How to cancel Java 8 completable future?

Question

I am playing with Java 8 completable futures. I have the following code:

CountDownLatch waitLatch = new CountDownLatch(1);

CompletableFuture future         


        

Answer 1

Apparently, it's intentional. The Javadoc for the method CompletableFuture::cancel states:

[Parameters:] mayInterruptIfRunning - this value has no effect in this implementation because interrupts are not used to control processing.

Interestingly, the method ForkJoinTask::cancel uses almost the same wording for the parameter mayInterruptIfRunning.

I have a guess on this issue:

• interruption is intended to be used with blocking operations, like sleep, wait or I/O operations,
• but neither CompletableFuture nor ForkJoinTask are intended to be used with blocking operations.

Instead of blocking, a CompletableFuture should create a new CompletionStage, and cpu-bound tasks are a prerequisite for the fork-join model. So, using interruption with either of them would defeat their purpose. And on the other hand, it might increase complexity, that's not required if used as intended.