timer: `sleep` future should become !Unpin

[carllerche]

This would allow using an intrusive-list for the timer.

[Darksonn]

Be aware that it is very commonly used in manual Future and Stream impls since it's the easiest way to hook into Tokio's timer.

[carllerche]

You think that adding Pin<Box<_>> in the docs w/ an example of a manual impl is enough?

[Darksonn]

If we keep it as a named type rather than an async fn, it's probably ok, although then their type becomes !Unpin too unless they box it.

[carllerche]

Is there a reason for it to stay a named type of boxing it is an acceptable strategy? We can document the pattern.

[Darksonn]

If it stays named, boxing is not forced since they can use pin-project.

[zaharidichev]

I am interested in picking that up if it is fine. If so, a bit of guidance will be highly appreciated.

[sfackler]

It should just require the addition of a PhantomPinned field in the Sleep type: https://docs.rs/tokio/0.3.1/src/tokio/time/sleep.rs.html#62-67

[zaharidichev]

I figured that much. My question was more around the transition to using intrusive list for the timer.

[carllerche]

This would be a breaking change and we haven't forked off for 1.0 yet. I also believe @bdonlan is exploring a bigger timer change right now.

[zaharidichev]

I see, that makes sense