How to debug a Callable in Java ExecutorService that returns Futures

Question

I have an ExecutorService that I use to multithread the processing of the some text, and the unit of work to be applied to a given chunk of text is defined as my ParserCallable which returns a Payload.

So I have a

List<Future<PayLoad>> list;

which is populated by handing off chunks of work to each ParserCallable.

I want to debug ParserCallable in this multithreaded environment, and I don't have any concern for which one, but I'm not sure how I can step into the execution of any ParserCallable's from my code.

Which looks something like

List<Future<PayLoad>> list = new ArrayList<Future<PayLoad>>();
ExecutorService executor = Executors.newFixedThreadPool(25);
for (int i = 0; i < blocks_of_work.size(); i++) {
   Callable<PayLoad> worker = new ParserCallable(blocks_of_work.get(i));
   Future<PayLoad> submit = executor.submit(worker);
   list.add(submit);
}

How I can debug any given ParserCallable in order to troubleshoot some errors I'm getting? Based on my code I'm not sure how to step into one of these callables.

Answer 1

You need to put a break point in the callable itself.

From a computer science theoretic standpoint, it's possible to enable smooth debugging (after all why does your language care whether the operation was sync or async?) but I don't believe this is supported in any mainstream language, like Java, yet.