Rewrite Barrier using WakerSet

[yoshuawuyts]

The broadcaster library has taken us very far, but unfortunately has dependencies on futures_channel. Now that we have WakerSet available internally (for now still, see #549) we should probably consider rewriting Barrier to use it.

It should both improve our compilation times, and performance. This would put us in a place where we could consider stabilizing the API. Thanks!

cc/ @tmccombs @stjepang

Refs

• Implement async_std::sync::Condvar #369
• Consider making waker_set its own crate #549
• Simplify RwLock using WakerSet #440
• [tracking] sync #217

[tmccombs]

I can take a stab at this.

[leo60228]

You could implement futures_sink::Sink for async_std::sync::Sender to get rid of the futures_channel dependency. That would require committing to the Sink API in async-std, though.

[yoshuawuyts]

@leo60228 we have no plans to include Sink in async-std currently. I believe #581 would close this issue, and is currently pending a review by @stjepang.