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javamultithreadingconcurrencyfuturefuturetask

Wait for at least one result from Java executor without busy waiting

I have a list of Future tasks 

   futureList.add(executor.submit(new Callable(someList)));

and while those are getting executed I want to get resulting items out of it. But how can I make it without looping all the time through it and checking if the futuretask is done, and then getting its result?

for (int i = 0; i < futureList.size(); i++) {
                    if (futureList.get(i).isDone()) {
    .....
}}

I thought about making some additional notify-wait structure but still I would have to know which thread finished so it doesn't help me avoid looping all the time. Any advice?

Solution

  • Use ExecutorCompletionService, it is designed exactly for this purpose, see API http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ExecutorCompletionService.html