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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="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" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../../dark.css" disabled><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../storage.js"></script><script src="../../crates.js"></script><script defer src="../../main.js"></script>
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<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="sidebar"><div class="sidebar-menu" role="button">☰</div><a class="sidebar-logo" href="../../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.png" alt="logo"></div>
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</a><div class="sidebar-elems"><h2 class="location">Other items in<br><a href="../index.html">tokio</a>::<wbr><a href="index.html">task</a></h2><div id="sidebar-vars" data-name="block_in_place" data-ty="fn" data-relpath=""></div><script defer src="sidebar-items.js"></script></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../../tokio/index.html"><img class="rust-logo" src="../../rust-logo.png" alt="logo"></a><nav class="sub"><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu" title="themes"><img width="18" height="18" alt="Pick another theme!" src="../../brush.svg"></button><div id="theme-choices" role="menu"></div></div><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" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" id="help-button" title="help">?</button><a id="settings-menu" href="../../settings.html" title="settings"><img width="18" height="18" alt="Change settings" src="../../wheel.svg"></a></div></form></nav></div><section id="main-content" class="content"><h1 class="fqn"><span class="in-band">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></span><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/task/blocking.rs.html#73-78" title="goto source code">[src]</a></span></h1><div class="docblock 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: <a class="trait" href="https://doc.rust-lang.org/1.59.0/core/ops/function/trait.FnOnce.html" title="trait core::ops::function::FnOnce">FnOnce</a>() -> 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
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blocking the executor.</p>
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<p>In general, issuing a blocking call or performing a lot of compute in a
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future without yielding is problematic, as it may prevent the executor
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from driving other tasks forward. Calling this function informs the
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executor that the currently executing task is about to block the thread,
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so the executor is able to hand off any other tasks it has to a new
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worker thread before that happens. See the <a href="../index.html#cpu-bound-tasks-and-blocking-code">CPU-bound tasks and blocking
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code</a> section for more information.</p>
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<p>Be aware that although this function avoids starving other independently
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spawned tasks, any other code running concurrently in the same task will
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be suspended during the call to <code>block_in_place</code>. This can happen e.g.
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when using the <a href="../macro.join.html"><code>join!</code></a> macro. To avoid this issue, use
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<a href="fn.spawn_blocking.html"><code>spawn_blocking</code></a> instead of <code>block_in_place</code>.</p>
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<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
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because in this case there are no other worker threads to hand off tasks
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to. On the other hand, calling the function outside a runtime is
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allowed. In this case, <code>block_in_place</code> just calls the provided closure
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normally.</p>
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<p>Code running behind <code>block_in_place</code> cannot be cancelled. When you shut
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down the executor, it will wait indefinitely for all blocking operations
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to finish. You can use <a href="../runtime/struct.Runtime.html#method.shutdown_timeout"><code>shutdown_timeout</code></a> to stop waiting for them
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after a certain timeout. Be aware that this will still not cancel the
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tasks — they are simply allowed to keep running after the method
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returns.</p>
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<h2 id="examples" class="section-header"><a href="#examples">Examples</a></h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">tokio::task</span>;
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<span class="ident">task::block_in_place</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> {
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<span class="comment">// do some compute-heavy work or call synchronous code</span>
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});</code></pre></div>
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<p>Code running inside <code>block_in_place</code> may use <code>block_on</code> to reenter the
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async context.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">tokio::task</span>;
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<span class="kw">use</span> <span class="ident">tokio::runtime::Handle</span>;
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<span class="ident">task::block_in_place</span>(<span class="kw">move</span> <span class="op">|</span><span class="op">|</span> {
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<span class="ident">Handle::current</span>().<span class="ident">block_on</span>(<span class="kw">async</span> <span class="kw">move</span> {
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<span class="comment">// do something async</span>
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});
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});</code></pre></div>
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<h2 id="panics" class="section-header"><a href="#panics">Panics</a></h2>
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<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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