4 ** The author disclaims copyright to this source code. In place of
5 ** a legal notice, here is a blessing:
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.
11 *************************************************************************
12 ** This file contains the C functions that implement mutexes for win32
14 ** $Id: mutex_w32.c,v 1.11 2008/06/26 10:41:19 danielk1977 Exp $
16 #include "sqliteInt.h"
19 ** The code in this file is only used if we are compiling multithreaded
22 #ifdef SQLITE_MUTEX_W32
25 ** Each recursive mutex is an instance of the following structure.
27 struct sqlite3_mutex {
28 CRITICAL_SECTION mutex; /* Mutex controlling the lock */
29 int id; /* Mutex type */
30 int nRef; /* Number of enterances */
31 DWORD owner; /* Thread holding this mutex */
35 ** Return true (non-zero) if we are running under WinNT, Win2K, WinXP,
36 ** or WinCE. Return false (zero) for Win95, Win98, or WinME.
38 ** Here is an interesting observation: Win95, Win98, and WinME lack
39 ** the LockFileEx() API. But we can still statically link against that
40 ** API as long as we don't call it win running Win95/98/ME. A call to
41 ** this routine is used to determine if the host is Win95/98/ME or
42 ** WinNT/2K/XP so that we will know whether or not we can safely call
43 ** the LockFileEx() API.
46 # define mutexIsNT() (1)
48 static int mutexIsNT(void){
49 static int osType = 0;
52 sInfo.dwOSVersionInfoSize = sizeof(sInfo);
54 osType = sInfo.dwPlatformId==VER_PLATFORM_WIN32_NT ? 2 : 1;
58 #endif /* SQLITE_OS_WINCE */
63 ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
64 ** intended for use only inside assert() statements.
66 static int winMutexHeld(sqlite3_mutex *p){
67 return p->nRef!=0 && p->owner==GetCurrentThreadId();
69 static int winMutexNotheld(sqlite3_mutex *p){
70 return p->nRef==0 || p->owner!=GetCurrentThreadId();
76 ** Initialize and deinitialize the mutex subsystem.
78 static int winMutexInit(void){ return SQLITE_OK; }
79 static int winMutexEnd(void){ return SQLITE_OK; }
82 ** The sqlite3_mutex_alloc() routine allocates a new
83 ** mutex and returns a pointer to it. If it returns NULL
84 ** that means that a mutex could not be allocated. SQLite
85 ** will unwind its stack and return an error. The argument
86 ** to sqlite3_mutex_alloc() is one of these integer constants:
89 ** <li> SQLITE_MUTEX_FAST 0
90 ** <li> SQLITE_MUTEX_RECURSIVE 1
91 ** <li> SQLITE_MUTEX_STATIC_MASTER 2
92 ** <li> SQLITE_MUTEX_STATIC_MEM 3
93 ** <li> SQLITE_MUTEX_STATIC_PRNG 4
96 ** The first two constants cause sqlite3_mutex_alloc() to create
97 ** a new mutex. The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
98 ** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
99 ** The mutex implementation does not need to make a distinction
100 ** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
101 ** not want to. But SQLite will only request a recursive mutex in
102 ** cases where it really needs one. If a faster non-recursive mutex
103 ** implementation is available on the host platform, the mutex subsystem
104 ** might return such a mutex in response to SQLITE_MUTEX_FAST.
106 ** The other allowed parameters to sqlite3_mutex_alloc() each return
107 ** a pointer to a static preexisting mutex. Three static mutexes are
108 ** used by the current version of SQLite. Future versions of SQLite
109 ** may add additional static mutexes. Static mutexes are for internal
110 ** use by SQLite only. Applications that use SQLite mutexes should
111 ** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
112 ** SQLITE_MUTEX_RECURSIVE.
114 ** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
115 ** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
116 ** returns a different mutex on every call. But for the static
117 ** mutex types, the same mutex is returned on every call that has
118 ** the same type number.
120 static sqlite3_mutex *winMutexAlloc(int iType){
124 case SQLITE_MUTEX_FAST:
125 case SQLITE_MUTEX_RECURSIVE: {
126 p = sqlite3MallocZero( sizeof(*p) );
129 InitializeCriticalSection(&p->mutex);
134 static sqlite3_mutex staticMutexes[6];
135 static int isInit = 0;
137 static long lock = 0;
138 if( InterlockedIncrement(&lock)==1 ){
140 for(i=0; i<sizeof(staticMutexes)/sizeof(staticMutexes[0]); i++){
141 InitializeCriticalSection(&staticMutexes[i].mutex);
148 assert( iType-2 >= 0 );
149 assert( iType-2 < sizeof(staticMutexes)/sizeof(staticMutexes[0]) );
150 p = &staticMutexes[iType-2];
160 ** This routine deallocates a previously
161 ** allocated mutex. SQLite is careful to deallocate every
162 ** mutex that it allocates.
164 static void winMutexFree(sqlite3_mutex *p){
166 assert( p->nRef==0 );
167 assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
168 DeleteCriticalSection(&p->mutex);
173 ** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
174 ** to enter a mutex. If another thread is already within the mutex,
175 ** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
176 ** SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK
177 ** upon successful entry. Mutexes created using SQLITE_MUTEX_RECURSIVE can
178 ** be entered multiple times by the same thread. In such cases the,
179 ** mutex must be exited an equal number of times before another thread
180 ** can enter. If the same thread tries to enter any other kind of mutex
181 ** more than once, the behavior is undefined.
183 static void winMutexEnter(sqlite3_mutex *p){
184 assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld(p) );
185 EnterCriticalSection(&p->mutex);
186 p->owner = GetCurrentThreadId();
189 static int winMutexTry(sqlite3_mutex *p){
190 int rc = SQLITE_BUSY;
191 assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld(p) );
193 ** The sqlite3_mutex_try() routine is very rarely used, and when it
194 ** is used it is merely an optimization. So it is OK for it to always
197 ** The TryEnterCriticalSection() interface is only available on WinNT.
198 ** And some windows compilers complain if you try to use it without
199 ** first doing some #defines that prevent SQLite from building on Win98.
200 ** For that reason, we will omit this optimization for now. See
204 if( mutexIsNT() && TryEnterCriticalSection(&p->mutex) ){
205 p->owner = GetCurrentThreadId();
214 ** The sqlite3_mutex_leave() routine exits a mutex that was
215 ** previously entered by the same thread. The behavior
216 ** is undefined if the mutex is not currently entered or
217 ** is not currently allocated. SQLite will never do either.
219 static void winMutexLeave(sqlite3_mutex *p){
221 assert( p->owner==GetCurrentThreadId() );
223 assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
224 LeaveCriticalSection(&p->mutex);
227 sqlite3_mutex_methods *sqlite3DefaultMutex(void){
228 static sqlite3_mutex_methods sMutex = {
244 #endif /* SQLITE_MUTEX_W32 */