SQLite

** and processing them in the order in which they arrive.
**
** An artifical delay of async.ioDelay milliseconds is inserted before
** each write operation in order to simulate the effect of a slow disk.
**
** Only one instance of this procedure may be running at a time.
*/
static void *asyncWriterThread(void *pIsStarted){
  sqlite3_vfs *pVfs = (sqlite3_vfs *)(async_vfs.pAppData);
  AsyncWrite *p = 0;
  int rc = SQLITE_OK;
  int holdingMutex = 0;

  if( pthread_mutex_trylock(&async.writerMutex) ){
    return 0;
  }
  (*(int *)pIsStarted) = 1;
  while( async.writerHaltNow==0 ){
    int doNotFree = 0;
    sqlite3_file *pBase = 0;

    if( !holdingMutex ){
      pthread_mutex_lock(&async.queueMutex);
    }

  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  pthread_t x;
  int rc;
  volatile int isStarted = 0;
  rc = pthread_create(&x, 0, asyncWriterThread, &isStarted);
  if( rc ){
    Tcl_AppendResult(interp, "failed to create the thread", 0);
    return TCL_ERROR;
  }
  pthread_detach(x);
  while( isStarted==0 ){
    sched_yield();
  }
  return TCL_OK;
}

/*
** sqlite3async_wait
**
** Wait for the current writer thread to terminate.
**
** If the current writer thread is set to run forever then this
** command would block forever.  To prevent that, an error is returned. 
*/
static int testAsyncWait(
  void * clientData,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
  int cnt = 10;
  assert(async.writerHaltNow==0);
  if( async.writerHaltNow==0 && async.writerHaltWhenIdle==0 ){
    Tcl_AppendResult(interp, "would block forever", (char*)0);
    return TCL_ERROR;
  }

  while( cnt-- && !pthread_mutex_trylock(&async.writerMutex) ){
    pthread_mutex_unlock(&async.writerMutex);