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Trac3r-rust/doc/crossbeam/deque/index.html

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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="API documentation for the Rust `deque` mod in crate `crossbeam`."><meta name="keywords" content="rust, rustlang, rust-lang, deque"><title>crossbeam::deque - Rust</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="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="shortcut icon" href="../../favicon.ico"><style type="text/css">#crate-search{background-image:url("../../down-arrow.svg");}</style></head><body class="rustdoc mod"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">&#9776;</div><a href='../../crossbeam/index.html'><div class='logo-container'><img src='../../rust-logo.png' alt='logo'></div></a><p class='location'>Module deque</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li></ul></div><p class='location'><a href='../index.html'>crossbeam</a></p><script>window.sidebarCurrent = {name: 'deque', ty: 'mod', relpath: '../'};</script><script defer src="../sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>&#x2212;</span>]</a></span><a class='srclink' href='../../src/crossbeam_deque/lib.rs.html#1-2008' title='goto source code'>[src]</a></span><span class='in-band'>Module <a href='../index.html'>crossbeam</a>::<wbr><a class="mod" href=''>deque</a></span></h1><div class='docblock'><p>Concurrent work-stealing deques.</p>
<p>These data structures are most commonly used in work-stealing schedulers. The typical setup
involves a number of threads, each having its own FIFO or LIFO queue (<em>worker</em>). There is also
one global FIFO queue (<em>injector</em>) and a list of references to <em>worker</em> queues that are able to
steal tasks (<em>stealers</em>).</p>
<p>We spawn a new task onto the scheduler by pushing it into the <em>injector</em> queue. Each worker
thread waits in a loop until it finds the next task to run and then runs it. To find a task, it
first looks into its local <em>worker</em> queue, and then into the <em>injector</em> and <em>stealers</em>.</p>
<h1 id="queues" class="section-header"><a href="#queues">Queues</a></h1>
<p><a href="struct.Stealer.html"><code>Injector</code></a> is a FIFO queue, where tasks are pushed and stolen from opposite ends. It is
shared among threads and is usually the entry point for new tasks.</p>
<p><a href="struct.Worker.html"><code>Worker</code></a> has two constructors:</p>
<ul>
<li><a href="struct.Worker.html#method.new_fifo"><code>new_fifo()</code></a> - Creates a FIFO queue, in which tasks are pushed and popped from opposite
ends.</li>
<li><a href="struct.Worker.html#method.new_lifo"><code>new_lifo()</code></a> - Creates a LIFO queue, in which tasks are pushed and popped from the same
end.</li>
</ul>
<p>Each <a href="struct.Worker.html"><code>Worker</code></a> is owned by a single thread and supports only push and pop operations.</p>
<p>Method <a href="struct.Worker.html#method.stealer"><code>stealer()</code></a> creates a <a href="struct.Stealer.html"><code>Stealer</code></a> that may be shared among threads and can only steal
tasks from its <a href="struct.Worker.html"><code>Worker</code></a>. Tasks are stolen from the end opposite to where they get pushed.</p>
<h1 id="stealing" class="section-header"><a href="#stealing">Stealing</a></h1>
<p>Steal operations come in three flavors:</p>
<ol>
<li><a href="struct.Stealer.html#method.steal"><code>steal()</code></a> - Steals one task.</li>
<li><a href="struct.Stealer.html#method.steal_batch"><code>steal_batch()</code></a> - Steals a batch of tasks and moves them into another worker.</li>
<li><a href="struct.Stealer.html#method.steal_batch_and_pop"><code>steal_batch_and_pop()</code></a> - Steals a batch of tasks, moves them into another queue, and pops
one task from that worker.</li>
</ol>
<p>In contrast to push and pop operations, stealing can spuriously fail with <a href="enum.Steal.html#variant.Retry"><code>Steal::Retry</code></a>, in
which case the steal operation needs to be retried.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>Suppose a thread in a work-stealing scheduler is idle and looking for the next task to run. To
find an available task, it might do the following:</p>
<ol>
<li>Try popping one task from the local worker queue.</li>
<li>Try stealing a batch of tasks from the global injector queue.</li>
<li>Try stealing one task from another thread using the stealer list.</li>
</ol>
<p>An implementation of this work-stealing strategy:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">crossbeam_deque</span>::{<span class="ident">Injector</span>, <span class="ident">Steal</span>, <span class="ident">Stealer</span>, <span class="ident">Worker</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">iter</span>;
<span class="kw">fn</span> <span class="ident">find_task</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>(
<span class="ident">local</span>: <span class="kw-2">&amp;</span><span class="ident">Worker</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>,
<span class="ident">global</span>: <span class="kw-2">&amp;</span><span class="ident">Injector</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>,
<span class="ident">stealers</span>: <span class="kw-2">&amp;</span>[<span class="ident">Stealer</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>],
) <span class="op">-</span><span class="op">&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {
<span class="comment">// Pop a task from the local queue, if not empty.</span>
<span class="ident">local</span>.<span class="ident">pop</span>().<span class="ident">or_else</span>(<span class="op">|</span><span class="op">|</span> {
<span class="comment">// Otherwise, we need to look for a task elsewhere.</span>
<span class="ident">iter</span>::<span class="ident">repeat_with</span>(<span class="op">|</span><span class="op">|</span> {
<span class="comment">// Try stealing a batch of tasks from the global queue.</span>
<span class="ident">global</span>.<span class="ident">steal_batch_and_pop</span>(<span class="ident">local</span>)
<span class="comment">// Or try stealing a task from one of the other threads.</span>
.<span class="ident">or_else</span>(<span class="op">|</span><span class="op">|</span> <span class="ident">stealers</span>.<span class="ident">iter</span>().<span class="ident">map</span>(<span class="op">|</span><span class="ident">s</span><span class="op">|</span> <span class="ident">s</span>.<span class="ident">steal</span>()).<span class="ident">collect</span>())
})
<span class="comment">// Loop while no task was stolen and any steal operation needs to be retried.</span>
.<span class="ident">find</span>(<span class="op">|</span><span class="ident">s</span><span class="op">|</span> <span class="op">!</span><span class="ident">s</span>.<span class="ident">is_retry</span>())
<span class="comment">// Extract the stolen task, if there is one.</span>
.<span class="ident">and_then</span>(<span class="op">|</span><span class="ident">s</span><span class="op">|</span> <span class="ident">s</span>.<span class="ident">success</span>())
})
}</pre></div>
</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
<table><tr class='module-item'><td><a class="struct" href="struct.Injector.html" title='crossbeam::deque::Injector struct'>Injector</a></td><td class='docblock-short'><p>An injector queue.</p>
</td></tr><tr class='module-item'><td><a class="struct" href="struct.Stealer.html" title='crossbeam::deque::Stealer struct'>Stealer</a></td><td class='docblock-short'><p>A stealer handle of a worker queue.</p>
</td></tr><tr class='module-item'><td><a class="struct" href="struct.Worker.html" title='crossbeam::deque::Worker struct'>Worker</a></td><td class='docblock-short'><p>A worker queue.</p>
</td></tr></table><h2 id='enums' class='section-header'><a href="#enums">Enums</a></h2>
<table><tr class='module-item'><td><a class="enum" href="enum.Steal.html" title='crossbeam::deque::Steal enum'>Steal</a></td><td class='docblock-short'><p>Possible outcomes of a steal operation.</p>
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