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<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-util-0.3.28/src/lock/mutex.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>mutex.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../normalize.css"><link rel="stylesheet" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../ayu.css" disabled><link rel="stylesheet" href="../../../dark.css" disabled><link rel="stylesheet" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script defer src="../../../source-script.js"></script><script defer src="../../../source-files.js"></script><script defer src="../../../main.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../futures_util/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../futures_util/index.html"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span>
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</pre><pre class="rust"><code><span class="kw">use </span>std::cell::UnsafeCell;
<span class="kw">use </span>std::marker::PhantomData;
<span class="kw">use </span>std::ops::{Deref, DerefMut};
<span class="kw">use </span>std::pin::Pin;
<span class="kw">use </span>std::sync::atomic::{AtomicUsize, Ordering};
<span class="kw">use </span>std::sync::{Arc, Mutex <span class="kw">as </span>StdMutex};
<span class="kw">use </span>std::{fmt, mem};
<span class="kw">use </span>slab::Slab;
<span class="kw">use </span>futures_core::future::{FusedFuture, Future};
<span class="kw">use </span>futures_core::task::{Context, Poll, Waker};
<span class="doccomment">/// A futures-aware mutex.
///
/// # Fairness
///
/// This mutex provides no fairness guarantees. Tasks may not acquire the mutex
/// in the order that they requested the lock, and it&#39;s possible for a single task
/// which repeatedly takes the lock to starve other tasks, which may be left waiting
/// indefinitely.
</span><span class="kw">pub struct </span>Mutex&lt;T: <span class="question-mark">?</span>Sized&gt; {
state: AtomicUsize,
waiters: StdMutex&lt;Slab&lt;Waiter&gt;&gt;,
value: UnsafeCell&lt;T&gt;,
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; fmt::Debug <span class="kw">for </span>Mutex&lt;T&gt; {
<span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
<span class="kw">let </span>state = <span class="self">self</span>.state.load(Ordering::SeqCst);
f.debug_struct(<span class="string">&quot;Mutex&quot;</span>)
.field(<span class="string">&quot;is_locked&quot;</span>, <span class="kw-2">&amp;</span>((state &amp; IS_LOCKED) != <span class="number">0</span>))
.field(<span class="string">&quot;has_waiters&quot;</span>, <span class="kw-2">&amp;</span>((state &amp; HAS_WAITERS) != <span class="number">0</span>))
.finish()
}
}
<span class="kw">impl</span>&lt;T&gt; From&lt;T&gt; <span class="kw">for </span>Mutex&lt;T&gt; {
<span class="kw">fn </span>from(t: T) -&gt; <span class="self">Self </span>{
<span class="self">Self</span>::new(t)
}
}
<span class="kw">impl</span>&lt;T: Default&gt; Default <span class="kw">for </span>Mutex&lt;T&gt; {
<span class="kw">fn </span>default() -&gt; <span class="self">Self </span>{
<span class="self">Self</span>::new(Default::default())
}
}
<span class="kw">enum </span>Waiter {
Waiting(Waker),
Woken,
}
<span class="kw">impl </span>Waiter {
<span class="kw">fn </span>register(<span class="kw-2">&amp;mut </span><span class="self">self</span>, waker: <span class="kw-2">&amp;</span>Waker) {
<span class="kw">match </span><span class="self">self </span>{
<span class="self">Self</span>::Waiting(w) <span class="kw">if </span>waker.will_wake(w) =&gt; {}
<span class="kw">_ </span>=&gt; <span class="kw-2">*</span><span class="self">self </span>= <span class="self">Self</span>::Waiting(waker.clone()),
}
}
<span class="kw">fn </span>wake(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="kw">match </span>mem::replace(<span class="self">self</span>, <span class="self">Self</span>::Woken) {
<span class="self">Self</span>::Waiting(waker) =&gt; waker.wake(),
<span class="self">Self</span>::Woken =&gt; {}
}
}
}
<span class="kw">const </span>IS_LOCKED: usize = <span class="number">1 </span>&lt;&lt; <span class="number">0</span>;
<span class="kw">const </span>HAS_WAITERS: usize = <span class="number">1 </span>&lt;&lt; <span class="number">1</span>;
<span class="kw">impl</span>&lt;T&gt; Mutex&lt;T&gt; {
<span class="doccomment">/// Creates a new futures-aware mutex.
</span><span class="kw">pub fn </span>new(t: T) -&gt; <span class="self">Self </span>{
<span class="self">Self </span>{
state: AtomicUsize::new(<span class="number">0</span>),
waiters: StdMutex::new(Slab::new()),
value: UnsafeCell::new(t),
}
}
<span class="doccomment">/// Consumes this mutex, returning the underlying data.
///
/// # Examples
///
/// ```
/// use futures::lock::Mutex;
///
/// let mutex = Mutex::new(0);
/// assert_eq!(mutex.into_inner(), 0);
/// ```
</span><span class="kw">pub fn </span>into_inner(<span class="self">self</span>) -&gt; T {
<span class="self">self</span>.value.into_inner()
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; Mutex&lt;T&gt; {
<span class="doccomment">/// Attempt to acquire the lock immediately.
///
/// If the lock is currently held, this will return `None`.
</span><span class="kw">pub fn </span>try_lock(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;MutexGuard&lt;<span class="lifetime">&#39;_</span>, T&gt;&gt; {
<span class="kw">let </span>old_state = <span class="self">self</span>.state.fetch_or(IS_LOCKED, Ordering::Acquire);
<span class="kw">if </span>(old_state &amp; IS_LOCKED) == <span class="number">0 </span>{
<span class="prelude-val">Some</span>(MutexGuard { mutex: <span class="self">self </span>})
} <span class="kw">else </span>{
<span class="prelude-val">None
</span>}
}
<span class="doccomment">/// Attempt to acquire the lock immediately.
///
/// If the lock is currently held, this will return `None`.
</span><span class="kw">pub fn </span>try_lock_owned(<span class="self">self</span>: <span class="kw-2">&amp;</span>Arc&lt;<span class="self">Self</span>&gt;) -&gt; <span class="prelude-ty">Option</span>&lt;OwnedMutexGuard&lt;T&gt;&gt; {
<span class="kw">let </span>old_state = <span class="self">self</span>.state.fetch_or(IS_LOCKED, Ordering::Acquire);
<span class="kw">if </span>(old_state &amp; IS_LOCKED) == <span class="number">0 </span>{
<span class="prelude-val">Some</span>(OwnedMutexGuard { mutex: <span class="self">self</span>.clone() })
} <span class="kw">else </span>{
<span class="prelude-val">None
</span>}
}
<span class="doccomment">/// Acquire the lock asynchronously.
///
/// This method returns a future that will resolve once the lock has been
/// successfully acquired.
</span><span class="kw">pub fn </span>lock(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; MutexLockFuture&lt;<span class="lifetime">&#39;_</span>, T&gt; {
MutexLockFuture { mutex: <span class="prelude-val">Some</span>(<span class="self">self</span>), wait_key: WAIT_KEY_NONE }
}
<span class="doccomment">/// Acquire the lock asynchronously.
///
/// This method returns a future that will resolve once the lock has been
/// successfully acquired.
</span><span class="kw">pub fn </span>lock_owned(<span class="self">self</span>: Arc&lt;<span class="self">Self</span>&gt;) -&gt; OwnedMutexLockFuture&lt;T&gt; {
OwnedMutexLockFuture { mutex: <span class="prelude-val">Some</span>(<span class="self">self</span>), wait_key: WAIT_KEY_NONE }
}
<span class="doccomment">/// 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.
///
/// # Examples
///
/// ```
/// # futures::executor::block_on(async {
/// use futures::lock::Mutex;
///
/// let mut mutex = Mutex::new(0);
/// *mutex.get_mut() = 10;
/// assert_eq!(*mutex.lock().await, 10);
/// # });
/// ```
</span><span class="kw">pub fn </span>get_mut(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;mut </span>T {
<span class="comment">// We know statically that there are no other references to `self`, so
// there&#39;s no need to lock the inner mutex.
</span><span class="kw">unsafe </span>{ <span class="kw-2">&amp;mut *</span><span class="self">self</span>.value.get() }
}
<span class="kw">fn </span>remove_waker(<span class="kw-2">&amp;</span><span class="self">self</span>, wait_key: usize, wake_another: bool) {
<span class="kw">if </span>wait_key != WAIT_KEY_NONE {
<span class="kw">let </span><span class="kw-2">mut </span>waiters = <span class="self">self</span>.waiters.lock().unwrap();
<span class="kw">match </span>waiters.remove(wait_key) {
Waiter::Waiting(<span class="kw">_</span>) =&gt; {}
Waiter::Woken =&gt; {
<span class="comment">// We were awoken, but then dropped before we could
// wake up to acquire the lock. Wake up another
// waiter.
</span><span class="kw">if </span>wake_another {
<span class="kw">if let </span><span class="prelude-val">Some</span>((_i, waiter)) = waiters.iter_mut().next() {
waiter.wake();
}
}
}
}
<span class="kw">if </span>waiters.is_empty() {
<span class="self">self</span>.state.fetch_and(!HAS_WAITERS, Ordering::Relaxed); <span class="comment">// released by mutex unlock
</span>}
}
}
<span class="comment">// Unlocks the mutex. Called by MutexGuard and MappedMutexGuard when they are
// dropped.
</span><span class="kw">fn </span>unlock(<span class="kw-2">&amp;</span><span class="self">self</span>) {
<span class="kw">let </span>old_state = <span class="self">self</span>.state.fetch_and(!IS_LOCKED, Ordering::AcqRel);
<span class="kw">if </span>(old_state &amp; HAS_WAITERS) != <span class="number">0 </span>{
<span class="kw">let </span><span class="kw-2">mut </span>waiters = <span class="self">self</span>.waiters.lock().unwrap();
<span class="kw">if let </span><span class="prelude-val">Some</span>((_i, waiter)) = waiters.iter_mut().next() {
waiter.wake();
}
}
}
}
<span class="comment">// Sentinel for when no slot in the `Slab` has been dedicated to this object.
</span><span class="kw">const </span>WAIT_KEY_NONE: usize = usize::MAX;
<span class="doccomment">/// A future which resolves when the target mutex has been successfully acquired, owned version.
</span><span class="kw">pub struct </span>OwnedMutexLockFuture&lt;T: <span class="question-mark">?</span>Sized&gt; {
<span class="comment">// `None` indicates that the mutex was successfully acquired.
</span>mutex: <span class="prelude-ty">Option</span>&lt;Arc&lt;Mutex&lt;T&gt;&gt;&gt;,
wait_key: usize,
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; fmt::Debug <span class="kw">for </span>OwnedMutexLockFuture&lt;T&gt; {
<span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
f.debug_struct(<span class="string">&quot;OwnedMutexLockFuture&quot;</span>)
.field(<span class="string">&quot;was_acquired&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.mutex.is_none())
.field(<span class="string">&quot;mutex&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.mutex)
.field(
<span class="string">&quot;wait_key&quot;</span>,
<span class="kw-2">&amp;</span>(<span class="kw">if </span><span class="self">self</span>.wait_key == WAIT_KEY_NONE { <span class="prelude-val">None </span>} <span class="kw">else </span>{ <span class="prelude-val">Some</span>(<span class="self">self</span>.wait_key) }),
)
.finish()
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; FusedFuture <span class="kw">for </span>OwnedMutexLockFuture&lt;T&gt; {
<span class="kw">fn </span>is_terminated(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; bool {
<span class="self">self</span>.mutex.is_none()
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; Future <span class="kw">for </span>OwnedMutexLockFuture&lt;T&gt; {
<span class="kw">type </span>Output = OwnedMutexGuard&lt;T&gt;;
<span class="kw">fn </span>poll(<span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;<span class="self">Self</span>::Output&gt; {
<span class="kw">let </span>this = <span class="self">self</span>.get_mut();
<span class="kw">let </span>mutex = this.mutex.as_ref().expect(<span class="string">&quot;polled OwnedMutexLockFuture after completion&quot;</span>);
<span class="kw">if let </span><span class="prelude-val">Some</span>(lock) = mutex.try_lock_owned() {
mutex.remove_waker(this.wait_key, <span class="bool-val">false</span>);
this.mutex = <span class="prelude-val">None</span>;
<span class="kw">return </span>Poll::Ready(lock);
}
{
<span class="kw">let </span><span class="kw-2">mut </span>waiters = mutex.waiters.lock().unwrap();
<span class="kw">if </span>this.wait_key == WAIT_KEY_NONE {
this.wait_key = waiters.insert(Waiter::Waiting(cx.waker().clone()));
<span class="kw">if </span>waiters.len() == <span class="number">1 </span>{
mutex.state.fetch_or(HAS_WAITERS, Ordering::Relaxed); <span class="comment">// released by mutex unlock
</span>}
} <span class="kw">else </span>{
waiters[this.wait_key].register(cx.waker());
}
}
<span class="comment">// Ensure that we haven&#39;t raced `MutexGuard::drop`&#39;s unlock path by
// attempting to acquire the lock again.
</span><span class="kw">if let </span><span class="prelude-val">Some</span>(lock) = mutex.try_lock_owned() {
mutex.remove_waker(this.wait_key, <span class="bool-val">false</span>);
this.mutex = <span class="prelude-val">None</span>;
<span class="kw">return </span>Poll::Ready(lock);
}
Poll::Pending
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; Drop <span class="kw">for </span>OwnedMutexLockFuture&lt;T&gt; {
<span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="kw">if let </span><span class="prelude-val">Some</span>(mutex) = <span class="self">self</span>.mutex.as_ref() {
<span class="comment">// This future was dropped before it acquired the mutex.
//
// Remove ourselves from the map, waking up another waiter if we
// had been awoken to acquire the lock.
</span>mutex.remove_waker(<span class="self">self</span>.wait_key, <span class="bool-val">true</span>);
}
}
}
<span class="doccomment">/// An RAII guard returned by the `lock_owned` and `try_lock_owned` methods.
/// When this structure is dropped (falls out of scope), the lock will be
/// unlocked.
</span><span class="kw">pub struct </span>OwnedMutexGuard&lt;T: <span class="question-mark">?</span>Sized&gt; {
mutex: Arc&lt;Mutex&lt;T&gt;&gt;,
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized + fmt::Debug&gt; fmt::Debug <span class="kw">for </span>OwnedMutexGuard&lt;T&gt; {
<span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
f.debug_struct(<span class="string">&quot;OwnedMutexGuard&quot;</span>)
.field(<span class="string">&quot;value&quot;</span>, &amp;&amp;<span class="kw-2">**</span><span class="self">self</span>)
.field(<span class="string">&quot;mutex&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.mutex)
.finish()
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; Drop <span class="kw">for </span>OwnedMutexGuard&lt;T&gt; {
<span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="self">self</span>.mutex.unlock()
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; Deref <span class="kw">for </span>OwnedMutexGuard&lt;T&gt; {
<span class="kw">type </span>Target = T;
<span class="kw">fn </span>deref(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>T {
<span class="kw">unsafe </span>{ <span class="kw-2">&amp;*</span><span class="self">self</span>.mutex.value.get() }
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; DerefMut <span class="kw">for </span>OwnedMutexGuard&lt;T&gt; {
<span class="kw">fn </span>deref_mut(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;mut </span>T {
<span class="kw">unsafe </span>{ <span class="kw-2">&amp;mut *</span><span class="self">self</span>.mutex.value.get() }
}
}
<span class="doccomment">/// A future which resolves when the target mutex has been successfully acquired.
</span><span class="kw">pub struct </span>MutexLockFuture&lt;<span class="lifetime">&#39;a</span>, T: <span class="question-mark">?</span>Sized&gt; {
<span class="comment">// `None` indicates that the mutex was successfully acquired.
</span>mutex: <span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>Mutex&lt;T&gt;&gt;,
wait_key: usize,
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; fmt::Debug <span class="kw">for </span>MutexLockFuture&lt;<span class="lifetime">&#39;_</span>, T&gt; {
<span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
f.debug_struct(<span class="string">&quot;MutexLockFuture&quot;</span>)
.field(<span class="string">&quot;was_acquired&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.mutex.is_none())
.field(<span class="string">&quot;mutex&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.mutex)
.field(
<span class="string">&quot;wait_key&quot;</span>,
<span class="kw-2">&amp;</span>(<span class="kw">if </span><span class="self">self</span>.wait_key == WAIT_KEY_NONE { <span class="prelude-val">None </span>} <span class="kw">else </span>{ <span class="prelude-val">Some</span>(<span class="self">self</span>.wait_key) }),
)
.finish()
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; FusedFuture <span class="kw">for </span>MutexLockFuture&lt;<span class="lifetime">&#39;_</span>, T&gt; {
<span class="kw">fn </span>is_terminated(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; bool {
<span class="self">self</span>.mutex.is_none()
}
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>, T: <span class="question-mark">?</span>Sized&gt; Future <span class="kw">for </span>MutexLockFuture&lt;<span class="lifetime">&#39;a</span>, T&gt; {
<span class="kw">type </span>Output = MutexGuard&lt;<span class="lifetime">&#39;a</span>, T&gt;;
<span class="kw">fn </span>poll(<span class="kw-2">mut </span><span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;<span class="self">Self</span>::Output&gt; {
<span class="kw">let </span>mutex = <span class="self">self</span>.mutex.expect(<span class="string">&quot;polled MutexLockFuture after completion&quot;</span>);
<span class="kw">if let </span><span class="prelude-val">Some</span>(lock) = mutex.try_lock() {
mutex.remove_waker(<span class="self">self</span>.wait_key, <span class="bool-val">false</span>);
<span class="self">self</span>.mutex = <span class="prelude-val">None</span>;
<span class="kw">return </span>Poll::Ready(lock);
}
{
<span class="kw">let </span><span class="kw-2">mut </span>waiters = mutex.waiters.lock().unwrap();
<span class="kw">if </span><span class="self">self</span>.wait_key == WAIT_KEY_NONE {
<span class="self">self</span>.wait_key = waiters.insert(Waiter::Waiting(cx.waker().clone()));
<span class="kw">if </span>waiters.len() == <span class="number">1 </span>{
mutex.state.fetch_or(HAS_WAITERS, Ordering::Relaxed); <span class="comment">// released by mutex unlock
</span>}
} <span class="kw">else </span>{
waiters[<span class="self">self</span>.wait_key].register(cx.waker());
}
}
<span class="comment">// Ensure that we haven&#39;t raced `MutexGuard::drop`&#39;s unlock path by
// attempting to acquire the lock again.
</span><span class="kw">if let </span><span class="prelude-val">Some</span>(lock) = mutex.try_lock() {
mutex.remove_waker(<span class="self">self</span>.wait_key, <span class="bool-val">false</span>);
<span class="self">self</span>.mutex = <span class="prelude-val">None</span>;
<span class="kw">return </span>Poll::Ready(lock);
}
Poll::Pending
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; Drop <span class="kw">for </span>MutexLockFuture&lt;<span class="lifetime">&#39;_</span>, T&gt; {
<span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="kw">if let </span><span class="prelude-val">Some</span>(mutex) = <span class="self">self</span>.mutex {
<span class="comment">// This future was dropped before it acquired the mutex.
//
// Remove ourselves from the map, waking up another waiter if we
// had been awoken to acquire the lock.
</span>mutex.remove_waker(<span class="self">self</span>.wait_key, <span class="bool-val">true</span>);
}
}
}
<span class="doccomment">/// An RAII guard returned by the `lock` and `try_lock` methods.
/// When this structure is dropped (falls out of scope), the lock will be
/// unlocked.
</span><span class="kw">pub struct </span>MutexGuard&lt;<span class="lifetime">&#39;a</span>, T: <span class="question-mark">?</span>Sized&gt; {
mutex: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>Mutex&lt;T&gt;,
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>, T: <span class="question-mark">?</span>Sized&gt; MutexGuard&lt;<span class="lifetime">&#39;a</span>, T&gt; {
<span class="doccomment">/// Returns a locked view over a portion of the locked data.
///
/// # Example
///
/// ```
/// # futures::executor::block_on(async {
/// use futures::lock::{Mutex, MutexGuard};
///
/// let data = Mutex::new(Some(&quot;value&quot;.to_string()));
/// {
/// let locked_str = MutexGuard::map(data.lock().await, |opt| opt.as_mut().unwrap());
/// assert_eq!(&amp;*locked_str, &quot;value&quot;);
/// }
/// # });
/// ```
</span><span class="attribute">#[inline]
</span><span class="kw">pub fn </span>map&lt;U: <span class="question-mark">?</span>Sized, F&gt;(this: <span class="self">Self</span>, f: F) -&gt; MappedMutexGuard&lt;<span class="lifetime">&#39;a</span>, T, U&gt;
<span class="kw">where
</span>F: FnOnce(<span class="kw-2">&amp;mut </span>T) -&gt; <span class="kw-2">&amp;mut </span>U,
{
<span class="kw">let </span>mutex = this.mutex;
<span class="kw">let </span>value = f(<span class="kw">unsafe </span>{ <span class="kw-2">&amp;mut *</span>this.mutex.value.get() });
<span class="comment">// Don&#39;t run the `drop` method for MutexGuard. The ownership of the underlying
// locked state is being moved to the returned MappedMutexGuard.
</span>mem::forget(this);
MappedMutexGuard { mutex, value, _marker: PhantomData }
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized + fmt::Debug&gt; fmt::Debug <span class="kw">for </span>MutexGuard&lt;<span class="lifetime">&#39;_</span>, T&gt; {
<span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
f.debug_struct(<span class="string">&quot;MutexGuard&quot;</span>).field(<span class="string">&quot;value&quot;</span>, &amp;&amp;<span class="kw-2">**</span><span class="self">self</span>).field(<span class="string">&quot;mutex&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.mutex).finish()
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; Drop <span class="kw">for </span>MutexGuard&lt;<span class="lifetime">&#39;_</span>, T&gt; {
<span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="self">self</span>.mutex.unlock()
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; Deref <span class="kw">for </span>MutexGuard&lt;<span class="lifetime">&#39;_</span>, T&gt; {
<span class="kw">type </span>Target = T;
<span class="kw">fn </span>deref(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>T {
<span class="kw">unsafe </span>{ <span class="kw-2">&amp;*</span><span class="self">self</span>.mutex.value.get() }
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; DerefMut <span class="kw">for </span>MutexGuard&lt;<span class="lifetime">&#39;_</span>, T&gt; {
<span class="kw">fn </span>deref_mut(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;mut </span>T {
<span class="kw">unsafe </span>{ <span class="kw-2">&amp;mut *</span><span class="self">self</span>.mutex.value.get() }
}
}
<span class="doccomment">/// An RAII guard returned by the `MutexGuard::map` and `MappedMutexGuard::map` methods.
/// When this structure is dropped (falls out of scope), the lock will be unlocked.
</span><span class="kw">pub struct </span>MappedMutexGuard&lt;<span class="lifetime">&#39;a</span>, T: <span class="question-mark">?</span>Sized, U: <span class="question-mark">?</span>Sized&gt; {
mutex: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>Mutex&lt;T&gt;,
value: <span class="kw-2">*mut </span>U,
_marker: PhantomData&lt;<span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span><span class="kw-2">mut </span>U&gt;,
}
<span class="kw">impl</span>&lt;<span class="lifetime">&#39;a</span>, T: <span class="question-mark">?</span>Sized, U: <span class="question-mark">?</span>Sized&gt; MappedMutexGuard&lt;<span class="lifetime">&#39;a</span>, T, U&gt; {
<span class="doccomment">/// Returns a locked view over a portion of the locked data.
///
/// # Example
///
/// ```
/// # futures::executor::block_on(async {
/// use futures::lock::{MappedMutexGuard, Mutex, MutexGuard};
///
/// let data = Mutex::new(Some(&quot;value&quot;.to_string()));
/// {
/// let locked_str = MutexGuard::map(data.lock().await, |opt| opt.as_mut().unwrap());
/// let locked_char = MappedMutexGuard::map(locked_str, |s| s.get_mut(0..1).unwrap());
/// assert_eq!(&amp;*locked_char, &quot;v&quot;);
/// }
/// # });
/// ```
</span><span class="attribute">#[inline]
</span><span class="kw">pub fn </span>map&lt;V: <span class="question-mark">?</span>Sized, F&gt;(this: <span class="self">Self</span>, f: F) -&gt; MappedMutexGuard&lt;<span class="lifetime">&#39;a</span>, T, V&gt;
<span class="kw">where
</span>F: FnOnce(<span class="kw-2">&amp;mut </span>U) -&gt; <span class="kw-2">&amp;mut </span>V,
{
<span class="kw">let </span>mutex = this.mutex;
<span class="kw">let </span>value = f(<span class="kw">unsafe </span>{ <span class="kw-2">&amp;mut *</span>this.value });
<span class="comment">// Don&#39;t run the `drop` method for MappedMutexGuard. The ownership of the underlying
// locked state is being moved to the returned MappedMutexGuard.
</span>mem::forget(this);
MappedMutexGuard { mutex, value, _marker: PhantomData }
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized, U: <span class="question-mark">?</span>Sized + fmt::Debug&gt; fmt::Debug <span class="kw">for </span>MappedMutexGuard&lt;<span class="lifetime">&#39;_</span>, T, U&gt; {
<span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
f.debug_struct(<span class="string">&quot;MappedMutexGuard&quot;</span>)
.field(<span class="string">&quot;value&quot;</span>, &amp;&amp;<span class="kw-2">**</span><span class="self">self</span>)
.field(<span class="string">&quot;mutex&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.mutex)
.finish()
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized, U: <span class="question-mark">?</span>Sized&gt; Drop <span class="kw">for </span>MappedMutexGuard&lt;<span class="lifetime">&#39;_</span>, T, U&gt; {
<span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="self">self</span>.mutex.unlock()
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized, U: <span class="question-mark">?</span>Sized&gt; Deref <span class="kw">for </span>MappedMutexGuard&lt;<span class="lifetime">&#39;_</span>, T, U&gt; {
<span class="kw">type </span>Target = U;
<span class="kw">fn </span>deref(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>U {
<span class="kw">unsafe </span>{ <span class="kw-2">&amp;*</span><span class="self">self</span>.value }
}
}
<span class="kw">impl</span>&lt;T: <span class="question-mark">?</span>Sized, U: <span class="question-mark">?</span>Sized&gt; DerefMut <span class="kw">for </span>MappedMutexGuard&lt;<span class="lifetime">&#39;_</span>, T, U&gt; {
<span class="kw">fn </span>deref_mut(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;mut </span>U {
<span class="kw">unsafe </span>{ <span class="kw-2">&amp;mut *</span><span class="self">self</span>.value }
}
}
<span class="comment">// Mutexes can be moved freely between threads and acquired on any thread so long
// as the inner value can be safely sent between threads.
</span><span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized + Send&gt; Send <span class="kw">for </span>Mutex&lt;T&gt; {}
<span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized + Send&gt; Sync <span class="kw">for </span>Mutex&lt;T&gt; {}
<span class="comment">// It&#39;s safe to switch which thread the acquire is being attempted on so long as
// `T` can be accessed on that thread.
</span><span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized + Send&gt; Send <span class="kw">for </span>MutexLockFuture&lt;<span class="lifetime">&#39;_</span>, T&gt; {}
<span class="comment">// doesn&#39;t have any interesting `&amp;self` methods (only Debug)
</span><span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; Sync <span class="kw">for </span>MutexLockFuture&lt;<span class="lifetime">&#39;_</span>, T&gt; {}
<span class="comment">// It&#39;s safe to switch which thread the acquire is being attempted on so long as
// `T` can be accessed on that thread.
</span><span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized + Send&gt; Send <span class="kw">for </span>OwnedMutexLockFuture&lt;T&gt; {}
<span class="comment">// doesn&#39;t have any interesting `&amp;self` methods (only Debug)
</span><span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized&gt; Sync <span class="kw">for </span>OwnedMutexLockFuture&lt;T&gt; {}
<span class="comment">// Safe to send since we don&#39;t track any thread-specific details-- the inner
// lock is essentially spinlock-equivalent (attempt to flip an atomic bool)
</span><span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized + Send&gt; Send <span class="kw">for </span>MutexGuard&lt;<span class="lifetime">&#39;_</span>, T&gt; {}
<span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized + Sync&gt; Sync <span class="kw">for </span>MutexGuard&lt;<span class="lifetime">&#39;_</span>, T&gt; {}
<span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized + Send&gt; Send <span class="kw">for </span>OwnedMutexGuard&lt;T&gt; {}
<span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized + Sync&gt; Sync <span class="kw">for </span>OwnedMutexGuard&lt;T&gt; {}
<span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized + Send, U: <span class="question-mark">?</span>Sized + Send&gt; Send <span class="kw">for </span>MappedMutexGuard&lt;<span class="lifetime">&#39;_</span>, T, U&gt; {}
<span class="kw">unsafe impl</span>&lt;T: <span class="question-mark">?</span>Sized + Sync, U: <span class="question-mark">?</span>Sized + Sync&gt; Sync <span class="kw">for </span>MappedMutexGuard&lt;<span class="lifetime">&#39;_</span>, T, U&gt; {}
<span class="attribute">#[test]
</span><span class="kw">fn </span>test_mutex_guard_debug_not_recurse() {
<span class="kw">let </span>mutex = Mutex::new(<span class="number">42</span>);
<span class="kw">let </span>guard = mutex.try_lock().unwrap();
<span class="kw">let _ </span>= <span class="macro">format!</span>(<span class="string">&quot;{:?}&quot;</span>, guard);
<span class="kw">let </span>guard = MutexGuard::map(guard, |n| n);
<span class="kw">let _ </span>= <span class="macro">format!</span>(<span class="string">&quot;{:?}&quot;</span>, guard);
}
</code></pre></div>
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