/*

** 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 */