Question

I’m feeding threads into an ExecutorService.

These threads are manipulating some data, and if there’s a conflict, the data object throws an exception, which is caught by the conflicting thread, which in turn aborts and does not complete execution.

When this happens, the aborting thread needs to be put back in the queue and fed back into the executor.

How can I tell if an exception was thrown, from the parent thread?

Answer 1

When you submit() a task on the ExecutorService you get a Future as a result. When the execution has finished you can call get() on that future. This will return the result if applicable, or it will throw an ExecutionException if the original task threw one. If you want the real exception object you can do getCause().

Also note that you would be putting a Task back into the service, that task is ran on a Thread which has not really terminated (just caught the exception and is waiting for a new one).

Here is an example usage (you can use Runnable if you don’t care for the result).

Callable<String> myCallable = ...;
Future<String> future = myExector.submit(myCallable);

// Do something else until myCallable.isDone() returns true.
try {
    String result = future.get();
}catch(ExecutionException e){
    // Handle error, perhaps create new Callable to submit.
}