/* ------------- Control and status methods -------------- */
/**
* If not already completed, completes this CompletableFuture with
* a {@link CancellationException}. Dependent CompletableFutures
* that have not already completed will also complete
* exceptionally, with a {@link CompletionException} caused by
* this {@code CancellationException}.
*
* @param mayInterruptIfRunning this value has no effect in this
* implementation because interrupts are not used to control
* processing.
*
* @return {@code true} if this task is now cancelled
*/
public boolean cancel(boolean mayInterruptIfRunning) {
boolean cancelled = (result == null) &&
internalComplete(new AltResult(new CancellationException()));
postComplete();
return cancelled || isCancelled();
}
mayInterruptIfRunning 参数实际并没有被用到，取消操作实际是软取消，并不会直接从线程池中进行取消操作，
实际测试发现 cancel 确实有问题，没有按照想象中快速取消超时任务，最终会导致线程池阻塞，不知道该怎么办
