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    use crate::cell::UnsafeCell;
    use crate::sys::mutex::{self, Mutex};
    use crate::time::Duration;

    pub struct Condvar { inner: UnsafeCell<libc::pthread_cond_t> }

    unsafe impl Send for Condvar {}
    unsafe impl Sync for Condvar {}

    const TIMESPEC_MAX: libc::timespec = libc::timespec {
        tv_sec: <libc::time_t>::max_value(),
        tv_nsec: 1_000_000_000 - 1,
    };

    fn saturating_cast_to_time_t(value: u64) -> libc::time_t {
        if value > <libc::time_t>::max_value() as u64 {
            <libc::time_t>::max_value()
        } else {
            value as libc::time_t
        }
    }

    impl Condvar {
        pub const fn new() -> Condvar {
            // Might be moved and address is changing it is better to avoid
            // initialization of potentially opaque OS data before it landed
            Condvar { inner: UnsafeCell::new(libc::PTHREAD_COND_INITIALIZER) }
        }

        #[cfg(any(target_os = "macos",
                  target_os = "ios",
                  target_os = "l4re",
                  target_os = "android",
                  target_os = "hermit"))]
        pub unsafe fn init(&mut self) {}

        #[cfg(not(any(target_os = "macos",
                      target_os = "ios",
                      target_os = "l4re",
                      target_os = "android",
                      target_os = "hermit")))]
        pub unsafe fn init(&mut self) {
            use crate::mem::MaybeUninit;
            let mut attr = MaybeUninit::<libc::pthread_condattr_t>::uninit();
            let r = libc::pthread_condattr_init(attr.as_mut_ptr());
            assert_eq!(r, 0);
            let r = libc::pthread_condattr_setclock(attr.as_mut_ptr(), libc::CLOCK_MONOTONIC);
            assert_eq!(r, 0);
            let r = libc::pthread_cond_init(self.inner.get(), attr.as_ptr());
            assert_eq!(r, 0);
            let r = libc::pthread_condattr_destroy(attr.as_mut_ptr());
            assert_eq!(r, 0);
        }

        #[inline]
        pub unsafe fn notify_one(&self) {
            let r = libc::pthread_cond_signal(self.inner.get());
            debug_assert_eq!(r, 0);
        }

        #[inline]
        pub unsafe fn notify_all(&self) {
            let r = libc::pthread_cond_broadcast(self.inner.get());
            debug_assert_eq!(r, 0);
        }

        #[inline]
        pub unsafe fn wait(&self, mutex: &Mutex) {
            let r = libc::pthread_cond_wait(self.inner.get(), mutex::raw(mutex));
            debug_assert_eq!(r, 0);
        }

        // This implementation is used on systems that support pthread_condattr_setclock
        // where we configure condition variable to use monotonic clock (instead of
        // default system clock). This approach avoids all problems that result
        // from changes made to the system time.
        #[cfg(not(any(target_os = "macos",
                      target_os = "ios",
                      target_os = "android",
                      target_os = "hermit")))]
        pub unsafe fn wait_timeout(&self, mutex: &Mutex, dur: Duration) -> bool {
            use crate::mem;

            let mut now: libc::timespec = mem::zeroed();
            let r = libc::clock_gettime(libc::CLOCK_MONOTONIC, &mut now);
            assert_eq!(r, 0);

            // Nanosecond calculations can't overflow because both values are below 1e9.
            let nsec = dur.subsec_nanos() + now.tv_nsec as u32;

            let sec = saturating_cast_to_time_t(dur.as_secs())
                .checked_add((nsec / 1_000_000_000) as libc::time_t)
                .and_then(|s| s.checked_add(now.tv_sec));
            let nsec = nsec % 1_000_000_000;

            let timeout = sec.map(|s| {
                libc::timespec { tv_sec: s, tv_nsec: nsec as _}
            }).unwrap_or(TIMESPEC_MAX);

            let r = libc::pthread_cond_timedwait(self.inner.get(), mutex::raw(mutex),
                                                &timeout);
            assert!(r == libc::ETIMEDOUT || r == 0);
            r == 0
        }

        // This implementation is modeled after libcxx's condition_variable
        // https://github.com/llvm-mirror/libcxx/blob/release_35/src/condition_variable.cpp#L46
        // https://github.com/llvm-mirror/libcxx/blob/release_35/include/__mutex_base#L367
        #[cfg(any(target_os = "macos", target_os = "ios", target_os = "android", target_os = "hermit"))]
        pub unsafe fn wait_timeout(&self, mutex: &Mutex, mut dur: Duration) -> bool {
            use crate::ptr;
            use crate::time::Instant;

            // 1000 years
            let max_dur = Duration::from_secs(1000 * 365 * 86400);

            if dur > max_dur {
                // OSX implementation of `pthread_cond_timedwait` is buggy
                // with super long durations. When duration is greater than
                // 0x100_0000_0000_0000 seconds, `pthread_cond_timedwait`
                // in macOS Sierra return error 316.
                //
                // This program demonstrates the issue:
                // https://gist.github.com/stepancheg/198db4623a20aad2ad7cddb8fda4a63c
                //
                // To work around this issue, and possible bugs of other OSes, timeout
                // is clamped to 1000 years, which is allowable per the API of `wait_timeout`
                // because of spurious wakeups.

                dur = max_dur;
            }

            // First, figure out what time it currently is, in both system and
            // stable time.  pthread_cond_timedwait uses system time, but we want to
            // report timeout based on stable time.
            let mut sys_now = libc::timeval { tv_sec: 0, tv_usec: 0 };
            let stable_now = Instant::now();
            let r = libc::gettimeofday(&mut sys_now, ptr::null_mut());
            debug_assert_eq!(r, 0);

            let nsec = dur.subsec_nanos() as libc::c_long +
                       (sys_now.tv_usec * 1000) as libc::c_long;
            let extra = (nsec / 1_000_000_000) as libc::time_t;
            let nsec = nsec % 1_000_000_000;
            let seconds = saturating_cast_to_time_t(dur.as_secs());

            let timeout = sys_now.tv_sec.checked_add(extra).and_then(|s| {
                s.checked_add(seconds)
            }).map(|s| {
                libc::timespec { tv_sec: s, tv_nsec: nsec }
            }).unwrap_or(TIMESPEC_MAX);

            // And wait!
            let r = libc::pthread_cond_timedwait(self.inner.get(), mutex::raw(mutex),
                                                &timeout);
            debug_assert!(r == libc::ETIMEDOUT || r == 0);

            // ETIMEDOUT is not a totally reliable method of determining timeout due
            // to clock shifts, so do the check ourselves
            stable_now.elapsed() < dur
        }

        #[inline]
        #[cfg(not(target_os = "dragonfly"))]
        pub unsafe fn destroy(&self) {
            let r = libc::pthread_cond_destroy(self.inner.get());
            debug_assert_eq!(r, 0);
        }

        #[inline]
        #[cfg(target_os = "dragonfly")]
        pub unsafe fn destroy(&self) {
            let r = libc::pthread_cond_destroy(self.inner.get());
            // On DragonFly pthread_cond_destroy() returns EINVAL if called on
            // a condvar that was just initialized with
            // libc::PTHREAD_COND_INITIALIZER. Once it is used or
            // pthread_cond_init() is called, this behaviour no longer occurs.
            debug_assert!(r == 0 || r == libc::EINVAL);
        }
    }

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