Java 1.6 - Return to the Main class from an executor service thread

Question

I'm executing three tasks from my Main class by creating 3 threads (extends Runnable) using the Executor Service and submitting them. Like below:

    ExecutorService executor = Executors
                        .newFixedThreadPool(3);

                A a= new A();
                B b= new B();
                C c= new C();

                /**
                 * Submit/Execute the jobs
                 */
                executor.execute(a);
                executor.execute(b);
                executor.execute(c);
                try {
                    latch.await();
                } catch (InterruptedException e) {
                    //handle - show info
                    executor.shutdownNow();
                }

When an exception occurs in the thread, I catch it and do System.exit(-1). But, I need to return to the main class if any exception occurs and execute some statements there. How to do this? Can we return something from these threads without FutureTask?

Answer 1

Instead of submitting the task via execute which does not give you any capability of catching exception outside the run methods, use submit which returns a Future<?> . You can then call get which may return an ExecutionException if something went wrong:

Future<?> fa = executor.submit(a);
try {
    fa.get();  // wait on the future
} catch(ExecutionException e) {
    System.out.println("Something went wrong: " + e.getCause());
    // do something specific
}

Answer 2

You can implement your own "FutureTask" class and give it as an argument to A's constructor:

MyFutureTask futureA = new MyFutureTask();
A a = new A(futureA);

Whenever an error happens in A you store the return value in your MyFutureTask and can then read it as your would with a normal FutureTask.