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
* util: add futures-io/tokio::io compatibility layer
This PR adds a compatibility layer with conversions between the
`tokio::io` and `futures-io` versions of the `AsyncRead` and
`AsyncWrite` traits.
I initially opened this PR against `tokio-compat`, but we decided that
a compatibility layer for current versions of the `tokio` and
`futures-io` crates (rather than for compatibility with legacy code)
ought to go in `tokio-util` instead. See:
https://github.com/tokio-rs/tokio-compat/pull/2#issuecomment-551310953
This is based on code originally written by @Nemo157 as part of the
`futures-tokio-compat` crate, and is contributed on behalf of the
original author:
https://github.com/Nemo157/futures-tokio-compat/issues/2#issuecomment-544118866Closestokio-rs/tokio-compat#2
Co-authored-by: Wim Looman <[email protected]>
Signed-off-by: Eliza Weisman <[email protected]>
Changes the set of `default` feature flags to `[]`. By default, only
core traits are included without specifying feature flags. This makes it
easier for users to pick the components they need.
For convenience, a `full` feature flag is included that includes all
components.
Tests are configured to require the `full` feature. Testing individual
feature flags will need to be moved to a separate crate.
Closes#1791
Colin Walters