channel::tick() behavior questions

[theof]

Hello !
When using channel::tick::recv() I expected it to compute its time to sleep with some kind of Instant saved at the time of the Channel instantiation.
Instead the Instant used is the one taken from the last message received, which has two effects :

• it guarantees that the specified duration at least elapses between two messages received
• it leads to a small shift from the initial Channel instantiation Instant, mostly due to the job scheduler not waking up the thread necessarily on time

If this was intended originally, then some documentation about the second effect is necessary.
If this is a bug, I would be happy to send a PR. However we must keep in mind that some users might rely on the first effect above.

Also, I think the channel::tick::recv should not have to loop around a thread::sleep as the latter already guarantees to sleep at least the provided duration, which leaves room for simplifying this file a lot.

[drrlvn]

Until I read this issue I had the same expectation of tick() as you did but after reading the code I think you're right.

IMO The time it takes to handle a message should not cause the time the next one is delivered to be shifted.

[theof]

Maybe we should bring that discussion to https://github.com/crossbeam-rs/rfcs ?

[ghost]

The next message delivery time is always max(last_delivery, now) + duration.

You're right that there is some unnecessary drift due to the way recv() is implemented. I submitted a fix in #456.