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    use crate::{Interest, Token};

    use libc::{EPOLLET, EPOLLIN, EPOLLOUT, EPOLLRDHUP};
    use log::error;
    use std::os::unix::io::{AsRawFd, RawFd};
    #[cfg(debug_assertions)]
    use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
    use std::time::Duration;
    use std::{cmp, i32, io, ptr};

    /// Unique id for use as `SelectorId`.
    #[cfg(debug_assertions)]
    static NEXT_ID: AtomicUsize = AtomicUsize::new(1);

    #[derive(Debug)]
    pub struct Selector {
        #[cfg(debug_assertions)]
        id: usize,
        ep: RawFd,
        #[cfg(debug_assertions)]
        has_waker: AtomicBool,
    }

    impl Selector {
        pub fn new() -> io::Result<Selector> {
            // According to libuv, `EPOLL_CLOEXEC` is not defined on Android API <
            // 21. But `EPOLL_CLOEXEC` is an alias for `O_CLOEXEC` on that platform,
            // so we use it instead.
            #[cfg(target_os = "android")]
            let flag = libc::O_CLOEXEC;
            #[cfg(not(target_os = "android"))]
            let flag = libc::EPOLL_CLOEXEC;

            syscall!(epoll_create1(flag)).map(|ep| Selector {
                #[cfg(debug_assertions)]
                id: NEXT_ID.fetch_add(1, Ordering::Relaxed),
                ep,
                #[cfg(debug_assertions)]
                has_waker: AtomicBool::new(false),
            })
        }

        pub fn try_clone(&self) -> io::Result<Selector> {
            syscall!(dup(self.ep)).map(|ep| Selector {
                // It's the same selector, so we use the same id.
                #[cfg(debug_assertions)]
                id: self.id,
                ep,
                #[cfg(debug_assertions)]
                has_waker: AtomicBool::new(self.has_waker.load(Ordering::Acquire)),
            })
        }

        pub fn select(&self, events: &mut Events, timeout: Option<Duration>) -> io::Result<()> {
            // A bug in kernels < 2.6.37 makes timeouts larger than LONG_MAX / CONFIG_HZ
            // (approx. 30 minutes with CONFIG_HZ=1200) effectively infinite on 32 bits
            // architectures. The magic number is the same constant used by libuv.
            #[cfg(target_pointer_width = "32")]
            const MAX_SAFE_TIMEOUT: u128 = 1789569;
            #[cfg(not(target_pointer_width = "32"))]
            const MAX_SAFE_TIMEOUT: u128 = libc::c_int::max_value() as u128;

            let timeout = timeout
                .map(|to| cmp::min(to.as_millis(), MAX_SAFE_TIMEOUT) as libc::c_int)
                .unwrap_or(-1);

            events.clear();
            syscall!(epoll_wait(
                self.ep,
                events.as_mut_ptr(),
                events.capacity() as i32,
                timeout,
            ))
            .map(|n_events| {
                // This is safe because `epoll_wait` ensures that `n_events` are
                // assigned.
                unsafe { events.set_len(n_events as usize) };
            })
        }

        pub fn register(&self, fd: RawFd, token: Token, interests: Interest) -> io::Result<()> {
            let mut event = libc::epoll_event {
                events: interests_to_epoll(interests),
                u64: usize::from(token) as u64,
            };

            syscall!(epoll_ctl(self.ep, libc::EPOLL_CTL_ADD, fd, &mut event)).map(|_| ())
        }

        pub fn reregister(&self, fd: RawFd, token: Token, interests: Interest) -> io::Result<()> {
            let mut event = libc::epoll_event {
                events: interests_to_epoll(interests),
                u64: usize::from(token) as u64,
            };

            syscall!(epoll_ctl(self.ep, libc::EPOLL_CTL_MOD, fd, &mut event)).map(|_| ())
        }

        pub fn deregister(&self, fd: RawFd) -> io::Result<()> {
            syscall!(epoll_ctl(self.ep, libc::EPOLL_CTL_DEL, fd, ptr::null_mut())).map(|_| ())
        }

        #[cfg(debug_assertions)]
        pub fn register_waker(&self) -> bool {
            self.has_waker.swap(true, Ordering::AcqRel)
        }
    }

    cfg_io_source! {
        impl Selector {
            #[cfg(debug_assertions)]
            pub fn id(&self) -> usize {
                self.id
            }
        }
    }

    impl AsRawFd for Selector {
        fn as_raw_fd(&self) -> RawFd {
            self.ep
        }
    }

    impl Drop for Selector {
        fn drop(&mut self) {
            if let Err(err) = syscall!(close(self.ep)) {
                error!("error closing epoll: {}", err);
            }
        }
    }

    fn interests_to_epoll(interests: Interest) -> u32 {
        let mut kind = EPOLLET;

        if interests.is_readable() {
            kind = kind | EPOLLIN | EPOLLRDHUP;
        }

        if interests.is_writable() {
            kind |= EPOLLOUT;
        }

        kind as u32
    }

    pub type Event = libc::epoll_event;
    pub type Events = Vec<Event>;

    pub mod event {
        use std::fmt;

        use crate::sys::Event;
        use crate::Token;

        pub fn token(event: &Event) -> Token {
            Token(event.u64 as usize)
        }

        pub fn is_readable(event: &Event) -> bool {
            (event.events as libc::c_int & libc::EPOLLIN) != 0
                || (event.events as libc::c_int & libc::EPOLLPRI) != 0
        }

        pub fn is_writable(event: &Event) -> bool {
            (event.events as libc::c_int & libc::EPOLLOUT) != 0
        }

        pub fn is_error(event: &Event) -> bool {
            (event.events as libc::c_int & libc::EPOLLERR) != 0
        }

        pub fn is_read_closed(event: &Event) -> bool {
            // Both halves of the socket have closed
            event.events as libc::c_int & libc::EPOLLHUP != 0
                // Socket has received FIN or called shutdown(SHUT_RD)
                || (event.events as libc::c_int & libc::EPOLLIN != 0
                    && event.events as libc::c_int & libc::EPOLLRDHUP != 0)
        }

        pub fn is_write_closed(event: &Event) -> bool {
            // Both halves of the socket have closed
            event.events as libc::c_int & libc::EPOLLHUP != 0
                // Unix pipe write end has closed
                || (event.events as libc::c_int & libc::EPOLLOUT != 0
                    && event.events as libc::c_int & libc::EPOLLERR != 0)
                // The other side (read end) of a Unix pipe has closed.
                || event.events as libc::c_int == libc::EPOLLERR
        }

        pub fn is_priority(event: &Event) -> bool {
            (event.events as libc::c_int & libc::EPOLLPRI) != 0
        }

        pub fn is_aio(_: &Event) -> bool {
            // Not supported in the kernel, only in libc.
            false
        }

        pub fn is_lio(_: &Event) -> bool {
            // Not supported.
            false
        }

        pub fn debug_details(f: &mut fmt::Formatter<'_>, event: &Event) -> fmt::Result {
            #[allow(clippy::trivially_copy_pass_by_ref)]
            fn check_events(got: &u32, want: &libc::c_int) -> bool {
                (*got as libc::c_int & want) != 0
            }
            debug_detail!(
                EventsDetails(u32),
                check_events,
                libc::EPOLLIN,
                libc::EPOLLPRI,
                libc::EPOLLOUT,
                libc::EPOLLRDNORM,
                libc::EPOLLRDBAND,
                libc::EPOLLWRNORM,
                libc::EPOLLWRBAND,
                libc::EPOLLMSG,
                libc::EPOLLERR,
                libc::EPOLLHUP,
                libc::EPOLLET,
                libc::EPOLLRDHUP,
                libc::EPOLLONESHOT,
                #[cfg(any(target_os = "linux", target_os = "solaris"))]
                libc::EPOLLEXCLUSIVE,
                #[cfg(any(target_os = "android", target_os = "linux"))]
                libc::EPOLLWAKEUP,
                libc::EPOLL_CLOEXEC,
            );

            // Can't reference fields in packed structures.
            let e_u64 = event.u64;
            f.debug_struct("epoll_event")
                .field("events", &EventsDetails(event.events))
                .field("u64", &e_u64)
                .finish()
        }
    }

    #[cfg(target_os = "android")]
    #[test]
    fn assert_close_on_exec_flag() {
        // This assertion need to be true for Selector::new.
        assert_eq!(libc::O_CLOEXEC, libc::EPOLL_CLOEXEC);
    }