feature: synchronization primitive library

[George-Miao]

Overview

A tool library that provides optionally synchronous primitives.

Referenece:

• https://github.com/compio-rs/compio/blob/master/compio-driver/src/fd/mod.rs
• https://github.com/compio-rs/compio/blob/master/compio-io/src/util/bilock.rs
• https://github.com/compio-rs/see
• https://docs.rs/async-notify/latest/async_notify/

What should be included (sync/unsync):

• Arc/Rc
• Mutex/RefCell
• Atomic/Cell
• Notify
• Maybe channels

Design questions

How to expose sync/unsync version?

Should:

1. sync and unsync both be exposed and let user to decide which to use, or
2. provide a feature gate to expose either sync/unsync and let user control the feature gate, or
3. do both, with sync/unsync be unconditionally exported in sub modules, and optional feature gates (like sync/unsync) so that a "default" implementation is exported

Should sync versions be swappable?

For example, let user to chose between future's async mutex and tokio's mutex?

[Berrysoft]

For the sync question: I would prefer exposing both versions, just like the crate once_cell.

For the swappable question: I think just futures is OK for now.

[George-Miao]

I have created the repo/crate: https://github.com/compio-rs/synchrony.

[AsakuraMizu]

I think we can keep this issue open until this crate is integrated into compio.

[George-Miao]

Sure