## Motivation
In Tokio 0.2, `AsyncRead` and `AsyncWrite` had `poll_write_buf` and
`poll_read_buf` methods for reading and writing to implementers of
`bytes` `Buf` and `BufMut` traits. In 0.3, these were removed, but
`poll_read_buf` was added as a free function in `tokio-util`. However,
there is currently no `poll_write_buf`.
Now that `AsyncWrite` has regained support for vectored writes in #3149,
there's a lot of potential benefit in having a `poll_write_buf` that
uses vectored writes when supported and non-vectored writes when not
supported, so that users don't have to reimplement this.
## Solution
This PR adds a `poll_write_buf` function to `tokio_util::io`, analogous
to the existing `poll_read_buf` function.
This function writes from a `Buf` to an `AsyncWrite`, advancing the
`Buf`'s internal cursor. In addition, when the `AsyncWrite` supports
vectored writes (i.e. its `is_write_vectored` method returns `true`),
it will use vectored IO.
I copied the documentation for this functions from the docs from Tokio
0.2's `AsyncWrite::poll_write_buf` , with some minor modifications as
appropriate.
Finally, I fixed a minor issue in the existing docs for `poll_read_buf`
and `read_buf`, and updated `tokio_util::codec` to use `poll_write_buf`.
Signed-off-by: Eliza Weisman <[email protected]>
This reverts commit fe2b997.
We are avoiding adding poll_read_buf to tokio itself for now. The patch is
reverted now in order to not block the v0.3.2 release (#3059).
* remove unnecessary wheel::Poll
the timer wheel uses the `wheel::Poll` struct as input when
advancing the timer to the next time step. the `Poll` struct
contains an instant representing the time step to advance to
and also contains an optional and mutable reference to an
`Expiration` struct. from what I can tell, the latter field
is only used in the context of polling the wheel and does not
need to be exposed outside of that method. without the
expiration field the `Poll` struct is nothing more than a
wrapper around the instant being polled. this change removes
the `Poll` struct and updates integration points accordingly.
* remove Stack trait in favor of concrete Stack implementation
* remove timer Registration struct
This change is intended to do the minimum to unblock 0.3; as such, for now, we
duplicate the internal `time::wheel` structures in tokio-util, rather than trying
to refactor things at this stage.
Co-authored-by: Bryan Donlan <[email protected]>
These functions have object safety issues. It also has been decided to
avoid vectored operations on the I/O traits. A later PR will bring back
vectored operations on specific types that support them.
Refs: #2879, #2716
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
* sync: move CancellationToken to tokio-util
The `CancellationToken` utility is only available with the
`tokio_unstable` flag. This was done as the API is not final, but it
adds friction for users.
This patch moves `CancellationToken` to tokio-util where it is generally
available. The tokio-util crate does not have any constraints on
breaking change releases.
* fix clippy
* clippy again
Adds a method to retrieve a mutable reference to the Framed stream's read buffer.
This makes it possible to e.g. externally clear the buffer to prevent the codec from
parsing stale data.
Alice Ryhl