CODEWITHSUNDEEP
javamultithreadingexecutorservice
th0masb
th0masb

Reputation: 309

Why are Java Errors swallowed on threads spawned by an ExecutorService instance?

I thought Java Errors were indications of serious problems and shouldn't be handled. Why then, does this code run fine?

public static void main(String[] args)
{
    ExecutorService executor = Executors.newSingleThreadExecutor();
    Future<?> future = executor.submit(() -> {throw new AssertionError();});
    while (!future.isDone()) {
    }
    System.out.println("done");
}

I had an unimplemented method which threw an AssertionError to remind me to implement it but it just got swallowed up with absolutely no indication that something was seriously wrong.

Upvotes: 2

Views: 803

Answers (1)

user10527814
user10527814

Reputation:

It's not swallowed, it's there:

public static void main(String[] args) {
        ExecutorService executor = Executors.newSingleThreadExecutor();
        Future<?> future = executor.submit(() -> {
            throw new AssertionError();
        });
        while (!future.isDone()) {
        }
        try {
            future.get();
        } catch (InterruptedException | ExecutionException e) {
            e.printStackTrace();
        }
        System.out.println("done");
    }

You get the error on calling get method that gives you the result of computation if succeeded or an error otherwise.

java.util.concurrent.ExecutionException: java.lang.AssertionError at java.util.concurrent.FutureTask.report(FutureTask.java:122) at java.util.concurrent.FutureTask.get(FutureTask.java:192) ...

Upvotes: 6

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