Creating a looping background task

Question

I'd like to create an AsyncTask that sits in the background and calls a web service every X seconds.

    private class BackgroundTask extends AsyncTask<Integer, Integer, Boolean> {
    protected Boolean doInBackground(Integer... params) {
        if (params.length > 0) {
            int intUserId = params[0];

            if (intUserId != -1) {
                boolean blnRunning = true;
                while (blnRunning) {
                    // perform query

                    try {
                        this.wait(15000);
                    }
                    catch (InterruptedException e) {
                        blnRunning = false;
                    }
                }
            }
        }

        return false;
    }

    protected void onPostExecute(Boolean blnLaunchStoreFavorites) {
        // do something?
    }
}

This is what I have.

Shortly after this.wait() is called, I get an error down in the bowels of ThreadPoolExecuter.class.

Uncaught handler: thread AsyncTask #2 exiting due to uncaught exception
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:200)
at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
at java.util.concurrent.FutureTask.run(FutureTask.java:137)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1068)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:561)
at java.lang.Thread.run(Thread.java:1096)

I'm not quite sure what is going on here. Any ideas?

Try putting another catch block after the one for InterruptedException but have it catch Exception and then use printStackTrace to see what exception is being thrown. — Squonk, Apr 05 '11 at 20:35
If this is a long running task, then maybe you should be using a Service. — Intrications, Apr 05 '11 at 20:48

score 1 · Answer 1 · answered Apr 05 '11 at 20:39

1

What about using Thread.sleep(15000) instead? Or are you making use of the notify semantics?

Also, is there a "caused by ..." entry in logcat as well?

answered Apr 05 '11 at 20:39

Matthew

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score 1 · Accepted Answer · answered Apr 05 '11 at 21:35

1

Firstly, this is going to kill your battery. Secondly, if you really, really want to do this, you should use a Service rather than an AsyncTask. The latter is only supposed to be used for short lived, one-time uses, not for continuous background polling.

answered Apr 05 '11 at 21:35

dave.c

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How would I make the Service sleep? – Andrew Apr 05 '11 at 22:43
@Andrew you could use [`Handler#postdelayed()`](http://developer.android.com/reference/android/os/Handler.html#postDelayed%28java.lang.Runnable,%20long%29) on a `Runnable` – dave.c Apr 05 '11 at 23:17
I'm a little confused about one thing. postDelayed takes a Runnable (with my web service code) and a long (time in milliseconds) that is the time from now at which the Runnable should be executed. My issue is, I want this to happen indefinitely, X amount of times, until I stop the Service. – Andrew Apr 06 '11 at 14:38
@Andrew so the last thing that your runnable will do after it has finished its work is to `removeCallbacks()` then `postDelayed()` on itself. Have a look at [this example](http://stackoverflow.com/questions/4302060/self-updating-every-10-seconds-widget-handler-postdelayed-problem) – dave.c Apr 06 '11 at 14:56
Though I do have to ask, why is using a Runnable & Handler less strenuous on the battery when done in a Service, as opposed to a Thread or AsyncTask? – Andrew Apr 06 '11 at 22:02
It's the fact that you are performing a poll every 15 seconds that will kill your battery, whether it's done with an `AsyncTask` or a `Service`. However if it is functionality that you need for your app then the best way to do it is with a `Service`. – dave.c Apr 06 '11 at 23:41

Creating a looping background task

2 Answers2