Scheduled executor: poll for result at fix rate and exit if timeout or result valid

Question

Problem: I have a requirement to call a dao method at fix rate say every 10 sec, then I need to check if the result is valid if yes exit, else keep on call

Answer 1

Make it a self-scheduling task. In pseudo code:

public class PollingTaskRunner {

...
CountDownLatch doneWait = new CountDownLatch(1);
volatile boolean done;

PollingTaskRunner(Runnable pollingTask, int frequency, int period) {
    ...
    endTime = now + period;
    executor.schedule(this, 0);
}

run() {

    try {
        pollingTask.run();
    } catch (Exception e) {
        ...
    }
    if (pollingTask.isComplete() || now + frequency > endTime) {
        done = true;
        doneWait.countDown();
        executor.shutdown();
    } else {
        executor.schedule(this, frequency);
    }
}

await() {
    doneWait.await();
}

isDone() {
    return done;
}
}

It is not that complicated but add plenty of debug statements the first time you run/test this so you know what is going on. Once it is running as intended, it is easy to re-use the pattern.

Answer 2

A slightly simpler method, you don't need a separate executor service for the terminator, you could simply push the terminator task into the same executor.

Even simpler. Have PollerTask place it's result in a BlockingQueue. Then have the PollingTaskRunner do a timed poll on that BlockingQueue. Whenever control is returned from the poll call ScheduledFuture.cancel because the task either succeeded or timed out.