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    // Copyright 2018 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::cell::UnsafeCell;
    use core::fmt;
    use core::marker::PhantomData;
    use core::mem;
    use core::ops::{Deref, DerefMut};

    #[cfg(feature = "owning_ref")]
    use owning_ref::StableAddress;

    #[cfg(feature = "serde")]
    use serde::{Deserialize, Deserializer, Serialize, Serializer};

    /// Basic operations for a mutex.
    ///
    /// Types implementing this trait can be used by `Mutex` to form a safe and
    /// fully-functioning mutex type.
    ///
    /// # Safety
    ///
    /// Implementations of this trait must ensure that the mutex is actually
    /// exclusive: a lock can't be acquired while the mutex is already locked.
    pub unsafe trait RawMutex {
        /// Initial value for an unlocked mutex.
        // A “non-constant” const item is a legacy way to supply an initialized value to downstream
        // static items. Can hopefully be replaced with `const fn new() -> Self` at some point.
        #[allow(clippy::declare_interior_mutable_const)]
        const INIT: Self;

        /// Marker type which determines whether a lock guard should be `Send`. Use
        /// one of the `GuardSend` or `GuardNoSend` helper types here.
        type GuardMarker;

        /// Acquires this mutex, blocking the current thread until it is able to do so.
        fn lock(&self);

        /// Attempts to acquire this mutex without blocking. Returns `true`
        /// if the lock was successfully acquired and `false` otherwise.
        fn try_lock(&self) -> bool;

        /// Unlocks this mutex.
        ///
        /// # Safety
        ///
        /// This method may only be called if the mutex is held in the current context, i.e. it must
        /// be paired with a successful call to [`lock`], [`try_lock`], [`try_lock_for`] or [`try_lock_until`].
        ///
        /// [`lock`]: #tymethod.lock
        /// [`try_lock`]: #tymethod.try_lock
        /// [`try_lock_for`]: trait.RawMutexTimed.html#tymethod.try_lock_for
        /// [`try_lock_until`]: trait.RawMutexTimed.html#tymethod.try_lock_until
        unsafe fn unlock(&self);

        /// Checks whether the mutex is currently locked.
        #[inline]
        fn is_locked(&self) -> bool {
            let acquired_lock = self.try_lock();
            if acquired_lock {
                // Safety: The lock has been successfully acquired above.
                unsafe {
                    self.unlock();
                }
            }
            !acquired_lock
        }
    }

    /// Additional methods for mutexes which support fair unlocking.
    ///
    /// Fair unlocking means that a lock is handed directly over to the next waiting
    /// thread if there is one, without giving other threads the opportunity to
    /// "steal" the lock in the meantime. This is typically slower than unfair
    /// unlocking, but may be necessary in certain circumstances.
    pub unsafe trait RawMutexFair: RawMutex {
        /// Unlocks this mutex using a fair unlock protocol.
        ///
        /// # Safety
        ///
        /// This method may only be called if the mutex is held in the current context, see
        /// the documentation of [`unlock`].
        ///
        /// [`unlock`]: trait.RawMutex.html#tymethod.unlock
        unsafe fn unlock_fair(&self);

        /// Temporarily yields the mutex to a waiting thread if there is one.
        ///
        /// This method is functionally equivalent to calling `unlock_fair` followed
        /// by `lock`, however it can be much more efficient in the case where there
        /// are no waiting threads.
        ///
        /// # Safety
        ///
        /// This method may only be called if the mutex is held in the current context, see
        /// the documentation of [`unlock`].
        ///
        /// [`unlock`]: trait.RawMutex.html#tymethod.unlock
        unsafe fn bump(&self) {
            self.unlock_fair();
            self.lock();
        }
    }

    /// Additional methods for mutexes which support locking with timeouts.
    ///
    /// The `Duration` and `Instant` types are specified as associated types so that
    /// this trait is usable even in `no_std` environments.
    pub unsafe trait RawMutexTimed: RawMutex {
        /// Duration type used for `try_lock_for`.
        type Duration;

        /// Instant type used for `try_lock_until`.
        type Instant;

        /// Attempts to acquire this lock until a timeout is reached.
        fn try_lock_for(&self, timeout: Self::Duration) -> bool;

        /// Attempts to acquire this lock until a timeout is reached.
        fn try_lock_until(&self, timeout: Self::Instant) -> bool;
    }

    /// 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.
    pub struct Mutex<R, T: ?Sized> {
        raw: R,
        data: UnsafeCell<T>,
    }

    unsafe impl<R: RawMutex + Send, T: ?Sized + Send> Send for Mutex<R, T> {}
    unsafe impl<R: RawMutex + Sync, T: ?Sized + Send> Sync for Mutex<R, T> {}

    impl<R: RawMutex, T> Mutex<R, T> {
        /// Creates a new mutex in an unlocked state ready for use.
        #[cfg(feature = "nightly")]
        #[inline]
        pub const fn new(val: T) -> Mutex<R, T> {
            Mutex {
                raw: R::INIT,
                data: UnsafeCell::new(val),
            }
        }

        /// Creates a new mutex in an unlocked state ready for use.
        #[cfg(not(feature = "nightly"))]
        #[inline]
        pub fn new(val: T) -> Mutex<R, T> {
            Mutex {
                raw: R::INIT,
                data: UnsafeCell::new(val),
            }
        }

        /// Consumes this mutex, returning the underlying data.
        #[inline]
        pub fn into_inner(self) -> T {
            self.data.into_inner()
        }
    }

    impl<R, T> Mutex<R, T> {
        /// Creates a new mutex based on a pre-existing raw mutex.
        ///
        /// This allows creating a mutex in a constant context on stable Rust.
        #[inline]
        pub const fn const_new(raw_mutex: R, val: T) -> Mutex<R, T> {
            Mutex {
                raw: raw_mutex,
                data: UnsafeCell::new(val),
            }
        }
    }

    impl<R: RawMutex, T: ?Sized> Mutex<R, T> {
        /// # Safety
        ///
        /// The lock must be held when calling this method.
        #[inline]
        unsafe fn guard(&self) -> MutexGuard<'_, R, T> {
            MutexGuard {
                mutex: self,
                marker: PhantomData,
            }
        }

        /// Acquires a mutex, blocking the current thread until it is able to do so.
        ///
        /// This function will block the local thread until it is available to acquire
        /// the mutex. Upon returning, the thread is the only thread with the mutex
        /// held. An RAII guard is returned to allow scoped unlock of the lock. When
        /// the guard goes out of scope, the mutex will be unlocked.
        ///
        /// Attempts to lock a mutex in the thread which already holds the lock will
        /// result in a deadlock.
        #[inline]
        pub fn lock(&self) -> MutexGuard<'_, R, T> {
            self.raw.lock();
            // SAFETY: The lock is held, as required.
            unsafe { self.guard() }
        }

        /// Attempts to acquire this lock.
        ///
        /// If the lock could not be acquired at this time, then `None` is returned.
        /// Otherwise, an RAII guard is returned. The lock will be unlocked when the
        /// guard is dropped.
        ///
        /// This function does not block.
        #[inline]
        pub fn try_lock(&self) -> Option<MutexGuard<'_, R, T>> {
            if self.raw.try_lock() {
                // SAFETY: The lock is held, as required.
                Some(unsafe { self.guard() })
            } else {
                None
            }
        }

        /// Returns a mutable reference to the underlying data.
        ///
        /// Since this call borrows the `Mutex` mutably, no actual locking needs to
        /// take place---the mutable borrow statically guarantees no locks exist.
        #[inline]
        pub fn get_mut(&mut self) -> &mut T {
            unsafe { &mut *self.data.get() }
        }

        /// Checks whether the mutex is currently locked.
        #[inline]
        pub fn is_locked(&self) -> bool {
            self.raw.is_locked()
        }

        /// Forcibly unlocks the mutex.
        ///
        /// This is useful when combined with `mem::forget` to hold a lock without
        /// the need to maintain a `MutexGuard` object alive, for example when
        /// dealing with FFI.
        ///
        /// # Safety
        ///
        /// This method must only be called if the current thread logically owns a
        /// `MutexGuard` but that guard has be discarded using `mem::forget`.
        /// Behavior is undefined if a mutex is unlocked when not locked.
        #[inline]
        pub unsafe fn force_unlock(&self) {
            self.raw.unlock();
        }

        /// Returns the underlying raw mutex object.
        ///
        /// Note that you will most likely need to import the `RawMutex` trait from
        /// `lock_api` to be able to call functions on the raw mutex.
        ///
        /// # Safety
        ///
        /// This method is unsafe because it allows unlocking a mutex while
        /// still holding a reference to a `MutexGuard`.
        #[inline]
        pub unsafe fn raw(&self) -> &R {
            &self.raw
        }

        /// Returns a raw pointer to the underlying data.
        ///
        /// This is useful when combined with `mem::forget` to hold a lock without
        /// the need to maintain a `MutexGuard` object alive, for example when
        /// dealing with FFI.
        ///
        /// # Safety
        ///
        /// You must ensure that there are no data races when dereferencing the
        /// returned pointer, for example if the current thread logically owns
        /// a `MutexGuard` but that guard has been discarded using `mem::forget`.
        #[inline]
        pub fn data_ptr(&self) -> *mut T {
            self.data.get()
        }
    }

    impl<R: RawMutexFair, T: ?Sized> Mutex<R, T> {
        /// Forcibly unlocks the mutex using a fair unlock procotol.
        ///
        /// This is useful when combined with `mem::forget` to hold a lock without
        /// the need to maintain a `MutexGuard` object alive, for example when
        /// dealing with FFI.
        ///
        /// # Safety
        ///
        /// This method must only be called if the current thread logically owns a
        /// `MutexGuard` but that guard has be discarded using `mem::forget`.
        /// Behavior is undefined if a mutex is unlocked when not locked.
        #[inline]
        pub unsafe fn force_unlock_fair(&self) {
            self.raw.unlock_fair();
        }
    }

    impl<R: RawMutexTimed, T: ?Sized> Mutex<R, T> {
        /// Attempts to acquire this lock until a timeout is reached.
        ///
        /// If the lock could not be acquired before the timeout expired, then
        /// `None` is returned. Otherwise, an RAII guard is returned. The lock will
        /// be unlocked when the guard is dropped.
        #[inline]
        pub fn try_lock_for(&self, timeout: R::Duration) -> Option<MutexGuard<'_, R, T>> {
            if self.raw.try_lock_for(timeout) {
                // SAFETY: The lock is held, as required.
                Some(unsafe { self.guard() })
            } else {
                None
            }
        }

        /// Attempts to acquire this lock until a timeout is reached.
        ///
        /// If the lock could not be acquired before the timeout expired, then
        /// `None` is returned. Otherwise, an RAII guard is returned. The lock will
        /// be unlocked when the guard is dropped.
        #[inline]
        pub fn try_lock_until(&self, timeout: R::Instant) -> Option<MutexGuard<'_, R, T>> {
            if self.raw.try_lock_until(timeout) {
                // SAFETY: The lock is held, as required.
                Some(unsafe { self.guard() })
            } else {
                None
            }
        }
    }

    impl<R: RawMutex, T: ?Sized + Default> Default for Mutex<R, T> {
        #[inline]
        fn default() -> Mutex<R, T> {
            Mutex::new(Default::default())
        }
    }

    impl<R: RawMutex, T> From<T> for Mutex<R, T> {
        #[inline]
        fn from(t: T) -> Mutex<R, T> {
            Mutex::new(t)
        }
    }

    impl<R: RawMutex, T: ?Sized + fmt::Debug> fmt::Debug for Mutex<R, T> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            match self.try_lock() {
                Some(guard) => f.debug_struct("Mutex").field("data", &&*guard).finish(),
                None => {
                    struct LockedPlaceholder;
                    impl fmt::Debug for LockedPlaceholder {
                        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                            f.write_str("<locked>")
                        }
                    }

                    f.debug_struct("Mutex")
                        .field("data", &LockedPlaceholder)
                        .finish()
                }
            }
        }
    }

    // Copied and modified from serde
    #[cfg(feature = "serde")]
    impl<R, T> Serialize for Mutex<R, T>
    where
        R: RawMutex,
        T: Serialize + ?Sized,
    {
        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: Serializer,
        {
            self.lock().serialize(serializer)
        }
    }

    #[cfg(feature = "serde")]
    impl<'de, R, T> Deserialize<'de> for Mutex<R, T>
    where
        R: RawMutex,
        T: Deserialize<'de> + ?Sized,
    {
        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where
            D: Deserializer<'de>,
        {
            Deserialize::deserialize(deserializer).map(Mutex::new)
        }
    }

    /// 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.
    #[must_use = "if unused the Mutex will immediately unlock"]
    pub struct MutexGuard<'a, R: RawMutex, T: ?Sized> {
        mutex: &'a Mutex<R, T>,
        marker: PhantomData<(&'a mut T, R::GuardMarker)>,
    }

    unsafe impl<'a, R: RawMutex + Sync + 'a, T: ?Sized + Sync + 'a> Sync for MutexGuard<'a, R, T> {}

    impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> MutexGuard<'a, R, T> {
        /// Returns a reference to the original `Mutex` object.
        pub fn mutex(s: &Self) -> &'a Mutex<R, T> {
            s.mutex
        }

        /// Makes a new `MappedMutexGuard` for a component of the locked data.
        ///
        /// This operation cannot fail as the `MutexGuard` passed
        /// in already locked the mutex.
        ///
        /// This is an associated function that needs to be
        /// used as `MutexGuard::map(...)`. A method would interfere with methods of
        /// the same name on the contents of the locked data.
        #[inline]
        pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedMutexGuard<'a, R, U>
        where
            F: FnOnce(&mut T) -> &mut U,
        {
            let raw = &s.mutex.raw;
            let data = f(unsafe { &mut *s.mutex.data.get() });
            mem::forget(s);
            MappedMutexGuard {
                raw,
                data,
                marker: PhantomData,
            }
        }

        /// Attempts to make a new `MappedMutexGuard` for a component of the
        /// locked data. The original guard is returned if the closure returns `None`.
        ///
        /// This operation cannot fail as the `MutexGuard` passed
        /// in already locked the mutex.
        ///
        /// This is an associated function that needs to be
        /// used as `MutexGuard::try_map(...)`. A method would interfere with methods of
        /// the same name on the contents of the locked data.
        #[inline]
        pub fn try_map<U: ?Sized, F>(s: Self, f: F) -> Result<MappedMutexGuard<'a, R, U>, Self>
        where
            F: FnOnce(&mut T) -> Option<&mut U>,
        {
            let raw = &s.mutex.raw;
            let data = match f(unsafe { &mut *s.mutex.data.get() }) {
                Some(data) => data,
                None => return Err(s),
            };
            mem::forget(s);
            Ok(MappedMutexGuard {
                raw,
                data,
                marker: PhantomData,
            })
        }

        /// Temporarily unlocks the mutex to execute the given function.
        ///
        /// This is safe because `&mut` guarantees that there exist no other
        /// references to the data protected by the mutex.
        #[inline]
        pub fn unlocked<F, U>(s: &mut Self, f: F) -> U
        where
            F: FnOnce() -> U,
        {
            // Safety: A MutexGuard always holds the lock.
            unsafe {
                s.mutex.raw.unlock();
            }
            defer!(s.mutex.raw.lock());
            f()
        }
    }

    impl<'a, R: RawMutexFair + 'a, T: ?Sized + 'a> MutexGuard<'a, R, T> {
        /// Unlocks the mutex using a fair unlock protocol.
        ///
        /// By default, mutexes are unfair and allow the current thread to re-lock
        /// the mutex before another has the chance to acquire the lock, even if
        /// that thread has been blocked on the mutex for a long time. This is the
        /// default because it allows much higher throughput as it avoids forcing a
        /// context switch on every mutex unlock. This can result in one thread
        /// acquiring a mutex many more times than other threads.
        ///
        /// However in some cases it can be beneficial to ensure fairness by forcing
        /// the lock to pass on to a waiting thread if there is one. This is done by
        /// using this method instead of dropping the `MutexGuard` normally.
        #[inline]
        pub fn unlock_fair(s: Self) {
            // Safety: A MutexGuard always holds the lock.
            unsafe {
                s.mutex.raw.unlock_fair();
            }
            mem::forget(s);
        }

        /// Temporarily unlocks the mutex to execute the given function.
        ///
        /// The mutex is unlocked using a fair unlock protocol.
        ///
        /// This is safe because `&mut` guarantees that there exist no other
        /// references to the data protected by the mutex.
        #[inline]
        pub fn unlocked_fair<F, U>(s: &mut Self, f: F) -> U
        where
            F: FnOnce() -> U,
        {
            // Safety: A MutexGuard always holds the lock.
            unsafe {
                s.mutex.raw.unlock_fair();
            }
            defer!(s.mutex.raw.lock());
            f()
        }

        /// Temporarily yields the mutex to a waiting thread if there is one.
        ///
        /// This method is functionally equivalent to calling `unlock_fair` followed
        /// by `lock`, however it can be much more efficient in the case where there
        /// are no waiting threads.
        #[inline]
        pub fn bump(s: &mut Self) {
            // Safety: A MutexGuard always holds the lock.
            unsafe {
                s.mutex.raw.bump();
            }
        }
    }

    impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Deref for MutexGuard<'a, R, T> {
        type Target = T;
        #[inline]
        fn deref(&self) -> &T {
            unsafe { &*self.mutex.data.get() }
        }
    }

    impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> DerefMut for MutexGuard<'a, R, T> {
        #[inline]
        fn deref_mut(&mut self) -> &mut T {
            unsafe { &mut *self.mutex.data.get() }
        }
    }

    impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Drop for MutexGuard<'a, R, T> {
        #[inline]
        fn drop(&mut self) {
            // Safety: A MutexGuard always holds the lock.
            unsafe {
                self.mutex.raw.unlock();
            }
        }
    }

    impl<'a, R: RawMutex + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug for MutexGuard<'a, R, T> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            fmt::Debug::fmt(&**self, f)
        }
    }

    impl<'a, R: RawMutex + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display for MutexGuard<'a, R, T> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            (**self).fmt(f)
        }
    }

    #[cfg(feature = "owning_ref")]
    unsafe impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> StableAddress for MutexGuard<'a, R, 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.
    #[must_use = "if unused the Mutex will immediately unlock"]
    pub struct MappedMutexGuard<'a, R: RawMutex, T: ?Sized> {
        raw: &'a R,
        data: *mut T,
        marker: PhantomData<&'a mut T>,
    }

    unsafe impl<'a, R: RawMutex + Sync + 'a, T: ?Sized + Sync + 'a> Sync
        for MappedMutexGuard<'a, R, T>
    {
    }
    unsafe impl<'a, R: RawMutex + 'a, T: ?Sized + Send + 'a> Send for MappedMutexGuard<'a, R, T> where
        R::GuardMarker: Send
    {
    }

    impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> MappedMutexGuard<'a, R, T> {
        /// Makes a new `MappedMutexGuard` for a component of the locked data.
        ///
        /// This operation cannot fail as the `MappedMutexGuard` passed
        /// in already locked the mutex.
        ///
        /// This is an associated function that needs to be
        /// used as `MappedMutexGuard::map(...)`. A method would interfere with methods of
        /// the same name on the contents of the locked data.
        #[inline]
        pub fn map<U: ?Sized, F>(s: Self, f: F) -> MappedMutexGuard<'a, R, U>
        where
            F: FnOnce(&mut T) -> &mut U,
        {
            let raw = s.raw;
            let data = f(unsafe { &mut *s.data });
            mem::forget(s);
            MappedMutexGuard {
                raw,
                data,
                marker: PhantomData,
            }
        }

        /// Attempts to make a new `MappedMutexGuard` for a component of the
        /// locked data. The original guard is returned if the closure returns `None`.
        ///
        /// This operation cannot fail as the `MappedMutexGuard` passed
        /// in already locked the mutex.
        ///
        /// This is an associated function that needs to be
        /// used as `MappedMutexGuard::try_map(...)`. A method would interfere with methods of
        /// the same name on the contents of the locked data.
        #[inline]
        pub fn try_map<U: ?Sized, F>(s: Self, f: F) -> Result<MappedMutexGuard<'a, R, U>, Self>
        where
            F: FnOnce(&mut T) -> Option<&mut U>,
        {
            let raw = s.raw;
            let data = match f(unsafe { &mut *s.data }) {
                Some(data) => data,
                None => return Err(s),
            };
            mem::forget(s);
            Ok(MappedMutexGuard {
                raw,
                data,
                marker: PhantomData,
            })
        }
    }

    impl<'a, R: RawMutexFair + 'a, T: ?Sized + 'a> MappedMutexGuard<'a, R, T> {
        /// Unlocks the mutex using a fair unlock protocol.
        ///
        /// By default, mutexes are unfair and allow the current thread to re-lock
        /// the mutex before another has the chance to acquire the lock, even if
        /// that thread has been blocked on the mutex for a long time. This is the
        /// default because it allows much higher throughput as it avoids forcing a
        /// context switch on every mutex unlock. This can result in one thread
        /// acquiring a mutex many more times than other threads.
        ///
        /// However in some cases it can be beneficial to ensure fairness by forcing
        /// the lock to pass on to a waiting thread if there is one. This is done by
        /// using this method instead of dropping the `MutexGuard` normally.
        #[inline]
        pub fn unlock_fair(s: Self) {
            // Safety: A MutexGuard always holds the lock.
            unsafe {
                s.raw.unlock_fair();
            }
            mem::forget(s);
        }
    }

    impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Deref for MappedMutexGuard<'a, R, T> {
        type Target = T;
        #[inline]
        fn deref(&self) -> &T {
            unsafe { &*self.data }
        }
    }

    impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> DerefMut for MappedMutexGuard<'a, R, T> {
        #[inline]
        fn deref_mut(&mut self) -> &mut T {
            unsafe { &mut *self.data }
        }
    }

    impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> Drop for MappedMutexGuard<'a, R, T> {
        #[inline]
        fn drop(&mut self) {
            // Safety: A MappedMutexGuard always holds the lock.
            unsafe {
                self.raw.unlock();
            }
        }
    }

    impl<'a, R: RawMutex + 'a, T: fmt::Debug + ?Sized + 'a> fmt::Debug for MappedMutexGuard<'a, R, T> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            fmt::Debug::fmt(&**self, f)
        }
    }

    impl<'a, R: RawMutex + 'a, T: fmt::Display + ?Sized + 'a> fmt::Display
        for MappedMutexGuard<'a, R, T>
    {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            (**self).fmt(f)
        }
    }

    #[cfg(feature = "owning_ref")]
    unsafe impl<'a, R: RawMutex + 'a, T: ?Sized + 'a> StableAddress for MappedMutexGuard<'a, R, T> {}