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    #[cfg(all(test, not(target_os = "emscripten")))]
    mod tests;

    use crate::cell::UnsafeCell;
    use crate::fmt;
    use crate::mem;
    use crate::ops::{Deref, DerefMut};
    use crate::ptr;
    use crate::sys_common::mutex as sys;
    use crate::sys_common::poison::{self, LockResult, TryLockError, TryLockResult};

    /// 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.
    ///
    /// # Poisoning
    ///
    /// The mutexes in this module implement a strategy called "poisoning" where a
    /// mutex is considered poisoned whenever a thread panics while holding the
    /// mutex. Once a mutex is poisoned, all other threads are unable to access the
    /// data by default as it is likely tainted (some invariant is not being
    /// upheld).
    ///
    /// For a mutex, this means that the [`lock`] and [`try_lock`] methods return a
    /// [`Result`] which indicates whether a mutex has been poisoned or not. Most
    /// usage of a mutex will simply [`unwrap()`] these results, propagating panics
    /// among threads to ensure that a possibly invalid invariant is not witnessed.
    ///
    /// A poisoned mutex, however, does not prevent all access to the underlying
    /// data. The [`PoisonError`] type has an [`into_inner`] method which will return
    /// the guard that would have otherwise been returned on a successful lock. This
    /// allows access to the data, despite the lock being poisoned.
    ///
    /// [`new`]: Self::new
    /// [`lock`]: Self::lock
    /// [`try_lock`]: Self::try_lock
    /// [`unwrap()`]: Result::unwrap
    /// [`PoisonError`]: super::PoisonError
    /// [`into_inner`]: super::PoisonError::into_inner
    ///
    /// # Examples
    ///
    /// ```
    /// use std::sync::{Arc, 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..N {
    ///     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.
    ///         //
    ///         // We unwrap() the return value to assert that we are not expecting
    ///         // threads to ever fail while holding the lock.
    ///         let mut data = data.lock().unwrap();
    ///         *data += 1;
    ///         if *data == N {
    ///             tx.send(()).unwrap();
    ///         }
    ///         // the lock is unlocked here when `data` goes out of scope.
    ///     });
    /// }
    ///
    /// rx.recv().unwrap();
    /// ```
    ///
    /// To recover from a poisoned mutex:
    ///
    /// ```
    /// use std::sync::{Arc, Mutex};
    /// use std::thread;
    ///
    /// let lock = Arc::new(Mutex::new(0_u32));
    /// let lock2 = Arc::clone(&lock);
    ///
    /// let _ = thread::spawn(move || -> () {
    ///     // This thread will acquire the mutex first, unwrapping the result of
    ///     // `lock` because the lock has not been poisoned.
    ///     let _guard = lock2.lock().unwrap();
    ///
    ///     // This panic while holding the lock (`_guard` is in scope) will poison
    ///     // the mutex.
    ///     panic!();
    /// }).join();
    ///
    /// // The lock is poisoned by this point, but the returned result can be
    /// // pattern matched on to return the underlying guard on both branches.
    /// let mut guard = match lock.lock() {
    ///     Ok(guard) => guard,
    ///     Err(poisoned) => poisoned.into_inner(),
    /// };
    ///
    /// *guard += 1;
    /// ```
    ///
    /// It is sometimes necessary to manually drop the mutex guard to unlock it
    /// sooner than the end of the enclosing scope.
    ///
    /// ```
    /// use std::sync::{Arc, Mutex};
    /// use std::thread;
    ///
    /// const N: usize = 3;
    ///
    /// let data_mutex = Arc::new(Mutex::new(vec![1, 2, 3, 4]));
    /// let res_mutex = Arc::new(Mutex::new(0));
    ///
    /// let mut threads = Vec::with_capacity(N);
    /// (0..N).for_each(|_| {
    ///     let data_mutex_clone = Arc::clone(&data_mutex);
    ///     let res_mutex_clone = Arc::clone(&res_mutex);
    ///
    ///     threads.push(thread::spawn(move || {
    ///         let mut data = data_mutex_clone.lock().unwrap();
    ///         // This is the result of some important and long-ish work.
    ///         let result = data.iter().fold(0, |acc, x| acc + x * 2);
    ///         data.push(result);
    ///         drop(data);
    ///         *res_mutex_clone.lock().unwrap() += result;
    ///     }));
    /// });
    ///
    /// let mut data = data_mutex.lock().unwrap();
    /// // This is the result of some important and long-ish work.
    /// let result = data.iter().fold(0, |acc, x| acc + x * 2);
    /// data.push(result);
    /// // We drop the `data` explicitly because it's not necessary anymore and the
    /// // thread still has work to do. This allow other threads to start working on
    /// // the data immediately, without waiting for the rest of the unrelated work
    /// // to be done here.
    /// //
    /// // It's even more important here than in the threads because we `.join` the
    /// // threads after that. If we had not dropped the mutex guard, a thread could
    /// // be waiting forever for it, causing a deadlock.
    /// drop(data);
    /// // Here the mutex guard is not assigned to a variable and so, even if the
    /// // scope does not end after this line, the mutex is still released: there is
    /// // no deadlock.
    /// *res_mutex.lock().unwrap() += result;
    ///
    /// threads.into_iter().for_each(|thread| {
    ///     thread
    ///         .join()
    ///         .expect("The thread creating or execution failed !")
    /// });
    ///
    /// assert_eq!(*res_mutex.lock().unwrap(), 800);
    /// ```
    #[stable(feature = "rust1", since = "1.0.0")]
    #[cfg_attr(not(test), rustc_diagnostic_item = "mutex_type")]
    pub struct Mutex<T: ?Sized> {
        inner: sys::MovableMutex,
        poison: poison::Flag,
        data: UnsafeCell<T>,
    }

    // these are the only places where `T: Send` matters; all other
    // functionality works fine on a single thread.
    #[stable(feature = "rust1", since = "1.0.0")]
    unsafe impl<T: ?Sized + Send> Send for Mutex<T> {}
    #[stable(feature = "rust1", since = "1.0.0")]
    unsafe impl<T: ?Sized + Send> Sync for Mutex<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.
    ///
    /// This structure is created by the [`lock`] and [`try_lock`] methods on
    /// [`Mutex`].
    ///
    /// [`lock`]: Mutex::lock
    /// [`try_lock`]: Mutex::try_lock
    #[must_use = "if unused the Mutex will immediately unlock"]
    #[stable(feature = "rust1", since = "1.0.0")]
    pub struct MutexGuard<'a, T: ?Sized + 'a> {
        lock: &'a Mutex<T>,
        poison: poison::Guard,
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> !Send for MutexGuard<'_, T> {}
    #[stable(feature = "mutexguard", since = "1.19.0")]
    unsafe impl<T: ?Sized + Sync> Sync for MutexGuard<'_, T> {}

    impl<T> Mutex<T> {
        /// Creates a new mutex in an unlocked state ready for use.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::sync::Mutex;
        ///
        /// let mutex = Mutex::new(0);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn new(t: T) -> Mutex<T> {
            Mutex {
                inner: sys::MovableMutex::new(),
                poison: poison::Flag::new(),
                data: UnsafeCell::new(t),
            }
        }
    }

    impl<T: ?Sized> Mutex<T> {
        /// 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 lock
        /// 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.
        ///
        /// The exact behavior on locking a mutex in the thread which already holds
        /// the lock is left unspecified. However, this function will not return on
        /// the second call (it might panic or deadlock, for example).
        ///
        /// # Errors
        ///
        /// If another user of this mutex panicked while holding the mutex, then
        /// this call will return an error once the mutex is acquired.
        ///
        /// # Panics
        ///
        /// This function might panic when called if the lock is already held by
        /// the current thread.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::sync::{Arc, Mutex};
        /// use std::thread;
        ///
        /// let mutex = Arc::new(Mutex::new(0));
        /// let c_mutex = Arc::clone(&mutex);
        ///
        /// thread::spawn(move || {
        ///     *c_mutex.lock().unwrap() = 10;
        /// }).join().expect("thread::spawn failed");
        /// assert_eq!(*mutex.lock().unwrap(), 10);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn lock(&self) -> LockResult<MutexGuard<'_, T>> {
            unsafe {
                self.inner.raw_lock();
                MutexGuard::new(self)
            }
        }

        /// Attempts to acquire this lock.
        ///
        /// If the lock could not be acquired at this time, then [`Err`] is returned.
        /// Otherwise, an RAII guard is returned. The lock will be unlocked when the
        /// guard is dropped.
        ///
        /// This function does not block.
        ///
        /// # Errors
        ///
        /// If another user of this mutex panicked while holding the mutex, then
        /// this call will return an error if the mutex would otherwise be
        /// acquired.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::sync::{Arc, Mutex};
        /// use std::thread;
        ///
        /// let mutex = Arc::new(Mutex::new(0));
        /// let c_mutex = Arc::clone(&mutex);
        ///
        /// thread::spawn(move || {
        ///     let mut lock = c_mutex.try_lock();
        ///     if let Ok(ref mut mutex) = lock {
        ///         **mutex = 10;
        ///     } else {
        ///         println!("try_lock failed");
        ///     }
        /// }).join().expect("thread::spawn failed");
        /// assert_eq!(*mutex.lock().unwrap(), 10);
        /// ```
        #[stable(feature = "rust1", since = "1.0.0")]
        pub fn try_lock(&self) -> TryLockResult<MutexGuard<'_, T>> {
            unsafe {
                if self.inner.try_lock() {
                    Ok(MutexGuard::new(self)?)
                } else {
                    Err(TryLockError::WouldBlock)
                }
            }
        }

        /// Determines whether the mutex is poisoned.
        ///
        /// If another thread is active, the mutex can still become poisoned at any
        /// time. You should not trust a `false` value for program correctness
        /// without additional synchronization.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::sync::{Arc, Mutex};
        /// use std::thread;
        ///
        /// let mutex = Arc::new(Mutex::new(0));
        /// let c_mutex = Arc::clone(&mutex);
        ///
        /// let _ = thread::spawn(move || {
        ///     let _lock = c_mutex.lock().unwrap();
        ///     panic!(); // the mutex gets poisoned
        /// }).join();
        /// assert_eq!(mutex.is_poisoned(), true);
        /// ```
        #[inline]
        #[stable(feature = "sync_poison", since = "1.2.0")]
        pub fn is_poisoned(&self) -> bool {
            self.poison.get()
        }

        /// Consumes this mutex, returning the underlying data.
        ///
        /// # Errors
        ///
        /// If another user of this mutex panicked while holding the mutex, then
        /// this call will return an error instead.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::sync::Mutex;
        ///
        /// let mutex = Mutex::new(0);
        /// assert_eq!(mutex.into_inner().unwrap(), 0);
        /// ```
        #[stable(feature = "mutex_into_inner", since = "1.6.0")]
        pub fn into_inner(self) -> LockResult<T>
        where
            T: Sized,
        {
            // We know statically that there are no outstanding references to
            // `self` so there's no need to lock the inner mutex.
            //
            // To get the inner value, we'd like to call `data.into_inner()`,
            // but because `Mutex` impl-s `Drop`, we can't move out of it, so
            // we'll have to destructure it manually instead.
            unsafe {
                // Like `let Mutex { inner, poison, data } = self`.
                let (inner, poison, data) = {
                    let Mutex { ref inner, ref poison, ref data } = self;
                    (ptr::read(inner), ptr::read(poison), ptr::read(data))
                };
                mem::forget(self);
                drop(inner);

                poison::map_result(poison.borrow(), |_| data.into_inner())
            }
        }

        /// 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.
        ///
        /// # Errors
        ///
        /// If another user of this mutex panicked while holding the mutex, then
        /// this call will return an error instead.
        ///
        /// # Examples
        ///
        /// ```
        /// use std::sync::Mutex;
        ///
        /// let mut mutex = Mutex::new(0);
        /// *mutex.get_mut().unwrap() = 10;
        /// assert_eq!(*mutex.lock().unwrap(), 10);
        /// ```
        #[stable(feature = "mutex_get_mut", since = "1.6.0")]
        pub fn get_mut(&mut self) -> LockResult<&mut T> {
            let data = self.data.get_mut();
            poison::map_result(self.poison.borrow(), |_| data)
        }
    }

    #[stable(feature = "mutex_from", since = "1.24.0")]
    impl<T> From<T> for Mutex<T> {
        /// Creates a new mutex in an unlocked state ready for use.
        /// This is equivalent to [`Mutex::new`].
        fn from(t: T) -> Self {
            Mutex::new(t)
        }
    }

    #[stable(feature = "mutex_default", since = "1.10.0")]
    impl<T: ?Sized + Default> Default for Mutex<T> {
        /// Creates a `Mutex<T>`, with the `Default` value for T.
        fn default() -> Mutex<T> {
            Mutex::new(Default::default())
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            match self.try_lock() {
                Ok(guard) => f.debug_struct("Mutex").field("data", &&*guard).finish(),
                Err(TryLockError::Poisoned(err)) => {
                    f.debug_struct("Mutex").field("data", &&**err.get_ref()).finish()
                }
                Err(TryLockError::WouldBlock) => {
                    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()
                }
            }
        }
    }

    impl<'mutex, T: ?Sized> MutexGuard<'mutex, T> {
        unsafe fn new(lock: &'mutex Mutex<T>) -> LockResult<MutexGuard<'mutex, T>> {
            poison::map_result(lock.poison.borrow(), |guard| MutexGuard { lock, poison: guard })
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Deref for MutexGuard<'_, T> {
        type Target = T;

        fn deref(&self) -> &T {
            unsafe { &*self.lock.data.get() }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> DerefMut for MutexGuard<'_, T> {
        fn deref_mut(&mut self) -> &mut T {
            unsafe { &mut *self.lock.data.get() }
        }
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl<T: ?Sized> Drop for MutexGuard<'_, T> {
        #[inline]
        fn drop(&mut self) {
            unsafe {
                self.lock.poison.done(&self.poison);
                self.lock.inner.raw_unlock();
            }
        }
    }

    #[stable(feature = "std_debug", since = "1.16.0")]
    impl<T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'_, T> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            fmt::Debug::fmt(&**self, f)
        }
    }

    #[stable(feature = "std_guard_impls", since = "1.20.0")]
    impl<T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'_, T> {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            (**self).fmt(f)
        }
    }

    pub fn guard_lock<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a sys::MovableMutex {
        &guard.lock.inner
    }

    pub fn guard_poison<'a, T: ?Sized>(guard: &MutexGuard<'a, T>) -> &'a poison::Flag {
        &guard.lock.poison
    }