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 /*
  17 ** The code in this file is only used if we are compiling multithreaded
  18 ** on a win32 system.
  19 */
  20 #ifdef SQLITE_MUTEX_W32
  21
  22 /*
  23 ** Each recursive mutex is an instance of the following structure.
  24 */
  25 struct sqlite3_mutex {
  26   CRITICAL_SECTION mutex;    /* Mutex controlling the lock */
  27   int id;                    /* Mutex type */
  28 #ifdef SQLITE_DEBUG
  29   volatile int nRef;         /* Number of enterances */
  30   volatile DWORD owner;      /* Thread holding this mutex */
  31   int trace;                 /* True to trace changes */
  32 #endif
  33 };
  34 #define SQLITE_W32_MUTEX_INITIALIZER { 0 }
  35 #ifdef SQLITE_DEBUG
  36 #define SQLITE3_MUTEX_INITIALIZER { SQLITE_W32_MUTEX_INITIALIZER, 0, 0L, (DWORD)0, 0 }
  37 #else
  38 #define SQLITE3_MUTEX_INITIALIZER { SQLITE_W32_MUTEX_INITIALIZER, 0 }
  39 #endif
  40
  41 /*
  42 ** Return true (non-zero) if we are running under WinNT, Win2K, WinXP,
  43 ** or WinCE.  Return false (zero) for Win95, Win98, or WinME.
  44 **
  45 ** Here is an interesting observation:  Win95, Win98, and WinME lack
  46 ** the LockFileEx() API.  But we can still statically link against that
  47 ** API as long as we don't call it win running Win95/98/ME.  A call to
  48 ** this routine is used to determine if the host is Win95/98/ME or
  49 ** WinNT/2K/XP so that we will know whether or not we can safely call
  50 ** the LockFileEx() API.
  51 **
  52 ** mutexIsNT() is only used for the TryEnterCriticalSection() API call,
  53 ** which is only available if your application was compiled with
  54 ** _WIN32_WINNT defined to a value >= 0x0400.  Currently, the only
  55 ** call to TryEnterCriticalSection() is #ifdef'ed out, so #ifdef
  56 ** this out as well.
  57 */
  58 #if 0
  59 #if SQLITE_OS_WINCE
  60 # define mutexIsNT()  (1)
  61 #else
  62   static int mutexIsNT(void){
  63     static int osType = 0;
  64     if( osType==0 ){
  65       OSVERSIONINFO sInfo;
  66       sInfo.dwOSVersionInfoSize = sizeof(sInfo);
  67       GetVersionEx(&sInfo);
  68       osType = sInfo.dwPlatformId==VER_PLATFORM_WIN32_NT ? 2 : 1;
  69     }
  70     return osType==2;
  71   }
  72 #endif /* SQLITE_OS_WINCE */
  73 #endif
  74
  75 #ifdef SQLITE_DEBUG
  76 /*
  77 ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
  78 ** intended for use only inside assert() statements.
  79 */
  80 static int winMutexHeld(sqlite3_mutex *p){
  81   return p->nRef!=0 && p->owner==GetCurrentThreadId();
  82 }
  83 static int winMutexNotheld2(sqlite3_mutex *p, DWORD tid){
  84   return p->nRef==0 || p->owner!=tid;
  85 }
  86 static int winMutexNotheld(sqlite3_mutex *p){
  87   DWORD tid = GetCurrentThreadId();
  88   return winMutexNotheld2(p, tid);
  89 }
  90 #endif
  91
  92
  93 /*
  94 ** Initialize and deinitialize the mutex subsystem.
  95 */
  96 static sqlite3_mutex winMutex_staticMutexes[6] = {
  97   SQLITE3_MUTEX_INITIALIZER,
  98   SQLITE3_MUTEX_INITIALIZER,
  99   SQLITE3_MUTEX_INITIALIZER,
 100   SQLITE3_MUTEX_INITIALIZER,
 101   SQLITE3_MUTEX_INITIALIZER,
 102   SQLITE3_MUTEX_INITIALIZER
 103 };
 104 static int winMutex_isInit = 0;
 105 /* As winMutexInit() and winMutexEnd() are called as part
 106 ** of the sqlite3_initialize and sqlite3_shutdown()
 107 ** processing, the "interlocked" magic is probably not
 108 ** strictly necessary.
 109 */
 110 static long winMutex_lock = 0;
 111
 112 static int winMutexInit(void){
 113   /* The first to increment to 1 does actual initialization */
 114   if( InterlockedCompareExchange(&winMutex_lock, 1, 0)==0 ){
 115     int i;
 116     for(i=0; i<ArraySize(winMutex_staticMutexes); i++){
 117       InitializeCriticalSection(&winMutex_staticMutexes[i].mutex);
 118     }
 119     winMutex_isInit = 1;
 120   }else{
 121     /* Someone else is in the process of initing the static mutexes */
 122     while( !winMutex_isInit ){
 123       Sleep(1);
 124     }
 125   }
 126   return SQLITE_OK;
 127 }
 128
 129 static int winMutexEnd(void){
 130   /* The first to decrement to 0 does actual shutdown
 131   ** (which should be the last to shutdown.) */
 132   if( InterlockedCompareExchange(&winMutex_lock, 0, 1)==1 ){
 133     if( winMutex_isInit==1 ){
 134       int i;
 135       for(i=0; i<ArraySize(winMutex_staticMutexes); i++){
 136         DeleteCriticalSection(&winMutex_staticMutexes[i].mutex);
 137       }
 138       winMutex_isInit = 0;
 139     }
 140   }
 141   return SQLITE_OK;
 142 }
 143
 144 /*
 145 ** The sqlite3_mutex_alloc() routine allocates a new
 146 ** mutex and returns a pointer to it.  If it returns NULL
 147 ** that means that a mutex could not be allocated.  SQLite
 148 ** will unwind its stack and return an error.  The argument
 149 ** to sqlite3_mutex_alloc() is one of these integer constants:
 150 **
 151 ** <ul>
 152 ** <li>  SQLITE_MUTEX_FAST
 153 ** <li>  SQLITE_MUTEX_RECURSIVE
 154 ** <li>  SQLITE_MUTEX_STATIC_MASTER
 155 ** <li>  SQLITE_MUTEX_STATIC_MEM
 156 ** <li>  SQLITE_MUTEX_STATIC_MEM2
 157 ** <li>  SQLITE_MUTEX_STATIC_PRNG
 158 ** <li>  SQLITE_MUTEX_STATIC_LRU
 159 ** <li>  SQLITE_MUTEX_STATIC_PMEM
 160 ** </ul>
 161 **
 162 ** The first two constants cause sqlite3_mutex_alloc() to create
 163 ** a new mutex.  The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
 164 ** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
 165 ** The mutex implementation does not need to make a distinction
 166 ** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
 167 ** not want to.  But SQLite will only request a recursive mutex in
 168 ** cases where it really needs one.  If a faster non-recursive mutex
 169 ** implementation is available on the host platform, the mutex subsystem
 170 ** might return such a mutex in response to SQLITE_MUTEX_FAST.
 171 **
 172 ** The other allowed parameters to sqlite3_mutex_alloc() each return
 173 ** a pointer to a static preexisting mutex.  Six static mutexes are
 174 ** used by the current version of SQLite.  Future versions of SQLite
 175 ** may add additional static mutexes.  Static mutexes are for internal
 176 ** use by SQLite only.  Applications that use SQLite mutexes should
 177 ** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
 178 ** SQLITE_MUTEX_RECURSIVE.
 179 **
 180 ** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
 181 ** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
 182 ** returns a different mutex on every call.  But for the static
 183 ** mutex types, the same mutex is returned on every call that has
 184 ** the same type number.
 185 */
 186 static sqlite3_mutex *winMutexAlloc(int iType){
 187   sqlite3_mutex *p;
 188
 189   switch( iType ){
 190     case SQLITE_MUTEX_FAST:
 191     case SQLITE_MUTEX_RECURSIVE: {
 192       p = sqlite3MallocZero( sizeof(*p) );
 193       if( p ){
 194 #ifdef SQLITE_DEBUG
 195         p->id = iType;
 196 #endif
 197         InitializeCriticalSection(&p->mutex);
 198       }
 199       break;
 200     }
 201     default: {
 202       assert( winMutex_isInit==1 );
 203       assert( iType-2 >= 0 );
 204       assert( iType-2 < ArraySize(winMutex_staticMutexes) );
 205       p = &winMutex_staticMutexes[iType-2];
 206 #ifdef SQLITE_DEBUG
 207       p->id = iType;
 208 #endif
 209       break;
 210     }
 211   }
 212   return p;
 213 }
 214
 215
 216 /*
 217 ** This routine deallocates a previously
 218 ** allocated mutex.  SQLite is careful to deallocate every
 219 ** mutex that it allocates.
 220 */
 221 static void winMutexFree(sqlite3_mutex *p){
 222   assert( p );
 223   assert( p->nRef==0 && p->owner==0 );
 224   assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
 225   DeleteCriticalSection(&p->mutex);
 226   sqlite3_free(p);
 227 }
 228
 229 /*
 230 ** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
 231 ** to enter a mutex.  If another thread is already within the mutex,
 232 ** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
 233 ** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK
 234 ** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can
 235 ** be entered multiple times by the same thread.  In such cases the,
 236 ** mutex must be exited an equal number of times before another thread
 237 ** can enter.  If the same thread tries to enter any other kind of mutex
 238 ** more than once, the behavior is undefined.
 239 */
 240 static void winMutexEnter(sqlite3_mutex *p){
 241 #ifdef SQLITE_DEBUG
 242   DWORD tid = GetCurrentThreadId();
 243   assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld2(p, tid) );
 244 #endif
 245   EnterCriticalSection(&p->mutex);
 246 #ifdef SQLITE_DEBUG
 247   assert( p->nRef>0 || p->owner==0 );
 248   p->owner = tid;
 249   p->nRef++;
 250   if( p->trace ){
 251     printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
 252   }
 253 #endif
 254 }
 255 static int winMutexTry(sqlite3_mutex *p){
 256 #ifndef NDEBUG
 257   DWORD tid = GetCurrentThreadId();
 258 #endif
 259   int rc = SQLITE_BUSY;
 260   assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld2(p, tid) );
 261   /*
 262   ** The sqlite3_mutex_try() routine is very rarely used, and when it
 263   ** is used it is merely an optimization.  So it is OK for it to always
 264   ** fail.
 265   **
 266   ** The TryEnterCriticalSection() interface is only available on WinNT.
 267   ** And some windows compilers complain if you try to use it without
 268   ** first doing some #defines that prevent SQLite from building on Win98.
 269   ** For that reason, we will omit this optimization for now.  See
 270   ** ticket #2685.
 271   */
 272 #if 0
 273   if( mutexIsNT() && TryEnterCriticalSection(&p->mutex) ){
 274     p->owner = tid;
 275     p->nRef++;
 276     rc = SQLITE_OK;
 277   }
 278 #else
 279   UNUSED_PARAMETER(p);
 280 #endif
 281 #ifdef SQLITE_DEBUG
 282   if( rc==SQLITE_OK && p->trace ){
 283     printf("try mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
 284   }
 285 #endif
 286   return rc;
 287 }
 288
 289 /*
 290 ** The sqlite3_mutex_leave() routine exits a mutex that was
 291 ** previously entered by the same thread.  The behavior
 292 ** is undefined if the mutex is not currently entered or
 293 ** is not currently allocated.  SQLite will never do either.
 294 */
 295 static void winMutexLeave(sqlite3_mutex *p){
 296 #ifndef NDEBUG
 297   DWORD tid = GetCurrentThreadId();
 298   assert( p->nRef>0 );
 299   assert( p->owner==tid );
 300   p->nRef--;
 301   if( p->nRef==0 ) p->owner = 0;
 302   assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
 303 #endif
 304   LeaveCriticalSection(&p->mutex);
 305 #ifdef SQLITE_DEBUG
 306   if( p->trace ){
 307     printf("leave mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
 308   }
 309 #endif
 310 }
 311
 312 sqlite3_mutex_methods const *sqlite3DefaultMutex(void){
 313   static const sqlite3_mutex_methods sMutex = {
 314     winMutexInit,
 315     winMutexEnd,
 316     winMutexAlloc,
 317     winMutexFree,
 318     winMutexEnter,
 319     winMutexTry,
 320     winMutexLeave,
 321 #ifdef SQLITE_DEBUG
 322     winMutexHeld,
 323     winMutexNotheld
 324 #else
 325     0,
 326     0
 327 #endif
 328   };
 329
 330   return &sMutex;
 331 }
 332 #endif /* SQLITE_MUTEX_W32 */