Question

I am working on a Java program and using Timer objects to run tasks every few minutes or hours. This works fine in normal operations, but I am running into a problem with “Sleep mode” on Mac (maybe on other OSes, but I haven’t tried yet).

Consider this code sample:

//Setup the timer to fire the ping worker (every 3 minutes)
_PingTimer.scheduleAtFixedRate(new TimerTask(){
        public void run(){
            Program.PingThread = new PingWorker(Settings.Username, Settings.UserHash, true, true);
            Program.PingThread.CheckOpenPort = true;
            Program.SwingExecutor.execute(Program.PingThread);
        }
    }, 0, 180000);

In normal operation this would fire every 3 minutes with enough accuracy (I’m not concerned about the exact second or anything). The problem with this is after sleeping the computer for a few hours or so it seems to just BLAST the system with backlogged timer requests.

It seems to be running all of the missed timer hits during sleep at once trying to make up for lost time.

Is there a way i can prevent this? I tried using synchronized and some other thread techniques, but this only ensures that they aren’t all running at the same time. They still continue to run one after another until the backlog is passed.

Thanks for any help you can provide!

Answer 1

Have you looked at the API? It clearly states the following:

In fixed-rate execution, each
execution is scheduled relative to the
scheduled execution time of the
initial execution. If an execution is
delayed for any reason (such as
garbage collection or other background
activity), two or more executions will
occur in rapid succession to “catch
up.” In the long run, the frequency of
execution will be exactly the
reciprocal of the specified period
(assuming the system clock underlying
Object.wait(long) is accurate).

This is one reason why you should consider using a ScheduledExecutorService. This link may also prove useful.