/rust/registry/src/index.crates.io-1949cf8c6b5b557f/spin-0.9.8/src/mutex/spin.rs

Source
//! A naïve spinning mutex.
//!
//! Waiting threads hammer an atomic variable until it becomes available. Best-case latency is low, but worst-case
//! latency is theoretically infinite.

use crate::{
    atomic::{AtomicBool, Ordering},
    RelaxStrategy, Spin,
};
use core::{
    cell::UnsafeCell,
    fmt,
    marker::PhantomData,
    mem::ManuallyDrop,
    ops::{Deref, DerefMut},
};

/// A [spin lock](https://en.m.wikipedia.org/wiki/Spinlock) providing mutually exclusive access to data.
///
/// # Example
///
/// ```
/// use spin;
///
/// let lock = spin::mutex::SpinMutex::<_>::new(0);
///
/// // Modify the data
/// *lock.lock() = 2;
///
/// // Read the data
/// let answer = *lock.lock();
/// assert_eq!(answer, 2);
/// ```
///
/// # Thread safety example
///
/// ```
/// use spin;
/// use std::sync::{Arc, Barrier};
///
/// let thread_count = 1000;
/// let spin_mutex = Arc::new(spin::mutex::SpinMutex::<_>::new(0));
///
/// // We use a barrier to ensure the readout happens after all writing
/// let barrier = Arc::new(Barrier::new(thread_count + 1));
///
/// # let mut ts = Vec::new();
/// for _ in (0..thread_count) {
///     let my_barrier = barrier.clone();
///     let my_lock = spin_mutex.clone();
/// # let t =
///     std::thread::spawn(move || {
///         let mut guard = my_lock.lock();
///         *guard += 1;
///
///         // Release the lock to prevent a deadlock
///         drop(guard);
///         my_barrier.wait();
///     });
/// # ts.push(t);
/// }
///
/// barrier.wait();
///
/// let answer = { *spin_mutex.lock() };
/// assert_eq!(answer, thread_count);
///
/// # for t in ts {
/// #     t.join().unwrap();
/// # }
/// ```
pub struct SpinMutex<T: ?Sized, R = Spin> {
    phantom: PhantomData<R>,
    pub(crate) lock: AtomicBool,
    data: UnsafeCell<T>,
}

/// A guard that provides mutable data access.
///
/// When the guard falls out of scope it will release the lock.
pub struct SpinMutexGuard<'a, T: ?Sized + 'a> {
    lock: &'a AtomicBool,
    data: *mut T,
}

// Same unsafe impls as `std::sync::Mutex`
unsafe impl<T: ?Sized + Send, R> Sync for SpinMutex<T, R> {}
unsafe impl<T: ?Sized + Send, R> Send for SpinMutex<T, R> {}

unsafe impl<T: ?Sized + Sync> Sync for SpinMutexGuard<'_, T> {}
unsafe impl<T: ?Sized + Send> Send for SpinMutexGuard<'_, T> {}

impl<T, R> SpinMutex<T, R> {
    /// Creates a new [`SpinMutex`] wrapping the supplied data.
    ///
    /// # Example
    ///
    /// ```
    /// use spin::mutex::SpinMutex;
    ///
    /// static MUTEX: SpinMutex<()> = SpinMutex::<_>::new(());
    ///
    /// fn demo() {
    ///     let lock = MUTEX.lock();
    ///     // do something with lock
    ///     drop(lock);
    /// }
    /// ```
    #[inline(always)]
    pub const fn new(data: T) -> Self {
        SpinMutex {
            lock: AtomicBool::new(false),
            data: UnsafeCell::new(data),
            phantom: PhantomData,
        }
    }

    /// Consumes this [`SpinMutex`] and unwraps the underlying data.
    ///
    /// # Example
    ///
    /// ```
    /// let lock = spin::mutex::SpinMutex::<_>::new(42);
    /// assert_eq!(42, lock.into_inner());
    /// ```
    #[inline(always)]
    pub fn into_inner(self) -> T {
        // We know statically that there are no outstanding references to
        // `self` so there's no need to lock.
        let SpinMutex { data, .. } = self;
        data.into_inner()
    }

    /// Returns a mutable pointer to the underlying data.
    ///
    /// This is mostly meant to be used for applications which require manual unlocking, but where
    /// storing both the lock and the pointer to the inner data gets inefficient.
    ///
    /// # Example
    /// ```
    /// let lock = spin::mutex::SpinMutex::<_>::new(42);
    ///
    /// unsafe {
    ///     core::mem::forget(lock.lock());
    ///
    ///     assert_eq!(lock.as_mut_ptr().read(), 42);
    ///     lock.as_mut_ptr().write(58);
    ///
    ///     lock.force_unlock();
    /// }
    ///
    /// assert_eq!(*lock.lock(), 58);
    ///
    /// ```
    #[inline(always)]
    pub fn as_mut_ptr(&self) -> *mut T {
        self.data.get()
    }
}

impl<T: ?Sized, R: RelaxStrategy> SpinMutex<T, R> {
    /// Locks the [`SpinMutex`] and returns a guard that permits access to the inner data.
    ///
    /// The returned value may be dereferenced for data access
    /// and the lock will be dropped when the guard falls out of scope.
    ///
    /// ```
    /// let lock = spin::mutex::SpinMutex::<_>::new(0);
    /// {
    ///     let mut data = lock.lock();
    ///     // The lock is now locked and the data can be accessed
    ///     *data += 1;
    ///     // The lock is implicitly dropped at the end of the scope
    /// }
    /// ```
    #[inline(always)]
    pub fn lock(&self) -> SpinMutexGuard<T> {
        // Can fail to lock even if the spinlock is not locked. May be more efficient than `try_lock`
        // when called in a loop.
        while self
            .lock
            .compare_exchange_weak(false, true, Ordering::Acquire, Ordering::Relaxed)
            .is_err()
        {
            // Wait until the lock looks unlocked before retrying
            while self.is_locked() {
                R::relax();
            }
        }

        SpinMutexGuard {
            lock: &self.lock,
            data: unsafe { &mut *self.data.get() },
        }
    }
}

impl<T: ?Sized, R> SpinMutex<T, R> {
    /// Returns `true` if the lock is currently held.
    ///
    /// # Safety
    ///
    /// This function provides no synchronization guarantees and so its result should be considered 'out of date'
    /// the instant it is called. Do not use it for synchronization purposes. However, it may be useful as a heuristic.
    #[inline(always)]
    pub fn is_locked(&self) -> bool {
        self.lock.load(Ordering::Relaxed)
    }

    /// Force unlock this [`SpinMutex`].
    ///
    /// # Safety
    ///
    /// This is *extremely* unsafe if the lock is not held by the current
    /// thread. However, this can be useful in some instances for exposing the
    /// lock to FFI that doesn't know how to deal with RAII.
    #[inline(always)]
    pub unsafe fn force_unlock(&self) {
        self.lock.store(false, Ordering::Release);
    }

    /// Try to lock this [`SpinMutex`], returning a lock guard if successful.
    ///
    /// # Example
    ///
    /// ```
    /// let lock = spin::mutex::SpinMutex::<_>::new(42);
    ///
    /// let maybe_guard = lock.try_lock();
    /// assert!(maybe_guard.is_some());
    ///
    /// // `maybe_guard` is still held, so the second call fails
    /// let maybe_guard2 = lock.try_lock();
    /// assert!(maybe_guard2.is_none());
    /// ```
    #[inline(always)]
    pub fn try_lock(&self) -> Option<SpinMutexGuard<T>> {
        // The reason for using a strong compare_exchange is explained here:
        // https://github.com/Amanieu/parking_lot/pull/207#issuecomment-575869107
        if self
            .lock
            .compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
            .is_ok()
        {
            Some(SpinMutexGuard {
                lock: &self.lock,
                data: unsafe { &mut *self.data.get() },
            })
        } else {
            None
        }
    }

    /// Returns a mutable reference to the underlying data.
    ///
    /// Since this call borrows the [`SpinMutex`] mutably, and a mutable reference is guaranteed to be exclusive in
    /// Rust, no actual locking needs to take place -- the mutable borrow statically guarantees no locks exist. As
    /// such, this is a 'zero-cost' operation.
    ///
    /// # Example
    ///
    /// ```
    /// let mut lock = spin::mutex::SpinMutex::<_>::new(0);
    /// *lock.get_mut() = 10;
    /// assert_eq!(*lock.lock(), 10);
    /// ```
    #[inline(always)]
    pub fn get_mut(&mut self) -> &mut T {
        // We know statically that there are no other references to `self`, so
        // there's no need to lock the inner mutex.
        unsafe { &mut *self.data.get() }
    }
}

impl<T: ?Sized + fmt::Debug, R> fmt::Debug for SpinMutex<T, R> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self.try_lock() {
            Some(guard) => write!(f, "Mutex {{ data: ")
                .and_then(|()| (&*guard).fmt(f))
                .and_then(|()| write!(f, "}}")),
            None => write!(f, "Mutex {{ <locked> }}"),
        }
    }
}

impl<T: ?Sized + Default, R> Default for SpinMutex<T, R> {
    fn default() -> Self {
        Self::new(Default::default())
    }
}

impl<T, R> From<T> for SpinMutex<T, R> {
    fn from(data: T) -> Self {
        Self::new(data)
    }
}

impl<'a, T: ?Sized> SpinMutexGuard<'a, T> {
    /// Leak the lock guard, yielding a mutable reference to the underlying data.
    ///
    /// Note that this function will permanently lock the original [`SpinMutex`].
    ///
    /// ```
    /// let mylock = spin::mutex::SpinMutex::<_>::new(0);
    ///
    /// let data: &mut i32 = spin::mutex::SpinMutexGuard::leak(mylock.lock());
    ///
    /// *data = 1;
    /// assert_eq!(*data, 1);
    /// ```
    #[inline(always)]
    pub fn leak(this: Self) -> &'a mut T {
        // Use ManuallyDrop to avoid stacked-borrow invalidation
        let mut this = ManuallyDrop::new(this);
        // We know statically that only we are referencing data
        unsafe { &mut *this.data }
    }
}

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

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

impl<'a, T: ?Sized> Deref for SpinMutexGuard<'a, T> {
    type Target = T;
    fn deref(&self) -> &T {
        // We know statically that only we are referencing data
        unsafe { &*self.data }
    }
}

impl<'a, T: ?Sized> DerefMut for SpinMutexGuard<'a, T> {
    fn deref_mut(&mut self) -> &mut T {
        // We know statically that only we are referencing data
        unsafe { &mut *self.data }
    }
}

impl<'a, T: ?Sized> Drop for SpinMutexGuard<'a, T> {
    /// The dropping of the MutexGuard will release the lock it was created from.
    fn drop(&mut self) {
        self.lock.store(false, Ordering::Release);
    }
}

#[cfg(feature = "lock_api")]
unsafe impl<R: RelaxStrategy> lock_api_crate::RawMutex for SpinMutex<(), R> {
    type GuardMarker = lock_api_crate::GuardSend;

    const INIT: Self = Self::new(());

    fn lock(&self) {
        // Prevent guard destructor running
        core::mem::forget(Self::lock(self));
    }

    fn try_lock(&self) -> bool {
        // Prevent guard destructor running
        Self::try_lock(self).map(core::mem::forget).is_some()
    }

    unsafe fn unlock(&self) {
        self.force_unlock();
    }

    fn is_locked(&self) -> bool {
        Self::is_locked(self)
    }
}

#[cfg(test)]
mod tests {
    use std::prelude::v1::*;

    use std::sync::atomic::{AtomicUsize, Ordering};
    use std::sync::mpsc::channel;
    use std::sync::Arc;
    use std::thread;

    type SpinMutex<T> = super::SpinMutex<T>;

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

    #[test]
    fn smoke() {
        let m = SpinMutex::<_>::new(());
        drop(m.lock());
        drop(m.lock());
    }

    #[test]
    fn lots_and_lots() {
        static M: SpinMutex<()> = SpinMutex::<_>::new(());
        static mut CNT: u32 = 0;
        const J: u32 = 1000;
        const K: u32 = 3;

        fn inc() {
            for _ in 0..J {
                unsafe {
                    let _g = M.lock();
                    CNT += 1;
                }
            }
        }

        let (tx, rx) = channel();
        let mut ts = Vec::new();
        for _ in 0..K {
            let tx2 = tx.clone();
            ts.push(thread::spawn(move || {
                inc();
                tx2.send(()).unwrap();
            }));
            let tx2 = tx.clone();
            ts.push(thread::spawn(move || {
                inc();
                tx2.send(()).unwrap();
            }));
        }

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

        for t in ts {
            t.join().unwrap();
        }
    }

    #[test]
    fn try_lock() {
        let mutex = SpinMutex::<_>::new(42);

        // First lock succeeds
        let a = mutex.try_lock();
        assert_eq!(a.as_ref().map(|r| **r), Some(42));

        // Additional lock fails
        let b = mutex.try_lock();
        assert!(b.is_none());

        // After dropping lock, it succeeds again
        ::core::mem::drop(a);
        let c = mutex.try_lock();
        assert_eq!(c.as_ref().map(|r| **r), Some(42));
    }

    #[test]
    fn test_into_inner() {
        let m = SpinMutex::<_>::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 = SpinMutex::<_>::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_mutex_arc_nested() {
        // Tests nested mutexes and access
        // to underlying data.
        let arc = Arc::new(SpinMutex::<_>::new(1));
        let arc2 = Arc::new(SpinMutex::<_>::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();
        t.join().unwrap();
    }

    #[test]
    fn test_mutex_arc_access_in_unwind() {
        let arc = Arc::new(SpinMutex::<_>::new(1));
        let arc2 = arc.clone();
        let _ = thread::spawn(move || -> () {
            struct Unwinder {
                i: Arc<SpinMutex<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: &SpinMutex<[i32]> = &SpinMutex::<_>::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_mutex_force_lock() {
        let lock = SpinMutex::<_>::new(());
        ::std::mem::forget(lock.lock());
        unsafe {
            lock.force_unlock();
        }
        assert!(lock.try_lock().is_some());
    }
}

Coverage Report

Created: 2025-10-12 06:35

Line	Count	Source
1		//! A naïve spinning mutex.
2		//!
3		//! Waiting threads hammer an atomic variable until it becomes available. Best-case latency is low, but worst-case
4		//! latency is theoretically infinite.
5
6		use crate::{
7		atomic::{AtomicBool, Ordering},
8		RelaxStrategy, Spin,
9		};
10		use core::{
11		cell::UnsafeCell,
12		fmt,
13		marker::PhantomData,
14		mem::ManuallyDrop,
15		ops::{Deref, DerefMut},
16		};
17
18		/// A [spin lock](https://en.m.wikipedia.org/wiki/Spinlock) providing mutually exclusive access to data.
19		///
20		/// # Example
21		///
22		/// ```
23		/// use spin;
24		///
25		/// let lock = spin::mutex::SpinMutex::<_>::new(0);
26		///
27		/// // Modify the data
28		/// *lock.lock() = 2;
29		///
30		/// // Read the data
31		/// let answer = *lock.lock();
32		/// assert_eq!(answer, 2);
33		/// ```
34		///
35		/// # Thread safety example
36		///
37		/// ```
38		/// use spin;
39		/// use std::sync::{Arc, Barrier};
40		///
41		/// let thread_count = 1000;
42		/// let spin_mutex = Arc::new(spin::mutex::SpinMutex::<_>::new(0));
43		///
44		/// // We use a barrier to ensure the readout happens after all writing
45		/// let barrier = Arc::new(Barrier::new(thread_count + 1));
46		///
47		/// # let mut ts = Vec::new();
48		/// for _ in (0..thread_count) {
49		/// let my_barrier = barrier.clone();
50		/// let my_lock = spin_mutex.clone();
51		/// # let t =
52		/// std::thread::spawn(move \|\| {
53		/// let mut guard = my_lock.lock();
54		/// *guard += 1;
55		///
56		/// // Release the lock to prevent a deadlock
57		/// drop(guard);
58		/// my_barrier.wait();
59		/// });
60		/// # ts.push(t);
61		/// }
62		///
63		/// barrier.wait();
64		///
65		/// let answer = { *spin_mutex.lock() };
66		/// assert_eq!(answer, thread_count);
67		///
68		/// # for t in ts {
69		/// # t.join().unwrap();
70		/// # }
71		/// ```
72		pub struct SpinMutex<T: ?Sized, R = Spin> {
73		phantom: PhantomData<R>,
74		pub(crate) lock: AtomicBool,
75		data: UnsafeCell<T>,
76		}
77
78		/// A guard that provides mutable data access.
79		///
80		/// When the guard falls out of scope it will release the lock.
81		pub struct SpinMutexGuard<'a, T: ?Sized + 'a> {
82		lock: &'a AtomicBool,
83		data: *mut T,
84		}
85
86		// Same unsafe impls as `std::sync::Mutex`
87		unsafe impl<T: ?Sized + Send, R> Sync for SpinMutex<T, R> {}
88		unsafe impl<T: ?Sized + Send, R> Send for SpinMutex<T, R> {}
89
90		unsafe impl<T: ?Sized + Sync> Sync for SpinMutexGuard<'_, T> {}
91		unsafe impl<T: ?Sized + Send> Send for SpinMutexGuard<'_, T> {}
92
93		impl<T, R> SpinMutex<T, R> {
94		/// Creates a new [`SpinMutex`] wrapping the supplied data.
95		///
96		/// # Example
97		///
98		/// ```
99		/// use spin::mutex::SpinMutex;
100		///
101		/// static MUTEX: SpinMutex<()> = SpinMutex::<_>::new(());
102		///
103		/// fn demo() {
104		/// let lock = MUTEX.lock();
105		/// // do something with lock
106		/// drop(lock);
107		/// }
108		/// ```
109		#[inline(always)]
110	0	pub const fn new(data: T) -> Self {
111	0	SpinMutex {
112	0	lock: AtomicBool::new(false),
113	0	data: UnsafeCell::new(data),
114	0	phantom: PhantomData,
115	0	}
116	0	} Unexecuted instantiation: <spin::mutex::spin::SpinMutex<alloc::collections::btree::map::BTreeMap<usize, alloc::boxed::Box<ring::digest::Context>>>>::new Unexecuted instantiation: <spin::mutex::spin::SpinMutex<_, _>>::new
117
118		/// Consumes this [`SpinMutex`] and unwraps the underlying data.
119		///
120		/// # Example
121		///
122		/// ```
123		/// let lock = spin::mutex::SpinMutex::<_>::new(42);
124		/// assert_eq!(42, lock.into_inner());
125		/// ```
126		#[inline(always)]
127	0	pub fn into_inner(self) -> T {
128		// We know statically that there are no outstanding references to
129		// `self` so there's no need to lock.
130	0	let SpinMutex { data, .. } = self;
131	0	data.into_inner()
132	0	}
133
134		/// Returns a mutable pointer to the underlying data.
135		///
136		/// This is mostly meant to be used for applications which require manual unlocking, but where
137		/// storing both the lock and the pointer to the inner data gets inefficient.
138		///
139		/// # Example
140		/// ```
141		/// let lock = spin::mutex::SpinMutex::<_>::new(42);
142		///
143		/// unsafe {
144		/// core::mem::forget(lock.lock());
145		///
146		/// assert_eq!(lock.as_mut_ptr().read(), 42);
147		/// lock.as_mut_ptr().write(58);
148		///
149		/// lock.force_unlock();
150		/// }
151		///
152		/// assert_eq!(*lock.lock(), 58);
153		///
154		/// ```
155		#[inline(always)]
156	0	pub fn as_mut_ptr(&self) -> *mut T {
157	0	self.data.get()
158	0	}
159		}
160
161		impl<T: ?Sized, R: RelaxStrategy> SpinMutex<T, R> {
162		/// Locks the [`SpinMutex`] and returns a guard that permits access to the inner data.
163		///
164		/// The returned value may be dereferenced for data access
165		/// and the lock will be dropped when the guard falls out of scope.
166		///
167		/// ```
168		/// let lock = spin::mutex::SpinMutex::<_>::new(0);
169		/// {
170		/// let mut data = lock.lock();
171		/// // The lock is now locked and the data can be accessed
172		/// *data += 1;
173		/// // The lock is implicitly dropped at the end of the scope
174		/// }
175		/// ```
176		#[inline(always)]
177	0	pub fn lock(&self) -> SpinMutexGuard<T> {
178		// Can fail to lock even if the spinlock is not locked. May be more efficient than `try_lock`
179		// when called in a loop.
180	0	while self
181	0	.lock
182	0	.compare_exchange_weak(false, true, Ordering::Acquire, Ordering::Relaxed)
183	0	.is_err()
184		{
185		// Wait until the lock looks unlocked before retrying
186	0	while self.is_locked() {
187	0	R::relax();
188	0	}
189		}
190
191	0	SpinMutexGuard {
192	0	lock: &self.lock,
193	0	data: unsafe { &mut *self.data.get() },
194	0	}
195	0	} Unexecuted instantiation: <spin::mutex::spin::SpinMutex<alloc::collections::btree::map::BTreeMap<usize, alloc::boxed::Box<ring::digest::Context>>>>::lock Unexecuted instantiation: <spin::mutex::spin::SpinMutex<_, _>>::lock
196		}
197
198		impl<T: ?Sized, R> SpinMutex<T, R> {
199		/// Returns `true` if the lock is currently held.
200		///
201		/// # Safety
202		///
203		/// This function provides no synchronization guarantees and so its result should be considered 'out of date'
204		/// the instant it is called. Do not use it for synchronization purposes. However, it may be useful as a heuristic.
205		#[inline(always)]
206	0	pub fn is_locked(&self) -> bool {
207	0	self.lock.load(Ordering::Relaxed)
208	0	} Unexecuted instantiation: <spin::mutex::spin::SpinMutex<alloc::collections::btree::map::BTreeMap<usize, alloc::boxed::Box<ring::digest::Context>>>>::is_locked Unexecuted instantiation: <spin::mutex::spin::SpinMutex<_, _>>::is_locked
209
210		/// Force unlock this [`SpinMutex`].
211		///
212		/// # Safety
213		///
214		/// This is extremely unsafe if the lock is not held by the current
215		/// thread. However, this can be useful in some instances for exposing the
216		/// lock to FFI that doesn't know how to deal with RAII.
217		#[inline(always)]
218	0	pub unsafe fn force_unlock(&self) {
219	0	self.lock.store(false, Ordering::Release);
220	0	}
221
222		/// Try to lock this [`SpinMutex`], returning a lock guard if successful.
223		///
224		/// # Example
225		///
226		/// ```
227		/// let lock = spin::mutex::SpinMutex::<_>::new(42);
228		///
229		/// let maybe_guard = lock.try_lock();
230		/// assert!(maybe_guard.is_some());
231		///
232		/// // `maybe_guard` is still held, so the second call fails
233		/// let maybe_guard2 = lock.try_lock();
234		/// assert!(maybe_guard2.is_none());
235		/// ```
236		#[inline(always)]
237	0	pub fn try_lock(&self) -> Option<SpinMutexGuard<T>> {
238		// The reason for using a strong compare_exchange is explained here:
239		// https://github.com/Amanieu/parking_lot/pull/207#issuecomment-575869107
240	0	if self
241	0	.lock
242	0	.compare_exchange(false, true, Ordering::Acquire, Ordering::Relaxed)
243	0	.is_ok()
244		{
245	0	Some(SpinMutexGuard {
246	0	lock: &self.lock,
247	0	data: unsafe { &mut *self.data.get() },
248	0	})
249		} else {
250	0	None
251		}
252	0	}
253
254		/// Returns a mutable reference to the underlying data.
255		///
256		/// Since this call borrows the [`SpinMutex`] mutably, and a mutable reference is guaranteed to be exclusive in
257		/// Rust, no actual locking needs to take place -- the mutable borrow statically guarantees no locks exist. As
258		/// such, this is a 'zero-cost' operation.
259		///
260		/// # Example
261		///
262		/// ```
263		/// let mut lock = spin::mutex::SpinMutex::<_>::new(0);
264		/// *lock.get_mut() = 10;
265		/// assert_eq!(*lock.lock(), 10);
266		/// ```
267		#[inline(always)]
268	0	pub fn get_mut(&mut self) -> &mut T {
269		// We know statically that there are no other references to `self`, so
270		// there's no need to lock the inner mutex.
271	0	unsafe { &mut *self.data.get() }
272	0	}
273		}
274
275		impl<T: ?Sized + fmt::Debug, R> fmt::Debug for SpinMutex<T, R> {
276	0	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
277	0	match self.try_lock() {
278	0	Some(guard) => write!(f, "Mutex {{ data: ")
279	0	.and_then(\|()\| (&*guard).fmt(f))
280	0	.and_then(\|()\| write!(f, "}}")),
281	0	None => write!(f, "Mutex {{ <locked> }}"),
282		}
283	0	}
284		}
285
286		impl<T: ?Sized + Default, R> Default for SpinMutex<T, R> {
287	0	fn default() -> Self {
288	0	Self::new(Default::default())
289	0	}
290		}
291
292		impl<T, R> From<T> for SpinMutex<T, R> {
293	0	fn from(data: T) -> Self {
294	0	Self::new(data)
295	0	}
296		}
297
298		impl<'a, T: ?Sized> SpinMutexGuard<'a, T> {
299		/// Leak the lock guard, yielding a mutable reference to the underlying data.
300		///
301		/// Note that this function will permanently lock the original [`SpinMutex`].
302		///
303		/// ```
304		/// let mylock = spin::mutex::SpinMutex::<_>::new(0);
305		///
306		/// let data: &mut i32 = spin::mutex::SpinMutexGuard::leak(mylock.lock());
307		///
308		/// *data = 1;
309		/// assert_eq!(*data, 1);
310		/// ```
311		#[inline(always)]
312	0	pub fn leak(this: Self) -> &'a mut T {
313		// Use ManuallyDrop to avoid stacked-borrow invalidation
314	0	let mut this = ManuallyDrop::new(this);
315		// We know statically that only we are referencing data
316	0	unsafe { &mut *this.data }
317	0	}
318		}
319
320		impl<'a, T: ?Sized + fmt::Debug> fmt::Debug for SpinMutexGuard<'a, T> {
321	0	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
322	0	fmt::Debug::fmt(&**self, f)
323	0	}
324		}
325
326		impl<'a, T: ?Sized + fmt::Display> fmt::Display for SpinMutexGuard<'a, T> {
327	0	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
328	0	fmt::Display::fmt(&**self, f)
329	0	}
330		}
331
332		impl<'a, T: ?Sized> Deref for SpinMutexGuard<'a, T> {
333		type Target = T;
334	0	fn deref(&self) -> &T {
335		// We know statically that only we are referencing data
336	0	unsafe { &*self.data }
337	0	} Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<alloc::collections::btree::map::BTreeMap<usize, alloc::boxed::Box<ring::digest::Context>>> as core::ops::deref::Deref>::deref Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<_> as core::ops::deref::Deref>::deref
338		}
339
340		impl<'a, T: ?Sized> DerefMut for SpinMutexGuard<'a, T> {
341	0	fn deref_mut(&mut self) -> &mut T {
342		// We know statically that only we are referencing data
343	0	unsafe { &mut *self.data }
344	0	} Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<dyn spdmlib::common::SpdmTransportEncap + core::marker::Sync + core::marker::Send> as core::ops::deref::DerefMut>::deref_mut Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<alloc::collections::btree::map::BTreeMap<usize, alloc::boxed::Box<ring::digest::Context>>> as core::ops::deref::DerefMut>::deref_mut Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<_> as core::ops::deref::DerefMut>::deref_mut
345		}
346
347		impl<'a, T: ?Sized> Drop for SpinMutexGuard<'a, T> {
348		/// The dropping of the MutexGuard will release the lock it was created from.
349	0	fn drop(&mut self) {
350	0	self.lock.store(false, Ordering::Release);
351	0	} Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<dyn spdmlib::common::SpdmDeviceIo + core::marker::Sync + core::marker::Send> as core::ops::drop::Drop>::drop Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<alloc::collections::vec_deque::VecDeque<u8>> as core::ops::drop::Drop>::drop Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<spdmlib::responder::context::ResponderContext> as core::ops::drop::Drop>::drop Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<&mut [u8]> as core::ops::drop::Drop>::drop Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<dyn spdmlib::common::SpdmTransportEncap + core::marker::Sync + core::marker::Send> as core::ops::drop::Drop>::drop Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<alloc::collections::btree::map::BTreeMap<usize, alloc::boxed::Box<ring::digest::Context>>> as core::ops::drop::Drop>::drop Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<_> as core::ops::drop::Drop>::drop Unexecuted instantiation: <spin::mutex::spin::SpinMutexGuard<fuzzlib::fake_device_io::FakeSpdmDeviceIoReceve> as core::ops::drop::Drop>::drop
352		}
353
354		#[cfg(feature = "lock_api")]
355		unsafe impl<R: RelaxStrategy> lock_api_crate::RawMutex for SpinMutex<(), R> {
356		type GuardMarker = lock_api_crate::GuardSend;
357
358		const INIT: Self = Self::new(());
359
360	0	fn lock(&self) {
361		// Prevent guard destructor running
362	0	core::mem::forget(Self::lock(self));
363	0	}
364
365	0	fn try_lock(&self) -> bool {
366		// Prevent guard destructor running
367	0	Self::try_lock(self).map(core::mem::forget).is_some()
368	0	}
369
370	0	unsafe fn unlock(&self) {
371	0	self.force_unlock();
372	0	}
373
374	0	fn is_locked(&self) -> bool {
375	0	Self::is_locked(self)
376	0	}
377		}
378
379		#[cfg(test)]
380		mod tests {
381		use std::prelude::v1::*;
382
383		use std::sync::atomic::{AtomicUsize, Ordering};
384		use std::sync::mpsc::channel;
385		use std::sync::Arc;
386		use std::thread;
387
388		type SpinMutex<T> = super::SpinMutex<T>;
389
390		#[derive(Eq, PartialEq, Debug)]
391		struct NonCopy(i32);
392
393		#[test]
394		fn smoke() {
395		let m = SpinMutex::<_>::new(());
396		drop(m.lock());
397		drop(m.lock());
398		}
399
400		#[test]
401		fn lots_and_lots() {
402		static M: SpinMutex<()> = SpinMutex::<_>::new(());
403		static mut CNT: u32 = 0;
404		const J: u32 = 1000;
405		const K: u32 = 3;
406
407		fn inc() {
408		for _ in 0..J {
409		unsafe {
410		let _g = M.lock();
411		CNT += 1;
412		}
413		}
414		}
415
416		let (tx, rx) = channel();
417		let mut ts = Vec::new();
418		for _ in 0..K {
419		let tx2 = tx.clone();
420		ts.push(thread::spawn(move \|\| {
421		inc();
422		tx2.send(()).unwrap();
423		}));
424		let tx2 = tx.clone();
425		ts.push(thread::spawn(move \|\| {
426		inc();
427		tx2.send(()).unwrap();
428		}));
429		}
430
431		drop(tx);
432		for _ in 0..2 * K {
433		rx.recv().unwrap();
434		}
435		assert_eq!(unsafe { CNT }, J * K * 2);
436
437		for t in ts {
438		t.join().unwrap();
439		}
440		}
441
442		#[test]
443		fn try_lock() {
444		let mutex = SpinMutex::<_>::new(42);
445
446		// First lock succeeds
447		let a = mutex.try_lock();
448		assert_eq!(a.as_ref().map(\|r\| **r), Some(42));
449
450		// Additional lock fails
451		let b = mutex.try_lock();
452		assert!(b.is_none());
453
454		// After dropping lock, it succeeds again
455		::core::mem::drop(a);
456		let c = mutex.try_lock();
457		assert_eq!(c.as_ref().map(\|r\| **r), Some(42));
458		}
459
460		#[test]
461		fn test_into_inner() {
462		let m = SpinMutex::<_>::new(NonCopy(10));
463		assert_eq!(m.into_inner(), NonCopy(10));
464		}
465
466		#[test]
467		fn test_into_inner_drop() {
468		struct Foo(Arc<AtomicUsize>);
469		impl Drop for Foo {
470		fn drop(&mut self) {
471		self.0.fetch_add(1, Ordering::SeqCst);
472		}
473		}
474		let num_drops = Arc::new(AtomicUsize::new(0));
475		let m = SpinMutex::<_>::new(Foo(num_drops.clone()));
476		assert_eq!(num_drops.load(Ordering::SeqCst), 0);
477		{
478		let _inner = m.into_inner();
479		assert_eq!(num_drops.load(Ordering::SeqCst), 0);
480		}
481		assert_eq!(num_drops.load(Ordering::SeqCst), 1);
482		}
483
484		#[test]
485		fn test_mutex_arc_nested() {
486		// Tests nested mutexes and access
487		// to underlying data.
488		let arc = Arc::new(SpinMutex::<_>::new(1));
489		let arc2 = Arc::new(SpinMutex::<_>::new(arc));
490		let (tx, rx) = channel();
491		let t = thread::spawn(move \|\| {
492		let lock = arc2.lock();
493		let lock2 = lock.lock();
494		assert_eq!(*lock2, 1);
495		tx.send(()).unwrap();
496		});
497		rx.recv().unwrap();
498		t.join().unwrap();
499		}
500
501		#[test]
502		fn test_mutex_arc_access_in_unwind() {
503		let arc = Arc::new(SpinMutex::<_>::new(1));
504		let arc2 = arc.clone();
505		let _ = thread::spawn(move \|\| -> () {
506		struct Unwinder {
507		i: Arc<SpinMutex<i32>>,
508		}
509		impl Drop for Unwinder {
510		fn drop(&mut self) {
511		*self.i.lock() += 1;
512		}
513		}
514		let _u = Unwinder { i: arc2 };
515		panic!();
516		})
517		.join();
518		let lock = arc.lock();
519		assert_eq!(*lock, 2);
520		}
521
522		#[test]
523		fn test_mutex_unsized() {
524		let mutex: &SpinMutex<[i32]> = &SpinMutex::<_>::new([1, 2, 3]);
525		{
526		let b = &mut *mutex.lock();
527		b[0] = 4;
528		b[2] = 5;
529		}
530		let comp: &[i32] = &[4, 2, 5];
531		assert_eq!(&*mutex.lock(), comp);
532		}
533
534		#[test]
535		fn test_mutex_force_lock() {
536		let lock = SpinMutex::<_>::new(());
537		::std::mem::forget(lock.lock());
538		unsafe {
539		lock.force_unlock();
540		}
541		assert!(lock.try_lock().is_some());
542		}
543		}