/*

 ** 2007 August 28

 **

 ** 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 OS/2

 **

 ** $Id: mutex_os2.c,v 1.10 2008/06/23 22:13:28 pweilbacher Exp $

 */

 #include "sqliteInt.h"

 /*

 ** The code in this file is only used if SQLITE_MUTEX_OS2 is defined.

 ** See the mutex.h file for details.

 */

 #ifdef SQLITE_MUTEX_OS2

 /********************** OS/2 Mutex Implementation **********************

 **

 ** This implementation of mutexes is built using the OS/2 API.

 */

 /*

 ** The mutex object

 ** Each recursive mutex is an instance of the following structure.

 */

 struct sqlite3_mutex {

   HMTX mutex;       /* Mutex controlling the lock */

   int  id;          /* Mutex type */

   int  nRef;        /* Number of references */

   TID  owner;       /* Thread holding this mutex */

 };

 #define OS2_MUTEX_INITIALIZER   0,0,0,0

 /*

 ** Initialize and deinitialize the mutex subsystem.

 */

 static int os2MutexInit(void){ return SQLITE_OK; }

 static int os2MutexEnd(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 *os2MutexAlloc(int iType){

   sqlite3_mutex *p = NULL;

   switch( iType ){

     case SQLITE_MUTEX_FAST:

     case SQLITE_MUTEX_RECURSIVE: {

       p = sqlite3MallocZero( sizeof(*p) );

       if( p ){

         p->id = iType;

         if( DosCreateMutexSem( 0, &p->mutex, 0, FALSE ) != NO_ERROR ){

           sqlite3_free( p );

           p = NULL;

         }

       }

       break;

     }

     default: {

       static volatile int isInit = 0;

       static sqlite3_mutex staticMutexes[] = {

         { OS2_MUTEX_INITIALIZER, },

         { OS2_MUTEX_INITIALIZER, },

         { OS2_MUTEX_INITIALIZER, },

         { OS2_MUTEX_INITIALIZER, },

         { OS2_MUTEX_INITIALIZER, },

         { OS2_MUTEX_INITIALIZER, },

       };

       if ( !isInit ){

         APIRET rc;

         PTIB ptib;

         PPIB ppib;

         HMTX mutex;

         char name[32];

         DosGetInfoBlocks( &ptib, &ppib );

         sqlite3_snprintf( sizeof(name), name, "\\SEM32\\SQLITE%04x",

                           ppib->pib_ulpid );

         while( !isInit ){

           mutex = 0;

           rc = DosCreateMutexSem( name, &mutex, 0, FALSE);

           if( rc == NO_ERROR ){

             int i;

             if( !isInit ){

               for( i = 0; i < sizeof(staticMutexes)/sizeof(staticMutexes[0]); i++ ){

                 DosCreateMutexSem( 0, &staticMutexes[i].mutex, 0, FALSE );

               }

               isInit = 1;

             }

             DosCloseMutexSem( mutex );

           }else if( rc == ERROR_DUPLICATE_NAME ){

             DosSleep( 1 );

           }else{

             return p;

           }

         }

       }

       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 os2MutexFree(sqlite3_mutex *p){

   if( p==0 ) return;

   assert( p->nRef==0 );

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

   DosCloseMutexSem( 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 os2MutexEnter(sqlite3_mutex *p){

   TID tid;

   PID holder1;

   ULONG holder2;

   if( p==0 ) return;

   assert( p->id==SQLITE_MUTEX_RECURSIVE || os2MutexNotheld(p) );

   DosRequestMutexSem(p->mutex, SEM_INDEFINITE_WAIT);

   DosQueryMutexSem(p->mutex, &holder1, &tid, &holder2);

   p->owner = tid;

   p->nRef++;

 }

 static int os2MutexTry(sqlite3_mutex *p){

   int rc;

   TID tid;

   PID holder1;

   ULONG holder2;

   if( p==0 ) return SQLITE_OK;

   assert( p->id==SQLITE_MUTEX_RECURSIVE || os2MutexNotheld(p) );

   if( DosRequestMutexSem(p->mutex, SEM_IMMEDIATE_RETURN) == NO_ERROR) {

     DosQueryMutexSem(p->mutex, &holder1, &tid, &holder2);

     p->owner = tid;

     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.

 */

 static void os2MutexLeave(sqlite3_mutex *p){

   TID tid;

   PID holder1;

   ULONG holder2;

   if( p==0 ) return;

   assert( p->nRef>0 );

   DosQueryMutexSem(p->mutex, &holder1, &tid, &holder2);

   assert( p->owner==tid );

   p->nRef--;

   assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );

   DosReleaseMutexSem(p->mutex);

 }

 #ifdef SQLITE_DEBUG

 /*

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

 ** intended for use inside assert() statements.

 */

 static int os2MutexHeld(sqlite3_mutex *p){

   TID tid;

   PID pid;

   ULONG ulCount;

   PTIB ptib;

   if( p!=0 ) {

     DosQueryMutexSem(p->mutex, &pid, &tid, &ulCount);

   } else {

     DosGetInfoBlocks(&ptib, NULL);

     tid = ptib->tib_ptib2->tib2_ultid;

   }

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

 }

 static int os2MutexNotheld(sqlite3_mutex *p){

   TID tid;

   PID pid;

   ULONG ulCount;

   PTIB ptib;

   if( p!= 0 ) {

     DosQueryMutexSem(p->mutex, &pid, &tid, &ulCount);

   } else {

     DosGetInfoBlocks(&ptib, NULL);

     tid = ptib->tib_ptib2->tib2_ultid;

   }

   return p==0 || p->nRef==0 || p->owner!=tid;

 }

 #endif

 sqlite3_mutex_methods *sqlite3DefaultMutex(void){

   static sqlite3_mutex_methods sMutex = {

     os2MutexInit,

     os2MutexEnd,

     os2MutexAlloc,

     os2MutexFree,

     os2MutexEnter,

     os2MutexTry,

     os2MutexLeave,

 #ifdef SQLITE_DEBUG

     os2MutexHeld,

     os2MutexNotheld

 #endif

   };

   return &sMutex;

 }

 #endif /* SQLITE_MUTEX_OS2 */