OS_WINRT
 133       InitializeCriticalSectionEx(&winMutex_staticMutexes[i].mutex, 0, 0);
 134 #else
 135       InitializeCriticalSection(&winMutex_staticMutexes[i].mutex);
 136 #endif
 137     }
 138     winMutex_isInit = 1;
 139   }else{
 140     /* Another thread is (in the process of) initializing the static
 141     ** mutexes */
 142     while( !winMutex_isInit ){
 143       sqlite3_win32_sleep(1);
 144     }
 145   }
 146   return SQLITE_OK;
 147 }
 148
 149 static int winMutexEnd(void){
 150   /* The first to decrement to 0 does actual shutdown
 151   ** (which should be the last to shutdown.) */
 152   if( InterlockedCompareExchange(&winMutex_lock, 0, 1)==1 ){
 153     if( winMutex_isInit==1 ){
 154       int i;
 155       for(i=0; i<ArraySize(winMutex_staticMutexes); i++){
 156         DeleteCriticalSection(&winMutex_staticMutexes[i].mutex);
 157       }
 158       winMutex_isInit = 0;
 159     }
 160   }
 161   return SQLITE_OK;
 162 }
 163
 164 /*
 165 ** The sqlite3_mutex_alloc() routine allocates a new
 166 ** mutex and returns a pointer to it.  If it returns NULL
 167 ** that means that a mutex could not be allocated.  SQLite
 168 ** will unwind its stack and return an error.  The argument
 169 ** to sqlite3_mutex_alloc() is one of these integer constants:
 170 **
 171 ** <ul>
 172 ** <li>  SQLITE_MUTEX_FAST
 173 ** <li>  SQLITE_MUTEX_RECURSIVE
 174 ** <li>  SQLITE_MUTEX_STATIC_MASTER
 175 ** <li>  SQLITE_MUTEX_STATIC_MEM
 176 ** <li>  SQLITE_MUTEX_STATIC_OPEN
 177 ** <li>  SQLITE_MUTEX_STATIC_PRNG
 178 ** <li>  SQLITE_MUTEX_STATIC_LRU
 179 ** <li>  SQLITE_MUTEX_STATIC_PMEM
 180 ** <li>  SQLITE_MUTEX_STATIC_APP1
 181 ** <li>  SQLITE_MUTEX_STATIC_APP2
 182 ** <li>  SQLITE_MUTEX_STATIC_APP3
 183 ** <li>  SQLITE_MUTEX_STATIC_VFS1
 184 ** <li>  SQLITE_MUTEX_STATIC_VFS2
 185 ** <li>  SQLITE_MUTEX_STATIC_VFS3
 186 ** </ul>
 187 **
 188 ** The first two constants cause sqlite3_mutex_alloc() to create
 189 ** a new mutex.  The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
 190 ** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
 191 ** The mutex implementation does not need to make a distinction
 192 ** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
 193 ** not want to.  But SQLite will only request a recursive mutex in
 194 ** cases where it really needs one.  If a faster non-recursive mutex
 195 ** implementation is available on the host platform, the mutex subsystem
 196 ** might return such a mutex in response to SQLITE_MUTEX_FAST.
 197 **
 198 ** The other allowed parameters to sqlite3_mutex_alloc() each return
 199 ** a pointer to a static preexisting mutex.  Six static mutexes are
 200 ** used by the current version of SQLite.  Future versions of SQLite
 201 ** may add additional static mutexes.  Static mutexes are for internal
 202 ** use by SQLite only.  Applications that use SQLite mutexes should
 203 ** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
 204 ** SQLITE_MUTEX_RECURSIVE.
 205 **
 206 ** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
 207 ** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
 208 ** returns a different mutex on every call.  But for the static
 209 ** mutex types, the same mutex is returned on every call that has
 210 ** the same type number.
 211 */
 212 static sqlite3_mutex *winMutexAlloc(int iType){
 213   sqlite3_mutex *p;
 214
 215   switch( iType ){
 216     case SQLITE_MUTEX_FAST:
 217     case SQLITE_MUTEX_RECURSIVE: {
 218       p = sqlite3MallocZero( sizeof(*p) );
 219       if( p ){
 220         p->id = iType;
 221 #ifdef SQLITE_DEBUG
 222 #ifdef SQLITE_WIN32_MUTEX_TRACE_DYNAMIC
 223         p->trace = 1;
 224 #endif
 225 #endif
 226 #if SQLITE_OS_WINRT
 227         InitializeCriticalSectionEx(&p->mutex, 0, 0);
 228 #else
 229         InitializeCriticalSection(&p->mutex);
 230 #endif
 231       }
 232       break;
 233     }
 234     default: {
 235 #ifdef SQLITE_ENABLE_API_ARMOR
 236       if( iType-2<0 || iType-2>=ArraySize(winMutex_staticMutexes) ){
 237         (void)SQLITE_MISUSE_BKPT;
 238         return 0;
 239       }
 240 #endif
 241       p = &winMutex_staticMutexes[iType-2];
 242       p->id = iType;
 243 #ifdef SQLITE_DEBUG
 244 #ifdef SQLITE_WIN32_MUTEX_TRACE_STATIC
 245       p->trace = 1;
 246 #endif
 247 #endif
 248       break;
 249     }
 250   }
 251   return p;
 252 }
 253
 254
 255 /*
 256 ** This routine deallocates a previously
 257 ** allocated mutex.  SQLite is careful to deallocate every
 258 ** mutex that it allocates.
 259 */
 260 static void winMutexFree(sqlite3_mutex *p){
 261   assert( p );
 262   assert( p->nRef==0 && p->owner==0 );
 263   if( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE ){
 264     DeleteCriticalSection(&p->mutex);
 265     sqlite3_free(p);
 266   }else{
 267 #ifdef SQLITE_ENABLE_API_ARMOR
 268     (void)SQLITE_MISUSE_BKPT;
 269 #endif
 270   }
 271 }
 272
 273 /*
 274 ** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
 275 ** to enter a mutex.  If another thread is already within the mutex,
 276 ** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
 277 ** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK
 278 ** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
 279 ** be entered multiple times by the same thread.  In such cases the,
 280 ** mutex must be exited an equal number of times before another thread
 281 ** can enter.  If the same thread tries to enter any other kind of mutex
 282 ** more than once, the behavior is undefined.
 283 */
 284 static void winMutexEnter(sqlite3_mutex *p){
 285 #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
 286   DWORD tid = GetCurrentThreadId();
 287 #endif
 288 #ifdef SQLITE_DEBUG
 289   assert( p );
 290   assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld2(p, tid) );
 291 #else
 292   assert( p );
 293 #endif
 294   assert( winMutex_isInit==1 );
 295   EnterCriticalSection(&p->mutex);
 296 #ifdef SQLITE_DEBUG
 297   assert( p->nRef>0 || p->owner==0 );
 298   p->owner = tid;
 299   p->nRef++;
 300   if( p->trace ){
 301     OSTRACE(("ENTER-MUTEX tid=%lu, mutex(%d)=%p (%d), nRef=%d\n",
 302              tid, p->id, p, p->trace, p->nRef));
 303   }
 304 #endif
 305 }
 306
 307 static int winMutexTry(sqlite3_mutex *p){
 308 #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
 309   DWORD tid = GetCurrentThreadId();
 310 #endif
 311   int rc = SQLITE_BUSY;
 312   assert( p );
 313   assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld2(p, tid) );
 314   /*
 315   ** The sqlite3_mutex_try() routine is very rarely used, and when it
 316   ** is used it is merely an optimization.  So it is OK for it to always
 317   ** fail.
 318   **
 319   ** The TryEnterCriticalSection() interface is only available on WinNT.
 320   ** And some windows compilers complain if you try to use it without
 321   ** first doing some #defines that prevent SQLite from building on Win98.
 322   ** For that reason, we will omit this optimization for now.  See
 323   ** ticket #2685.
 324   */
 325 #if defined(_WIN32_WINNT) && _WIN32_WINNT >= 0x0400
 326   assert( winMutex_isInit==1 );
 327   assert( winMutex_isNt>=-1 && winMutex_isNt<=1 );
 328   if( winMutex_isNt<0 ){
 329     winMutex_isNt = sqlite3_win32_is_nt();
 330   }
 331   assert( winMutex_isNt==0 || winMutex_isNt==1 );
 332   if( winMutex_isNt && TryEnterCriticalSection(&p->mutex) ){
 333 #ifdef SQLITE_DEBUG
 334     p->owner = tid;
 335     p->nRef++;
 336 #endif
 337     rc = SQLITE_OK;
 338   }
 339 #else
 340   UNUSED_PARAMETER(p);
 341 #endif
 342 #ifdef SQLITE_DEBUG
 343   if( p->trace ){
 344     OSTRACE(("TRY-MUTEX tid=%lu, mutex(%d)=%p (%d), owner=%lu, nRef=%d, rc=%s\n",
 345              tid, p->id, p, p->trace, p->owner, p->nRef, sqlite3ErrName(rc)));
 346   }
 347 #endif
 348   return rc;
 349 }
 350
 351 /*
 352 ** The sqlite3_mutex_leave() routine exits a mutex that was
 353 ** previously entered by the same thread.  The behavior
 354 ** is undefined if the mutex is not currently entered or
 355 ** is not currently allocated.  SQLite will never do either.
 356 */
 357 static void winMutexLeave(sqlite3_mutex *p){
 358 #if defined(SQLITE_DEBUG) || defined(SQLITE_TEST)
 359   DWORD tid = GetCurrentThreadId();
 360 #endif
 361   assert( p );
 362 #ifdef SQLITE_DEBUG
 363   assert( p->nRef>0 );
 364   assert( p->owner==tid );
 365   p->nRef--;
 366   if( p->nRef==0 ) p->owner = 0;
 367   assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
 368 #endif
 369   assert( winMutex_isInit==1 );
 370   LeaveCriticalSection(&p->mutex);
 371 #ifdef SQLITE_DEBUG
 372   if( p->trace ){
 373     OSTRACE(("LEAVE-MUTEX tid=%lu, mutex(%d)=%p (%d), nRef=%d\n",
 374              tid, p->id, p, p->trace, p->nRef));
 375   }
 376 #endif
 377 }
 378
 379 sqlite3_mutex_methods const *sqlite3DefaultMutex(void){
 380   static const sqlite3_mutex_methods sMutex = {
 381     winMutexInit,
 382     winMutexEnd,
 383     winMutexAlloc,
 384     winMutexFree,
 385     winMutexEnter,
 386     winMutexTry,
 387     winMutexLeave,
 388 #ifdef SQLITE_DEBUG
 389     winMutexHeld,
 390     winMutexNotheld
 391 #else
 392     0,
 393     0
 394 #endif
 395   };
 396   return &sMutex;
 397 }
 398
 399 #endif /* SQLITE_MUTEX_W32 */