If you discard a reference to a Future, will it still run?

Question

In my method, I have to call another method (AnotherMethod) that returns a future.

eg.

private static void myMethod() {
    Future<MyObj> mjObj = AnotherMethod();
    return;
}

I don't actually care about the value returned by AnotherMethod (eg. the value of myObj), but I do want AnotherMethod to run fully.

If I discard the reference to the future (as in the above example), will AnotherMethod still finish running?

I understand it won't finish before returning from myMethod, but will it still complete at some point even though there's no reference to myObj anymore?

There is no guarantee that a future will ever run. But if you create it, say, via an executor, then the executor still has a reference to it. — Andy Turner, Aug 09 '18 at 17:11
Really depends on what `AnotherMethod()` does, simply creating a Future does not run it (as in `new Future()` - that's just a boring Object). If that method on the other hand sends some task to an `Executor` then it's referenced by the task queue and eventually executed. — zapl, Aug 09 '18 at 17:11
Possible duplicate of [Java Concurrency: Is cancelling Futures necessary for them to be Garbage Collected?](https://stackoverflow.com/questions/20135304/java-concurrency-is-cancelling-futures-necessary-for-them-to-be-garbage-collect) — Randy L, Aug 09 '18 at 19:07

score 2 · Accepted Answer · answered Aug 09 '18 at 17:13

First of all, AnotherMethod always will be performed from the start to the end because you call it. As for concurrency, if AnotherMethod starts a Thread or submits task to an executor then this concurrent execution will not be interrupted. Garbage collector does not interrupt threads because they are GC roots - top level objects in JVM.

If you discard a reference to a Future, will it still run?

1 Answers1