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45 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="Runs the provided blocking function on the current thread without blocking the executor."><title>block_in_place in tokio::task - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Italic-81dc35de.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-MediumItalic-ccf7e434.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"href="../../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../../static.files/rustdoc-ca0dd0c4.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="1.93.1 (01f6ddf75 2026-02-11) (Arch Linux rust 1:1.93.1-1)" data-channel="1.93.1" data-search-js="search-9e2438ea.js" data-stringdex-js="stringdex-a3946164.js" data-settings-js="settings-c38705f0.js" ><script src="../../static.files/storage-e2aeef58.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../static.files/main-a410ff4d.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-263c88ec.css"></noscript><link rel="alternate icon" type="image/png" href="../../static.files/favicon-32x32-eab170b8.png"><link rel="icon" type="image/svg+xml" href="../../static.files/favicon-044be391.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]--><rustdoc-topbar><h2><a href="#">block_in_place</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../tokio/index.html">tokio</a><span class="version">1.49.0</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">block_<wbr>in_<wbr>place</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#examples" title="Examples">Examples</a></li><li><a href="#panics" title="Panics">Panics</a></li></ul></section><div id="rustdoc-modnav"><h2><a href="index.html">In tokio::<wbr>task</a></h2></div></div></nav><div class="sidebar-resizer" title="Drag to resize sidebar"></div><main><div class="width-limiter"><section id="main-content" class="content"><div class="main-heading"><div class="rustdoc-breadcrumbs"><a href="../index.html">tokio</a>::<wbr><a href="index.html">task</a></div><h1>Function <span class="fn">block_<wbr>in_<wbr>place</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/task/blocking.rs.html#74-79">Source</a> </span></div><pre class="rust item-decl"><code>pub fn block_in_place<F, R>(f: F) -> R<div class="where">where
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F: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/ops/function/trait.FnOnce.html" title="trait core::ops::function::FnOnce">FnOnce</a>() -> R,</div></code></pre><details class="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" title="macro tokio::join"><code>join!</code></a> macro. To avoid this issue, use
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<a href="fn.spawn_blocking.html" title="fn tokio::task::spawn_blocking"><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" title="associated function tokio::runtime::Builder::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" title="method tokio::runtime::Runtime::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"><a class="doc-anchor" href="#examples">§</a>Examples</h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::task;
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task::block_in_place(<span class="kw">move </span>|| {
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<span class="comment">// do some compute-heavy work or call synchronous code
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</span>});</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>tokio::task;
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<span class="kw">use </span>tokio::runtime::Handle;
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task::block_in_place(<span class="kw">move </span>|| {
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Handle::current().block_on(<span class="kw">async move </span>{
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<span class="comment">// do something async
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</span>});
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});</code></pre></div><h2 id="panics"><a class="doc-anchor" href="#panics">§</a>Panics</h2>
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<p>This function panics if called from a <a href="../runtime/struct.Builder.html#method.new_current_thread" title="associated function tokio::runtime::Builder::new_current_thread"><code>current_thread</code></a> runtime.</p>
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</div></details></section></div></main></body></html> |