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58 lines
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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 `join` macro in crate `tokio`."><meta name="keywords" content="rust, rustlang, rust-lang, join"><title>tokio::join - 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: "join", 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><span class="help-button">?</span>
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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/join.rs.html#57-119" title="goto source code">[src]</a></span><span class="in-band">Macro <a href="index.html">tokio</a>::<wbr><a class="macro" href="">join</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">join</span> {
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(@ {
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<span class="comment">// One `_` for each branch in the `join!` macro. This is not used once</span>
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<span class="comment">// normalization is complete.</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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<span class="comment">// Normalized join! branches</span>
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$( ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">skip</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>:<span class="ident">expr</span>, )<span class="op">*</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">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">e</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">e</span>:<span class="ident">expr</span>),<span class="op">*</span> $(,)<span class="question-mark">?</span>) <span class="op">=</span><span class="op">></span> { ... };
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}</pre></div>
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</div><div class="docblock"><p>Wait on multiple concurrent branches, returning when <strong>all</strong> branches
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complete.</p>
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<p>The <code>join!</code> macro must be used inside of async functions, closures, and
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blocks.</p>
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<p>The <code>join!</code> macro takes a list of async expressions and evaluates them
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concurrently on the same task. Each async expression evaluates to a future
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and the futures from each expression are multiplexed on the current task.</p>
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<p>When working with async expressions returning <code>Result</code>, <code>join!</code> will wait
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for <strong>all</strong> branches complete regardless if any complete with <code>Err</code>. Use
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<a href="../tokio/macro.try_join.html"><code>try_join!</code></a> to return early when <code>Err</code> is encountered.</p>
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<h1 id="notes" class="section-header"><a href="#notes">Notes</a></h1>
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<p>The supplied futures are stored inline and does not require allocating a
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<code>Vec</code>.</p>
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<h3 id="runtime-characteristics" class="section-header"><a href="#runtime-characteristics">Runtime characteristics</a></h3>
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<p>By running all async expressions on the current task, the expressions are
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able to run <strong>concurrently</strong> but not in <strong>parallel</strong>. This means all
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expressions are run on the same thread and if one branch blocks the thread,
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all other expressions will be unable to continue. If parallelism is
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required, spawn each async expression using <a href="../tokio/fn.spawn.html"><code>tokio::spawn</code></a> and pass the
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join handle to <code>join!</code>.</p>
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<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
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<p>Basic join with two branches</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="ident">async</span> <span class="kw">fn</span> <span class="ident">do_stuff_async</span>() {
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<span class="comment">// async work</span>
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}
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<span class="ident">async</span> <span class="kw">fn</span> <span class="ident">more_async_work</span>() {
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<span class="comment">// more here</span>
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}
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<span class="attribute">#[<span class="ident">tokio</span>::<span class="ident">main</span>]</span>
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<span class="ident">async</span> <span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="kw">let</span> (<span class="ident">first</span>, <span class="ident">second</span>) <span class="op">=</span> <span class="ident">tokio</span>::<span class="macro">join</span><span class="macro">!</span>(
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<span class="ident">do_stuff_async</span>(),
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<span class="ident">more_async_work</span>());
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<span class="comment">// do something with the values</span>
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}</pre></div>
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