| <!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-channel-0.3.28/src/mpsc/queue.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>queue.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_channel/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_channel/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="comment">/* Copyright (c) 2010-2011 Dmitry Vyukov. All rights reserved. |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions are met: |
| * |
| * 1. Redistributions of source code must retain the above copyright notice, |
| * this list of conditions and the following disclaimer. |
| * |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * |
| * THIS SOFTWARE IS PROVIDED BY DMITRY VYUKOV "AS IS" AND ANY EXPRESS OR IMPLIED |
| * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF |
| * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT |
| * SHALL DMITRY VYUKOV OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, |
| * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
| * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR |
| * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF |
| * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE |
| * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF |
| * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
| * |
| * The views and conclusions contained in the software and documentation are |
| * those of the authors and should not be interpreted as representing official |
| * policies, either expressed or implied, of Dmitry Vyukov. |
| */ |
| |
| </span><span class="doccomment">//! A mostly lock-free multi-producer, single consumer queue for sending |
| //! messages between asynchronous tasks. |
| //! |
| //! The queue implementation is essentially the same one used for mpsc channels |
| //! in the standard library. |
| //! |
| //! Note that the current implementation of this queue has a caveat of the `pop` |
| //! method, and see the method for more information about it. Due to this |
| //! caveat, this queue may not be appropriate for all use-cases. |
| |
| </span><span class="comment">// http://www.1024cores.net/home/lock-free-algorithms |
| // /queues/non-intrusive-mpsc-node-based-queue |
| |
| // NOTE: this implementation is lifted from the standard library and only |
| // slightly modified |
| |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">use </span><span class="self">self</span>::PopResult::<span class="kw-2">*</span>; |
| |
| <span class="kw">use </span>std::cell::UnsafeCell; |
| <span class="kw">use </span>std::ptr; |
| <span class="kw">use </span>std::sync::atomic::{AtomicPtr, Ordering}; |
| <span class="kw">use </span>std::thread; |
| |
| <span class="doccomment">/// A result of the `pop` function. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">enum </span>PopResult<T> { |
| <span class="doccomment">/// Some data has been popped |
| </span>Data(T), |
| <span class="doccomment">/// The queue is empty |
| </span>Empty, |
| <span class="doccomment">/// The queue is in an inconsistent state. Popping data should succeed, but |
| /// some pushers have yet to make enough progress in order allow a pop to |
| /// succeed. It is recommended that a pop() occur "in the near future" in |
| /// order to see if the sender has made progress or not |
| </span>Inconsistent, |
| } |
| |
| <span class="kw">struct </span>Node<T> { |
| next: AtomicPtr<<span class="self">Self</span>>, |
| value: <span class="prelude-ty">Option</span><T>, |
| } |
| |
| <span class="doccomment">/// The multi-producer single-consumer structure. This is not cloneable, but it |
| /// may be safely shared so long as it is guaranteed that there is only one |
| /// popper at a time (many pushers are allowed). |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>Queue<T> { |
| head: AtomicPtr<Node<T>>, |
| tail: UnsafeCell<<span class="kw-2">*mut </span>Node<T>>, |
| } |
| |
| <span class="kw">unsafe impl</span><T: Send> Send <span class="kw">for </span>Queue<T> {} |
| <span class="kw">unsafe impl</span><T: Send> Sync <span class="kw">for </span>Queue<T> {} |
| |
| <span class="kw">impl</span><T> Node<T> { |
| <span class="kw">unsafe fn </span>new(v: <span class="prelude-ty">Option</span><T>) -> <span class="kw-2">*mut </span><span class="self">Self </span>{ |
| Box::into_raw(Box::new(<span class="self">Self </span>{ next: AtomicPtr::new(ptr::null_mut()), value: v })) |
| } |
| } |
| |
| <span class="kw">impl</span><T> Queue<T> { |
| <span class="doccomment">/// Creates a new queue that is safe to share among multiple producers and |
| /// one consumer. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>new() -> <span class="self">Self </span>{ |
| <span class="kw">let </span>stub = <span class="kw">unsafe </span>{ Node::new(<span class="prelude-val">None</span>) }; |
| <span class="self">Self </span>{ head: AtomicPtr::new(stub), tail: UnsafeCell::new(stub) } |
| } |
| |
| <span class="doccomment">/// Pushes a new value onto this queue. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>push(<span class="kw-2">&</span><span class="self">self</span>, t: T) { |
| <span class="kw">unsafe </span>{ |
| <span class="kw">let </span>n = Node::new(<span class="prelude-val">Some</span>(t)); |
| <span class="kw">let </span>prev = <span class="self">self</span>.head.swap(n, Ordering::AcqRel); |
| (<span class="kw-2">*</span>prev).next.store(n, Ordering::Release); |
| } |
| } |
| |
| <span class="doccomment">/// Pops some data from this queue. |
| /// |
| /// Note that the current implementation means that this function cannot |
| /// return `Option<T>`. It is possible for this queue to be in an |
| /// inconsistent state where many pushes have succeeded and completely |
| /// finished, but pops cannot return `Some(t)`. This inconsistent state |
| /// happens when a pusher is preempted at an inopportune moment. |
| /// |
| /// This inconsistent state means that this queue does indeed have data, but |
| /// it does not currently have access to it at this time. |
| /// |
| /// This function is unsafe because only one thread can call it at a time. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>pop(<span class="kw-2">&</span><span class="self">self</span>) -> PopResult<T> { |
| <span class="kw">let </span>tail = <span class="kw-2">*</span><span class="self">self</span>.tail.get(); |
| <span class="kw">let </span>next = (<span class="kw-2">*</span>tail).next.load(Ordering::Acquire); |
| |
| <span class="kw">if </span>!next.is_null() { |
| <span class="kw-2">*</span><span class="self">self</span>.tail.get() = next; |
| <span class="macro">assert!</span>((<span class="kw-2">*</span>tail).value.is_none()); |
| <span class="macro">assert!</span>((<span class="kw-2">*</span>next).value.is_some()); |
| <span class="kw">let </span>ret = (<span class="kw-2">*</span>next).value.take().unwrap(); |
| drop(Box::from_raw(tail)); |
| <span class="kw">return </span>Data(ret); |
| } |
| |
| <span class="kw">if </span><span class="self">self</span>.head.load(Ordering::Acquire) == tail { |
| Empty |
| } <span class="kw">else </span>{ |
| Inconsistent |
| } |
| } |
| |
| <span class="doccomment">/// Pop an element similarly to `pop` function, but spin-wait on inconsistent |
| /// queue state instead of returning `Inconsistent`. |
| /// |
| /// This function is unsafe because only one thread can call it at a time. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>pop_spin(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><T> { |
| <span class="kw">loop </span>{ |
| <span class="kw">match </span><span class="self">self</span>.pop() { |
| Empty => <span class="kw">return </span><span class="prelude-val">None</span>, |
| Data(t) => <span class="kw">return </span><span class="prelude-val">Some</span>(t), |
| <span class="comment">// Inconsistent means that there will be a message to pop |
| // in a short time. This branch can only be reached if |
| // values are being produced from another thread, so there |
| // are a few ways that we can deal with this: |
| // |
| // 1) Spin |
| // 2) thread::yield_now() |
| // 3) task::current().unwrap() & return Pending |
| // |
| // For now, thread::yield_now() is used, but it would |
| // probably be better to spin a few times then yield. |
| </span>Inconsistent => { |
| thread::yield_now(); |
| } |
| } |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T> Drop <span class="kw">for </span>Queue<T> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="kw">unsafe </span>{ |
| <span class="kw">let </span><span class="kw-2">mut </span>cur = <span class="kw-2">*</span><span class="self">self</span>.tail.get(); |
| <span class="kw">while </span>!cur.is_null() { |
| <span class="kw">let </span>next = (<span class="kw-2">*</span>cur).next.load(Ordering::Relaxed); |
| drop(Box::from_raw(cur)); |
| cur = next; |
| } |
| } |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="futures_channel" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |