Struct tokio::io::PollEvented [−][src]
Associates an I/O resource that implements the std::io::Read
and/or
std::io::Write
traits with the reactor that drives it.
PollEvented
uses Registration
internally to take a type that
implements mio::Evented
as well as std::io::Read
and or
std::io::Write
and associate it with a reactor that will drive it.
Once the mio::Evented
type is wrapped by PollEvented
, it can be
used from within the future’s execution model. As such, the
PollEvented
type provides AsyncRead
and AsyncWrite
implementations using the underlying I/O resource as well as readiness
events provided by the reactor.
Note: While PollEvented
is Sync
(if the underlying I/O type is
Sync
), the caller must ensure that there are at most two tasks that
use a PollEvented
instance concurrently. One for reading and one for
writing. While violating this requirement is “safe” from a Rust memory
model point of view, it will result in unexpected behavior in the form
of lost notifications and tasks hanging.
Readiness events
Besides just providing AsyncRead
and AsyncWrite
implementations,
this type also supports access to the underlying readiness event stream.
While similar in function to what Registration
provides, the
semantics are a bit different.
Two functions are provided to access the readiness events:
poll_read_ready
and poll_write_ready
. These functions return the
current readiness state of the PollEvented
instance. If
poll_read_ready
indicates read readiness, immediately calling
poll_read_ready
again will also indicate read readiness.
When the operation is attempted and is unable to succeed due to the I/O
resource not being ready, the caller must call clear_read_ready
or
clear_write_ready
. This clears the readiness state until a new
readiness event is received.
This allows the caller to implement additional functions. For example,
TcpListener
implements poll_accept by using poll_read_ready
and
clear_read_ready
.
use tokio::io::PollEvented; use futures::ready; use mio::Ready; use mio::net::{TcpStream, TcpListener}; use std::io; use std::task::{Context, Poll}; struct MyListener { poll_evented: PollEvented<TcpListener>, } impl MyListener { pub fn poll_accept(&mut self, cx: &mut Context<'_>) -> Poll<Result<TcpStream, io::Error>> { let ready = Ready::readable(); ready!(self.poll_evented.poll_read_ready(cx, ready))?; match self.poll_evented.get_ref().accept() { Ok((socket, _)) => Poll::Ready(Ok(socket)), Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => { self.poll_evented.clear_read_ready(cx, ready)?; Poll::Pending } Err(e) => Poll::Ready(Err(e)), } } }
Platform-specific events
PollEvented
also allows receiving platform-specific mio::Ready
events.
These events are included as part of the read readiness event stream. The
write readiness event stream is only for Ready::writable()
events.
Implementations
impl<E> PollEvented<E> where
E: Evented,
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E: Evented,
pub fn new(io: E) -> Result<Self>
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Creates a new PollEvented
associated with the default reactor.
Panics
This function panics if thread-local runtime is not set.
The runtime is usually set implicitly when this function is called
from a future driven by a tokio runtime, otherwise runtime can be set
explicitly with Handle::enter
function.
pub fn new_with_ready(io: E, ready: Ready) -> Result<Self>
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Creates a new PollEvented
associated with the default reactor, for specific mio::Ready
state. new_with_ready
should be used over new
when you need control over the readiness
state, such as when a file descriptor only allows reads. This does not add hup
or error
so if you are interested in those states, you will need to add them to the readiness state
passed to this function.
An example to listen to read only
#[cfg(unix)] mio::Ready::from_usize( mio::Ready::readable().as_usize() | mio::unix::UnixReady::error().as_usize() | mio::unix::UnixReady::hup().as_usize() );
Panics
This function panics if thread-local runtime is not set.
The runtime is usually set implicitly when this function is called
from a future driven by a tokio runtime, otherwise runtime can be set
explicitly with Handle::enter
function.
pub fn get_ref(&self) -> &Eⓘ
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Returns a shared reference to the underlying I/O object this readiness stream is wrapping.
pub fn get_mut(&mut self) -> &mut Eⓘ
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Returns a mutable reference to the underlying I/O object this readiness stream is wrapping.
pub fn into_inner(self) -> Result<E>
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Consumes self, returning the inner I/O object
This function will deregister the I/O resource from the reactor before returning. If the deregistration operation fails, an error is returned.
Note that deregistering does not guarantee that the I/O resource can be registered with a different reactor. Some I/O resource types can only be associated with a single reactor instance for their lifetime.
pub fn poll_read_ready(
&self,
cx: &mut Context<'_>,
mask: Ready
) -> Poll<Result<Ready>>
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&self,
cx: &mut Context<'_>,
mask: Ready
) -> Poll<Result<Ready>>
Checks the I/O resource’s read readiness state.
The mask argument allows specifying what readiness to notify on. This
can be any value, including platform specific readiness, except
writable
. HUP is always implicitly included on platforms that support
it.
If the resource is not ready for a read then Poll::Pending
is returned
and the current task is notified once a new event is received.
The I/O resource will remain in a read-ready state until readiness is
cleared by calling clear_read_ready
.
Panics
This function panics if:
ready
includes writable.- called from outside of a task context.
Warning
This method may not be called concurrently. It takes &self
to allow
calling it concurrently with poll_write_ready
.
pub fn clear_read_ready(&self, cx: &mut Context<'_>, ready: Ready) -> Result<()>
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Clears the I/O resource’s read readiness state and registers the current task to be notified once a read readiness event is received.
After calling this function, poll_read_ready
will return
Poll::Pending
until a new read readiness event has been received.
The mask
argument specifies the readiness bits to clear. This may not
include writable
or hup
.
Panics
This function panics if:
ready
includes writable or HUP- called from outside of a task context.
pub fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<Result<Ready>>
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Checks the I/O resource’s write readiness state.
This always checks for writable readiness and also checks for HUP readiness on platforms that support it.
If the resource is not ready for a write then Poll::Pending
is
returned and the current task is notified once a new event is received.
The I/O resource will remain in a write-ready state until readiness is
cleared by calling clear_write_ready
.
Panics
This function panics if:
ready
contains bits besideswritable
andhup
.- called from outside of a task context.
Warning
This method may not be called concurrently. It takes &self
to allow
calling it concurrently with poll_read_ready
.
pub fn clear_write_ready(&self, cx: &mut Context<'_>) -> Result<()>
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Resets the I/O resource’s write readiness state and registers the current task to be notified once a write readiness event is received.
This only clears writable readiness. HUP (on platforms that support HUP) cannot be cleared as it is a final state.
After calling this function, poll_write_ready(Ready::writable())
will
return NotReady
until a new write readiness event has been received.
Panics
This function will panic if called from outside of a task context.
Trait Implementations
impl<E> AsyncRead for PollEvented<E> where
E: Evented + Read + Unpin,
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E: Evented + Read + Unpin,
fn poll_read(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut [u8]
) -> Poll<Result<usize>>
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self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut [u8]
) -> Poll<Result<usize>>
unsafe fn prepare_uninitialized_buffer(
&self,
buf: &mut [MaybeUninit<u8>]
) -> bool
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&self,
buf: &mut [MaybeUninit<u8>]
) -> bool
fn poll_read_buf<B: BufMut>(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut B
) -> Poll<Result<usize>> where
Self: Sized,
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self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut B
) -> Poll<Result<usize>> where
Self: Sized,
impl<E> AsyncWrite for PollEvented<E> where
E: Evented + Write + Unpin,
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E: Evented + Write + Unpin,
fn poll_write(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8]
) -> Poll<Result<usize>>
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self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &[u8]
) -> Poll<Result<usize>>
fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<()>>
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fn poll_shutdown(
self: Pin<&mut Self>,
_cx: &mut Context<'_>
) -> Poll<Result<()>>
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self: Pin<&mut Self>,
_cx: &mut Context<'_>
) -> Poll<Result<()>>
fn poll_write_buf<B: Buf>(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut B
) -> Poll<Result<usize, Error>> where
Self: Sized,
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self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut B
) -> Poll<Result<usize, Error>> where
Self: Sized,
impl<E: Evented + Debug> Debug for PollEvented<E>
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impl<E: Evented> Drop for PollEvented<E>
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Auto Trait Implementations
impl<E> !RefUnwindSafe for PollEvented<E>
impl<E> Send for PollEvented<E> where
E: Send,
E: Send,
impl<E> Sync for PollEvented<E> where
E: Sync,
E: Sync,
impl<E> Unpin for PollEvented<E> where
E: Unpin,
E: Unpin,
impl<E> !UnwindSafe for PollEvented<E>
Blanket Implementations
impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,
impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
pub fn borrow_mut(&mut self) -> &mut Tⓘ
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impl<T> From<T> for T
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,