Delay::reset(0) should cause the delay to poll as Ready immediately

[Lucretiel]

Currently, the following pesudocode:

let delay = Delay::new(Duration::from_secs(10));
thread::sleep(5);
delay.reset(Duration::from_secs(0));
assert_eq!(delay.poll_unpin(...), Poll::Ready(()));

Will spuriously fail on line 4, because resetting the Delay to 0 doesn't guarantee that it's immediately ready. While this makes sense if the 0-duration timer is unconditionally scheduled onto the thread, I found it a bit surprising; could a guarantee be established that this code passes?

[yoshuawuyts]

@Lucretiel Thanks for opening this issue. I think what you're proposing sounds reasonable!. If you'd be willing to write a patch and a test for it, I'd be happy to review + merge!

[Lucretiel]

Sure, I'll look into it! Can you assign this bug to me so it shows up on my dashboard?

[Lucretiel]

Unfortunately this ended up being nontrivial; I wasn't confident enough in how the bit flags were being manipulated to implement this. I'll leave the issue open but right now I'm not going to be the one to implement it.