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    #![cfg_attr(not(feature = "rt"), allow(dead_code))]

    //! Signal driver

    use crate::io::driver::{Driver as IoDriver, Interest};
    use crate::io::PollEvented;
    use crate::park::Park;
    use crate::signal::registry::globals;

    use mio::net::UnixStream;
    use std::io::{self, Read};
    use std::ptr;
    use std::sync::{Arc, Weak};
    use std::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
    use std::time::Duration;

    /// Responsible for registering wakeups when an OS signal is received, and
    /// subsequently dispatching notifications to any signal listeners as appropriate.
    ///
    /// Note: this driver relies on having an enabled IO driver in order to listen to
    /// pipe write wakeups.
    #[derive(Debug)]
    pub(crate) struct Driver {
        /// Thread parker. The `Driver` park implementation delegates to this.
        park: IoDriver,

        /// A pipe for receiving wake events from the signal handler
        receiver: PollEvented<UnixStream>,

        /// Shared state
        inner: Arc<Inner>,
    }

    #[derive(Clone, Debug, Default)]
    pub(crate) struct Handle {
        inner: Weak<Inner>,
    }

    #[derive(Debug)]
    pub(super) struct Inner(());

    // ===== impl Driver =====

    impl Driver {
        /// Creates a new signal `Driver` instance that delegates wakeups to `park`.
        pub(crate) fn new(park: IoDriver) -> io::Result<Self> {
            use std::mem::ManuallyDrop;
            use std::os::unix::io::{AsRawFd, FromRawFd};

            // NB: We give each driver a "fresh" reciever file descriptor to avoid
            // the issues described in alexcrichton/tokio-process#42.
            //
            // In the past we would reuse the actual receiver file descriptor and
            // swallow any errors around double registration of the same descriptor.
            // I'm not sure if the second (failed) registration simply doesn't end
            // up receiving wake up notifications, or there could be some race
            // condition when consuming readiness events, but having distinct
            // descriptors for distinct PollEvented instances appears to mitigate
            // this.
            //
            // Unfortunately we cannot just use a single global PollEvented instance
            // either, since we can't compare Handles or assume they will always
            // point to the exact same reactor.
            //
            // Mio 0.7 removed `try_clone()` as an API due to unexpected behavior
            // with registering dups with the same reactor. In this case, duping is
            // safe as each dup is registered with separate reactors **and** we
            // only expect at least one dup to receive the notification.

            // Manually drop as we don't actually own this instance of UnixStream.
            let receiver_fd = globals().receiver.as_raw_fd();

            // safety: there is nothing unsafe about this, but the `from_raw_fd` fn is marked as unsafe.
            let original =
                ManuallyDrop::new(unsafe { std::os::unix::net::UnixStream::from_raw_fd(receiver_fd) });
            let receiver = UnixStream::from_std(original.try_clone()?);
            let receiver = PollEvented::new_with_interest_and_handle(
                receiver,
                Interest::READABLE | Interest::WRITABLE,
                park.handle(),
            )?;

            Ok(Self {
                park,
                receiver,
                inner: Arc::new(Inner(())),
            })
        }

        /// Returns a handle to this event loop which can be sent across threads
        /// and can be used as a proxy to the event loop itself.
        pub(crate) fn handle(&self) -> Handle {
            Handle {
                inner: Arc::downgrade(&self.inner),
            }
        }

        fn process(&self) {
            // Check if the pipe is ready to read and therefore has "woken" us up
            //
            // To do so, we will `poll_read_ready` with a noop waker, since we don't
            // need to actually be notified when read ready...
            let waker = unsafe { Waker::from_raw(RawWaker::new(ptr::null(), &NOOP_WAKER_VTABLE)) };
            let mut cx = Context::from_waker(&waker);

            let ev = match self.receiver.registration().poll_read_ready(&mut cx) {
                Poll::Ready(Ok(ev)) => ev,
                Poll::Ready(Err(e)) => panic!("reactor gone: {}", e),
                Poll::Pending => return, // No wake has arrived, bail
            };

            // Drain the pipe completely so we can receive a new readiness event
            // if another signal has come in.
            let mut buf = [0; 128];
            loop {
                match (&*self.receiver).read(&mut buf) {
                    Ok(0) => panic!("EOF on self-pipe"),
                    Ok(_) => continue, // Keep reading
                    Err(e) if e.kind() == io::ErrorKind::WouldBlock => break,
                    Err(e) => panic!("Bad read on self-pipe: {}", e),
                }
            }

            self.receiver.registration().clear_readiness(ev);

            // Broadcast any signals which were received
            globals().broadcast();
        }
    }

    const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop);

    unsafe fn noop_clone(_data: *const ()) -> RawWaker {
        RawWaker::new(ptr::null(), &NOOP_WAKER_VTABLE)
    }

    unsafe fn noop(_data: *const ()) {}

    // ===== impl Park for Driver =====

    impl Park for Driver {
        type Unpark = <IoDriver as Park>::Unpark;
        type Error = io::Error;

        fn unpark(&self) -> Self::Unpark {
            self.park.unpark()
        }

        fn park(&mut self) -> Result<(), Self::Error> {
            self.park.park()?;
            self.process();
            Ok(())
        }

        fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
            self.park.park_timeout(duration)?;
            self.process();
            Ok(())
        }

        fn shutdown(&mut self) {
            self.park.shutdown()
        }
    }

    // ===== impl Handle =====

    impl Handle {
        pub(super) fn check_inner(&self) -> io::Result<()> {
            if self.inner.strong_count() > 0 {
                Ok(())
            } else {
                Err(io::Error::new(io::ErrorKind::Other, "signal driver gone"))
            }
        }
    }

    cfg_rt! {
        impl Handle {
            /// Returns a handle to the current driver
            ///
            /// # Panics
            ///
            /// This function panics if there is no current signal driver set.
            pub(super) fn current() -> Self {
                crate::runtime::context::signal_handle().expect(
                    "there is no signal driver running, must be called from the context of Tokio runtime",
                )
            }
        }
    }

    cfg_not_rt! {
        impl Handle {
            /// Returns a handle to the current driver
            ///
            /// # Panics
            ///
            /// This function panics if there is no current signal driver set.
            pub(super) fn current() -> Self {
                panic!(
                    "there is no signal driver running, must be called from the context of Tokio runtime or with\
                    `rt` enabled.",
                )
            }
        }
    }