/* ** 2007 August 14 ** ** The author disclaims copyright to this source code. In place of ** a legal notice, here is a blessing: ** ** May you do good and not evil. ** May you find forgiveness for yourself and forgive others. ** May you share freely, never taking more than you give. ** ************************************************************************* ** This file contains the C functions that implement mutexes for win32 */ #include "sqliteInt.h" /* ** The code in this file is only used if we are compiling multithreaded ** on a win32 system. */ #ifdef SQLITE_MUTEX_W32 /* ** Each recursive mutex is an instance of the following structure. */ struct sqlite3_mutex { CRITICAL_SECTION mutex; /* Mutex controlling the lock */ int id; /* Mutex type */ #ifdef SQLITE_DEBUG volatile int nRef; /* Number of enterances */ volatile DWORD owner; /* Thread holding this mutex */ int trace; /* True to trace changes */ #endif }; #define SQLITE_W32_MUTEX_INITIALIZER { 0 } #ifdef SQLITE_DEBUG #define SQLITE3_MUTEX_INITIALIZER { SQLITE_W32_MUTEX_INITIALIZER, 0, 0L, (DWORD)0, 0 } #else #define SQLITE3_MUTEX_INITIALIZER { SQLITE_W32_MUTEX_INITIALIZER, 0 } #endif /* ** Return true (non-zero) if we are running under WinNT, Win2K, WinXP, ** or WinCE. Return false (zero) for Win95, Win98, or WinME. ** ** Here is an interesting observation: Win95, Win98, and WinME lack ** the LockFileEx() API. But we can still statically link against that ** API as long as we don't call it win running Win95/98/ME. A call to ** this routine is used to determine if the host is Win95/98/ME or ** WinNT/2K/XP so that we will know whether or not we can safely call ** the LockFileEx() API. ** ** mutexIsNT() is only used for the TryEnterCriticalSection() API call, ** which is only available if your application was compiled with ** _WIN32_WINNT defined to a value >= 0x0400. Currently, the only ** call to TryEnterCriticalSection() is #ifdef'ed out, so #ifdef ** this out as well. */ #if 0 #if SQLITE_OS_WINCE # define mutexIsNT() (1) #else static int mutexIsNT(void){ static int osType = 0; if( osType==0 ){ OSVERSIONINFO sInfo; sInfo.dwOSVersionInfoSize = sizeof(sInfo); GetVersionEx(&sInfo); osType = sInfo.dwPlatformId==VER_PLATFORM_WIN32_NT ? 2 : 1; } return osType==2; } #endif /* SQLITE_OS_WINCE */ #endif #ifdef SQLITE_DEBUG /* ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are ** intended for use only inside assert() statements. */ static int winMutexHeld(sqlite3_mutex *p){ return p->nRef!=0 && p->owner==GetCurrentThreadId(); } static int winMutexNotheld2(sqlite3_mutex *p, DWORD tid){ return p->nRef==0 || p->owner!=tid; } static int winMutexNotheld(sqlite3_mutex *p){ DWORD tid = GetCurrentThreadId(); return winMutexNotheld2(p, tid); } #endif /* ** Initialize and deinitialize the mutex subsystem. */ static sqlite3_mutex winMutex_staticMutexes[6] = { SQLITE3_MUTEX_INITIALIZER, SQLITE3_MUTEX_INITIALIZER, SQLITE3_MUTEX_INITIALIZER, SQLITE3_MUTEX_INITIALIZER, SQLITE3_MUTEX_INITIALIZER, SQLITE3_MUTEX_INITIALIZER }; static int winMutex_isInit = 0; /* As winMutexInit() and winMutexEnd() are called as part ** of the sqlite3_initialize and sqlite3_shutdown() ** processing, the "interlocked" magic is probably not ** strictly necessary. */ static long winMutex_lock = 0; static int winMutexInit(void){ /* The first to increment to 1 does actual initialization */ if( InterlockedCompareExchange(&winMutex_lock, 1, 0)==0 ){ int i; for(i=0; i<ArraySize(winMutex_staticMutexes); i++){ InitializeCriticalSection(&winMutex_staticMutexes[i].mutex); } winMutex_isInit = 1; }else{ /* Someone else is in the process of initing the static mutexes */ while( !winMutex_isInit ){ Sleep(1); } } return SQLITE_OK; } static int winMutexEnd(void){ /* The first to decrement to 0 does actual shutdown ** (which should be the last to shutdown.) */ if( InterlockedCompareExchange(&winMutex_lock, 0, 1)==1 ){ if( winMutex_isInit==1 ){ int i; for(i=0; i<ArraySize(winMutex_staticMutexes); i++){ DeleteCriticalSection(&winMutex_staticMutexes[i].mutex); } winMutex_isInit = 0; } } return SQLITE_OK; } /* ** The sqlite3_mutex_alloc() routine allocates a new ** mutex and returns a pointer to it. If it returns NULL ** that means that a mutex could not be allocated. SQLite ** will unwind its stack and return an error. The argument ** to sqlite3_mutex_alloc() is one of these integer constants: ** ** <ul> ** <li> SQLITE_MUTEX_FAST ** <li> SQLITE_MUTEX_RECURSIVE ** <li> SQLITE_MUTEX_STATIC_MASTER ** <li> SQLITE_MUTEX_STATIC_MEM ** <li> SQLITE_MUTEX_STATIC_MEM2 ** <li> SQLITE_MUTEX_STATIC_PRNG ** <li> SQLITE_MUTEX_STATIC_LRU ** <li> SQLITE_MUTEX_STATIC_PMEM ** </ul> ** ** The first two constants cause sqlite3_mutex_alloc() to create ** a new mutex. The new mutex is recursive when SQLITE_MUTEX_RECURSIVE ** is used but not necessarily so when SQLITE_MUTEX_FAST is used. ** The mutex implementation does not need to make a distinction ** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does ** not want to. But SQLite will only request a recursive mutex in ** cases where it really needs one. If a faster non-recursive mutex ** implementation is available on the host platform, the mutex subsystem ** might return such a mutex in response to SQLITE_MUTEX_FAST. ** ** The other allowed parameters to sqlite3_mutex_alloc() each return ** a pointer to a static preexisting mutex. Six static mutexes are ** used by the current version of SQLite. Future versions of SQLite ** may add additional static mutexes. Static mutexes are for internal ** use by SQLite only. Applications that use SQLite mutexes should ** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or ** SQLITE_MUTEX_RECURSIVE. ** ** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST ** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc() ** returns a different mutex on every call. But for the static ** mutex types, the same mutex is returned on every call that has ** the same type number. */ static sqlite3_mutex *winMutexAlloc(int iType){ sqlite3_mutex *p; switch( iType ){ case SQLITE_MUTEX_FAST: case SQLITE_MUTEX_RECURSIVE: { p = sqlite3MallocZero( sizeof(*p) ); if( p ){ #ifdef SQLITE_DEBUG p->id = iType; #endif InitializeCriticalSection(&p->mutex); } break; } default: { assert( winMutex_isInit==1 ); assert( iType-2 >= 0 ); assert( iType-2 < ArraySize(winMutex_staticMutexes) ); p = &winMutex_staticMutexes[iType-2]; #ifdef SQLITE_DEBUG p->id = iType; #endif break; } } return p; } /* ** This routine deallocates a previously ** allocated mutex. SQLite is careful to deallocate every ** mutex that it allocates. */ static void winMutexFree(sqlite3_mutex *p){ assert( p ); assert( p->nRef==0 && p->owner==0 ); assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE ); DeleteCriticalSection(&p->mutex); sqlite3_free(p); } /* ** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt ** to enter a mutex. If another thread is already within the mutex, ** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return ** SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK ** upon successful entry. Mutexes created using SQLITE_MUTEX_RECURSIVE can ** be entered multiple times by the same thread. In such cases the, ** mutex must be exited an equal number of times before another thread ** can enter. If the same thread tries to enter any other kind of mutex ** more than once, the behavior is undefined. */ static void winMutexEnter(sqlite3_mutex *p){ #ifdef SQLITE_DEBUG DWORD tid = GetCurrentThreadId(); assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld2(p, tid) ); #endif EnterCriticalSection(&p->mutex); #ifdef SQLITE_DEBUG assert( p->nRef>0 || p->owner==0 ); p->owner = tid; p->nRef++; if( p->trace ){ printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef); } #endif } static int winMutexTry(sqlite3_mutex *p){ #ifndef NDEBUG DWORD tid = GetCurrentThreadId(); #endif int rc = SQLITE_BUSY; assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld2(p, tid) ); /* ** The sqlite3_mutex_try() routine is very rarely used, and when it ** is used it is merely an optimization. So it is OK for it to always ** fail. ** ** The TryEnterCriticalSection() interface is only available on WinNT. ** And some windows compilers complain if you try to use it without ** first doing some #defines that prevent SQLite from building on Win98. ** For that reason, we will omit this optimization for now. See ** ticket #2685. */ #if 0 if( mutexIsNT() && TryEnterCriticalSection(&p->mutex) ){ p->owner = tid; p->nRef++; rc = SQLITE_OK; } #else UNUSED_PARAMETER(p); #endif #ifdef SQLITE_DEBUG if( rc==SQLITE_OK && p->trace ){ printf("try mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef); } #endif return rc; } /* ** The sqlite3_mutex_leave() routine exits a mutex that was ** previously entered by the same thread. The behavior ** is undefined if the mutex is not currently entered or ** is not currently allocated. SQLite will never do either. */ static void winMutexLeave(sqlite3_mutex *p){ #ifndef NDEBUG DWORD tid = GetCurrentThreadId(); assert( p->nRef>0 ); assert( p->owner==tid ); p->nRef--; if( p->nRef==0 ) p->owner = 0; assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE ); #endif LeaveCriticalSection(&p->mutex); #ifdef SQLITE_DEBUG if( p->trace ){ printf("leave mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef); } #endif } sqlite3_mutex_methods const *sqlite3DefaultMutex(void){ static const sqlite3_mutex_methods sMutex = { winMutexInit, winMutexEnd, winMutexAlloc, winMutexFree, winMutexEnter, winMutexTry, winMutexLeave, #ifdef SQLITE_DEBUG winMutexHeld, winMutexNotheld #else 0, 0 #endif }; return &sMutex; } #endif /* SQLITE_MUTEX_W32 */