Monitoring the death of a parent process (via Dispatch Sources)

void MonitorParentProcess()  {     pid_t parentPID = getppid();     dispatch_queue_t queue =  dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);     dispatch_source_t source = dispatch_source_create(DISPATCH_SOURCE_TYPE_PROC,                                                     parentPID, DISPATCH_PROC_EXIT,queue);if (source) {        dispatch_source_set_event_handler(source, ^{           MySetAppExitFlag();           dispatch_source_cancel(source);           dispatch_release(source);});        dispatch_resume(source);     }}