<!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="API documentation for the Rust `park` fn in crate `std`."> <meta name="keywords" content="rust, rustlang, rust-lang, park"> <title>std::thread::park - Rust</title> <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="../../dark.css"> <link rel="stylesheet" type="text/css" href="../../main.css" id="themeStyle"> <script src="../../storage.js"></script> <link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"> </head> <body class="rustdoc fn"> <!--[if lte IE 8]> <div class="warning"> This old browser is unsupported and will most likely display funky things. </div> <![endif]--> <nav class="sidebar"> <div class="sidebar-menu">☰</div> <a href='../../std/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a> <p class='location'><a href='../index.html'>std</a>::<wbr><a href='index.html'>thread</a></p><script>window.sidebarCurrent = {name: 'park', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script> </nav> <div class="theme-picker"> <button id="theme-picker" aria-label="Pick another theme!"> <img src="../../brush.svg" width="18" alt="Pick another theme!"> </button> <div id="theme-choices"></div> </div> <script src="../../theme.js"></script> <nav class="sub"> <form class="search-form js-only"> <div class="search-container"> <input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"> </div> </form> </nav> <section id='main' class="content"> <h1 class='fqn'><span class='in-band'>Function <a href='../index.html'>std</a>::<wbr><a href='index.html'>thread</a>::<wbr><a class="fn" href=''>park</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><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/std/thread/mod.rs.html#783-806' title='goto source code'>[src]</a></span></h1> <pre class='rust fn'>pub fn park()</pre><div class='docblock'><p>Blocks unless or until the current thread's token is made available.</p> <p>A call to <code>park</code> does not guarantee that the thread will remain parked forever, and callers should be prepared for this possibility.</p> <h1 id="park-and-unpark" class="section-header"><a href="#park-and-unpark">park and unpark</a></h1> <p>Every thread is equipped with some basic low-level blocking support, via the <a href="../../std/thread/fn.park.html"><code>thread::park</code></a> function and <a href="../../std/thread/struct.Thread.html#method.unpark"><code>thread::Thread::unpark</code></a> method. <a href="../../std/thread/fn.park.html"><code>park</code></a> blocks the current thread, which can then be resumed from another thread by calling the <a href="../../std/thread/struct.Thread.html#method.unpark"><code>unpark</code></a> method on the blocked thread's handle.</p> <p>Conceptually, each <a href="../../std/thread/struct.Thread.html"><code>Thread</code></a> handle has an associated token, which is initially not present:</p> <ul> <li> <p>The <a href="../../std/thread/fn.park.html"><code>thread::park</code></a> function blocks the current thread unless or until the token is available for its thread handle, at which point it atomically consumes the token. It may also return <em>spuriously</em>, without consuming the token. <a href="../../std/thread/fn.park_timeout.html"><code>thread::park_timeout</code></a> does the same, but allows specifying a maximum time to block the thread for.</p> </li> <li> <p>The <a href="../../std/thread/struct.Thread.html#method.unpark"><code>unpark</code></a> method on a <a href="../../std/thread/struct.Thread.html"><code>Thread</code></a> atomically makes the token available if it wasn't already.</p> </li> </ul> <p>In other words, each <a href="../../std/thread/struct.Thread.html"><code>Thread</code></a> acts a bit like a spinlock that can be locked and unlocked using <code>park</code> and <code>unpark</code>.</p> <p>The API is typically used by acquiring a handle to the current thread, placing that handle in a shared data structure so that other threads can find it, and then <code>park</code>ing. When some desired condition is met, another thread calls <a href="../../std/thread/struct.Thread.html#method.unpark"><code>unpark</code></a> on the handle.</p> <p>The motivation for this design is twofold:</p> <ul> <li> <p>It avoids the need to allocate mutexes and condvars when building new synchronization primitives; the threads already provide basic blocking/signaling.</p> </li> <li> <p>It can be implemented very efficiently on many platforms.</p> </li> </ul> <h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1> <pre class="rust rust-example-rendered"> <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">thread</span>; <span class="kw">use</span> <span class="ident">std</span>::<span class="ident">time</span>::<span class="ident">Duration</span>; <span class="kw">let</span> <span class="ident">parked_thread</span> <span class="op">=</span> <span class="ident">thread</span>::<span class="ident">Builder</span>::<span class="ident">new</span>() .<span class="ident">spawn</span>(<span class="op">||</span> { <span class="macro">println</span><span class="macro">!</span>(<span class="string">"Parking thread"</span>); <span class="ident">thread</span>::<span class="ident">park</span>(); <span class="macro">println</span><span class="macro">!</span>(<span class="string">"Thread unparked"</span>); }) .<span class="ident">unwrap</span>(); <span class="comment">// Let some time pass for the thread to be spawned.</span> <span class="ident">thread</span>::<span class="ident">sleep</span>(<span class="ident">Duration</span>::<span class="ident">from_millis</span>(<span class="number">10</span>)); <span class="macro">println</span><span class="macro">!</span>(<span class="string">"Unpark the thread"</span>); <span class="ident">parked_thread</span>.<span class="ident">thread</span>().<span class="ident">unpark</span>(); <span class="ident">parked_thread</span>.<span class="ident">join</span>().<span class="ident">unwrap</span>();<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Athread%3B%0Ause%20std%3A%3Atime%3A%3ADuration%3B%0A%0Alet%20parked_thread%20%3D%20thread%3A%3ABuilder%3A%3Anew()%0A%20%20%20%20.spawn(%7C%7C%20%7B%0A%20%20%20%20%20%20%20%20println!(%22Parking%20thread%22)%3B%0A%20%20%20%20%20%20%20%20thread%3A%3Apark()%3B%0A%20%20%20%20%20%20%20%20println!(%22Thread%20unparked%22)%3B%0A%20%20%20%20%7D)%0A%20%20%20%20.unwrap()%3B%0A%0A%2F%2F%20Let%20some%20time%20pass%20for%20the%20thread%20to%20be%20spawned.%0Athread%3A%3Asleep(Duration%3A%3Afrom_millis(10))%3B%0A%0Aprintln!(%22Unpark%20the%20thread%22)%3B%0Aparked_thread.thread().unpark()%3B%0A%0Aparked_thread.join().unwrap()%3B%0A%7D">Run</a></pre> </div></section> <section id='search' class="content hidden"></section> <section class="footer"></section> <aside id="help" class="hidden"> <div> <h1 class="hidden">Help</h1> <div class="shortcuts"> <h2>Keyboard Shortcuts</h2> <dl> <dt><kbd>?</kbd></dt> <dd>Show this help dialog</dd> <dt><kbd>S</kbd></dt> <dd>Focus the search field</dd> <dt><kbd>↑</kbd></dt> <dd>Move up in search results</dd> <dt><kbd>↓</kbd></dt> <dd>Move down in search results</dd> <dt><kbd>↹</kbd></dt> <dd>Switch tab</dd> <dt><kbd>⏎</kbd></dt> <dd>Go to active search result</dd> <dt><kbd>+</kbd></dt> <dd>Expand all sections</dd> <dt><kbd>-</kbd></dt> <dd>Collapse all sections</dd> </dl> </div> <div class="infos"> <h2>Search Tricks</h2> <p> Prefix searches with a type followed by a colon (e.g. <code>fn:</code>) to restrict the search to a given type. </p> <p> Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>. </p> <p> Search functions by type signature (e.g. <code>vec -> usize</code> or <code>* -> vec</code>) </p> </div> </div> </aside> <script> window.rootPath = "../../"; window.currentCrate = "std"; </script> <script src="../../main.js"></script> <script defer src="../../search-index.js"></script> </body> </html>