Timers need to work in 1:1 mode

[alexcrichton]

Right now they're heavily based on channels in M:N mode, and this does not easily work at all in 1:1 mode. These abstractions either need to be completely redesigned in order to support being able to work in 1:1 and M:N mode, or they need to get a reasonable implementation in 1:1 mode.

The current best idea that I have for this is to have a global "worker thread" which is an "event loop" for timers and signals. Also remember that whatever design is settled on must have a solution for all platforms.

[alexcrichton]

repurposing this for just timers, signals will be deferred to a new issue.

[alexcrichton]

See #11203 for signals.

[thestinger]

How about adding blocking receive with a timeout to channels and using sleep(reltime) and sleep_until(abstime) in other cases? It would be unnecessary to use a select abstraction if channels had the functionality built-in, and it's a natural operation to perform on a condition variable.

[alexcrichton]

I agree that if channels had timeout functionality built in that much of this might not be necessary, but I personally do not know how to do this efficiently.

For now though, this should probably be discussed in a separate issue. I would still like to have an API with timers as channels, and if we can later upgrade the implementation to use receive with timeouts that's great, but we don't have the ability to do that right now.

[thestinger]

@alexcrichton: There's already a condition variable on native channels as far as I know, so the natural way to expose this functionality is a pthread_cond_timedwait call (or a call to the Vista and later win32 equivalent). The M:N form can do whatever it does now for channels internally, and can be made more efficient later.

Exposing the natural, high-level API makes a lot more sense to me than exposing the lowest common denominator between native and green tasks as they are implemented at the moment. It won't require much implementation work to expose something else, if you don't try to make it faster for green threads than the current timer API.