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Sean McArthur
a0557840eb
This refactors I/O registration in a few ways: - Cleans up the cached readiness in `PollEvented`. This cache used to be helpful when readiness was a linked list of `*mut Node`s in `Registration`. Previous refactors have turned `Registration` into just an `AtomicUsize` holding the current readiness, so the cache is just extra work and complexity. Gone. - Polling the `Registration` for readiness now gives a `ReadyEvent`, which includes the driver tick. This event must be passed back into `clear_readiness`, so that the readiness is only cleared from `Registration` if the tick hasn't changed. Previously, it was possible to clear the readiness even though another thread had *just* polled the driver and found the socket ready again. - Registration now also contains an `async fn readiness`, which stores wakers in an instrusive linked list. This allows an unbounded number of tasks to register for readiness (previously, only 1 per direction (read and write)). By using the intrusive linked list, there is no concern of leaking the storage of the wakers, since they are stored inside the `async fn` and released when the future is dropped. - Registration retains a `poll_readiness(Direction)` method, to support `AsyncRead` and `AsyncWrite`. They aren't able to use `async fn`s, and so there are 2 reserved slots for those methods. - IO types where it makes sense to have multiple tasks waiting on them now take advantage of this new `async fn readiness`, such as `UdpSocket` and `UnixDatagram`. Additionally, this makes the `io-driver` "feature" internal-only (no longer documented, not part of public API), and adds a second internal-only feature, `io-readiness`, to group together linked list part of registration that is only used by some of the IO types. After a bit of discussion, changing stream-based transports (like `TcpStream`) to have `async fn read(&self)` is punted, since that is likely too easy of a footgun to activate. Refs: #2779, #2728
tokio-util
Utilities for encoding and decoding frames.
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