Struct PollEvented

pub struct PollEvented<E> { /* private fields */ }

A concrete implementation of a stream of readiness notifications for I/O objects that originates from an event loop.

Created by the PollEvented::new method, each PollEvented is associated with a specific event loop and source of events that will be registered with an event loop.

An instance of PollEvented is essentially the bridge between the mio world and the tokio-core world, providing abstractions to receive notifications about changes to an object’s mio::Ready state.

Each readiness stream has a number of methods to test whether the underlying object is readable or writable. Once the methods return that an object is readable/writable, then it will continue to do so until the need_read or need_write methods are called.

That is, this object is typically wrapped in another form of I/O object. It’s the responsibility of the wrapper to inform the readiness stream when a “would block” I/O event is seen. The readiness stream will then take care of any scheduling necessary to get notified when the event is ready again.

You can find more information about creating a custom I/O object online.

Readiness to read/write

A PollEvented allows listening and waiting for an arbitrary mio::Ready instance, including the platform-specific contents of mio::Ready. At most two future tasks, however, can be waiting on a PollEvented. The need_read and need_write methods can block two separate tasks, one on reading and one on writing. Not all I/O events correspond to read/write, however!

To account for this a PollEvented gets a little interesting when working with an arbitrary instance of mio::Ready that may not map precisely to “write” and “read” tasks. Currently it is defined that instances of mio::Ready that do not return true from is_writable are all notified through need_read, or the read task.

In other words, poll_ready with the mio::UnixReady::hup event will block the read task of this PollEvented if the hup event isn’t available. Essentially a good rule of thumb is that if you’re using the poll_ready method you want to also use need_read to signal blocking and you should otherwise probably avoid using two tasks on the same PollEvented.

Implementations

impl<E: Evented> PollEvented<E>

pub fn new(io: E, handle: &Handle) -> Result<PollEvented<E>>

Creates a new readiness stream associated with the provided loop_handle and for the given source.

This method returns a future which will resolve to the readiness stream when it’s ready.

pub fn deregister(self, _: &Handle) -> Result<()>

Deregisters this source of events from the reactor core specified.

This method can optionally be called to unregister the underlying I/O object with the event loop that the handle provided points to. Typically this method is not required as this automatically happens when E is dropped, but for some use cases the E object doesn’t represent an owned reference, so dropping it won’t automatically unregister with the event loop.

This consumes self as it will no longer provide events after the method is called, and will likely return an error if this PollEvented was created on a separate event loop from the handle specified.

impl<E> PollEvented<E>

pub fn poll_read(&self) -> Async<()>

Tests to see if this source is ready to be read from or not.

If this stream is not ready for a read then NotReady will be returned and the current task will be scheduled to receive a notification when the stream is readable again. In other words, this method is only safe to call from within the context of a future’s task, typically done in a Future::poll method.

This is mostly equivalent to self.poll_ready(Ready::readable()).

Panics

This function will panic if called outside the context of a future’s task.

pub fn poll_write(&self) -> Async<()>

Tests to see if this source is ready to be written to or not.

If this stream is not ready for a write then NotReady will be returned and the current task will be scheduled to receive a notification when the stream is writable again. In other words, this method is only safe to call from within the context of a future’s task, typically done in a Future::poll method.

This is mostly equivalent to self.poll_ready(Ready::writable()).

Panics

This function will panic if called outside the context of a future’s task.

pub fn poll_ready(&self, mask: Ready) -> Async<Ready>

Test to see whether this source fulfills any condition listed in mask provided.

The mask given here is a mio Ready set of possible events. This can contain any events like read/write but also platform-specific events such as hup and error. The mask indicates events that are interested in being ready.

If any event in mask is ready then it is returned through Async::Ready. The Ready set returned is guaranteed to not be empty and contains all events that are currently ready in the mask provided.

If no events are ready in the mask provided then the current task is scheduled to receive a notification when any of them become ready. If the writable event is contained within mask then this PollEvented’s write task will be blocked and otherwise the read task will be blocked. This is generally only relevant if you’re working with this PollEvented object on multiple tasks.

Panics

This function will panic if called outside the context of a future’s task.

pub fn need_read(&self)

Indicates to this source of events that the corresponding I/O object is no longer readable, but it needs to be.

This function, like poll_read, is only safe to call from the context of a future’s task (typically in a Future::poll implementation). It informs this readiness stream that the underlying object is no longer readable, typically because a “would block” error was seen.

All readiness bits associated with this stream except the writable bit will be reset when this method is called. The current task is then scheduled to receive a notification whenever anything changes other than the writable bit. Note that this typically just means the readable bit is used here, but if you’re using a custom I/O object for events like hup/error this may also be relevant.

Note that it is also only valid to call this method if poll_read previously indicated that the object is readable. That is, this function must always be paired with calls to poll_read previously.

Panics

This function will panic if called outside the context of a future’s task.

pub fn need_write(&self)

Indicates to this source of events that the corresponding I/O object is no longer writable, but it needs to be.

This function, like poll_write, is only safe to call from the context of a future’s task (typically in a Future::poll implementation). It informs this readiness stream that the underlying object is no longer writable, typically because a “would block” error was seen.

The flag indicating that this stream is writable is unset and the current task is scheduled to receive a notification when the stream is then again writable.

Note that it is also only valid to call this method if poll_write previously indicated that the object is writable. That is, this function must always be paired with calls to poll_write previously.

Panics

This function will panic if called outside the context of a future’s task.

pub fn remote(&self) -> &Remote

Returns a reference to the event loop handle that this readiness stream is associated with.

pub fn get_ref(&self) -> &E

Returns a shared reference to the underlying I/O object this readiness stream is wrapping.

pub fn get_mut(&mut self) -> &mut E

Returns a mutable reference to the underlying I/O object this readiness stream is wrapping.

Trait Implementations

impl<'a, E> AsyncRead for &'a PollEvented<E>

where &'a E: Read,

unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool

Prepares an uninitialized buffer to be safe to pass to read. Returns true if the supplied buffer was zeroed out.

fn poll_read(&mut self, buf: &mut [u8]) -> Result<Async<usize>, Error>

Attempt to read from the AsyncRead into buf.

fn read_buf<B>(&mut self, buf: &mut B) -> Result<Async<usize>, Error>

where B: BufMut, Self: Sized,

Pull some bytes from this source into the specified BufMut, returning how many bytes were read.

fn framed<T>(self, codec: T) -> Framed<Self, T>

where T: Encoder + Decoder, Self: Sized + AsyncWrite,

👎Deprecated since 0.1.7: Use tokio_codec::Decoder::framed instead

Provides a Stream and Sink interface for reading and writing to this I/O object, using Decode and Encode to read and write the raw data.

fn split(self) -> (ReadHalf<Self>, WriteHalf<Self>)

where Self: Sized + AsyncWrite,

Helper method for splitting this read/write object into two halves.

impl<E: Read> AsyncRead for PollEvented<E>

unsafe fn prepare_uninitialized_buffer(&self, buf: &mut [u8]) -> bool

Prepares an uninitialized buffer to be safe to pass to read. Returns true if the supplied buffer was zeroed out.

fn poll_read(&mut self, buf: &mut [u8]) -> Result<Async<usize>, Error>

Attempt to read from the AsyncRead into buf.

fn read_buf<B>(&mut self, buf: &mut B) -> Result<Async<usize>, Error>

where B: BufMut, Self: Sized,

Pull some bytes from this source into the specified BufMut, returning how many bytes were read.

fn framed<T>(self, codec: T) -> Framed<Self, T>

where T: Encoder + Decoder, Self: Sized + AsyncWrite,

👎Deprecated since 0.1.7: Use tokio_codec::Decoder::framed instead

Provides a Stream and Sink interface for reading and writing to this I/O object, using Decode and Encode to read and write the raw data.

fn split(self) -> (ReadHalf<Self>, WriteHalf<Self>)

where Self: Sized + AsyncWrite,

Helper method for splitting this read/write object into two halves.

impl<'a, E> AsyncWrite for &'a PollEvented<E>

where &'a E: Write,

fn shutdown(&mut self) -> Poll<(), Error>

Initiates or attempts to shut down this writer, returning success when the I/O connection has completely shut down.

fn poll_write(&mut self, buf: &[u8]) -> Result<Async<usize>, Error>

Attempt to write bytes from buf into the object.

fn poll_flush(&mut self) -> Result<Async<()>, Error>

Attempt to flush the object, ensuring that any buffered data reach their destination.

fn write_buf<B>(&mut self, buf: &mut B) -> Result<Async<usize>, Error>

where B: Buf, Self: Sized,

Write a Buf into this value, returning how many bytes were written.

impl<E: Write> AsyncWrite for PollEvented<E>

fn shutdown(&mut self) -> Poll<(), Error>

Initiates or attempts to shut down this writer, returning success when the I/O connection has completely shut down.

fn poll_write(&mut self, buf: &[u8]) -> Result<Async<usize>, Error>

Attempt to write bytes from buf into the object.

fn poll_flush(&mut self) -> Result<Async<()>, Error>

Attempt to flush the object, ensuring that any buffered data reach their destination.

fn write_buf<B>(&mut self, buf: &mut B) -> Result<Async<usize>, Error>

where B: Buf, Self: Sized,

Write a Buf into this value, returning how many bytes were written.

impl<E: Evented + Debug> Debug for PollEvented<E>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'a, E> Read for &'a PollEvented<E>

where &'a E: Read,

fn read(&mut self, buf: &mut [u8]) -> Result<usize>

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize, Error>

Like read, except that it reads into a slice of buffers.

fn is_read_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Reader has an efficient read_vectored implementation.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>

Reads all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

Reads all bytes until EOF in this source, appending them to buf.

fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>

Reads the exact number of bytes required to fill buf.

fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> Result<(), Error>

🔬This is a nightly-only experimental API. (read_buf)

Pull some bytes from this source into the specified buffer.

fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<(), Error>

🔬This is a nightly-only experimental API. (read_buf)

Reads the exact number of bytes required to fill cursor.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self>

where Self: Sized,

Transforms this Read instance to an Iterator over its bytes.

fn chain<R>(self, next: R) -> Chain<Self, R>

where R: Read, Self: Sized,

Creates an adapter which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self>

where Self: Sized,

Creates an adapter which will read at most limit bytes from it.

impl<E: Read> Read for PollEvented<E>

fn read(&mut self, buf: &mut [u8]) -> Result<usize>

Pull some bytes from this source into the specified buffer, returning how many bytes were read.

fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> Result<usize, Error>

Like read, except that it reads into a slice of buffers.

fn is_read_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Reader has an efficient read_vectored implementation.

fn read_to_end(&mut self, buf: &mut Vec<u8>) -> Result<usize, Error>

Reads all bytes until EOF in this source, placing them into buf.

fn read_to_string(&mut self, buf: &mut String) -> Result<usize, Error>

Reads all bytes until EOF in this source, appending them to buf.

fn read_exact(&mut self, buf: &mut [u8]) -> Result<(), Error>

Reads the exact number of bytes required to fill buf.

fn read_buf(&mut self, buf: BorrowedCursor<'_>) -> Result<(), Error>

🔬This is a nightly-only experimental API. (read_buf)

Pull some bytes from this source into the specified buffer.

fn read_buf_exact(&mut self, cursor: BorrowedCursor<'_>) -> Result<(), Error>

🔬This is a nightly-only experimental API. (read_buf)

Reads the exact number of bytes required to fill cursor.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adaptor for this instance of Read.

fn bytes(self) -> Bytes<Self>

where Self: Sized,

Transforms this Read instance to an Iterator over its bytes.

fn chain<R>(self, next: R) -> Chain<Self, R>

where R: Read, Self: Sized,

Creates an adapter which will chain this stream with another.

fn take(self, limit: u64) -> Take<Self>

where Self: Sized,

Creates an adapter which will read at most limit bytes from it.

impl<'a, E> Write for &'a PollEvented<E>

where &'a E: Write,

fn write(&mut self, buf: &[u8]) -> Result<usize>

Writes a buffer into this writer, returning how many bytes were written.

fn flush(&mut self) -> Result<()>

Flushes this output stream, ensuring that all intermediately buffered contents reach their destination.

fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize, Error>

Like write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Writer has an efficient write_vectored implementation.

fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>

Attempts to write an entire buffer into this writer.

fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error>

🔬This is a nightly-only experimental API. (write_all_vectored)

Attempts to write multiple buffers into this writer.

fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<(), Error>

Writes a formatted string into this writer, returning any error encountered.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Write.

impl<E: Write> Write for PollEvented<E>

fn write(&mut self, buf: &[u8]) -> Result<usize>

Writes a buffer into this writer, returning how many bytes were written.

fn flush(&mut self) -> Result<()>

Flushes this output stream, ensuring that all intermediately buffered contents reach their destination.

fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize, Error>

Like write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Writer has an efficient write_vectored implementation.

fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>

Attempts to write an entire buffer into this writer.

fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error>

🔬This is a nightly-only experimental API. (write_all_vectored)

Attempts to write multiple buffers into this writer.

fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<(), Error>

Writes a formatted string into this writer, returning any error encountered.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Creates a “by reference” adapter for this instance of Write.