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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 crate::raw_fair_mutex::RawFairMutex;
    use lock_api;

    /// A mutual exclusive primitive that is always fair, 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.
    ///
    /// The regular mutex provided by `parking_lot` uses eventual locking fairness
    /// (after some time it will default to the fair algorithm), but eventual
    /// fairness does not provide the same garantees a always fair method would.
    /// Fair mutexes are generally slower, but sometimes needed. This wrapper was
    /// created to avoid using a unfair protocol when it's forbidden by mistake.
    ///
    /// In a fair mutex the lock is provided to whichever thread asked first,
    /// they form a queue and always follow the first-in first-out order. This
    /// means some thread in the queue won't be able to steal the lock and use it fast
    /// to increase throughput, at the cost of latency. Since the response time will grow
    /// for some threads that are waiting for the lock and losing to faster but later ones,
    /// but it may make sending more responses possible.
    ///
    /// A fair mutex may not be interesting if threads have different priorities (this is known as
    /// priority inversion).
    ///
    /// # 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
    ///   `FairMutex` 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.
    ///
    /// # Examples
    ///
    /// ```
    /// use parking_lot::FairMutex;
    /// use std::sync::{Arc, mpsc::channel};
    /// use std::thread;
    ///
    /// 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(FairMutex::new(0));
    ///
    /// let (tx, rx) = channel();
    /// for _ in 0..10 {
    ///     let (data, tx) = (Arc::clone(&data), 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 FairMutex<T> = lock_api::Mutex<RawFairMutex, T>;

    /// Creates a new fair mutex in an unlocked state ready for use.
    ///
    /// This allows creating a fair mutex in a constant context on stable Rust.
    pub const fn const_fair_mutex<T>(val: T) -> FairMutex<T> {
        FairMutex::const_new(<RawFairMutex as lock_api::RawMutex>::INIT, val)
    }

    /// 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 FairMutexGuard<'a, T> = lock_api::MutexGuard<'a, RawFairMutex, T>;

    /// An RAII mutex guard returned by `FairMutexGuard::map`, which can point to a
    /// subfield of the protected data.
    ///
    /// The main difference between `MappedFairMutexGuard` and `FairMutexGuard` 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 MappedFairMutexGuard<'a, T> = lock_api::MappedMutexGuard<'a, RawFairMutex, T>;

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

        #[cfg(feature = "serde")]
        use bincode::{deserialize, serialize};

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

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

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

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

            fn inc(m: &FairMutex<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 = FairMutex::new(());
            *m.try_lock().unwrap() = ();
        }

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

        #[test]
        fn test_mutex_arc_nested() {
            // Tests nested mutexes and access
            // to underlying data.
            let arc = Arc::new(FairMutex::new(1));
            let arc2 = Arc::new(FairMutex::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(FairMutex::new(1));
            let arc2 = arc.clone();
            let _ = thread::spawn(move || {
                struct Unwinder {
                    i: Arc<FairMutex<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: &FairMutex<[i32]> = &FairMutex::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 = FairMutex::new(());
            sync(mutex.lock());
        }

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

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

        #[cfg(feature = "serde")]
        #[test]
        fn test_serde() {
            let contents: Vec<u8> = vec![0, 1, 2];
            let mutex = FairMutex::new(contents.clone());

            let serialized = serialize(&mutex).unwrap();
            let deserialized: FairMutex<Vec<u8>> = deserialize(&serialized).unwrap();

            assert_eq!(*(mutex.lock()), *(deserialized.lock()));
            assert_eq!(contents, *(deserialized.lock()));
        }
    }