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    //! Unix-specific types for signal handling.
    //!
    //! This module is only defined on Unix platforms and contains the primary
    //! `Signal` type for receiving notifications of signals.

    #![cfg(unix)]

    use crate::signal::registry::{globals, EventId, EventInfo, Globals, Init, Storage};
    use crate::sync::mpsc::error::TryRecvError;
    use crate::sync::mpsc::{channel, Receiver};

    use libc::c_int;
    use mio::net::UnixStream;
    use std::io::{self, Error, ErrorKind, Write};
    use std::pin::Pin;
    use std::sync::atomic::{AtomicBool, Ordering};
    use std::sync::Once;
    use std::task::{Context, Poll};

    pub(crate) mod driver;
    use self::driver::Handle;

    pub(crate) type OsStorage = Vec<SignalInfo>;

    // Number of different unix signals
    // (FreeBSD has 33)
    const SIGNUM: usize = 33;

    impl Init for OsStorage {
        fn init() -> Self {
            (0..SIGNUM).map(|_| SignalInfo::default()).collect()
        }
    }

    impl Storage for OsStorage {
        fn event_info(&self, id: EventId) -> Option<&EventInfo> {
            self.get(id).map(|si| &si.event_info)
        }

        fn for_each<'a, F>(&'a self, f: F)
        where
            F: FnMut(&'a EventInfo),
        {
            self.iter().map(|si| &si.event_info).for_each(f)
        }
    }

    #[derive(Debug)]
    pub(crate) struct OsExtraData {
        sender: UnixStream,
        receiver: UnixStream,
    }

    impl Init for OsExtraData {
        fn init() -> Self {
            let (receiver, sender) = UnixStream::pair().expect("failed to create UnixStream");

            Self { sender, receiver }
        }
    }

    /// Represents the specific kind of signal to listen for.
    #[derive(Debug, Clone, Copy)]
    pub struct SignalKind(c_int);

    impl SignalKind {
        /// Allows for listening to any valid OS signal.
        ///
        /// For example, this can be used for listening for platform-specific
        /// signals.
        /// ```rust,no_run
        /// # use tokio::signal::unix::SignalKind;
        /// # let signum = -1;
        /// // let signum = libc::OS_SPECIFIC_SIGNAL;
        /// let kind = SignalKind::from_raw(signum);
        /// ```
        pub fn from_raw(signum: c_int) -> Self {
            Self(signum)
        }

        /// Represents the SIGALRM signal.
        ///
        /// On Unix systems this signal is sent when a real-time timer has expired.
        /// By default, the process is terminated by this signal.
        pub fn alarm() -> Self {
            Self(libc::SIGALRM)
        }

        /// Represents the SIGCHLD signal.
        ///
        /// On Unix systems this signal is sent when the status of a child process
        /// has changed. By default, this signal is ignored.
        pub fn child() -> Self {
            Self(libc::SIGCHLD)
        }

        /// Represents the SIGHUP signal.
        ///
        /// On Unix systems this signal is sent when the terminal is disconnected.
        /// By default, the process is terminated by this signal.
        pub fn hangup() -> Self {
            Self(libc::SIGHUP)
        }

        /// Represents the SIGINFO signal.
        ///
        /// On Unix systems this signal is sent to request a status update from the
        /// process. By default, this signal is ignored.
        #[cfg(any(
            target_os = "dragonfly",
            target_os = "freebsd",
            target_os = "macos",
            target_os = "netbsd",
            target_os = "openbsd"
        ))]
        pub fn info() -> Self {
            Self(libc::SIGINFO)
        }

        /// Represents the SIGINT signal.
        ///
        /// On Unix systems this signal is sent to interrupt a program.
        /// By default, the process is terminated by this signal.
        pub fn interrupt() -> Self {
            Self(libc::SIGINT)
        }

        /// Represents the SIGIO signal.
        ///
        /// On Unix systems this signal is sent when I/O operations are possible
        /// on some file descriptor. By default, this signal is ignored.
        pub fn io() -> Self {
            Self(libc::SIGIO)
        }

        /// Represents the SIGPIPE signal.
        ///
        /// On Unix systems this signal is sent when the process attempts to write
        /// to a pipe which has no reader. By default, the process is terminated by
        /// this signal.
        pub fn pipe() -> Self {
            Self(libc::SIGPIPE)
        }

        /// Represents the SIGQUIT signal.
        ///
        /// On Unix systems this signal is sent to issue a shutdown of the
        /// process, after which the OS will dump the process core.
        /// By default, the process is terminated by this signal.
        pub fn quit() -> Self {
            Self(libc::SIGQUIT)
        }

        /// Represents the SIGTERM signal.
        ///
        /// On Unix systems this signal is sent to issue a shutdown of the
        /// process. By default, the process is terminated by this signal.
        pub fn terminate() -> Self {
            Self(libc::SIGTERM)
        }

        /// Represents the SIGUSR1 signal.
        ///
        /// On Unix systems this is a user defined signal.
        /// By default, the process is terminated by this signal.
        pub fn user_defined1() -> Self {
            Self(libc::SIGUSR1)
        }

        /// Represents the SIGUSR2 signal.
        ///
        /// On Unix systems this is a user defined signal.
        /// By default, the process is terminated by this signal.
        pub fn user_defined2() -> Self {
            Self(libc::SIGUSR2)
        }

        /// Represents the SIGWINCH signal.
        ///
        /// On Unix systems this signal is sent when the terminal window is resized.
        /// By default, this signal is ignored.
        pub fn window_change() -> Self {
            Self(libc::SIGWINCH)
        }
    }

    pub(crate) struct SignalInfo {
        event_info: EventInfo,
        init: Once,
        initialized: AtomicBool,
    }

    impl Default for SignalInfo {
        fn default() -> SignalInfo {
            SignalInfo {
                event_info: Default::default(),
                init: Once::new(),
                initialized: AtomicBool::new(false),
            }
        }
    }

    /// Our global signal handler for all signals registered by this module.
    ///
    /// The purpose of this signal handler is to primarily:
    ///
    /// 1. Flag that our specific signal was received (e.g. store an atomic flag)
    /// 2. Wake up the driver by writing a byte to a pipe
    ///
    /// Those two operations should both be async-signal safe.
    fn action(globals: Pin<&'static Globals>, signal: c_int) {
        globals.record_event(signal as EventId);

        // Send a wakeup, ignore any errors (anything reasonably possible is
        // full pipe and then it will wake up anyway).
        let mut sender = &globals.sender;
        drop(sender.write(&[1]));
    }

    /// Enables this module to receive signal notifications for the `signal`
    /// provided.
    ///
    /// This will register the signal handler if it hasn't already been registered,
    /// returning any error along the way if that fails.
    fn signal_enable(signal: c_int, handle: Handle) -> io::Result<()> {
        if signal < 0 || signal_hook_registry::FORBIDDEN.contains(&signal) {
            return Err(Error::new(
                ErrorKind::Other,
                format!("Refusing to register signal {}", signal),
            ));
        }

        // Check that we have a signal driver running
        handle.check_inner()?;

        let globals = globals();
        let siginfo = match globals.storage().get(signal as EventId) {
            Some(slot) => slot,
            None => return Err(io::Error::new(io::ErrorKind::Other, "signal too large")),
        };
        let mut registered = Ok(());
        siginfo.init.call_once(|| {
            registered = unsafe {
                signal_hook_registry::register(signal, move || action(globals, signal)).map(|_| ())
            };
            if registered.is_ok() {
                siginfo.initialized.store(true, Ordering::Relaxed);
            }
        });
        registered?;
        // If the call_once failed, it won't be retried on the next attempt to register the signal. In
        // such case it is not run, registered is still `Ok(())`, initialized is still `false`.
        if siginfo.initialized.load(Ordering::Relaxed) {
            Ok(())
        } else {
            Err(Error::new(
                ErrorKind::Other,
                "Failed to register signal handler",
            ))
        }
    }

    /// A stream of events for receiving a particular type of OS signal.
    ///
    /// In general signal handling on Unix is a pretty tricky topic, and this
    /// structure is no exception! There are some important limitations to keep in
    /// mind when using `Signal` streams:
    ///
    /// * Signals handling in Unix already necessitates coalescing signals
    ///   together sometimes. This `Signal` stream is also no exception here in
    ///   that it will also coalesce signals. That is, even if the signal handler
    ///   for this process runs multiple times, the `Signal` stream may only return
    ///   one signal notification. Specifically, before `poll` is called, all
    ///   signal notifications are coalesced into one item returned from `poll`.
    ///   Once `poll` has been called, however, a further signal is guaranteed to
    ///   be yielded as an item.
    ///
    ///   Put another way, any element pulled off the returned stream corresponds to
    ///   *at least one* signal, but possibly more.
    ///
    /// * Signal handling in general is relatively inefficient. Although some
    ///   improvements are possible in this crate, it's recommended to not plan on
    ///   having millions of signal channels open.
    ///
    /// If you've got any questions about this feel free to open an issue on the
    /// repo! New approaches to alleviate some of these limitations are always
    /// appreciated!
    ///
    /// # Caveats
    ///
    /// The first time that a `Signal` instance is registered for a particular
    /// signal kind, an OS signal-handler is installed which replaces the default
    /// platform behavior when that signal is received, **for the duration of the
    /// entire process**.
    ///
    /// For example, Unix systems will terminate a process by default when it
    /// receives SIGINT. But, when a `Signal` instance is created to listen for
    /// this signal, the next SIGINT that arrives will be translated to a stream
    /// event, and the process will continue to execute. **Even if this `Signal`
    /// instance is dropped, subsequent SIGINT deliveries will end up captured by
    /// Tokio, and the default platform behavior will NOT be reset**.
    ///
    /// Thus, applications should take care to ensure the expected signal behavior
    /// occurs as expected after listening for specific signals.
    ///
    /// # Examples
    ///
    /// Wait for SIGHUP
    ///
    /// ```rust,no_run
    /// use tokio::signal::unix::{signal, SignalKind};
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn std::error::Error>> {
    ///     // An infinite stream of hangup signals.
    ///     let mut stream = signal(SignalKind::hangup())?;
    ///
    ///     // Print whenever a HUP signal is received
    ///     loop {
    ///         stream.recv().await;
    ///         println!("got signal HUP");
    ///     }
    /// }
    /// ```
    #[must_use = "streams do nothing unless polled"]
    #[derive(Debug)]
    pub struct Signal {
        rx: Receiver<()>,
    }

    /// Creates a new stream which will receive notifications when the current
    /// process receives the specified signal `kind`.
    ///
    /// This function will create a new stream which binds to the default reactor.
    /// The `Signal` stream is an infinite stream which will receive
    /// notifications whenever a signal is received. More documentation can be
    /// found on `Signal` itself, but to reiterate:
    ///
    /// * Signals may be coalesced beyond what the kernel already does.
    /// * Once a signal handler is registered with the process the underlying
    ///   libc signal handler is never unregistered.
    ///
    /// A `Signal` stream can be created for a particular signal number
    /// multiple times. When a signal is received then all the associated
    /// channels will receive the signal notification.
    ///
    /// # Errors
    ///
    /// * If the lower-level C functions fail for some reason.
    /// * If the previous initialization of this specific signal failed.
    /// * If the signal is one of
    ///   [`signal_hook::FORBIDDEN`](fn@signal_hook_registry::register#panics)
    pub fn signal(kind: SignalKind) -> io::Result<Signal> {
        signal_with_handle(kind, Handle::current())
    }

    pub(crate) fn signal_with_handle(kind: SignalKind, handle: Handle) -> io::Result<Signal> {
        let signal = kind.0;

        // Turn the signal delivery on once we are ready for it
        signal_enable(signal, handle)?;

        // One wakeup in a queue is enough, no need for us to buffer up any
        // more.
        let (tx, rx) = channel(1);
        globals().register_listener(signal as EventId, tx);

        Ok(Signal { rx })
    }

    impl Signal {
        /// Receives the next signal notification event.
        ///
        /// `None` is returned if no more events can be received by this stream.
        ///
        /// # Examples
        ///
        /// Wait for SIGHUP
        ///
        /// ```rust,no_run
        /// use tokio::signal::unix::{signal, SignalKind};
        ///
        /// #[tokio::main]
        /// async fn main() -> Result<(), Box<dyn std::error::Error>> {
        ///     // An infinite stream of hangup signals.
        ///     let mut stream = signal(SignalKind::hangup())?;
        ///
        ///     // Print whenever a HUP signal is received
        ///     loop {
        ///         stream.recv().await;
        ///         println!("got signal HUP");
        ///     }
        /// }
        /// ```
        pub async fn recv(&mut self) -> Option<()> {
            use crate::future::poll_fn;
            poll_fn(|cx| self.poll_recv(cx)).await
        }

        /// Polls to receive the next signal notification event, outside of an
        /// `async` context.
        ///
        /// This method returns:
        ///
        ///  * `Poll::Pending` if no signals are available but the channel is not
        ///    closed.
        ///  * `Poll::Ready(Some(()))` if a signal is available.
        ///  * `Poll::Ready(None)` if the channel has been closed and all signals
        ///    sent before it was closed have been received.
        ///
        /// # Examples
        ///
        /// Polling from a manually implemented future
        ///
        /// ```rust,no_run
        /// use std::pin::Pin;
        /// use std::future::Future;
        /// use std::task::{Context, Poll};
        /// use tokio::signal::unix::Signal;
        ///
        /// struct MyFuture {
        ///     signal: Signal,
        /// }
        ///
        /// impl Future for MyFuture {
        ///     type Output = Option<()>;
        ///
        ///     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        ///         println!("polling MyFuture");
        ///         self.signal.poll_recv(cx)
        ///     }
        /// }
        /// ```
        pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
            self.rx.poll_recv(cx)
        }

        /// Try to receive a signal notification without blocking or registering a waker.
        pub(crate) fn try_recv(&mut self) -> Result<(), TryRecvError> {
            self.rx.try_recv()
        }
    }

    // Work around for abstracting streams internally
    pub(crate) trait InternalStream: Unpin {
        fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>>;
        fn try_recv(&mut self) -> Result<(), TryRecvError>;
    }

    impl InternalStream for Signal {
        fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
            self.poll_recv(cx)
        }

        fn try_recv(&mut self) -> Result<(), TryRecvError> {
            self.try_recv()
        }
    }

    pub(crate) fn ctrl_c() -> io::Result<Signal> {
        signal(SignalKind::interrupt())
    }

    #[cfg(all(test, not(loom)))]
    mod tests {
        use super::*;

        #[test]
        fn signal_enable_error_on_invalid_input() {
            signal_enable(-1, Handle::default()).unwrap_err();
        }

        #[test]
        fn signal_enable_error_on_forbidden_input() {
            signal_enable(signal_hook_registry::FORBIDDEN[0], Handle::default()).unwrap_err();
        }
    }