blob: e552b6ba10a356aadc491d0de9e2e6c3a75966c9 [file] [log] [blame]
use crate::{event, sys, Events, Interest, Token};
use log::trace;
#[cfg(unix)]
use std::os::unix::io::{AsRawFd, RawFd};
use std::time::Duration;
use std::{fmt, io};
/// Polls for readiness events on all registered values.
///
/// `Poll` allows a program to monitor a large number of [`event::Source`]s,
/// waiting until one or more become "ready" for some class of operations; e.g.
/// reading and writing. An event source is considered ready if it is possible
/// to immediately perform a corresponding operation; e.g. [`read`] or
/// [`write`].
///
/// To use `Poll`, an `event::Source` must first be registered with the `Poll`
/// instance using the [`register`] method on its associated `Register`,
/// supplying readiness interest. The readiness interest tells `Poll` which
/// specific operations on the handle to monitor for readiness. A `Token` is
/// also passed to the [`register`] function. When `Poll` returns a readiness
/// event, it will include this token. This associates the event with the
/// event source that generated the event.
///
/// [`event::Source`]: ./event/trait.Source.html
/// [`read`]: ./net/struct.TcpStream.html#method.read
/// [`write`]: ./net/struct.TcpStream.html#method.write
/// [`register`]: struct.Registry.html#method.register
///
/// # Examples
///
/// A basic example -- establishing a `TcpStream` connection.
///
#[cfg_attr(all(feature = "os-poll", feature = "net"), doc = "```")]
#[cfg_attr(not(all(feature = "os-poll", feature = "net")), doc = "```ignore")]
/// # use std::error::Error;
/// # fn main() -> Result<(), Box<dyn Error>> {
/// use mio::{Events, Poll, Interest, Token};
/// use mio::net::TcpStream;
///
/// use std::net::{self, SocketAddr};
///
/// // Bind a server socket to connect to.
/// let addr: SocketAddr = "127.0.0.1:0".parse()?;
/// let server = net::TcpListener::bind(addr)?;
///
/// // Construct a new `Poll` handle as well as the `Events` we'll store into
/// let mut poll = Poll::new()?;
/// let mut events = Events::with_capacity(1024);
///
/// // Connect the stream
/// let mut stream = TcpStream::connect(server.local_addr()?)?;
///
/// // Register the stream with `Poll`
/// poll.registry().register(&mut stream, Token(0), Interest::READABLE | Interest::WRITABLE)?;
///
/// // Wait for the socket to become ready. This has to happens in a loop to
/// // handle spurious wakeups.
/// loop {
/// poll.poll(&mut events, None)?;
///
/// for event in &events {
/// if event.token() == Token(0) && event.is_writable() {
/// // The socket connected (probably, it could still be a spurious
/// // wakeup)
/// return Ok(());
/// }
/// }
/// }
/// # }
/// ```
///
/// # Portability
///
/// Using `Poll` provides a portable interface across supported platforms as
/// long as the caller takes the following into consideration:
///
/// ### Spurious events
///
/// [`Poll::poll`] may return readiness events even if the associated
/// event source is not actually ready. Given the same code, this may
/// happen more on some platforms than others. It is important to never assume
/// that, just because a readiness event was received, that the associated
/// operation will succeed as well.
///
/// If operation fails with [`WouldBlock`], then the caller should not treat
/// this as an error, but instead should wait until another readiness event is
/// received.
///
/// ### Draining readiness
///
/// Once a readiness event is received, the corresponding operation must be
/// performed repeatedly until it returns [`WouldBlock`]. Unless this is done,
/// there is no guarantee that another readiness event will be delivered, even
/// if further data is received for the event source.
///
/// [`WouldBlock`]: std::io::ErrorKind::WouldBlock
///
/// ### Readiness operations
///
/// The only readiness operations that are guaranteed to be present on all
/// supported platforms are [`readable`] and [`writable`]. All other readiness
/// operations may have false negatives and as such should be considered
/// **hints**. This means that if a socket is registered with [`readable`]
/// interest and either an error or close is received, a readiness event will
/// be generated for the socket, but it **may** only include `readable`
/// readiness. Also note that, given the potential for spurious events,
/// receiving a readiness event with `read_closed`, `write_closed`, or `error`
/// doesn't actually mean that a `read` on the socket will return a result
/// matching the readiness event.
///
/// In other words, portable programs that explicitly check for [`read_closed`],
/// [`write_closed`], or [`error`] readiness should be doing so as an
/// **optimization** and always be able to handle an error or close situation
/// when performing the actual read operation.
///
/// [`readable`]: ./event/struct.Event.html#method.is_readable
/// [`writable`]: ./event/struct.Event.html#method.is_writable
/// [`error`]: ./event/struct.Event.html#method.is_error
/// [`read_closed`]: ./event/struct.Event.html#method.is_read_closed
/// [`write_closed`]: ./event/struct.Event.html#method.is_write_closed
///
/// ### Registering handles
///
/// Unless otherwise noted, it should be assumed that types implementing
/// [`event::Source`] will never become ready unless they are registered with
/// `Poll`.
///
/// For example:
///
#[cfg_attr(all(feature = "os-poll", feature = "net"), doc = "```")]
#[cfg_attr(not(all(feature = "os-poll", feature = "net")), doc = "```ignore")]
/// # use std::error::Error;
/// # use std::net;
/// # fn main() -> Result<(), Box<dyn Error>> {
/// use mio::{Poll, Interest, Token};
/// use mio::net::TcpStream;
/// use std::net::SocketAddr;
/// use std::time::Duration;
/// use std::thread;
///
/// let address: SocketAddr = "127.0.0.1:0".parse()?;
/// let listener = net::TcpListener::bind(address)?;
/// let mut sock = TcpStream::connect(listener.local_addr()?)?;
///
/// thread::sleep(Duration::from_secs(1));
///
/// let poll = Poll::new()?;
///
/// // The connect is not guaranteed to have started until it is registered at
/// // this point
/// poll.registry().register(&mut sock, Token(0), Interest::READABLE | Interest::WRITABLE)?;
/// # Ok(())
/// # }
/// ```
///
/// ### Dropping `Poll`
///
/// When the `Poll` instance is dropped it may cancel in-flight operations for
/// the registered [event sources], meaning that no further events for them may
/// be received. It also means operations on the registered event sources may no
/// longer work. It is up to the user to keep the `Poll` instance alive while
/// registered event sources are being used.
///
/// [event sources]: ./event/trait.Source.html
///
/// # Implementation notes
///
/// `Poll` is backed by the selector provided by the operating system.
///
/// | OS | Selector |
/// |---------------|-----------|
/// | Android | [epoll] |
/// | DragonFly BSD | [kqueue] |
/// | FreeBSD | [kqueue] |
/// | Linux | [epoll] |
/// | NetBSD | [kqueue] |
/// | OpenBSD | [kqueue] |
/// | Solaris | [epoll] |
/// | illumos | [epoll] |
/// | Windows | [IOCP] |
/// | iOS | [kqueue] |
/// | macOS | [kqueue] |
///
/// On all supported platforms, socket operations are handled by using the
/// system selector. Platform specific extensions (e.g. [`SourceFd`]) allow
/// accessing other features provided by individual system selectors. For
/// example, Linux's [`signalfd`] feature can be used by registering the FD with
/// `Poll` via [`SourceFd`].
///
/// On all platforms except windows, a call to [`Poll::poll`] is mostly just a
/// direct call to the system selector. However, [IOCP] uses a completion model
/// instead of a readiness model. In this case, `Poll` must adapt the completion
/// model Mio's API. While non-trivial, the bridge layer is still quite
/// efficient. The most expensive part being calls to `read` and `write` require
/// data to be copied into an intermediate buffer before it is passed to the
/// kernel.
///
/// [epoll]: http://man7.org/linux/man-pages/man7/epoll.7.html
/// [kqueue]: https://www.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2
/// [IOCP]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365198(v=vs.85).aspx
/// [`signalfd`]: http://man7.org/linux/man-pages/man2/signalfd.2.html
/// [`SourceFd`]: unix/struct.SourceFd.html
/// [`Poll::poll`]: struct.Poll.html#method.poll
pub struct Poll {
registry: Registry,
}
/// Registers I/O resources.
pub struct Registry {
selector: sys::Selector,
}
impl Poll {
/// Create a separate `Registry` which can be used to register
/// `event::Source`s.
pub fn registry(&self) -> &Registry {
&self.registry
}
/// Wait for readiness events
///
/// Blocks the current thread and waits for readiness events for any of the
/// [`event::Source`]s that have been registered with this `Poll` instance.
/// The function will block until either at least one readiness event has
/// been received or `timeout` has elapsed. A `timeout` of `None` means that
/// `poll` will block until a readiness event has been received.
///
/// The supplied `events` will be cleared and newly received readiness events
/// will be pushed onto the end. At most `events.capacity()` events will be
/// returned. If there are further pending readiness events, they will be
/// returned on the next call to `poll`.
///
/// A single call to `poll` may result in multiple readiness events being
/// returned for a single event source. For example, if a TCP socket becomes
/// both readable and writable, it may be possible for a single readiness
/// event to be returned with both [`readable`] and [`writable`] readiness
/// **OR** two separate events may be returned, one with [`readable`] set
/// and one with [`writable`] set.
///
/// Note that the `timeout` will be rounded up to the system clock
/// granularity (usually 1ms), and kernel scheduling delays mean that
/// the blocking interval may be overrun by a small amount.
///
/// See the [struct] level documentation for a higher level discussion of
/// polling.
///
/// [`event::Source`]: ./event/trait.Source.html
/// [`readable`]: struct.Interest.html#associatedconstant.READABLE
/// [`writable`]: struct.Interest.html#associatedconstant.WRITABLE
/// [struct]: struct.Poll.html
/// [`iter`]: ./event/struct.Events.html#method.iter
///
/// # Notes
///
/// This returns any errors without attempting to retry, previous versions
/// of Mio would automatically retry the poll call if it was interrupted
/// (if `EINTR` was returned).
///
/// # Examples
///
/// A basic example -- establishing a `TcpStream` connection.
///
#[cfg_attr(all(feature = "os-poll", feature = "net"), doc = "```")]
#[cfg_attr(not(all(feature = "os-poll", feature = "net")), doc = "```ignore")]
/// # use std::error::Error;
/// # fn main() -> Result<(), Box<dyn Error>> {
/// use mio::{Events, Poll, Interest, Token};
/// use mio::net::TcpStream;
///
/// use std::net::{TcpListener, SocketAddr};
/// use std::thread;
///
/// // Bind a server socket to connect to.
/// let addr: SocketAddr = "127.0.0.1:0".parse()?;
/// let server = TcpListener::bind(addr)?;
/// let addr = server.local_addr()?.clone();
///
/// // Spawn a thread to accept the socket
/// thread::spawn(move || {
/// let _ = server.accept();
/// });
///
/// // Construct a new `Poll` handle as well as the `Events` we'll store into
/// let mut poll = Poll::new()?;
/// let mut events = Events::with_capacity(1024);
///
/// // Connect the stream
/// let mut stream = TcpStream::connect(addr)?;
///
/// // Register the stream with `Poll`
/// poll.registry().register(
/// &mut stream,
/// Token(0),
/// Interest::READABLE | Interest::WRITABLE)?;
///
/// // Wait for the socket to become ready. This has to happens in a loop to
/// // handle spurious wakeups.
/// loop {
/// poll.poll(&mut events, None)?;
///
/// for event in &events {
/// if event.token() == Token(0) && event.is_writable() {
/// // The socket connected (probably, it could still be a spurious
/// // wakeup)
/// return Ok(());
/// }
/// }
/// }
/// # }
/// ```
///
/// [struct]: #
pub fn poll(&mut self, events: &mut Events, timeout: Option<Duration>) -> io::Result<()> {
self.registry.selector.select(events.sys(), timeout)
}
}
cfg_os_poll! {
impl Poll {
/// Return a new `Poll` handle.
///
/// This function will make a syscall to the operating system to create
/// the system selector. If this syscall fails, `Poll::new` will return
/// with the error.
///
/// See [struct] level docs for more details.
///
/// [struct]: struct.Poll.html
///
/// # Examples
///
/// ```
/// # use std::error::Error;
/// # fn main() -> Result<(), Box<dyn Error>> {
/// use mio::{Poll, Events};
/// use std::time::Duration;
///
/// let mut poll = match Poll::new() {
/// Ok(poll) => poll,
/// Err(e) => panic!("failed to create Poll instance; err={:?}", e),
/// };
///
/// // Create a structure to receive polled events
/// let mut events = Events::with_capacity(1024);
///
/// // Wait for events, but none will be received because no
/// // `event::Source`s have been registered with this `Poll` instance.
/// poll.poll(&mut events, Some(Duration::from_millis(500)))?;
/// assert!(events.is_empty());
/// # Ok(())
/// # }
/// ```
pub fn new() -> io::Result<Poll> {
sys::Selector::new().map(|selector| Poll {
registry: Registry { selector },
})
}
}
}
#[cfg(unix)]
impl AsRawFd for Poll {
fn as_raw_fd(&self) -> RawFd {
self.registry.as_raw_fd()
}
}
impl fmt::Debug for Poll {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("Poll").finish()
}
}
impl Registry {
/// Register an [`event::Source`] with the `Poll` instance.
///
/// Once registered, the `Poll` instance will monitor the event source for
/// readiness state changes. When it notices a state change, it will return
/// a readiness event for the handle the next time [`poll`] is called.
///
/// See [`Poll`] docs for a high level overview.
///
/// # Arguments
///
/// `source: &S: event::Source`: This is the source of events that the
/// `Poll` instance should monitor for readiness state changes.
///
/// `token: Token`: The caller picks a token to associate with the socket.
/// When [`poll`] returns an event for the handle, this token is included.
/// This allows the caller to map the event to its source. The token
/// associated with the `event::Source` can be changed at any time by
/// calling [`reregister`].
///
/// See documentation on [`Token`] for an example showing how to pick
/// [`Token`] values.
///
/// `interest: Interest`: Specifies which operations `Poll` should monitor
/// for readiness. `Poll` will only return readiness events for operations
/// specified by this argument.
///
/// If a socket is registered with readable interest and the socket becomes
/// writable, no event will be returned from [`poll`].
///
/// The readiness interest for an `event::Source` can be changed at any time
/// by calling [`reregister`].
///
/// # Notes
///
/// Callers must ensure that if a source being registered with a `Poll`
/// instance was previously registered with that `Poll` instance, then a
/// call to [`deregister`] has already occurred. Consecutive calls to
/// `register` is unspecified behavior.
///
/// Unless otherwise specified, the caller should assume that once an event
/// source is registered with a `Poll` instance, it is bound to that `Poll`
/// instance for the lifetime of the event source. This remains true even
/// if the event source is deregistered from the poll instance using
/// [`deregister`].
///
/// [`event::Source`]: ./event/trait.Source.html
/// [`poll`]: struct.Poll.html#method.poll
/// [`reregister`]: struct.Registry.html#method.reregister
/// [`deregister`]: struct.Registry.html#method.deregister
/// [`Token`]: struct.Token.html
///
/// # Examples
///
#[cfg_attr(all(feature = "os-poll", feature = "net"), doc = "```")]
#[cfg_attr(not(all(feature = "os-poll", feature = "net")), doc = "```ignore")]
/// # use std::error::Error;
/// # use std::net;
/// # fn main() -> Result<(), Box<dyn Error>> {
/// use mio::{Events, Poll, Interest, Token};
/// use mio::net::TcpStream;
/// use std::net::SocketAddr;
/// use std::time::{Duration, Instant};
///
/// let mut poll = Poll::new()?;
///
/// let address: SocketAddr = "127.0.0.1:0".parse()?;
/// let listener = net::TcpListener::bind(address)?;
/// let mut socket = TcpStream::connect(listener.local_addr()?)?;
///
/// // Register the socket with `poll`
/// poll.registry().register(
/// &mut socket,
/// Token(0),
/// Interest::READABLE | Interest::WRITABLE)?;
///
/// let mut events = Events::with_capacity(1024);
/// let start = Instant::now();
/// let timeout = Duration::from_millis(500);
///
/// loop {
/// let elapsed = start.elapsed();
///
/// if elapsed >= timeout {
/// // Connection timed out
/// return Ok(());
/// }
///
/// let remaining = timeout - elapsed;
/// poll.poll(&mut events, Some(remaining))?;
///
/// for event in &events {
/// if event.token() == Token(0) {
/// // Something (probably) happened on the socket.
/// return Ok(());
/// }
/// }
/// }
/// # }
/// ```
pub fn register<S>(&self, source: &mut S, token: Token, interests: Interest) -> io::Result<()>
where
S: event::Source + ?Sized,
{
trace!(
"registering event source with poller: token={:?}, interests={:?}",
token,
interests
);
source.register(self, token, interests)
}
/// Re-register an [`event::Source`] with the `Poll` instance.
///
/// Re-registering an event source allows changing the details of the
/// registration. Specifically, it allows updating the associated `token`
/// and `interests` specified in previous `register` and `reregister` calls.
///
/// The `reregister` arguments fully override the previous values. In other
/// words, if a socket is registered with [`readable`] interest and the call
/// to `reregister` specifies [`writable`], then read interest is no longer
/// requested for the handle.
///
/// The event source must have previously been registered with this instance
/// of `Poll`, otherwise the behavior is unspecified.
///
/// See the [`register`] documentation for details about the function
/// arguments and see the [`struct`] docs for a high level overview of
/// polling.
///
/// # Examples
///
#[cfg_attr(all(feature = "os-poll", feature = "net"), doc = "```")]
#[cfg_attr(not(all(feature = "os-poll", feature = "net")), doc = "```ignore")]
/// # use std::error::Error;
/// # use std::net;
/// # fn main() -> Result<(), Box<dyn Error>> {
/// use mio::{Poll, Interest, Token};
/// use mio::net::TcpStream;
/// use std::net::SocketAddr;
///
/// let poll = Poll::new()?;
///
/// let address: SocketAddr = "127.0.0.1:0".parse()?;
/// let listener = net::TcpListener::bind(address)?;
/// let mut socket = TcpStream::connect(listener.local_addr()?)?;
///
/// // Register the socket with `poll`, requesting readable
/// poll.registry().register(
/// &mut socket,
/// Token(0),
/// Interest::READABLE)?;
///
/// // Reregister the socket specifying write interest instead. Even though
/// // the token is the same it must be specified.
/// poll.registry().reregister(
/// &mut socket,
/// Token(0),
/// Interest::WRITABLE)?;
/// # Ok(())
/// # }
/// ```
///
/// [`event::Source`]: ./event/trait.Source.html
/// [`struct`]: struct.Poll.html
/// [`register`]: struct.Registry.html#method.register
/// [`readable`]: ./event/struct.Event.html#is_readable
/// [`writable`]: ./event/struct.Event.html#is_writable
pub fn reregister<S>(&self, source: &mut S, token: Token, interests: Interest) -> io::Result<()>
where
S: event::Source + ?Sized,
{
trace!(
"reregistering event source with poller: token={:?}, interests={:?}",
token,
interests
);
source.reregister(self, token, interests)
}
/// Deregister an [`event::Source`] with the `Poll` instance.
///
/// When an event source is deregistered, the `Poll` instance will no longer
/// monitor it for readiness state changes. Deregistering clears up any
/// internal resources needed to track the handle. After an explicit call
/// to this method completes, it is guaranteed that the token previously
/// registered to this handle will not be returned by a future poll, so long
/// as a happens-before relationship is established between this call and
/// the poll.
///
/// The event source must have previously been registered with this instance
/// of `Poll`, otherwise the behavior is unspecified.
///
/// A handle can be passed back to `register` after it has been
/// deregistered; however, it must be passed back to the **same** `Poll`
/// instance, otherwise the behavior is unspecified.
///
/// # Examples
///
#[cfg_attr(all(feature = "os-poll", feature = "net"), doc = "```")]
#[cfg_attr(not(all(feature = "os-poll", feature = "net")), doc = "```ignore")]
/// # use std::error::Error;
/// # use std::net;
/// # fn main() -> Result<(), Box<dyn Error>> {
/// use mio::{Events, Poll, Interest, Token};
/// use mio::net::TcpStream;
/// use std::net::SocketAddr;
/// use std::time::Duration;
///
/// let mut poll = Poll::new()?;
///
/// let address: SocketAddr = "127.0.0.1:0".parse()?;
/// let listener = net::TcpListener::bind(address)?;
/// let mut socket = TcpStream::connect(listener.local_addr()?)?;
///
/// // Register the socket with `poll`
/// poll.registry().register(
/// &mut socket,
/// Token(0),
/// Interest::READABLE)?;
///
/// poll.registry().deregister(&mut socket)?;
///
/// let mut events = Events::with_capacity(1024);
///
/// // Set a timeout because this poll should never receive any events.
/// poll.poll(&mut events, Some(Duration::from_secs(1)))?;
/// assert!(events.is_empty());
/// # Ok(())
/// # }
/// ```
pub fn deregister<S>(&self, source: &mut S) -> io::Result<()>
where
S: event::Source + ?Sized,
{
trace!("deregistering event source from poller");
source.deregister(self)
}
/// Creates a new independently owned `Registry`.
///
/// Event sources registered with this `Registry` will be registered with
/// the original `Registry` and `Poll` instance.
pub fn try_clone(&self) -> io::Result<Registry> {
self.selector
.try_clone()
.map(|selector| Registry { selector })
}
/// Internal check to ensure only a single `Waker` is active per [`Poll`]
/// instance.
#[cfg(debug_assertions)]
pub(crate) fn register_waker(&self) {
if self.selector.register_waker() {
panic!("Only a single `Waker` can be active per `Poll` instance");
}
}
}
impl fmt::Debug for Registry {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("Registry").finish()
}
}
#[cfg(unix)]
impl AsRawFd for Registry {
fn as_raw_fd(&self) -> RawFd {
self.selector.as_raw_fd()
}
}
/// Get access to the `sys::Selector` from `Registry`.
pub(crate) fn selector(registry: &Registry) -> &sys::Selector {
&registry.selector
}
cfg_os_poll! {
#[cfg(unix)]
#[test]
pub fn as_raw_fd() {
let poll = Poll::new().unwrap();
assert!(poll.as_raw_fd() > 0);
}
}