| <!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."><meta name="keywords" content="rust, rustlang, rust-lang, join"><title>join in tokio - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../normalize.css"><link rel="stylesheet" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../ayu.css" disabled><link rel="stylesheet" href="../dark.css" disabled><link rel="stylesheet" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script defer src="sidebar-items.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../favicon.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">☰</button><a class="sidebar-logo" href="../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><div class="sidebar-elems"><h2><a href="index.html">In tokio</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Macro <a href="index.html">tokio</a>::<wbr><a class="macro" href="#">join</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../src/tokio/macros/join.rs.html#57-164">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><div class="example-wrap"><pre class="rust macro"><code><span class="macro">macro_rules! </span>join { |
| (@ { |
| <span class="comment">// One `_` for each branch in the `join!` macro. This is not used once |
| // normalization is complete. |
| </span>( $(<span class="macro-nonterminal">$count</span>:tt)* ) |
| |
| <span class="comment">// The expression `0+1+1+ ... +1` equal to the number of branches. |
| </span>( $(<span class="macro-nonterminal">$total</span>:tt)* ) |
| |
| <span class="comment">// Normalized join! branches |
| </span>$( ( $(<span class="macro-nonterminal">$skip</span>:tt)* ) <span class="macro-nonterminal">$e</span>:expr, )* |
| |
| }) => { ... }; |
| (@ { ( $(<span class="macro-nonterminal">$s</span>:tt)* ) ( $(<span class="macro-nonterminal">$n</span>:tt)* ) $(<span class="macro-nonterminal">$t</span>:tt)* } <span class="macro-nonterminal">$e</span>:expr, $(<span class="macro-nonterminal">$r</span>:tt)* ) => { ... }; |
| ( $(<span class="macro-nonterminal">$e</span>:expr),* $(,)<span class="question-mark">?</span>) => { ... }; |
| }</code></pre></div> |
| </div><details class="rustdoc-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 |
| complete.</p> |
| <p>The <code>join!</code> macro must be used inside of async functions, closures, and |
| blocks.</p> |
| <p>The <code>join!</code> macro takes a list of async expressions and evaluates them |
| concurrently on the same task. Each async expression evaluates to a future |
| and the futures from each expression are multiplexed on the current task.</p> |
| <p>When working with async expressions returning <code>Result</code>, <code>join!</code> will wait |
| for <strong>all</strong> branches complete regardless if any complete with <code>Err</code>. Use |
| <a href="macro.try_join.html"><code>try_join!</code></a> to return early when <code>Err</code> is encountered.</p> |
| <h2 id="notes"><a href="#notes">Notes</a></h2> |
| <p>The supplied futures are stored inline and does not require allocating a |
| <code>Vec</code>.</p> |
| <h4 id="runtime-characteristics"><a href="#runtime-characteristics">Runtime characteristics</a></h4> |
| <p>By running all async expressions on the current task, the expressions are |
| able to run <strong>concurrently</strong> but not in <strong>parallel</strong>. This means all |
| expressions are run on the same thread and if one branch blocks the thread, |
| all other expressions will be unable to continue. If parallelism is |
| required, spawn each async expression using <a href="task/fn.spawn.html"><code>tokio::spawn</code></a> and pass the |
| join handle to <code>join!</code>.</p> |
| <h2 id="examples"><a href="#examples">Examples</a></h2> |
| <p>Basic join with two branches</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">async fn </span>do_stuff_async() { |
| <span class="comment">// async work |
| </span>} |
| |
| <span class="kw">async fn </span>more_async_work() { |
| <span class="comment">// more here |
| </span>} |
| |
| <span class="attribute">#[tokio::main] |
| </span><span class="kw">async fn </span>main() { |
| <span class="kw">let </span>(first, second) = <span class="macro">tokio::join!</span>( |
| do_stuff_async(), |
| more_async_work()); |
| |
| <span class="comment">// do something with the values |
| </span>}</code></pre></div> |
| </div></details></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="tokio" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
