/*

** 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 */