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    // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.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 sys::mutex as imp;

    /// An OS-based mutual exclusion lock.
    ///
    /// This is the thinnest cross-platform wrapper around OS mutexes. All usage of
    /// this mutex is unsafe and it is recommended to instead use the safe wrapper
    /// at the top level of the crate instead of this type.
    pub struct Mutex(imp::Mutex);

    unsafe impl Sync for Mutex {}

    impl Mutex {
        /// Creates a new mutex for use.
        ///
        /// Behavior is undefined if the mutex is moved after it is
        /// first used with any of the functions below.
        pub const fn new() -> Mutex { Mutex(imp::Mutex::new()) }

        /// Prepare the mutex for use.
        ///
        /// This should be called once the mutex is at a stable memory address.
        #[inline]
        pub unsafe fn init(&mut self) { self.0.init() }

        /// Locks the mutex blocking the current thread until it is available.
        ///
        /// Behavior is undefined if the mutex has been moved between this and any
        /// previous function call.
        #[inline]
        pub unsafe fn raw_lock(&self) { self.0.lock() }

        /// Calls raw_lock() and then returns an RAII guard to guarantee the mutex
        /// will be unlocked.
        #[inline]
        pub unsafe fn lock(&self) -> MutexGuard {
            self.raw_lock();
            MutexGuard(&self.0)
        }

        /// Attempts to lock the mutex without blocking, returning whether it was
        /// successfully acquired or not.
        ///
        /// Behavior is undefined if the mutex has been moved between this and any
        /// previous function call.
        #[inline]
        pub unsafe fn try_lock(&self) -> bool { self.0.try_lock() }

        /// Unlocks the mutex.
        ///
        /// Behavior is undefined if the current thread does not actually hold the
        /// mutex.
        ///
        /// Consider switching from the pair of raw_lock() and raw_unlock() to
        /// lock() whenever possible.
        #[inline]
        pub unsafe fn raw_unlock(&self) { self.0.unlock() }

        /// Deallocates all resources associated with this mutex.
        ///
        /// Behavior is undefined if there are current or will be future users of
        /// this mutex.
        #[inline]
        pub unsafe fn destroy(&self) { self.0.destroy() }
    }

    // not meant to be exported to the outside world, just the containing module
    pub fn raw(mutex: &Mutex) -> &imp::Mutex { &mutex.0 }

    #[must_use]
    /// A simple RAII utility for the above Mutex without the poisoning semantics.
    pub struct MutexGuard<'a>(&'a imp::Mutex);

    impl<'a> Drop for MutexGuard<'a> {
        #[inline]
        fn drop(&mut self) {
            unsafe { self.0.unlock(); }
        }
    }

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