Question

I’d like to execute multiple callables parallel. But it seems that the ExecutorService always waits until all callables are finnished.

I’ve tried the following:

final int nThreads = 10;
ExecutorService executorService = Executors.newFixedThreadPool(nThreads);
List<PrimeCallable> tasks = new ArrayList<PrimeCallable>();
for(int i = 0; i < nThreads; i++) {
    tasks.add(new PrimeCallable(0, i * 100 + 100, "thread" + i));
}

try {
    for(Future<List<Integer>> result : executorService.invokeAll(tasks)) {
        List<Integer> integers = result.get();
        for(Integer i : integers){
            System.out.println(i);
        }
    }
} catch (InterruptedException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
} catch (ExecutionException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

Now, the for loop is called when all callables in the executorService are finnished. As far as I know, there is no executorService.isParallel setter ;-).

What would be the right approach to let callables run parallel?

Thanks for your hints!

Answer 1

The javadocs for invokeAll says;

Executes the given tasks, returning a
list of Futures holding their status
and results when all complete. Future.isDone() is true for each element of the returned list.

So invokeAll blocks until each task in the collection is complete.