/*

 ** 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

 **

 ** $Id$

 */

 #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 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 /* OS_WINCE */

 /*

 ** 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.

 */

 sqlite3_mutex *sqlite3_mutex_alloc(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[5];

       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.

 */

 void sqlite3_mutex_free(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.

 */

 void sqlite3_mutex_enter(sqlite3_mutex *p){

   assert( p );

   assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );

   EnterCriticalSection(&p->mutex);

   p->owner = GetCurrentThreadId(); 

   p->nRef++;

 }

 int sqlite3_mutex_try(sqlite3_mutex *p){

   int rc;

   assert( p );

   assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );

   if( mutexIsNT() && TryEnterCriticalSection(&p->mutex) ){

     p->owner = GetCurrentThreadId();

     p->nRef++;

     rc = SQLITE_OK;

   }else{

     rc = SQLITE_BUSY;

   }

   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.

 */

 void sqlite3_mutex_leave(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);

 }

 /*

 ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are

 ** intended for use only inside assert() statements.

 */

 int sqlite3_mutex_held(sqlite3_mutex *p){

   return p==0 || (p->nRef!=0 && p->owner==GetCurrentThreadId());

 }

 int sqlite3_mutex_notheld(sqlite3_mutex *p){

   return p==0 || p->nRef==0 || p->owner!=GetCurrentThreadId();

 }

 #endif /* SQLITE_MUTEX_W32 */