Scheduling periodic tasks and clock drift

Question

I would like to schedule a periodic task which executes every X hours. I have a service which is written in Java and I was thinking of creating a long running background thread

Answer 1

Is clock drift on my host an issue I should be worried about?

Yes, clock drift can be an issue when using ScheduledThreadPoolExecutor.

CronScheduler is specifically designed to be proof against clock drift.

Example usage:

Duration syncPeriod = Duration.ofMinutes(1);
CronScheduler cron = CronScheduler.create(syncPeriod);

// If you need just precisely "once every X hours", irrespective of the
// starting time
cron.scheduleAtFixedRate(0, X, TimeUnit.HOURS, runTimeMillis -> {
    // Do the task
});

// If you need "once every X hours" in terms of wall clock time,
// in some time zone:
ZoneId myTZ = ZoneId.systemDefault();
cron.scheduleAtRoundTimesInDay(Duration.ofHours(X), myTZ, runTimeMillis -> {
    // Do the task
});

See Javadocs for scheduleAtRoundTimesInDay.