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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="Waits on multiple concurrent branches, returning when all branches complete."><title>join in tokio - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-Medium-e1aa3f0a.woff2,SourceCodePro-Regular-8badfe75.ttf.woff2,SourceCodePro-Semibold-aa29a496.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../static.files/rustdoc-42caa33d.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="tokio" data-themes="" data-resource-suffix="" data-rustdoc-version="1.84.1 (e71f9a9a9 2025-01-27)" data-channel="1.84.1" data-search-js="search-92e6798f.js" data-settings-js="settings-0f613d39.js" ><script src="../static.files/storage-59e33391.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-5f194d8c.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-893ab5e7.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-6580c154.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-044be391.svg"></head><body class="rustdoc macro"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../tokio/index.html">tokio</a><span class="version">1.42.0</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">join</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#notes" title="Notes">Notes</a><ul><li><a href="#runtime-characteristics" title="Runtime characteristics">Runtime characteristics</a></li></ul></li><li><a href="#examples" title="Examples">Examples</a></li></ul></section><div id="rustdoc-modnav"><h2 class="in-crate"><a href="index.html">In crate tokio</a></h2></div></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><span class="rustdoc-breadcrumbs"><a href="index.html">tokio</a></span><h1>Macro <span class="macro">join</span><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../src/tokio/macros/join.rs.html#64-66">Source</a> </span></div><pre class="rust item-decl"><code>macro_rules! join {
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($($future:expr),*) => { ... };
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}</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Waits 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="macro.try_join.html" title="macro tokio::try_join"><code>try_join!</code></a> to return early when <code>Err</code> is encountered.</p>
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<h2 id="notes"><a class="doc-anchor" href="#notes">§</a>Notes</h2>
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<p>The supplied futures are stored inline and do not require allocating a
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<code>Vec</code>.</p>
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<h4 id="runtime-characteristics"><a class="doc-anchor" href="#runtime-characteristics">§</a>Runtime characteristics</h4>
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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="task/fn.spawn.html" title="fn tokio::task::spawn"><code>tokio::spawn</code></a> and pass the
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join handle to <code>join!</code>.</p>
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<h2 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h2>
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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"><code><span class="kw">async fn </span>do_stuff_async() {
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<span class="comment">// async work
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</span>}
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<span class="kw">async fn </span>more_async_work() {
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<span class="comment">// more here
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</span>}
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<span class="attr">#[tokio::main]
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</span><span class="kw">async fn </span>main() {
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<span class="kw">let </span>(first, second) = <span class="macro">tokio::join!</span>(
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do_stuff_async(),
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more_async_work());
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<span class="comment">// do something with the values
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</span>}</code></pre></div>
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</div></details></section></div></main></body></html> |