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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 `select` macro in crate `tokio`."><meta name="keywords" content="rust, rustlang, rust-lang, select"><title>tokio::select - 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="../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><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../favicon.svg">
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<link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc macro"><!--[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='../tokio/index.html'><div class='logo-container rust-logo'><img src='../rust-logo.png' alt='logo'></div></a><div class="sidebar-elems"><p class="location"><a href="index.html">tokio</a></p><script>window.sidebarCurrent = {name: "select", ty: "macro", relpath: ""};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu"><img src="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices" role="menu"></div></div><script src="../theme.js"></script><nav class="sub"><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" disabled autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" class="help-button">?</button>
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<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/tokio/macros/select.rs.html#288-487" title="goto source code">[src]</a></span><span class="in-band">Macro <a href="index.html">tokio</a>::<wbr><a class="macro" href="">select</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><div class="example-wrap"><pre class="rust macro">
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<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/tokio/macros/select.rs.html#343-554" title="goto source code">[src]</a></span><span class="in-band">Macro <a href="index.html">tokio</a>::<wbr><a class="macro" href="">select</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><div class="example-wrap"><pre class="rust macro">
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<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">select</span> {
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(@ {
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<span class="comment">// The index of the future to poll first (in bias mode), or the RNG</span>
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<span class="comment">// expression to use to pick a future to poll first.</span>
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<span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>;
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<span class="comment">// One `_` for each branch in the `select!` macro. Passing this to</span>
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<span class="comment">// `count!` converts $skip to an integer.</span>
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( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">count</span>:<span class="ident">tt</span>)<span class="op">*</span> )
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@@ -20,16 +24,17 @@
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; <span class="macro-nonterminal">$</span><span class="kw">else</span>:<span class="macro-nonterminal">expr</span>
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}) <span class="op">=</span><span class="op">></span> { ... };
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(@ { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="kw">else</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="kw">else</span>:<span class="macro-nonterminal">expr</span> $(,)<span class="question-mark">?</span>) <span class="op">=</span><span class="op">></span> { ... };
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(@ { ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>, <span class="kw">if</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">c</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">block</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">block</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>, <span class="kw">if</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">c</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">block</span> $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">block</span> $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>, <span class="kw">if</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">c</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">expr</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">expr</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>, <span class="kw">if</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">c</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">expr</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">expr</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { <span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>; $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { <span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>; $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="kw">else</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="kw">else</span>:<span class="macro-nonterminal">expr</span> $(,)<span class="question-mark">?</span>) <span class="op">=</span><span class="op">></span> { ... };
|
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(@ { <span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>; ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>, <span class="kw">if</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">c</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">block</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { <span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>; ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">block</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
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(@ { <span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>; ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>, <span class="kw">if</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">c</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">block</span> $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
|
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(@ { <span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>; ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">block</span> $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
|
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(@ { <span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>; ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>, <span class="kw">if</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">c</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">expr</span> ) <span class="op">=</span><span class="op">></span> { ... };
|
||||
(@ { <span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>; ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">expr</span> ) <span class="op">=</span><span class="op">></span> { ... };
|
||||
(@ { <span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>; ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span>, <span class="kw">if</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">c</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">expr</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
|
||||
(@ { <span class="ident">start</span><span class="op">=</span><span class="macro-nonterminal">$</span><span class="macro-nonterminal">start</span>:<span class="ident">expr</span>; ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">f</span>:<span class="ident">expr</span> <span class="op">=</span><span class="op">></span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">h</span>:<span class="ident">expr</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
|
||||
(<span class="ident">biased</span>; <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
|
||||
( <span class="macro-nonterminal">$</span><span class="macro-nonterminal">p</span>:<span class="ident">pat</span> <span class="op">=</span> $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { ... };
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() <span class="op">=</span><span class="op">></span> { ... };
|
||||
}</pre></div>
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@@ -139,8 +144,23 @@ run uninterrupted despite the sleep having elapsed.</p>
|
||||
}
|
||||
}</pre></div>
|
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<h3 id="fairness" class="section-header"><a href="#fairness">Fairness</a></h3>
|
||||
<p><code>select!</code> randomly picks a branch to check first. This provides some level
|
||||
of fairness when calling <code>select!</code> in a loop with branches that are always
|
||||
<p>By default, <code>select!</code> randomly picks a branch to check first. This provides
|
||||
some level of fairness when calling <code>select!</code> in a loop with branches that
|
||||
are always ready.</p>
|
||||
<p>This behavior can be overridden by adding <code>biased;</code> to the beginning of the
|
||||
macro usage. See the exmples for details. This will cause <code>select</code> to poll
|
||||
the futures in the order they appear from top to bottom. There are a few
|
||||
reasons you may want this:</p>
|
||||
<ul>
|
||||
<li>The random number generation of <code>tokio::select!</code> has a non-zero CPU cost</li>
|
||||
<li>Your futures may interact in a way where known polling order is significant</li>
|
||||
</ul>
|
||||
<p>But there is an important caveat to this mode. It becomes your responsibility
|
||||
to ensure that the polling order of your futures is fair. If for example you
|
||||
are selecting between a stream and a shutdown future, and the stream has a
|
||||
huge volume of messages and zero or nearly zero time between them, you should
|
||||
place the shutdown future earlier in the <code>select!</code> list to ensure that it is
|
||||
always polled, and will not be ignored due to the stream being constantly
|
||||
ready.</p>
|
||||
<h1 id="panics" class="section-header"><a href="#panics">Panics</a></h1>
|
||||
<p><code>select!</code> panics if all branches are disabled <strong>and</strong> there is no provided
|
||||
@@ -276,4 +296,41 @@ future can be made <a href="https://doc.rust-lang.org/nightly/core/marker/trait.
|
||||
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">res</span>.<span class="number">0</span>, <span class="string">"first"</span>);
|
||||
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">res</span>.<span class="number">1</span>, <span class="string">"second"</span>);
|
||||
}</pre></div>
|
||||
<p>Using the <code>biased;</code> mode to control polling order.</p>
|
||||
|
||||
<div class="example-wrap"><pre class="rust rust-example-rendered">
|
||||
<span class="attribute">#[<span class="ident">tokio</span>::<span class="ident">main</span>]</span>
|
||||
<span class="kw">async</span> <span class="kw">fn</span> <span class="ident">main</span>() {
|
||||
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">count</span> <span class="op">=</span> <span class="number">0u8</span>;
|
||||
|
||||
<span class="kw">loop</span> {
|
||||
<span class="ident">tokio</span>::<span class="macro">select</span><span class="macro">!</span> {
|
||||
<span class="comment">// If you run this example without `biased;`, the polling order is</span>
|
||||
<span class="comment">// psuedo-random, and the assertions on the value of count will</span>
|
||||
<span class="comment">// (probably) fail.</span>
|
||||
<span class="ident">biased</span>;
|
||||
|
||||
<span class="kw">_</span> <span class="op">=</span> <span class="kw">async</span> {}, <span class="kw">if</span> <span class="ident">count</span> <span class="op"><</span> <span class="number">1</span> <span class="op">=</span><span class="op">></span> {
|
||||
<span class="ident">count</span> <span class="op">+</span><span class="op">=</span> <span class="number">1</span>;
|
||||
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">count</span>, <span class="number">1</span>);
|
||||
}
|
||||
<span class="kw">_</span> <span class="op">=</span> <span class="kw">async</span> {}, <span class="kw">if</span> <span class="ident">count</span> <span class="op"><</span> <span class="number">2</span> <span class="op">=</span><span class="op">></span> {
|
||||
<span class="ident">count</span> <span class="op">+</span><span class="op">=</span> <span class="number">1</span>;
|
||||
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">count</span>, <span class="number">2</span>);
|
||||
}
|
||||
<span class="kw">_</span> <span class="op">=</span> <span class="kw">async</span> {}, <span class="kw">if</span> <span class="ident">count</span> <span class="op"><</span> <span class="number">3</span> <span class="op">=</span><span class="op">></span> {
|
||||
<span class="ident">count</span> <span class="op">+</span><span class="op">=</span> <span class="number">1</span>;
|
||||
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">count</span>, <span class="number">3</span>);
|
||||
}
|
||||
<span class="kw">_</span> <span class="op">=</span> <span class="kw">async</span> {}, <span class="kw">if</span> <span class="ident">count</span> <span class="op"><</span> <span class="number">4</span> <span class="op">=</span><span class="op">></span> {
|
||||
<span class="ident">count</span> <span class="op">+</span><span class="op">=</span> <span class="number">1</span>;
|
||||
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">count</span>, <span class="number">4</span>);
|
||||
}
|
||||
|
||||
<span class="kw">else</span> <span class="op">=</span><span class="op">></span> {
|
||||
<span class="kw">break</span>;
|
||||
}
|
||||
};
|
||||
}
|
||||
}</pre></div>
|
||||
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|
||||
Reference in New Issue
Block a user