Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 682 insertions, 0 deletions

diff --git a/third_party/rust/mio/src/poll.rs b/third_party/rust/mio/src/poll.rs
new file mode 100644
index 0000000000..fd643fdd00
--- /dev/null
+++ b/third_party/rust/mio/src/poll.rs
@@ -0,0 +1,682 @@
+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
+///
+/// ### Accessing raw fd/socket/handle
+///
+/// Mio makes it possible for many types to be converted into a raw file
+/// descriptor (fd, Unix), socket (Windows) or handle (Windows). This makes it
+/// possible to support more operations on the type than Mio supports, for
+/// example it makes [mio-aio] possible. However accessing the raw fd is not
+/// without it's pitfalls.
+///
+/// Specifically performing I/O operations outside of Mio on these types (via
+/// the raw fd) has unspecified behaviour. It could cause no more events to be
+/// generated for the type even though it returned `WouldBlock` (in an operation
+/// directly accessing the fd). The behaviour is OS specific and Mio can only
+/// guarantee cross-platform behaviour if it can control the I/O.
+///
+/// [mio-aio]: https://github.com/asomers/mio-aio
+///
+/// *The following is **not** guaranteed, just a description of the current
+/// situation!* Mio is allowed to change the following without it being considered
+/// a breaking change, don't depend on this, it's just here to inform the user.
+/// Currently the kqueue and epoll implementation support direct I/O operations
+/// on the fd without Mio's knowledge. Windows however needs **all** I/O
+/// operations to go through Mio otherwise it is not able to update it's
+/// internal state properly and won't generate events.
+///
+/// # Implementation notes
+///
+/// `Poll` is backed by the selector provided by the operating system.
+///
+/// |      OS       |  Selector |
+/// |---------------|-----------|
+/// | Android       | [epoll]   |
+/// | DragonFly BSD | [kqueue]  |
+/// | FreeBSD       | [kqueue]  |
+/// | iOS           | [kqueue]  |
+/// | illumos       | [epoll]   |
+/// | Linux         | [epoll]   |
+/// | NetBSD        | [kqueue]  |
+/// | OpenBSD       | [kqueue]  |
+/// | Windows       | [IOCP]    |
+/// | 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: &mut 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) {
+        assert!(
+            !self.selector.register_waker(),
+            "Only a single `Waker` can be active per `Poll` instance"
+        );
+    }
+
+    /// Get access to the `sys::Selector`.
+    pub(crate) fn selector(&self) -> &sys::Selector {
+        &self.selector
+    }
+}
+
+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()
+    }
+}
+
+cfg_os_poll! {
+    #[cfg(unix)]
+    #[test]
+    pub fn as_raw_fd() {
+        let poll = Poll::new().unwrap();
+        assert!(poll.as_raw_fd() > 0);
+    }
+}