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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 lock_api;
    use raw_mutex::RawMutex;

    /// A mutual exclusion primitive useful for protecting shared data
    ///
    /// This mutex will block threads waiting for the lock to become available. The
    /// mutex can also be statically initialized or created via a `new`
    /// constructor. Each mutex has a type parameter which represents the data that
    /// it is protecting. The data can only be accessed through the RAII guards
    /// returned from `lock` and `try_lock`, which guarantees that the data is only
    /// ever accessed when the mutex is locked.
    ///
    /// # Fairness
    ///
    /// A typical unfair lock can often end up in a situation where a single thread
    /// quickly acquires and releases the same mutex in succession, which can starve
    /// other threads waiting to acquire the mutex. While this improves performance
    /// because it doesn't force a context switch when a thread tries to re-acquire
    /// a mutex it has just released, this can starve other threads.
    ///
    /// This mutex uses [eventual fairness](https://trac.webkit.org/changeset/203350)
    /// to ensure that the lock will be fair on average without sacrificing
    /// performance. This is done by forcing a fair unlock on average every 0.5ms,
    /// which will force the lock to go to the next thread waiting for the mutex.
    ///
    /// Additionally, any critical section longer than 1ms will always use a fair
    /// unlock, which has a negligible performance impact compared to the length of
    /// the critical section.
    ///
    /// You can also force a fair unlock by calling `MutexGuard::unlock_fair` when
    /// unlocking a mutex instead of simply dropping the `MutexGuard`.
    ///
    /// # Differences from the standard library `Mutex`
    ///
    /// - No poisoning, the lock is released normally on panic.
    /// - Only requires 1 byte of space, whereas the standard library boxes the
    ///   `Mutex` due to platform limitations.
    /// - Can be statically constructed (requires the `const_fn` nightly feature).
    /// - Does not require any drop glue when dropped.
    /// - Inline fast path for the uncontended case.
    /// - Efficient handling of micro-contention using adaptive spinning.
    /// - Allows raw locking & unlocking without a guard.
    /// - Supports eventual fairness so that the mutex is fair on average.
    /// - Optionally allows making the mutex fair by calling `MutexGuard::unlock_fair`.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::sync::Arc;
    /// use parking_lot::Mutex;
    /// use std::thread;
    /// use std::sync::mpsc::channel;
    ///
    /// const N: usize = 10;
    ///
    /// // Spawn a few threads to increment a shared variable (non-atomically), and
    /// // let the main thread know once all increments are done.
    /// //
    /// // Here we're using an Arc to share memory among threads, and the data inside
    /// // the Arc is protected with a mutex.
    /// let data = Arc::new(Mutex::new(0));
    ///
    /// let (tx, rx) = channel();
    /// for _ in 0..10 {
    ///     let (data, tx) = (data.clone(), tx.clone());
    ///     thread::spawn(move || {
    ///         // The shared state can only be accessed once the lock is held.
    ///         // Our non-atomic increment is safe because we're the only thread
    ///         // which can access the shared state when the lock is held.
    ///         let mut data = data.lock();
    ///         *data += 1;
    ///         if *data == N {
    ///             tx.send(()).unwrap();
    ///         }
    ///         // the lock is unlocked here when `data` goes out of scope.
    ///     });
    /// }
    ///
    /// rx.recv().unwrap();
    /// ```
    pub type Mutex<T> = lock_api::Mutex<RawMutex, T>;

    /// An RAII implementation of a "scoped lock" of a mutex. When this structure is
    /// dropped (falls out of scope), the lock will be unlocked.
    ///
    /// The data protected by the mutex can be accessed through this guard via its
    /// `Deref` and `DerefMut` implementations.
    pub type MutexGuard<'a, T> = lock_api::MutexGuard<'a, RawMutex, T>;

    /// An RAII mutex guard returned by `MutexGuard::map`, which can point to a
    /// subfield of the protected data.
    ///
    /// The main difference between `MappedMutexGuard` and `MutexGuard` is that the
    /// former doesn't support temporarily unlocking and re-locking, since that
    /// could introduce soundness issues if the locked object is modified by another
    /// thread.
    pub type MappedMutexGuard<'a, T> = lock_api::MappedMutexGuard<'a, RawMutex, T>;

    #[cfg(test)]
    mod tests {
        use std::sync::atomic::{AtomicUsize, Ordering};
        use std::sync::mpsc::channel;
        use std::sync::Arc;
        use std::thread;
        use {Condvar, Mutex};

        struct Packet<T>(Arc<(Mutex<T>, Condvar)>);

        #[derive(Eq, PartialEq, Debug)]
        struct NonCopy(i32);

        unsafe impl<T: Send> Send for Packet<T> {}
        unsafe impl<T> Sync for Packet<T> {}

        #[test]
        fn smoke() {
            let m = Mutex::new(());
            drop(m.lock());
            drop(m.lock());
        }

        #[test]
        fn lots_and_lots() {
            const J: u32 = 1000;
            const K: u32 = 3;

            let m = Arc::new(Mutex::new(0));

            fn inc(m: &Mutex<u32>) {
                for _ in 0..J {
                    *m.lock() += 1;
                }
            }

            let (tx, rx) = channel();
            for _ in 0..K {
                let tx2 = tx.clone();
                let m2 = m.clone();
                thread::spawn(move || {
                    inc(&m2);
                    tx2.send(()).unwrap();
                });
                let tx2 = tx.clone();
                let m2 = m.clone();
                thread::spawn(move || {
                    inc(&m2);
                    tx2.send(()).unwrap();
                });
            }

            drop(tx);
            for _ in 0..2 * K {
                rx.recv().unwrap();
            }
            assert_eq!(*m.lock(), J * K * 2);
        }

        #[test]
        fn try_lock() {
            let m = Mutex::new(());
            *m.try_lock().unwrap() = ();
        }

        #[test]
        fn test_into_inner() {
            let m = Mutex::new(NonCopy(10));
            assert_eq!(m.into_inner(), NonCopy(10));
        }

        #[test]
        fn test_into_inner_drop() {
            struct Foo(Arc<AtomicUsize>);
            impl Drop for Foo {
                fn drop(&mut self) {
                    self.0.fetch_add(1, Ordering::SeqCst);
                }
            }
            let num_drops = Arc::new(AtomicUsize::new(0));
            let m = Mutex::new(Foo(num_drops.clone()));
            assert_eq!(num_drops.load(Ordering::SeqCst), 0);
            {
                let _inner = m.into_inner();
                assert_eq!(num_drops.load(Ordering::SeqCst), 0);
            }
            assert_eq!(num_drops.load(Ordering::SeqCst), 1);
        }

        #[test]
        fn test_get_mut() {
            let mut m = Mutex::new(NonCopy(10));
            *m.get_mut() = NonCopy(20);
            assert_eq!(m.into_inner(), NonCopy(20));
        }

        #[test]
        fn test_mutex_arc_condvar() {
            let packet = Packet(Arc::new((Mutex::new(false), Condvar::new())));
            let packet2 = Packet(packet.0.clone());
            let (tx, rx) = channel();
            let _t = thread::spawn(move || {
                // wait until parent gets in
                rx.recv().unwrap();
                let &(ref lock, ref cvar) = &*packet2.0;
                let mut lock = lock.lock();
                *lock = true;
                cvar.notify_one();
            });

            let &(ref lock, ref cvar) = &*packet.0;
            let mut lock = lock.lock();
            tx.send(()).unwrap();
            assert!(!*lock);
            while !*lock {
                cvar.wait(&mut lock);
            }
        }

        #[test]
        fn test_mutex_arc_nested() {
            // Tests nested mutexes and access
            // to underlying data.
            let arc = Arc::new(Mutex::new(1));
            let arc2 = Arc::new(Mutex::new(arc));
            let (tx, rx) = channel();
            let _t = thread::spawn(move || {
                let lock = arc2.lock();
                let lock2 = lock.lock();
                assert_eq!(*lock2, 1);
                tx.send(()).unwrap();
            });
            rx.recv().unwrap();
        }

        #[test]
        fn test_mutex_arc_access_in_unwind() {
            let arc = Arc::new(Mutex::new(1));
            let arc2 = arc.clone();
            let _ = thread::spawn(move || -> () {
                struct Unwinder {
                    i: Arc<Mutex<i32>>,
                }
                impl Drop for Unwinder {
                    fn drop(&mut self) {
                        *self.i.lock() += 1;
                    }
                }
                let _u = Unwinder { i: arc2 };
                panic!();
            })
            .join();
            let lock = arc.lock();
            assert_eq!(*lock, 2);
        }

        #[test]
        fn test_mutex_unsized() {
            let mutex: &Mutex<[i32]> = &Mutex::new([1, 2, 3]);
            {
                let b = &mut *mutex.lock();
                b[0] = 4;
                b[2] = 5;
            }
            let comp: &[i32] = &[4, 2, 5];
            assert_eq!(&*mutex.lock(), comp);
        }

        #[test]
        fn test_mutexguard_sync() {
            fn sync<T: Sync>(_: T) {}

            let mutex = Mutex::new(());
            sync(mutex.lock());
        }

        #[test]
        fn test_mutex_debug() {
            let mutex = Mutex::new(vec![0u8, 10]);

            assert_eq!(format!("{:?}", mutex), "Mutex { data: [0, 10] }");
            assert_eq!(
                format!("{:#?}", mutex),
                "Mutex {
        data: [
            0,
            10
        ]
    }"
            );
            let _lock = mutex.lock();
            assert_eq!(format!("{:?}", mutex), "Mutex { <locked> }");
        }
    }

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