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//! Readiness tracking streams, backing I/O objects. //! //! This module contains the core type which is used to back all I/O on object //! in `tokio-core`. The `PollEvented` type is the implementation detail of //! all I/O. Each `PollEvented` manages registration with a reactor, //! acquisition of a token, and tracking of the readiness state on the //! underlying I/O primitive. use std::fmt; use std::io::{self, Read, Write}; use std::sync::atomic::{AtomicUsize, Ordering}; use futures::{Async, Poll}; use mio::event::Evented; use mio::Ready; use tokio_io::{AsyncRead, AsyncWrite}; use reactor::{Handle, Remote}; use reactor::io_token::IoToken; /// 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]. /// /// [online]: https://tokio.rs/docs/going-deeper-tokio/core-low-level/#custom-io /// /// ## 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`. pub struct PollEvented<E> { token: IoToken, handle: Remote, readiness: AtomicUsize, io: E, } impl<E: Evented + fmt::Debug> fmt::Debug for PollEvented<E> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { f.debug_struct("PollEvented") .field("io", &self.io) .finish() } } impl<E: Evented> 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 new(io: E, handle: &Handle) -> io::Result<PollEvented<E>> { Ok(PollEvented { token: try!(IoToken::new(&io, handle)), handle: handle.remote().clone(), readiness: AtomicUsize::new(0), io: io, }) } /// 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. pub fn deregister(self, handle: &Handle) -> io::Result<()> { let inner = match handle.inner.upgrade() { Some(inner) => inner, None => return Ok(()), }; let ret = inner.borrow_mut().deregister_source(&self.io); return ret } } impl<E> PollEvented<E> { /// 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_read(&self) -> Async<()> { self.poll_ready(super::read_ready()) .map(|_| ()) } /// 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_write(&self) -> Async<()> { self.poll_ready(Ready::writable()) .map(|_| ()) } /// 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 poll_ready(&self, mask: Ready) -> Async<Ready> { let bits = super::ready2usize(mask); match self.readiness.load(Ordering::SeqCst) & bits { 0 => {} n => return Async::Ready(super::usize2ready(n)), } self.readiness.fetch_or(self.token.take_readiness(), Ordering::SeqCst); match self.readiness.load(Ordering::SeqCst) & bits { 0 => { if mask.is_writable() { self.need_write(); } else { self.need_read(); } Async::NotReady } n => Async::Ready(super::usize2ready(n)), } } /// 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_read(&self) { let bits = super::ready2usize(super::read_ready()); self.readiness.fetch_and(!bits, Ordering::SeqCst); self.token.schedule_read(&self.handle) } /// 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 need_write(&self) { let bits = super::ready2usize(Ready::writable()); self.readiness.fetch_and(!bits, Ordering::SeqCst); self.token.schedule_write(&self.handle) } /// Returns a reference to the event loop handle that this readiness stream /// is associated with. pub fn remote(&self) -> &Remote { &self.handle } /// Returns a shared reference to the underlying I/O object this readiness /// stream is wrapping. pub fn get_ref(&self) -> &E { &self.io } /// Returns a mutable reference to the underlying I/O object this readiness /// stream is wrapping. pub fn get_mut(&mut self) -> &mut E { &mut self.io } } impl<E: Read> Read for PollEvented<E> { fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { if let Async::NotReady = self.poll_read() { return Err(io::ErrorKind::WouldBlock.into()) } let r = self.get_mut().read(buf); if is_wouldblock(&r) { self.need_read(); } return r } } impl<E: Write> Write for PollEvented<E> { fn write(&mut self, buf: &[u8]) -> io::Result<usize> { if let Async::NotReady = self.poll_write() { return Err(io::ErrorKind::WouldBlock.into()) } let r = self.get_mut().write(buf); if is_wouldblock(&r) { self.need_write(); } return r } fn flush(&mut self) -> io::Result<()> { if let Async::NotReady = self.poll_write() { return Err(io::ErrorKind::WouldBlock.into()) } let r = self.get_mut().flush(); if is_wouldblock(&r) { self.need_write(); } return r } } impl<E: Read> AsyncRead for PollEvented<E> { } impl<E: Write> AsyncWrite for PollEvented<E> { fn shutdown(&mut self) -> Poll<(), io::Error> { Ok(().into()) } } #[allow(deprecated)] impl<E: Read + Write> ::io::Io for PollEvented<E> { fn poll_read(&mut self) -> Async<()> { <PollEvented<E>>::poll_read(self) } fn poll_write(&mut self) -> Async<()> { <PollEvented<E>>::poll_write(self) } } impl<'a, E> Read for &'a PollEvented<E> where &'a E: Read, { fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { if let Async::NotReady = self.poll_read() { return Err(io::ErrorKind::WouldBlock.into()) } let r = self.get_ref().read(buf); if is_wouldblock(&r) { self.need_read(); } return r } } impl<'a, E> Write for &'a PollEvented<E> where &'a E: Write, { fn write(&mut self, buf: &[u8]) -> io::Result<usize> { if let Async::NotReady = self.poll_write() { return Err(io::ErrorKind::WouldBlock.into()) } let r = self.get_ref().write(buf); if is_wouldblock(&r) { self.need_write(); } return r } fn flush(&mut self) -> io::Result<()> { if let Async::NotReady = self.poll_write() { return Err(io::ErrorKind::WouldBlock.into()) } let r = self.get_ref().flush(); if is_wouldblock(&r) { self.need_write(); } return r } } impl<'a, E> AsyncRead for &'a PollEvented<E> where &'a E: Read, { } impl<'a, E> AsyncWrite for &'a PollEvented<E> where &'a E: Write, { fn shutdown(&mut self) -> Poll<(), io::Error> { Ok(().into()) } } #[allow(deprecated)] impl<'a, E> ::io::Io for &'a PollEvented<E> where &'a E: Read + Write, { fn poll_read(&mut self) -> Async<()> { <PollEvented<E>>::poll_read(self) } fn poll_write(&mut self) -> Async<()> { <PollEvented<E>>::poll_write(self) } } fn is_wouldblock<T>(r: &io::Result<T>) -> bool { match *r { Ok(_) => false, Err(ref e) => e.kind() == io::ErrorKind::WouldBlock, } } impl<E> Drop for PollEvented<E> { fn drop(&mut self) { self.token.drop_source(&self.handle); } }