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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 `scope_fifo` fn in crate `rayon`."><meta name="keywords" content="rust, rustlang, rust-lang, scope_fifo"><title>rayon::scope_fifo - 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 fn"><!--[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">☰</div><a href='../rayon/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><div class="sidebar-elems"><p class='location'><a href='index.html'>rayon</a></p><script>window.sidebarCurrent = {name: 'scope_fifo', ty: 'fn', 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'>−</span>]</a></span><a class='srclink' href='../src/rayon_core/scope/mod.rs.html#379-388' title='goto source code'>[src]</a></span><span class='in-band'>Function <a href='index.html'>rayon</a>::<wbr><a class="fn" href=''>scope_fifo</a></span></h1><pre class='rust fn'>pub fn scope_fifo<'scope, OP, R>(op: OP) -> R <span class="where fmt-newline">where<br> OP: for<'s> <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/function/trait.FnOnce.html" title="trait core::ops::function::FnOnce">FnOnce</a>(&'s <a class="struct" href="../rayon/struct.ScopeFifo.html" title="struct rayon::ScopeFifo">ScopeFifo</a><'scope>) -> R + 'scope + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a>,<br> R: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a>, </span></pre><div class='docblock'><p>Create a "fork-join" scope <code>s</code> with FIFO order, and invokes the
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closure with a reference to <code>s</code>. This closure can then spawn
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asynchronous tasks into <code>s</code>. Those tasks may run asynchronously with
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respect to the closure; they may themselves spawn additional tasks
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into <code>s</code>. When the closure returns, it will block until all tasks
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that have been spawned into <code>s</code> complete.</p>
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<h1 id="task-execution" class="section-header"><a href="#task-execution">Task execution</a></h1>
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<p>Tasks in a <code>scope_fifo()</code> run similarly to <a href="fn.scope.html"><code>scope()</code></a>, but there's a
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difference in the order of execution. Consider a similar example:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="comment">// point start</span>
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<span class="ident">rayon</span>::<span class="ident">scope_fifo</span>(<span class="op">|</span><span class="ident">s</span><span class="op">|</span> {
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<span class="ident">s</span>.<span class="ident">spawn_fifo</span>(<span class="op">|</span><span class="ident">s</span><span class="op">|</span> { <span class="comment">// task s.1</span>
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<span class="ident">s</span>.<span class="ident">spawn_fifo</span>(<span class="op">|</span><span class="ident">s</span><span class="op">|</span> { <span class="comment">// task s.1.1</span>
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<span class="ident">rayon</span>::<span class="ident">scope_fifo</span>(<span class="op">|</span><span class="ident">t</span><span class="op">|</span> {
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<span class="ident">t</span>.<span class="ident">spawn_fifo</span>(<span class="op">|</span><span class="kw">_</span><span class="op">|</span> ()); <span class="comment">// task t.1</span>
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<span class="ident">t</span>.<span class="ident">spawn_fifo</span>(<span class="op">|</span><span class="kw">_</span><span class="op">|</span> ()); <span class="comment">// task t.2</span>
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});
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});
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});
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<span class="ident">s</span>.<span class="ident">spawn_fifo</span>(<span class="op">|</span><span class="ident">s</span><span class="op">|</span> { <span class="comment">// task s.2</span>
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});
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<span class="comment">// point mid</span>
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});
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<span class="comment">// point end</span></pre></div>
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<p>The various tasks that are run will execute roughly like so:</p>
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<pre><code class="language-notrust">| (start)
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| (FIFO scope `s` created)
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+--------------------+ (task s.1)
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+-------+ (task s.2) |
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| | +---+ (task s.1.1)
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| | | |
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| | | | (FIFO scope `t` created)
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| | | +----------------+ (task t.1)
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| | | +---+ (task t.2) |
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| (mid) | | | | |
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: | | + <-+------------+ (scope `t` ends)
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: | | |
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|<------+------------+---+ (scope `s` ends)
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| (end)
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</code></pre>
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<p>Under <code>scope_fifo()</code>, the spawns are prioritized in a FIFO order on
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the thread from which they were spawned, as opposed to <code>scope()</code>'s
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LIFO. So in this example, we can expect <code>s.1</code> to execute before
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<code>s.2</code>, and <code>t.1</code> before <code>t.2</code>. Other threads also steal tasks in
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FIFO order, as usual. Overall, this has roughly the same order as
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the now-deprecated <a href="struct.ThreadPoolBuilder.html#method.breadth_first"><code>breadth_first</code></a> option, except the effect is
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isolated to a particular scope. If spawns are intermingled from any
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combination of <code>scope()</code> and <code>scope_fifo()</code>, or from different
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threads, their order is only specified with respect to spawns in the
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same scope and thread.</p>
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<p>For more details on this design, see Rayon <a href="https://github.com/rayon-rs/rfcs/blob/master/accepted/rfc0001-scope-scheduling.md">RFC #1</a>.</p>
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<h1 id="panics" class="section-header"><a href="#panics">Panics</a></h1>
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<p>If a panic occurs, either in the closure given to <code>scope_fifo()</code> or
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in any of the spawned jobs, that panic will be propagated and the
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call to <code>scope_fifo()</code> will panic. If multiple panics occurs, it is
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non-deterministic which of their panic values will propagate.
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Regardless, once a task is spawned using <code>scope.spawn_fifo()</code>, it
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will execute, even if the spawning task should later panic.
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<code>scope_fifo()</code> returns once all spawned jobs have completed, and any
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panics are propagated at that point.</p>
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