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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="API documentation for the Rust `parking_lot_core` crate."><meta name="keywords" content="rust, rustlang, rust-lang, parking_lot_core"><title>parking_lot_core - 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="../light.css" id="themeStyle"><script src="../storage.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="shortcut icon" href="../favicon.ico"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc mod"><!--[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='../parking_lot_core/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><p class='location'>Crate parking_lot_core</p><div class="sidebar-elems"><a id='all-types' href='all.html'><p>See all parking_lot_core's items</p></a><div class="block items"><ul><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li><li><a href="#enums">Enums</a></li><li><a href="#constants">Constants</a></li><li><a href="#functions">Functions</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'parking_lot_core', ty: 'mod', relpath: '../'};</script></div></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"><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><a id="settings-menu" href="../settings.html"><img src="../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><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/parking_lot_core/lib.rs.html#8-84' title='goto source code'>[src]</a></span><span class='in-band'>Crate <a class="mod" href=''>parking_lot_core</a></span></h1><div class='docblock'><p>This library exposes a low-level API for creating your own efficient
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synchronization primitives.</p>
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<h1 id="the-parking-lot" class="section-header"><a href="#the-parking-lot">The parking lot</a></h1>
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<p>To keep synchronization primitives small, all thread queuing and suspending
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functionality is offloaded to the <em>parking lot</em>. The idea behind this is based
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on the Webkit <a href="https://webkit.org/blog/6161/locking-in-webkit/"><code>WTF::ParkingLot</code></a>
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class, which essentially consists of a hash table mapping of lock addresses
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to queues of parked (sleeping) threads. The Webkit parking lot was itself
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inspired by Linux <a href="http://man7.org/linux/man-pages/man2/futex.2.html">futexes</a>,
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but it is more powerful since it allows invoking callbacks while holding a
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queue lock.</p>
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<p>There are two main operations that can be performed on the parking lot:</p>
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<ul>
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<li><em>Parking</em> refers to suspending the thread while simultaneously enqueuing it
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on a queue keyed by some address.</li>
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<li><em>Unparking</em> refers to dequeuing a thread from a queue keyed by some address
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and resuming it.</li>
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</ul>
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<p>See the documentation of the individual functions for more details.</p>
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<h1 id="building-custom-synchronization-primitives" class="section-header"><a href="#building-custom-synchronization-primitives">Building custom synchronization primitives</a></h1>
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<p>Building custom synchronization primitives is very simple since the parking
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lot takes care of all the hard parts for you. A simple example for a
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custom primitive would be to integrate a <code>Mutex</code> inside another data type.
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Since a mutex only requires 2 bits, it can share space with other data.
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For example, one could create an <code>ArcMutex</code> type that combines the atomic
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reference count and the two mutex bits in the same atomic word.</p>
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</div><h2 id='modules' class='section-header'><a href="#modules">Modules</a></h2>
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<table><tr class='module-item'><td><a class="mod" href="deadlock/index.html" title='parking_lot_core::deadlock mod'>deadlock</a></td><td class='docblock-short'><p>[Experimental] Deadlock detection</p>
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</td></tr></table><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table><tr class='module-item'><td><a class="struct" href="struct.ParkToken.html" title='parking_lot_core::ParkToken struct'>ParkToken</a></td><td class='docblock-short'><p>A value associated with a parked thread which can be used by <code>unpark_filter</code>.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.SpinWait.html" title='parking_lot_core::SpinWait struct'>SpinWait</a></td><td class='docblock-short'><p>A counter used to perform exponential backoff in spin loops.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.UnparkResult.html" title='parking_lot_core::UnparkResult struct'>UnparkResult</a></td><td class='docblock-short'><p>Result of an unpark operation.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.UnparkToken.html" title='parking_lot_core::UnparkToken struct'>UnparkToken</a></td><td class='docblock-short'><p>A value which is passed from an unparker to a parked thread.</p>
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</td></tr></table><h2 id='enums' class='section-header'><a href="#enums">Enums</a></h2>
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<table><tr class='module-item'><td><a class="enum" href="enum.FilterOp.html" title='parking_lot_core::FilterOp enum'>FilterOp</a></td><td class='docblock-short'><p>Operation that <code>unpark_filter</code> should perform for each thread.</p>
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</td></tr><tr class='module-item'><td><a class="enum" href="enum.ParkResult.html" title='parking_lot_core::ParkResult enum'>ParkResult</a></td><td class='docblock-short'><p>Result of a park operation.</p>
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</td></tr><tr class='module-item'><td><a class="enum" href="enum.RequeueOp.html" title='parking_lot_core::RequeueOp enum'>RequeueOp</a></td><td class='docblock-short'><p>Operation that <code>unpark_requeue</code> should perform.</p>
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</td></tr></table><h2 id='constants' class='section-header'><a href="#constants">Constants</a></h2>
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<table><tr class='module-item'><td><a class="constant" href="constant.DEFAULT_PARK_TOKEN.html" title='parking_lot_core::DEFAULT_PARK_TOKEN constant'>DEFAULT_PARK_TOKEN</a></td><td class='docblock-short'><p>A default park token to use.</p>
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</td></tr><tr class='module-item'><td><a class="constant" href="constant.DEFAULT_UNPARK_TOKEN.html" title='parking_lot_core::DEFAULT_UNPARK_TOKEN constant'>DEFAULT_UNPARK_TOKEN</a></td><td class='docblock-short'><p>A default unpark token to use.</p>
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</td></tr></table><h2 id='functions' class='section-header'><a href="#functions">Functions</a></h2>
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<table><tr class='module-item'><td><a class="fn" href="fn.park.html" title='parking_lot_core::park fn'>park</a><a title='unsafe function' href='#'><sup>⚠</sup></a></td><td class='docblock-short'><p>Parks the current thread in the queue associated with the given key.</p>
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</td></tr><tr class='module-item'><td><a class="fn" href="fn.unpark_all.html" title='parking_lot_core::unpark_all fn'>unpark_all</a><a title='unsafe function' href='#'><sup>⚠</sup></a></td><td class='docblock-short'><p>Unparks all threads in the queue associated with the given key.</p>
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</td></tr><tr class='module-item'><td><a class="fn" href="fn.unpark_filter.html" title='parking_lot_core::unpark_filter fn'>unpark_filter</a><a title='unsafe function' href='#'><sup>⚠</sup></a></td><td class='docblock-short'><p>Unparks a number of threads from the front of the queue associated with
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<code>key</code> depending on the results of a filter function which inspects the
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<code>ParkToken</code> associated with each thread.</p>
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</td></tr><tr class='module-item'><td><a class="fn" href="fn.unpark_one.html" title='parking_lot_core::unpark_one fn'>unpark_one</a><a title='unsafe function' href='#'><sup>⚠</sup></a></td><td class='docblock-short'><p>Unparks one thread from the queue associated with the given key.</p>
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</td></tr><tr class='module-item'><td><a class="fn" href="fn.unpark_requeue.html" title='parking_lot_core::unpark_requeue fn'>unpark_requeue</a><a title='unsafe function' href='#'><sup>⚠</sup></a></td><td class='docblock-short'><p>Removes all threads from the queue associated with <code>key_from</code>, optionally
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unparks the first one and requeues the rest onto the queue associated with
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<code>key_to</code>.</p>
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