**
**    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.
**
*************************************************************************
**
** $Id: test_async.c,v 1.47 2008/09/15 15:49:34 danielk1977 Exp $
**
** This file contains an example implementation of an asynchronous IO 
** backend for SQLite.
**
** WHAT IS ASYNCHRONOUS I/O?
**
** With asynchronous I/O, write requests are handled by a separate thread
................................................................................
  aHolder[iIdx] = 0;
  rc = pthread_cond_wait(pCond, pMutex);
  if( rc==0 ){
    aHolder[iIdx] = pthread_self();
  }
  return rc;
}
















/* Call our async_XX wrappers instead of selected pthread_XX functions */
#define pthread_mutex_lock    async_mutex_lock
#define pthread_mutex_unlock  async_mutex_unlock
#define pthread_mutex_trylock async_mutex_trylock
#define pthread_cond_wait     async_cond_wait





#endif   /* !defined(NDEBUG) */

/*
** Add an entry to the end of the global write-op list. pWrite should point 
** to an AsyncWrite structure allocated using sqlite3_malloc().  The writer
** thread will call sqlite3_free() to free the structure after the specified
** operation has been completed.
................................................................................
        ** structures for this file. Obtain the async.lockMutex mutex 
        ** before doing so.
        */
        pthread_mutex_lock(&async.lockMutex);
        rc = unlinkAsyncFile(pData);
        pthread_mutex_unlock(&async.lockMutex);






        async.pQueueFirst = p->pNext;
        sqlite3_free(pData);
        doNotFree = 1;
        break;
      }

      case ASYNC_UNLOCK: {
................................................................................
      holdingMutex = 1;
    }
    /* ASYNC_TRACE(("UNLINK %p\n", p)); */
    if( p==async.pQueueLast ){
      async.pQueueLast = 0;
    }
    if( !doNotFree ){

      async.pQueueFirst = p->pNext;
      sqlite3_free(p);
    }
    assert( holdingMutex );

    /* An IO error has occured. We cannot report the error back to the
    ** connection that requested the I/O since the error happened 

**
**    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.
**
*************************************************************************
**
** $Id: test_async.c,v 1.48 2008/09/26 20:02:50 drh Exp $
**
** This file contains an example implementation of an asynchronous IO 
** backend for SQLite.
**
** WHAT IS ASYNCHRONOUS I/O?
**
** With asynchronous I/O, write requests are handled by a separate thread
................................................................................
  aHolder[iIdx] = 0;
  rc = pthread_cond_wait(pCond, pMutex);
  if( rc==0 ){
    aHolder[iIdx] = pthread_self();
  }
  return rc;
}

/*
** Assert that the mutex is held by the current thread.
*/
static void assert_mutex_is_held(pthread_mutex_t *pMutex){
  int iIdx;
  pthread_mutex_t *aMutex = (pthread_mutex_t *)(&async);
  pthread_t *aHolder = (pthread_t *)(&asyncdebug);

  for(iIdx=0; iIdx<3; iIdx++){
    if( pMutex==&aMutex[iIdx] ) break;
  }
  assert(iIdx<3);
  assert( aHolder[iIdx]==pthread_self() );
}

/* Call our async_XX wrappers instead of selected pthread_XX functions */
#define pthread_mutex_lock    async_mutex_lock
#define pthread_mutex_unlock  async_mutex_unlock
#define pthread_mutex_trylock async_mutex_trylock
#define pthread_cond_wait     async_cond_wait

#else    /* if defined(NDEBUG) */

#define assert_mutex_is_held(X)    /* A no-op when not debugging */

#endif   /* !defined(NDEBUG) */

/*
** Add an entry to the end of the global write-op list. pWrite should point 
** to an AsyncWrite structure allocated using sqlite3_malloc().  The writer
** thread will call sqlite3_free() to free the structure after the specified
** operation has been completed.
................................................................................
        ** structures for this file. Obtain the async.lockMutex mutex 
        ** before doing so.
        */
        pthread_mutex_lock(&async.lockMutex);
        rc = unlinkAsyncFile(pData);
        pthread_mutex_unlock(&async.lockMutex);

        if( !holdingMutex ){
          pthread_mutex_lock(&async.queueMutex);
          holdingMutex = 1;
        }
        assert_mutex_is_held(&async.queueMutex);
        async.pQueueFirst = p->pNext;
        sqlite3_free(pData);
        doNotFree = 1;
        break;
      }

      case ASYNC_UNLOCK: {
................................................................................
      holdingMutex = 1;
    }
    /* ASYNC_TRACE(("UNLINK %p\n", p)); */
    if( p==async.pQueueLast ){
      async.pQueueLast = 0;
    }
    if( !doNotFree ){
      assert_mutex_is_held(&async.queueMutex);
      async.pQueueFirst = p->pNext;
      sqlite3_free(p);
    }
    assert( holdingMutex );

    /* An IO error has occured. We cannot report the error back to the
    ** connection that requested the I/O since the error happened