Update futures to the version merged in std (async/await)

[Hoverbear]

Context:

Futures 0.2 has been released and it requires work to upgrade. We are using 0.1: https://github.com/pingcap/grpc-rs/blob/d119e6f7f7943bc3e6910a2c5f3cd9d6b1abca28/Cargo.toml#L20

It may be preferable to wait for Futures 0.3 according to this post.

Dependencies:

• No known

Dependents:

• Update to futures 0.2 tikv#2845

[bbigras]

It seems it's recommended to wait for 0.3 since it will also be a breaking change. Also it will be a pita if some crates upgrade to 2.0 and some do not.

Would you suggest that the ecosystem goes through two breaking changes (now and for 0.3) or should libraries like Tokio maintain support for both 0.1 and 0.2 and then have a single breaking change when 0.3 is released.

The latter. I consider 0.2 a "snapshot" that's good for experimentation but shouldn't be used heavily, since stable 0.3 should be coming in a couple of months or less.

https://www.reddit.com/r/rust/comments/8ac85w/futures_02_is_here/dwxm9on/

[Hoverbear]

@bbigras This is very interesting. Thank you for sharing this.

[xen0n]

Hi, what's the current plan on this? It's cumbersome to have an async fn core for your business logic while exposing them as gRPC service right now.

[BusyJay]

There is no one working on this for now. We may not have time to do it before the middle of next month. But we are open for contributions.

Anyone interested in this feel free to send your patch. Just remember to tell us your plan here first so that no one is doing the duplicated work.

[BusyJay]

This is duplicated with #237. Let's trace the problem there. By the way, PR #447 is trying to migrate grpc-rs to futures 0.3, any comment and review is appreciated.