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Diffstat (limited to 'vendor/spin/src/mutex/spin.rs')
| -rw-r--r-- | vendor/spin/src/mutex/spin.rs | 543 |
1 files changed, 0 insertions, 543 deletions
diff --git a/vendor/spin/src/mutex/spin.rs b/vendor/spin/src/mutex/spin.rs deleted file mode 100644 index fc97472..0000000 --- a/vendor/spin/src/mutex/spin.rs +++ /dev/null @@ -1,543 +0,0 @@ -//! 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()); - } -} |