| <!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="Runs the provided blocking function on the current thread without blocking the executor."><meta name="keywords" content="rust, rustlang, rust-lang, block_in_place"><title>block_in_place in tokio::task - 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 fn"><!--[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::task</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">Function <a href="../index.html">tokio</a>::<wbr><a href="index.html">task</a>::<wbr><a class="fn" href="#">block_in_place</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/task/blocking.rs.html#74-79">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"><pre class="rust fn"><code>pub fn block_in_place<F, R>(f: F) -> R<span class="where fmt-newline">where<br> F: FnOnce() -> R,</span></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Runs the provided blocking function on the current thread without |
| blocking the executor.</p> |
| <p>In general, issuing a blocking call or performing a lot of compute in a |
| future without yielding is problematic, as it may prevent the executor |
| from driving other tasks forward. Calling this function informs the |
| executor that the currently executing task is about to block the thread, |
| so the executor is able to hand off any other tasks it has to a new |
| worker thread before that happens. See the <a href="../index.html#cpu-bound-tasks-and-blocking-code">CPU-bound tasks and blocking |
| code</a> section for more information.</p> |
| <p>Be aware that although this function avoids starving other independently |
| spawned tasks, any other code running concurrently in the same task will |
| be suspended during the call to <code>block_in_place</code>. This can happen e.g. |
| when using the <a href="../macro.join.html"><code>join!</code></a> macro. To avoid this issue, use |
| <a href="fn.spawn_blocking.html"><code>spawn_blocking</code></a> instead of <code>block_in_place</code>.</p> |
| <p>Note that this function cannot be used within a <a href="../runtime/struct.Builder.html#method.new_current_thread"><code>current_thread</code></a> runtime |
| because in this case there are no other worker threads to hand off tasks |
| to. On the other hand, calling the function outside a runtime is |
| allowed. In this case, <code>block_in_place</code> just calls the provided closure |
| normally.</p> |
| <p>Code running behind <code>block_in_place</code> cannot be cancelled. When you shut |
| down the executor, it will wait indefinitely for all blocking operations |
| to finish. You can use <a href="../runtime/struct.Runtime.html#method.shutdown_timeout"><code>shutdown_timeout</code></a> to stop waiting for them |
| after a certain timeout. Be aware that this will still not cancel the |
| tasks — they are simply allowed to keep running after the method |
| returns.</p> |
| <h2 id="examples"><a href="#examples">Examples</a></h2> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::task; |
| |
| task::block_in_place(<span class="kw">move </span>|| { |
| <span class="comment">// do some compute-heavy work or call synchronous code |
| </span>});</code></pre></div> |
| <p>Code running inside <code>block_in_place</code> may use <code>block_on</code> to reenter the |
| async context.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::task; |
| <span class="kw">use </span>tokio::runtime::Handle; |
| |
| task::block_in_place(<span class="kw">move </span>|| { |
| Handle::current().block_on(<span class="kw">async move </span>{ |
| <span class="comment">// do something async |
| </span>}); |
| });</code></pre></div> |
| <h2 id="panics"><a href="#panics">Panics</a></h2> |
| <p>This function panics if called from a <a href="../runtime/struct.Builder.html#method.new_current_thread"><code>current_thread</code></a> runtime.</p> |
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