TaskHeartbeatRunable taskHB = new TaskHeartbeatRunable(workerData);
AsyncLoopThread taskHBThread = new AsyncLoopThread(taskHB);
threads.add(taskHBThread);
// refresh hearbeat to Local dir
RunnableCallback heartbeat_fn = new WorkerHeartbeatRunable(workerData);
AsyncLoopThread hb = new AsyncLoopThread(heartbeat_fn, false, null,
Thread.NORM_PRIORITY, true);
threads.add(hb);
// shutdown task callbacks