Exception exception when using ExecutorService

Question

I want to wait for two tasks to finish, and then return the result from them, but sometimes I get this error. What for? Where did the CancellationException come from?

public class ShouldVoteTask extends AbstractWorkerTask<Void, Void, Boolean> { private final int placeID; private final int userID; public ShouldVoteTask(final int placeID, final int userID) { this.placeID = placeID; this.userID = userID; } @Override protected Boolean doInBackground(final Void... params) { try { // Prepare callables. final IsMaxRatingCallable call1 = new IsMaxRatingCallable(placeID); final DidVoteCallable call2 = new DidVoteCallable(placeID, userID); final List<Callable<Boolean>> callables = new ArrayList<Callable<Boolean>>(); callables.add(call1); callables.add(call2); // Execute them. final ExecutorService service = Executors.newFixedThreadPool(2); final List<Future<Boolean>> futures = service.invokeAll(callables, 5, TimeUnit.SECONDS); // Check the result. boolean result = true; for(final Future<Boolean> future : futures) { if(future.get()) { result = false; } } return result; } catch (final InterruptedException e) { e.printStackTrace(); } catch (final ExecutionException e) { e.printStackTrace(); } return false; } } private class IsMaxRatingCallable implements Callable<Boolean> { private final int placeID; public IsMaxRatingCallable(final int placeID) { this.placeID = placeID; } @Override public Boolean call() throws Exception { return Places.isMaxRating(placeID); } } private class DidVoteCallable implements Callable<Boolean> { private final int placeID; private final int userID; public DidVoteCallable(final int placeID, final int userID) { this.placeID = placeID; this.userID = userID; } @Override public Boolean call() throws Exception { return Votes.didVote(placeID, userID); } } 

Mistake

 E/AndroidRuntime(19014): FATAL EXCEPTION: AsyncTask #1 E/AndroidRuntime(19014): java.lang.RuntimeException: An error occured while executing doInBackground() E/AndroidRuntime(19014): at android.os.AsyncTask$3.done(AsyncTask.java:200) E/AndroidRuntime(19014): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274) E/AndroidRuntime(19014): at java.util.concurrent.FutureTask.setException(FutureTask.java:125) E/AndroidRuntime(19014): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308) E/AndroidRuntime(19014): at java.util.concurrent.FutureTask.run(FutureTask.java:138) E/AndroidRuntime(19014): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088) E/AndroidRuntime(19014): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581) E/AndroidRuntime(19014): at java.lang.Thread.run(Thread.java:1027) E/AndroidRuntime(19014): Caused by: java.util.concurrent.CancellationException E/AndroidRuntime(19014): at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:222) E/AndroidRuntime(19014): at java.util.concurrent.FutureTask.get(FutureTask.java:83) E/AndroidRuntime(19014): at com.vfa.android.planet.task.ShouldVoteTask.doInBackground(ShouldVoteTask.java:43) E/AndroidRuntime(19014): at com.vfa.android.planet.task.ShouldVoteTask.doInBackground(ShouldVoteTask.java:1) E/AndroidRuntime(19014): at android.os.AsyncTask$2.call(AsyncTask.java:185) E/AndroidRuntime(19014): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306) E/AndroidRuntime(19014): ... 4 more 

Answer 1

You request your service provider to make your calls with a timeout of 5 seconds. According to javadoc :

tasks that are not completed [at the end of the timeout] are canceled

I assume that future.get() throws a CancellationException because the timeout is reached and the executor calls future.cancel() .

You can:

• increase timeout
• catch InterruptedException in your ad to handle cancellation gracefully