Future cancellation documentation

• After cancel(...)
  
  , isDone()
  
  there should always be true
  
  . It doesn't matter what you returned cancel(...)
  
  .
• If it cancel(...)
  
  returns true
  
  , it means that this future is canceled andisCancelled()==true
  
  
• If it cancel(...)
  
  returns false
  
  , it means that completion was not caused by this callcancel()
  
  
• cancel(false)
  
  means that the method cancel
  
  should not try to cancel a task that is trying to complete the future (meaning "task" depending on the implementation Future
  
  ), the task will continue to run, but the future is canceled (isDone () == true).
• cancel(true)
  
  means there should be an attempt to cancel the running task, whether the attempt is successful or not, the future will be canceled (isDone () == true).

Remember, this is a contract, it must be implemented by the implementation Future

.

Edit: isDone()

always true aftercancel()

Here's an experiment with some of the scenarios:

@Test
public void test() throws ExecutionException, InterruptedException {
    ExecutorService threadExecutor = Executors.newFixedThreadPool(1);
    CompletableFuture c1 = new CompletableFuture();
    CompletableFuture c2 = new CompletableFuture();
    Future<String> future = threadExecutor.submit(() -> {
        try {
            c1.complete(null);
            Thread.sleep(10000);
            c2.complete("normal");
        } catch (InterruptedException e) {
            c2.complete("interrupted");
        }
        return "aaa";
    });
    c1.join(); // waits for the task start
    // future.get(); // awaits the completion
    System.out.println("cancel:     " + future.cancel(true));
    //System.out.println("cancel:     " + future.cancel(false));
    System.out.println("isDone:     " + future.isDone());
    System.out.println("isCanceled: " + future.isCancelled());
    System.out.println("task:       " + c2.join());
}