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/*
** 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
**
** $Id: mutex_w32.c,v 1.11 2008/06/26 10:41:19 danielk1977 Exp $
*/
#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 */
int nRef; /* Number of enterances */
DWORD owner; /* Thread holding this mutex */
};
/*
** 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.
*/
#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 */
#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 winMutexNotheld(sqlite3_mutex *p){
return p->nRef==0 || p->owner!=GetCurrentThreadId();
}
#endif
/*
** Initialize and deinitialize the mutex subsystem.
*/
static int winMutexInit(void){ return SQLITE_OK; }
static int winMutexEnd(void){ 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 0
** <li> SQLITE_MUTEX_RECURSIVE 1
** <li> SQLITE_MUTEX_STATIC_MASTER 2
** <li> SQLITE_MUTEX_STATIC_MEM 3
** <li> SQLITE_MUTEX_STATIC_PRNG 4
** </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. Three 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 ){
p->id = iType;
InitializeCriticalSection(&p->mutex);
}
break;
}
default: {
static sqlite3_mutex staticMutexes[6];
static int isInit = 0;
while( !isInit ){
static long lock = 0;
if( InterlockedIncrement(&lock)==1 ){
int i;
for(i=0; i<sizeof(staticMutexes)/sizeof(staticMutexes[0]); i++){
InitializeCriticalSection(&staticMutexes[i].mutex);
}
isInit = 1;
}else{
Sleep(1);
}
}
assert( iType-2 >= 0 );
assert( iType-2 < sizeof(staticMutexes)/sizeof(staticMutexes[0]) );
p = &staticMutexes[iType-2];
p->id = iType;
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 );
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){
assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld(p) );
EnterCriticalSection(&p->mutex);
p->owner = GetCurrentThreadId();
p->nRef++;
}
static int winMutexTry(sqlite3_mutex *p){
int rc = SQLITE_BUSY;
assert( p->id==SQLITE_MUTEX_RECURSIVE || winMutexNotheld(p) );
/*
** 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 = GetCurrentThreadId();
p->nRef++;
rc = SQLITE_OK;
}
#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){
assert( p->nRef>0 );
assert( p->owner==GetCurrentThreadId() );
p->nRef--;
assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
LeaveCriticalSection(&p->mutex);
}
sqlite3_mutex_methods *sqlite3DefaultMutex(void){
static sqlite3_mutex_methods sMutex = {
winMutexInit,
winMutexEnd,
winMutexAlloc,
winMutexFree,
winMutexEnter,
winMutexTry,
winMutexLeave,
#ifdef SQLITE_DEBUG
winMutexHeld,
winMutexNotheld
#endif
};
return &sMutex;
}
#endif /* SQLITE_MUTEX_W32 */
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