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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::rwlock as imp;

    /// An OS-based reader-writer lock.
    ///
    /// This structure is entirely unsafe and serves as the lowest layer of a
    /// cross-platform binding of system rwlocks. It is recommended to use the
    /// safer types at the top level of this crate instead of this type.
    pub struct RWLock(imp::RWLock);

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

        /// Acquires shared access to the underlying lock, blocking the current
        /// thread to do so.
        ///
        /// Behavior is undefined if the rwlock has been moved between this and any
        /// previous method call.
        #[inline]
        pub unsafe fn read(&self) { self.0.read() }

        /// Attempts to acquire shared access to this lock, returning whether it
        /// succeeded or not.
        ///
        /// This function does not block the current thread.
        ///
        /// Behavior is undefined if the rwlock has been moved between this and any
        /// previous method call.
        #[inline]
        pub unsafe fn try_read(&self) -> bool { self.0.try_read() }

        /// Acquires write access to the underlying lock, blocking the current thread
        /// to do so.
        ///
        /// Behavior is undefined if the rwlock has been moved between this and any
        /// previous method call.
        #[inline]
        pub unsafe fn write(&self) { self.0.write() }

        /// Attempts to acquire exclusive access to this lock, returning whether it
        /// succeeded or not.
        ///
        /// This function does not block the current thread.
        ///
        /// Behavior is undefined if the rwlock has been moved between this and any
        /// previous method call.
        #[inline]
        pub unsafe fn try_write(&self) -> bool { self.0.try_write() }

        /// Unlocks previously acquired shared access to this lock.
        ///
        /// Behavior is undefined if the current thread does not have shared access.
        #[inline]
        pub unsafe fn read_unlock(&self) { self.0.read_unlock() }

        /// Unlocks previously acquired exclusive access to this lock.
        ///
        /// Behavior is undefined if the current thread does not currently have
        /// exclusive access.
        #[inline]
        pub unsafe fn write_unlock(&self) { self.0.write_unlock() }

        /// Destroys OS-related resources with this RWLock.
        ///
        /// Behavior is undefined if there are any currently active users of this
        /// lock.
        #[inline]
        pub unsafe fn destroy(&self) { self.0.destroy() }
    }

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