Dear all,
For learning Akka, I wrote below in Java to test fault-tolerance.
I have a master actor to assign job to worker actors, in the master actor,
simply divide the job into several pieces and use round robin router to
assign to workers (i.e. let workers add slices of a summation).
In the worker onReceive, I let the first worker who does its job to throw
an Exception, please consider below code:
WorkerActor/onReceive:
if(RetryCount >=1 ) {
RetryCount--;
throw new Exception("exception thrown from worker");
}
WorkerActor/preRestart:
public void preRestart(Throwable cause, Option<Object> msg) {
System.out.println("Thread "+Thread.currentThread().getId()+" get restart
message ");
if(cause instanceof Exception && msg.nonEmpty()) {
WorkerMessage workerMsg = (WorkerMessage)msg.get();
getSelf().forward(workerMsg, getContext());
//getSelf().tell(workerMsg, getSender());
}
else {
return;
}
}
For the master actor:
router = getContext().actorOf(
Props.create(WorkerActor.class).withRouter(
new RoundRobinRouter(10)));
private static SupervisorStrategy strategy = new OneForOneStrategy(10,
Duration.create(1, TimeUnit.MINUTES),
new Function<Throwable, Directive>() {
public Directive apply(Throwable exception) throws Exception {
if (exception instanceof Exception) {
return SupervisorStrategy.restart();
} else {
return SupervisorStrategy.escalate();
}
}
});
@Override
public SupervisorStrategy supervisorStrategy() {
return strategy;
}
I have 10 workers running and tasks assigned in round-robin algorithm,
after running the example, the restart run as expected, but I have several
questions:
1) All 10 workers' preRestart get called, why is that, is that correct as I
used OneForOneStrategy and I thrown exception only from one worker?
I use the msg.nonEmpty() to get rid of those null msg passed in as from
my running result, all 10 workers run the preRestart which I am quite
confused.
2) After one worker forwards the message, another worker receives the
message and re-process it, they are not the same thread, is that correct?
Thread 11 processing worker 1
Thread 11 throw exception
Thread 18 processing worker 1
>From the output, thread 11 throw exception and thread 18 process later for
fail-over. From understanding, if one child actor failed, then parent actor
should invoke that child actor's preRestart method only, not for all child
actors. Is that correct?
Thanks in advance!
Regards,
George
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