Java ScheduledExecutorService executing faster than intended

Question

I'm currently having issues with a ScheduledExecutorService executing faster than the given timeframe.

scheduleAtFixedRate states that subsequent executions may be late but it does not wait the given time afterwords.

GrabPutTask simply grabs information from a source, assigns the capture time, and sends it to a database. Because the interval becomes less than a second, the database entry gives an error in regards to a duplicate entry.

Is there a way to execute the task at a fixed time AFTER the previous task has completed?

I've read here that the tasks "bunch up" in a queue but a solution for my needs was not presented.

private static final ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);

public static void main(String[] args)
{
    //
    ..
    //
    //Creating the looping thread.
    try
    {
        scheduler.scheduleAtFixedRate(new GrabPutTask(), (long) 1, (long) (seconds * 1000), TimeUnit.MILLISECONDS);
        LOGGER.info(String.format("DBUpdater connected and running. (GetAddr: %s, SetAddr: %s, Poll Rate: %.2f, Sector Number: %s, Number of PLCs: %d)",
                                  FROM_IP.split(":", 2)[0] + ":" + fromServer.getPort(), dataSource.getURL(), seconds, SECTOR, NUMBER_OF_PLCS_ON_MASTER));
    }
    catch (IllegalArgumentException ex)
    {
        LOGGER.log(Level.SEVERE, null, ex);
        printUsage();
        System.exit(1);
    }
}

Example execution time intervals:

Event Called: 2014/02/12 14:19:07.199
Event Called: 2014/02/12 14:19:08.199
Event Called: 2014/02/12 14:19:09.199
Event Called: 2014/02/12 14:19:10.199
Event Called: 2014/02/12 14:19:11.199
Event Called: 2014/02/12 14:19:12.199
Event Called: 2014/02/12 14:19:13.199
Event Called: 2014/02/12 14:19:14.199
Event Called: 2014/02/12 14:19:15.199
Event Called: 2014/02/12 14:19:16.199
Event Called: 2014/02/12 14:19:17.199
Event Called: 2014/02/12 14:19:18.199
...
Event Called: 2014/02/12 14:20:21.415 (A load on the server it seems)
Event Called: 2014/02/12 14:20:22.215
Event Called: 2014/02/12 14:20:23.425
Event Called: 2014/02/12 14:20:24.422
Event Called: 2014/02/12 14:20:25.276
Event Called: 2014/02/12 14:20:25.997

Answer 1

scheduleWithFixedRate tries to "catch up" if execution is delayed for whatever reason. You can use scheduleWithFixedDelay to keep the system from starting the clock until after the previous execution; delays will accumulate and won't catch up.

Answer 2

To sleep for any amount of time.

try {
    Thread.sleep(someTime);
} catch(InterruptedException ex) {
    Thread.currentThread().interrupt();
}