ExecutorService.invokeAll does NOT support collection of runnable task

Question

Wanted to run collection of Runnable task through invokeAll(..) method of ExecutorService. But that's not supported as of now (supports collection of Callable task only)

Any specific reason for this? What's the alternative to do something similar.

Answer 1

Runnable task = new Runnable() { 
     public void run() {

     }
};

Callable<Object> c = Executors.callable(task);

Just found that, Executors provides utility method to convert Runnable task into a Callable task. That explains why we don't have overloaded invokeAll which takes Runnable task as well.

Answer 2

Simply transform the runnables into callables:

List<Callable<Void>> callables = new ArrayList<>();
for (Runnable r : runnables) {
    callables.add(toCallable(r));
}
executor.invokeAll(callables);

private Callable<Void> toCallable(final Runnable runnable) {
    return new Callable<Void>() {
        @Override
        public Void call() {
            runnable.run();
            return null;
        }
    };
}