forked from mirror/async-std
refactor: switch to async-mutex for Mutex implementation
dignifiedquire
5 years ago
parent
43de93312c
commit
18dffe8b43
@ -1,294 +0,0 @@
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use std::cell::UnsafeCell;
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use std::fmt;
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use std::ops::{Deref, DerefMut};
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use std::pin::Pin;
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use std::sync::atomic::{AtomicBool, Ordering};
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use std::future::Future;
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use crate::sync::WakerSet;
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use crate::task::{Context, Poll};
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/// A mutual exclusion primitive for protecting shared data.
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///
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/// This type is an async version of [`std::sync::Mutex`].
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///
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/// [`std::sync::Mutex`]: https://doc.rust-lang.org/std/sync/struct.Mutex.html
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///
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/// # Examples
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///
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/// ```
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::{Arc, Mutex};
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/// use async_std::task;
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///
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/// let m = Arc::new(Mutex::new(0));
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/// let mut tasks = vec![];
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///
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/// for _ in 0..10 {
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/// let m = m.clone();
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/// tasks.push(task::spawn(async move {
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/// *m.lock().await += 1;
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/// }));
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/// }
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///
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/// for t in tasks {
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/// t.await;
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/// }
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/// assert_eq!(*m.lock().await, 10);
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/// #
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/// # })
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/// ```
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pub struct Mutex<T: ?Sized> {
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locked: AtomicBool,
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wakers: WakerSet,
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value: UnsafeCell<T>,
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}
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unsafe impl<T: ?Sized + Send> Send for Mutex<T> {}
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unsafe impl<T: ?Sized + Send> Sync for Mutex<T> {}
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impl<T> Mutex<T> {
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/// Creates a new mutex.
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///
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/// # Examples
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///
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/// ```
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/// use async_std::sync::Mutex;
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///
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/// let mutex = Mutex::new(0);
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/// ```
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pub fn new(t: T) -> Mutex<T> {
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Mutex {
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locked: AtomicBool::new(false),
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wakers: WakerSet::new(),
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value: UnsafeCell::new(t),
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}
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}
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}
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impl<T: ?Sized> Mutex<T> {
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/// Acquires the lock.
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///
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/// Returns a guard that releases the lock when dropped.
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///
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/// # Examples
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///
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/// ```
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::{Arc, Mutex};
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/// use async_std::task;
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///
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/// let m1 = Arc::new(Mutex::new(10));
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/// let m2 = m1.clone();
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///
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/// task::spawn(async move {
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/// *m1.lock().await = 20;
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/// })
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/// .await;
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///
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/// assert_eq!(*m2.lock().await, 20);
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/// #
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/// # })
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/// ```
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pub async fn lock(&self) -> MutexGuard<'_, T> {
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pub struct LockFuture<'a, T: ?Sized> {
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mutex: &'a Mutex<T>,
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opt_key: Option<usize>,
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}
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impl<'a, T: ?Sized> Future for LockFuture<'a, T> {
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type Output = MutexGuard<'a, T>;
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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loop {
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// If the current task is in the set, remove it.
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if let Some(key) = self.opt_key.take() {
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self.mutex.wakers.remove(key);
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}
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// Try acquiring the lock.
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match self.mutex.try_lock() {
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Some(guard) => return Poll::Ready(guard),
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None => {
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// Insert this lock operation.
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self.opt_key = Some(self.mutex.wakers.insert(cx));
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// If the mutex is still locked, return.
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if self.mutex.locked.load(Ordering::SeqCst) {
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return Poll::Pending;
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}
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}
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}
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}
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}
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}
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impl<T: ?Sized> Drop for LockFuture<'_, T> {
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fn drop(&mut self) {
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// If the current task is still in the set, that means it is being cancelled now.
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if let Some(key) = self.opt_key {
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self.mutex.wakers.cancel(key);
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}
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}
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}
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LockFuture {
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mutex: self,
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opt_key: None,
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}
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.await
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}
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/// Attempts to acquire the lock.
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///
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/// If the lock could not be acquired at this time, then [`None`] is returned. Otherwise, a
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/// guard is returned that releases the lock when dropped.
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///
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/// [`None`]: https://doc.rust-lang.org/std/option/enum.Option.html#variant.None
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///
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/// # Examples
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///
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/// ```
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::{Arc, Mutex};
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/// use async_std::task;
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///
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/// let m1 = Arc::new(Mutex::new(10));
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/// let m2 = m1.clone();
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///
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/// task::spawn(async move {
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/// if let Some(mut guard) = m1.try_lock() {
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/// *guard = 20;
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/// } else {
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/// println!("try_lock failed");
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/// }
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/// })
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/// .await;
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///
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/// assert_eq!(*m2.lock().await, 20);
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/// #
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/// # })
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/// ```
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#[inline]
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pub fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
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if !self.locked.swap(true, Ordering::SeqCst) {
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Some(MutexGuard(self))
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} else {
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None
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}
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}
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/// Consumes the mutex, returning the underlying data.
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///
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/// # Examples
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///
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/// ```
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/// use async_std::sync::Mutex;
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///
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/// let mutex = Mutex::new(10);
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/// assert_eq!(mutex.into_inner(), 10);
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/// ```
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pub fn into_inner(self) -> T where T: Sized {
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self.value.into_inner()
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}
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/// Returns a mutable reference to the underlying data.
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///
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/// Since this call borrows the mutex mutably, no actual locking takes place -- the mutable
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/// borrow statically guarantees no locks exist.
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///
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/// # Examples
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///
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/// ```
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::sync::Mutex;
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///
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/// let mut mutex = Mutex::new(0);
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/// *mutex.get_mut() = 10;
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/// assert_eq!(*mutex.lock().await, 10);
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/// #
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/// # })
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/// ```
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pub fn get_mut(&mut self) -> &mut T {
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unsafe { &mut *self.value.get() }
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}
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}
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impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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struct Locked;
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impl fmt::Debug for Locked {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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f.write_str("<locked>")
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}
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}
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match self.try_lock() {
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None => f.debug_struct("Mutex").field("data", &Locked).finish(),
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Some(guard) => f.debug_struct("Mutex").field("data", &&*guard).finish(),
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}
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}
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}
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impl<T> From<T> for Mutex<T> {
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fn from(val: T) -> Mutex<T> {
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Mutex::new(val)
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}
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}
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impl<T: ?Sized + Default> Default for Mutex<T> {
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fn default() -> Mutex<T> {
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Mutex::new(Default::default())
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}
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}
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/// A guard that releases the lock when dropped.
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pub struct MutexGuard<'a, T: ?Sized>(&'a Mutex<T>);
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unsafe impl<T: ?Sized + Send> Send for MutexGuard<'_, T> {}
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unsafe impl<T: ?Sized + Sync> Sync for MutexGuard<'_, T> {}
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impl<T: ?Sized> Drop for MutexGuard<'_, T> {
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fn drop(&mut self) {
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// Use `SeqCst` ordering to synchronize with `WakerSet::insert()` and `WakerSet::update()`.
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self.0.locked.store(false, Ordering::SeqCst);
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// Notify a blocked `lock()` operation if none were notified already.
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self.0.wakers.notify_any();
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}
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}
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impl<T: ?Sized +fmt::Debug> fmt::Debug for MutexGuard<'_, T> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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fmt::Debug::fmt(&**self, f)
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}
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}
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impl<T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'_, T> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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(**self).fmt(f)
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}
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}
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impl<T: ?Sized> Deref for MutexGuard<'_, T> {
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type Target = T;
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fn deref(&self) -> &T {
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unsafe { &*self.0.value.get() }
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}
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}
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impl<T: ?Sized> DerefMut for MutexGuard<'_, T> {
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fn deref_mut(&mut self) -> &mut T {
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unsafe { &mut *self.0.value.get() }
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}
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}
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#[cfg(feature = "unstable")]
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pub fn guard_lock<'a, T>(guard: &MutexGuard<'a, T>) -> &'a Mutex<T> {
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guard.0
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}
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