Created SettableListenableFuture with tests

[matsev]

A SettableListenableFuture implementation of Spring's ListenableFuture
The class is inspired by Google Guava’s
com.google.common.util.concurrent.SettableFuture, but this
implementation uses ReentrantReadWriteLock and CountDownLatch
internally to handle thread synchronization.

Issue: SPR-11614

[rstoyanchev]

I have a use case for this. However, I am wondering if the implementation couldn't be simpler.

Rather than re-implementing Future, couldn't we use ListeableTaskFuture with a "settable" Callable? Here is a commit that shows what I mean.

The only tests that don't pass are due to CancellationException getting delivered to the callbacks. I am actually not sure what the right behavior is. I could argue that a CancellationException delivered to as an onFailure callback is useful. Either way it is an orthogonal question.

[matsev]

Looks good, and I agree that it is a simpler solution than mine.

When wrote the tests that you refer to, I did not consider that the actual call to cancel() method would trigger a CancellationException and you have a point, perhaps it should?

The reason why I wrote those tests was I wanted to verify that ListenableFutureCallback's onSuccess() and onFailure() methods were not triggered after the SettableListenableFuture.cancel() was called. Consequently, if it decided that cancel() should trigger a CancellationException, then those two tests should be rewritten so that any subsequent call to set() does not trigger the onSuccess() callback, and any subsequent call to setException() does not trigger any more calls to onFailure().

[sdeleuze]

I agree that CancellationException delivered to an onFailure callback is useful, and it is also consistent with Java 8 CompletableFuture behavior. @rstoyanchev I have updated the 2 related tests in my fork.

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[matsev]

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[rstoyanchev]

This has been merged into master. Thanks!

I did re-write the cancellation tests to expect CancellationException in onFailure as discussed.