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    // Copyright 2016 Amanieu d'Antras
    //
    // Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
    // http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
    // http://opensource.org/licenses/MIT>, at your option. This file may not be
    // copied, modified, or distributed except according to those terms.

    use core::{
        ptr,
        sync::atomic::{AtomicI32, Ordering},
    };
    use instant::Instant;
    use libc;
    use std::thread;

    // x32 Linux uses a non-standard type for tv_nsec in timespec.
    // See https://sourceware.org/bugzilla/show_bug.cgi?id=16437
    #[cfg(all(target_arch = "x86_64", target_pointer_width = "32"))]
    #[allow(non_camel_case_types)]
    type tv_nsec_t = i64;
    #[cfg(not(all(target_arch = "x86_64", target_pointer_width = "32")))]
    #[allow(non_camel_case_types)]
    type tv_nsec_t = libc::c_long;

    fn errno() -> libc::c_int {
        #[cfg(target_os = "linux")]
        unsafe {
            *libc::__errno_location()
        }
        #[cfg(target_os = "android")]
        unsafe {
            *libc::__errno()
        }
    }

    // Helper type for putting a thread to sleep until some other thread wakes it up
    pub struct ThreadParker {
        futex: AtomicI32,
    }

    impl super::ThreadParkerT for ThreadParker {
        type UnparkHandle = UnparkHandle;

        const IS_CHEAP_TO_CONSTRUCT: bool = true;

        #[inline]
        fn new() -> ThreadParker {
            ThreadParker {
                futex: AtomicI32::new(0),
            }
        }

        #[inline]
        unsafe fn prepare_park(&self) {
            self.futex.store(1, Ordering::Relaxed);
        }

        #[inline]
        unsafe fn timed_out(&self) -> bool {
            self.futex.load(Ordering::Relaxed) != 0
        }

        #[inline]
        unsafe fn park(&self) {
            while self.futex.load(Ordering::Acquire) != 0 {
                self.futex_wait(None);
            }
        }

        #[inline]
        unsafe fn park_until(&self, timeout: Instant) -> bool {
            while self.futex.load(Ordering::Acquire) != 0 {
                let now = Instant::now();
                if timeout <= now {
                    return false;
                }
                let diff = timeout - now;
                if diff.as_secs() as libc::time_t as u64 != diff.as_secs() {
                    // Timeout overflowed, just sleep indefinitely
                    self.park();
                    return true;
                }
                let ts = libc::timespec {
                    tv_sec: diff.as_secs() as libc::time_t,
                    tv_nsec: diff.subsec_nanos() as tv_nsec_t,
                };
                self.futex_wait(Some(ts));
            }
            true
        }

        // Locks the parker to prevent the target thread from exiting. This is
        // necessary to ensure that thread-local ThreadData objects remain valid.
        // This should be called while holding the queue lock.
        #[inline]
        unsafe fn unpark_lock(&self) -> UnparkHandle {
            // We don't need to lock anything, just clear the state
            self.futex.store(0, Ordering::Release);

            UnparkHandle { futex: &self.futex }
        }
    }

    impl ThreadParker {
        #[inline]
        fn futex_wait(&self, ts: Option<libc::timespec>) {
            let ts_ptr = ts
                .as_ref()
                .map(|ts_ref| ts_ref as *const _)
                .unwrap_or(ptr::null());
            let r = unsafe {
                libc::syscall(
                    libc::SYS_futex,
                    &self.futex,
                    libc::FUTEX_WAIT | libc::FUTEX_PRIVATE_FLAG,
                    1,
                    ts_ptr,
                )
            };
            debug_assert!(r == 0 || r == -1);
            if r == -1 {
                debug_assert!(
                    errno() == libc::EINTR
                        || errno() == libc::EAGAIN
                        || (ts.is_some() && errno() == libc::ETIMEDOUT)
                );
            }
        }
    }

    pub struct UnparkHandle {
        futex: *const AtomicI32,
    }

    impl super::UnparkHandleT for UnparkHandle {
        #[inline]
        unsafe fn unpark(self) {
            // The thread data may have been freed at this point, but it doesn't
            // matter since the syscall will just return EFAULT in that case.
            let r = libc::syscall(
                libc::SYS_futex,
                self.futex,
                libc::FUTEX_WAKE | libc::FUTEX_PRIVATE_FLAG,
                1,
            );
            debug_assert!(r == 0 || r == 1 || r == -1);
            if r == -1 {
                debug_assert_eq!(errno(), libc::EFAULT);
            }
        }
    }

    #[inline]
    pub fn thread_yield() {
        thread::yield_now();
    }