<!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 `/home/sangenya/.cargo/registry/src/github.com-1ecc6299db9ec823/crossbeam-utils-0.8.5/src/sync/parker.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>parker.rs - source</title><link rel="stylesheet" type="text/css" href="../../../normalize.css"><link rel="stylesheet" type="text/css" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../../../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../../../ayu.css" disabled ><script id="default-settings"></script><script src="../../../storage.js"></script><script src="../../../crates.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../../../favicon.svg">
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</pre><pre class="rust">
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::primitive::sync::atomic::AtomicUsize</span>;
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::primitive::sync</span>::{<span class="ident">Arc</span>, <span class="ident">Condvar</span>, <span class="ident">Mutex</span>};
<span class="kw">use</span> <span class="ident">core::sync::atomic::Ordering::SeqCst</span>;
<span class="kw">use</span> <span class="ident">std::fmt</span>;
<span class="kw">use</span> <span class="ident">std::marker::PhantomData</span>;
<span class="kw">use</span> <span class="ident">std::time</span>::{<span class="ident">Duration</span>, <span class="ident">Instant</span>};
<span class="doccomment">/// A thread parking primitive.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Conceptually, each `Parker` has an associated token which is initially not present:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * The [`park`] method blocks the current thread unless or until the token is available, at</span>
<span class="doccomment">/// which point it automatically consumes the token.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * The [`park_timeout`] and [`park_deadline`] methods work the same as [`park`], but block for</span>
<span class="doccomment">/// a specified maximum time.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * The [`unpark`] method atomically makes the token available if it wasn't already. Because the</span>
<span class="doccomment">/// token is initially absent, [`unpark`] followed by [`park`] will result in the second call</span>
<span class="doccomment">/// returning immediately.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In other words, each `Parker` acts a bit like a spinlock that can be locked and unlocked using</span>
<span class="doccomment">/// [`park`] and [`unpark`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">/// use std::time::Duration;</span>
<span class="doccomment">/// use crossbeam_utils::sync::Parker;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">/// let u = p.unparker().clone();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Make the token available.</span>
<span class="doccomment">/// u.unpark();</span>
<span class="doccomment">/// // Wakes up immediately and consumes the token.</span>
<span class="doccomment">/// p.park();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// thread::spawn(move || {</span>
<span class="doccomment">/// thread::sleep(Duration::from_millis(500));</span>
<span class="doccomment">/// u.unpark();</span>
<span class="doccomment">/// });</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Wakes up when `u.unpark()` provides the token.</span>
<span class="doccomment">/// p.park();</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`park`]: Parker::park</span>
<span class="doccomment">/// [`park_timeout`]: Parker::park_timeout</span>
<span class="doccomment">/// [`park_deadline`]: Parker::park_deadline</span>
<span class="doccomment">/// [`unpark`]: Unparker::unpark</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Parker</span> {
<span class="ident">unparker</span>: <span class="ident">Unparker</span>,
<span class="ident">_marker</span>: <span class="ident">PhantomData</span><span class="op"><</span><span class="kw-2">*</span><span class="kw">const</span> ()<span class="op">></span>,
}
<span class="kw">unsafe</span> <span class="kw">impl</span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">Parker</span> {}
<span class="kw">impl</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">Parker</span> {
<span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="self">Self</span> {
<span class="ident">unparker</span>: <span class="ident">Unparker</span> {
<span class="ident">inner</span>: <span class="ident">Arc::new</span>(<span class="ident">Inner</span> {
<span class="ident">state</span>: <span class="ident">AtomicUsize::new</span>(<span class="ident">EMPTY</span>),
<span class="ident">lock</span>: <span class="ident">Mutex::new</span>(()),
<span class="ident">cvar</span>: <span class="ident">Condvar::new</span>(),
}),
},
<span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
}
}
}
<span class="kw">impl</span> <span class="ident">Parker</span> {
<span class="doccomment">/// Creates a new `Parker`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::Parker;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-</span><span class="op">></span> <span class="ident">Parker</span> {
<span class="self">Self</span><span class="ident">::default</span>()
}
<span class="doccomment">/// Blocks the current thread until the token is made available.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::Parker;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">/// let u = p.unparker().clone();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Make the token available.</span>
<span class="doccomment">/// u.unpark();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Wakes up immediately and consumes the token.</span>
<span class="doccomment">/// p.park();</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">park</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="self">self</span>.<span class="ident">unparker</span>.<span class="ident">inner</span>.<span class="ident">park</span>(<span class="prelude-val">None</span>);
}
<span class="doccomment">/// Blocks the current thread until the token is made available, but only for a limited time.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::time::Duration;</span>
<span class="doccomment">/// use crossbeam_utils::sync::Parker;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Waits for the token to become available, but will not wait longer than 500 ms.</span>
<span class="doccomment">/// p.park_timeout(Duration::from_millis(500));</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">park_timeout</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">timeout</span>: <span class="ident">Duration</span>) {
<span class="self">self</span>.<span class="ident">park_deadline</span>(<span class="ident">Instant::now</span>() <span class="op">+</span> <span class="ident">timeout</span>)
}
<span class="doccomment">/// Blocks the current thread until the token is made available, or until a certain deadline.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::time::{Duration, Instant};</span>
<span class="doccomment">/// use crossbeam_utils::sync::Parker;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">/// let deadline = Instant::now() + Duration::from_millis(500);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Waits for the token to become available, but will not wait longer than 500 ms.</span>
<span class="doccomment">/// p.park_deadline(deadline);</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">park_deadline</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">deadline</span>: <span class="ident">Instant</span>) {
<span class="self">self</span>.<span class="ident">unparker</span>.<span class="ident">inner</span>.<span class="ident">park</span>(<span class="prelude-val">Some</span>(<span class="ident">deadline</span>))
}
<span class="doccomment">/// Returns a reference to an associated [`Unparker`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The returned [`Unparker`] doesn't have to be used by reference - it can also be cloned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::Parker;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">/// let u = p.unparker().clone();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Make the token available.</span>
<span class="doccomment">/// u.unpark();</span>
<span class="doccomment">/// // Wakes up immediately and consumes the token.</span>
<span class="doccomment">/// p.park();</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`park`]: Parker::park</span>
<span class="doccomment">/// [`park_timeout`]: Parker::park_timeout</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">unparker</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">Unparker</span> {
<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">unparker</span>
}
<span class="doccomment">/// Converts a `Parker` into a raw pointer.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::Parker;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">/// let raw = Parker::into_raw(p);</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">into_raw</span>(<span class="ident">this</span>: <span class="ident">Parker</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">*</span><span class="kw">const</span> () {
<span class="ident">Unparker::into_raw</span>(<span class="ident">this</span>.<span class="ident">unparker</span>)
}
<span class="doccomment">/// Converts a raw pointer into a `Parker`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method is safe to use only with pointers returned by [`Parker::into_raw`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::Parker;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">/// let raw = Parker::into_raw(p);</span>
<span class="doccomment">/// let p = unsafe { Parker::from_raw(raw) };</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">from_raw</span>(<span class="ident">ptr</span>: <span class="kw-2">*</span><span class="kw">const</span> ()) <span class="op">-</span><span class="op">></span> <span class="ident">Parker</span> {
<span class="ident">Parker</span> {
<span class="ident">unparker</span>: <span class="ident">Unparker::from_raw</span>(<span class="ident">ptr</span>),
<span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
}
}
}
<span class="kw">impl</span> <span class="ident">fmt::Debug</span> <span class="kw">for</span> <span class="ident">Parker</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::Result</span> {
<span class="ident">f</span>.<span class="ident">pad</span>(<span class="string">"Parker { .. }"</span>)
}
}
<span class="doccomment">/// Unparks a thread parked by the associated [`Parker`].</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Unparker</span> {
<span class="ident">inner</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">Inner</span><span class="op">></span>,
}
<span class="kw">unsafe</span> <span class="kw">impl</span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">Unparker</span> {}
<span class="kw">unsafe</span> <span class="kw">impl</span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">Unparker</span> {}
<span class="kw">impl</span> <span class="ident">Unparker</span> {
<span class="doccomment">/// Atomically makes the token available if it is not already.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method will wake up the thread blocked on [`park`] or [`park_timeout`], if there is</span>
<span class="doccomment">/// any.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">/// use std::time::Duration;</span>
<span class="doccomment">/// use crossbeam_utils::sync::Parker;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">/// let u = p.unparker().clone();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// thread::spawn(move || {</span>
<span class="doccomment">/// thread::sleep(Duration::from_millis(500));</span>
<span class="doccomment">/// u.unpark();</span>
<span class="doccomment">/// });</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Wakes up when `u.unpark()` provides the token.</span>
<span class="doccomment">/// p.park();</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`park`]: Parker::park</span>
<span class="doccomment">/// [`park_timeout`]: Parker::park_timeout</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">unpark</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">unpark</span>()
}
<span class="doccomment">/// Converts an `Unparker` into a raw pointer.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::{Parker, Unparker};</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">/// let u = p.unparker().clone();</span>
<span class="doccomment">/// let raw = Unparker::into_raw(u);</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">into_raw</span>(<span class="ident">this</span>: <span class="ident">Unparker</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">*</span><span class="kw">const</span> () {
<span class="ident">Arc::into_raw</span>(<span class="ident">this</span>.<span class="ident">inner</span>) <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> ()
}
<span class="doccomment">/// Converts a raw pointer into an `Unparker`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method is safe to use only with pointers returned by [`Unparker::into_raw`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::{Parker, Unparker};</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let p = Parker::new();</span>
<span class="doccomment">/// let u = p.unparker().clone();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let raw = Unparker::into_raw(u);</span>
<span class="doccomment">/// let u = unsafe { Unparker::from_raw(raw) };</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">from_raw</span>(<span class="ident">ptr</span>: <span class="kw-2">*</span><span class="kw">const</span> ()) <span class="op">-</span><span class="op">></span> <span class="ident">Unparker</span> {
<span class="ident">Unparker</span> {
<span class="ident">inner</span>: <span class="ident">Arc::from_raw</span>(<span class="ident">ptr</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Inner</span>),
}
}
}
<span class="kw">impl</span> <span class="ident">fmt::Debug</span> <span class="kw">for</span> <span class="ident">Unparker</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::Result</span> {
<span class="ident">f</span>.<span class="ident">pad</span>(<span class="string">"Unparker { .. }"</span>)
}
}
<span class="kw">impl</span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">Unparker</span> {
<span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">Unparker</span> {
<span class="ident">Unparker</span> {
<span class="ident">inner</span>: <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">clone</span>(),
}
}
}
<span class="kw">const</span> <span class="ident">EMPTY</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">0</span>;
<span class="kw">const</span> <span class="ident">PARKED</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">1</span>;
<span class="kw">const</span> <span class="ident">NOTIFIED</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">2</span>;
<span class="kw">struct</span> <span class="ident">Inner</span> {
<span class="ident">state</span>: <span class="ident">AtomicUsize</span>,
<span class="ident">lock</span>: <span class="ident">Mutex</span><span class="op"><</span>()<span class="op">></span>,
<span class="ident">cvar</span>: <span class="ident">Condvar</span>,
}
<span class="kw">impl</span> <span class="ident">Inner</span> {
<span class="kw">fn</span> <span class="ident">park</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">deadline</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Instant</span><span class="op">></span>) {
<span class="comment">// If we were previously notified then we consume this notification and return quickly.</span>
<span class="kw">if</span> <span class="self">self</span>
.<span class="ident">state</span>
.<span class="ident">compare_exchange</span>(<span class="ident">NOTIFIED</span>, <span class="ident">EMPTY</span>, <span class="ident">SeqCst</span>, <span class="ident">SeqCst</span>)
.<span class="ident">is_ok</span>()
{
<span class="kw">return</span>;
}
<span class="comment">// If the timeout is zero, then there is no need to actually block.</span>
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">deadline</span>) <span class="op">=</span> <span class="ident">deadline</span> {
<span class="kw">if</span> <span class="ident">deadline</span> <span class="op"><</span><span class="op">=</span> <span class="ident">Instant::now</span>() {
<span class="kw">return</span>;
}
}
<span class="comment">// Otherwise we need to coordinate going to sleep.</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">m</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">lock</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">compare_exchange</span>(<span class="ident">EMPTY</span>, <span class="ident">PARKED</span>, <span class="ident">SeqCst</span>, <span class="ident">SeqCst</span>) {
<span class="prelude-val">Ok</span>(<span class="kw">_</span>) <span class="op">=</span><span class="op">></span> {}
<span class="comment">// Consume this notification to avoid spurious wakeups in the next park.</span>
<span class="prelude-val">Err</span>(<span class="ident">NOTIFIED</span>) <span class="op">=</span><span class="op">></span> {
<span class="comment">// We must read `state` here, even though we know it will be `NOTIFIED`. This is</span>
<span class="comment">// because `unpark` may have been called again since we read `NOTIFIED` in the</span>
<span class="comment">// `compare_exchange` above. We must perform an acquire operation that synchronizes</span>
<span class="comment">// with that `unpark` to observe any writes it made before the call to `unpark`. To</span>
<span class="comment">// do that we must read from the write it made to `state`.</span>
<span class="kw">let</span> <span class="ident">old</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">EMPTY</span>, <span class="ident">SeqCst</span>);
<span class="macro">assert_eq!</span>(<span class="ident">old</span>, <span class="ident">NOTIFIED</span>, <span class="string">"park state changed unexpectedly"</span>);
<span class="kw">return</span>;
}
<span class="prelude-val">Err</span>(<span class="ident">n</span>) <span class="op">=</span><span class="op">></span> <span class="macro">panic!</span>(<span class="string">"inconsistent park_timeout state: {}"</span>, <span class="ident">n</span>),
}
<span class="kw">loop</span> {
<span class="comment">// Block the current thread on the conditional variable.</span>
<span class="ident">m</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">deadline</span> {
<span class="prelude-val">None</span> <span class="op">=</span><span class="op">></span> <span class="self">self</span>.<span class="ident">cvar</span>.<span class="ident">wait</span>(<span class="ident">m</span>).<span class="ident">unwrap</span>(),
<span class="prelude-val">Some</span>(<span class="ident">deadline</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">now</span> <span class="op">=</span> <span class="ident">Instant::now</span>();
<span class="kw">if</span> <span class="ident">now</span> <span class="op"><</span> <span class="ident">deadline</span> {
<span class="comment">// We could check for a timeout here, in the return value of wait_timeout,</span>
<span class="comment">// but in the case that a timeout and an unpark arrive simultaneously, we</span>
<span class="comment">// prefer to report the former.</span>
<span class="self">self</span>.<span class="ident">cvar</span>.<span class="ident">wait_timeout</span>(<span class="ident">m</span>, <span class="ident">deadline</span> <span class="op">-</span> <span class="ident">now</span>).<span class="ident">unwrap</span>().<span class="number">0</span>
} <span class="kw">else</span> {
<span class="comment">// We've timed out; swap out the state back to empty on our way out</span>
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">EMPTY</span>, <span class="ident">SeqCst</span>) {
<span class="ident">NOTIFIED</span> <span class="op">|</span> <span class="ident">PARKED</span> <span class="op">=</span><span class="op">></span> <span class="kw">return</span>,
<span class="ident">n</span> <span class="op">=</span><span class="op">></span> <span class="macro">panic!</span>(<span class="string">"inconsistent park_timeout state: {}"</span>, <span class="ident">n</span>),
};
}
}
};
<span class="kw">if</span> <span class="self">self</span>
.<span class="ident">state</span>
.<span class="ident">compare_exchange</span>(<span class="ident">NOTIFIED</span>, <span class="ident">EMPTY</span>, <span class="ident">SeqCst</span>, <span class="ident">SeqCst</span>)
.<span class="ident">is_ok</span>()
{
<span class="comment">// got a notification</span>
<span class="kw">return</span>;
}
<span class="comment">// Spurious wakeup, go back to sleep. Alternatively, if we timed out, it will be caught</span>
<span class="comment">// in the branch above, when we discover the deadline is in the past</span>
}
}
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">unpark</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="comment">// To ensure the unparked thread will observe any writes we made before this call, we must</span>
<span class="comment">// perform a release operation that `park` can synchronize with. To do that we must write</span>
<span class="comment">// `NOTIFIED` even if `state` is already `NOTIFIED`. That is why this must be a swap rather</span>
<span class="comment">// than a compare-and-swap that returns if it reads `NOTIFIED` on failure.</span>
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">NOTIFIED</span>, <span class="ident">SeqCst</span>) {
<span class="ident">EMPTY</span> <span class="op">=</span><span class="op">></span> <span class="kw">return</span>, <span class="comment">// no one was waiting</span>
<span class="ident">NOTIFIED</span> <span class="op">=</span><span class="op">></span> <span class="kw">return</span>, <span class="comment">// already unparked</span>
<span class="ident">PARKED</span> <span class="op">=</span><span class="op">></span> {} <span class="comment">// gotta go wake someone up</span>
<span class="kw">_</span> <span class="op">=</span><span class="op">></span> <span class="macro">panic!</span>(<span class="string">"inconsistent state in unpark"</span>),
}
<span class="comment">// There is a period between when the parked thread sets `state` to `PARKED` (or last</span>
<span class="comment">// checked `state` in the case of a spurious wakeup) and when it actually waits on `cvar`.</span>
<span class="comment">// If we were to notify during this period it would be ignored and then when the parked</span>
<span class="comment">// thread went to sleep it would never wake up. Fortunately, it has `lock` locked at this</span>
<span class="comment">// stage so we can acquire `lock` to wait until it is ready to receive the notification.</span>
<span class="comment">//</span>
<span class="comment">// Releasing `lock` before the call to `notify_one` means that when the parked thread wakes</span>
<span class="comment">// it doesn't get woken only to have to wait for us to release `lock`.</span>
<span class="ident">drop</span>(<span class="self">self</span>.<span class="ident">lock</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>());
<span class="self">self</span>.<span class="ident">cvar</span>.<span class="ident">notify_one</span>();
}
}
</pre></div>
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