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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="Epoch-based memory reclamation."><title>crossbeam_epoch - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-ac92e1bbe349e143.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="crossbeam_epoch" data-themes="" data-resource-suffix="" data-rustdoc-version="1.76.0 (07dca489a 2024-02-04)" data-channel="1.76.0" data-search-js="search-2b6ce74ff89ae146.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../static.files/storage-f2adc0d6ca4d09fb.js"></script><script defer src="../crates.js"></script><script defer src="../static.files/main-305769736d49e732.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-feafe1bb7466e4bd.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-16x16-8b506e7a72182f1c.png"><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc mod crate"><!--[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></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../crossbeam_epoch/index.html">crossbeam_epoch</a><span class="version">0.9.18</span></h2></div><div class="sidebar-elems"><ul class="block">
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<li><a id="all-types" href="all.html">All Items</a></li></ul><section><ul class="block"><li><a href="#structs">Structs</a></li><li><a href="#traits">Traits</a></li><li><a href="#functions">Functions</a></li><li><a href="#types">Type Aliases</a></li></ul></section></div></nav><div class="sidebar-resizer"></div>
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<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../crossbeam_epoch/all.html" title="show sidebar"></a></div><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" tabindex="-1"><a href="../help.html" title="help">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Crate <a class="mod" href="#">crossbeam_epoch</a><button id="copy-path" title="Copy item path to clipboard"><img src="../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../src/crossbeam_epoch/lib.rs.html#1-166">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Epoch-based memory reclamation.</p>
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<p>An interesting problem concurrent collections deal with comes from the remove operation.
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Suppose that a thread removes an element from a lock-free map, while another thread is reading
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that same element at the same time. The first thread must wait until the second thread stops
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reading the element. Only then it is safe to destruct it.</p>
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<p>Programming languages that come with garbage collectors solve this problem trivially. The
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garbage collector will destruct the removed element when no thread can hold a reference to it
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anymore.</p>
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<p>This crate implements a basic memory reclamation mechanism, which is based on epochs. When an
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element gets removed from a concurrent collection, it is inserted into a pile of garbage and
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marked with the current epoch. Every time a thread accesses a collection, it checks the current
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epoch, attempts to increment it, and destructs some garbage that became so old that no thread
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can be referencing it anymore.</p>
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<p>That is the general mechanism behind epoch-based memory reclamation, but the details are a bit
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more complicated. Anyhow, memory reclamation is designed to be fully automatic and something
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users of concurrent collections don’t have to worry much about.</p>
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<h2 id="pointers"><a href="#pointers">Pointers</a></h2>
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<p>Concurrent collections are built using atomic pointers. This module provides <a href="struct.Atomic.html" title="struct crossbeam_epoch::Atomic"><code>Atomic</code></a>, which
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is just a shared atomic pointer to a heap-allocated object. Loading an <a href="struct.Atomic.html" title="struct crossbeam_epoch::Atomic"><code>Atomic</code></a> yields a
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<a href="struct.Shared.html" title="struct crossbeam_epoch::Shared"><code>Shared</code></a>, which is an epoch-protected pointer through which the loaded object can be safely
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read.</p>
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<h2 id="pinning"><a href="#pinning">Pinning</a></h2>
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<p>Before an <a href="struct.Atomic.html" title="struct crossbeam_epoch::Atomic"><code>Atomic</code></a> can be loaded, a participant must be <a href="fn.pin.html" title="fn crossbeam_epoch::pin"><code>pin</code></a>ned. By pinning a participant
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we declare that any object that gets removed from now on must not be destructed just
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yet. Garbage collection of newly removed objects is suspended until the participant gets
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unpinned.</p>
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<h2 id="garbage"><a href="#garbage">Garbage</a></h2>
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<p>Objects that get removed from concurrent collections must be stashed away until all currently
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pinned participants get unpinned. Such objects can be stored into a thread-local or global
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storage, where they are kept until the right time for their destruction comes.</p>
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<p>There is a global shared instance of garbage queue. You can <a href="struct.Guard.html#method.defer" title="method crossbeam_epoch::Guard::defer"><code>defer</code></a> the execution of an
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arbitrary function until the global epoch is advanced enough. Most notably, concurrent data
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structures may defer the deallocation of an object.</p>
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<h2 id="apis"><a href="#apis">APIs</a></h2>
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<p>For majority of use cases, just use the default garbage collector by invoking <a href="fn.pin.html" title="fn crossbeam_epoch::pin"><code>pin</code></a>. If you
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want to create your own garbage collector, use the <a href="struct.Collector.html" title="struct crossbeam_epoch::Collector"><code>Collector</code></a> API.</p>
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</div></details><h2 id="structs" class="section-header"><a href="#structs">Structs</a></h2><ul class="item-table"><li><div class="item-name"><a class="struct" href="struct.Atomic.html" title="struct crossbeam_epoch::Atomic">Atomic</a></div><div class="desc docblock-short">An atomic pointer that can be safely shared between threads.</div></li><li><div class="item-name"><a class="struct" href="struct.Collector.html" title="struct crossbeam_epoch::Collector">Collector</a></div><div class="desc docblock-short">An epoch-based garbage collector.</div></li><li><div class="item-name"><a class="struct" href="struct.CompareExchangeError.html" title="struct crossbeam_epoch::CompareExchangeError">CompareExchangeError</a></div><div class="desc docblock-short">The error returned on failed compare-and-swap operation.</div></li><li><div class="item-name"><a class="struct" href="struct.Guard.html" title="struct crossbeam_epoch::Guard">Guard</a></div><div class="desc docblock-short">A guard that keeps the current thread pinned.</div></li><li><div class="item-name"><a class="struct" href="struct.LocalHandle.html" title="struct crossbeam_epoch::LocalHandle">LocalHandle</a></div><div class="desc docblock-short">A handle to a garbage collector.</div></li><li><div class="item-name"><a class="struct" href="struct.Owned.html" title="struct crossbeam_epoch::Owned">Owned</a></div><div class="desc docblock-short">An owned heap-allocated object.</div></li><li><div class="item-name"><a class="struct" href="struct.Shared.html" title="struct crossbeam_epoch::Shared">Shared</a></div><div class="desc docblock-short">A pointer to an object protected by the epoch GC.</div></li></ul><h2 id="traits" class="section-header"><a href="#traits">Traits</a></h2><ul class="item-table"><li><div class="item-name"><a class="trait" href="trait.CompareAndSetOrdering.html" title="trait crossbeam_epoch::CompareAndSetOrdering">CompareAndSetOrdering</a><span class="stab deprecated" title="">Deprecated</span></div><div class="desc docblock-short">Memory orderings for compare-and-set operations.</div></li><li><div class="item-name"><a class="trait" href="trait.Pointable.html" title="trait crossbeam_epoch::Pointable">Pointable</a></div><div class="desc docblock-short">Types that are pointed to by a single word.</div></li><li><div class="item-name"><a class="trait" href="trait.Pointer.html" title="trait crossbeam_epoch::Pointer">Pointer</a></div><div class="desc docblock-short">A trait for either <code>Owned</code> or <code>Shared</code> pointers.</div></li></ul><h2 id="functions" class="section-header"><a href="#functions">Functions</a></h2><ul class="item-table"><li><div class="item-name"><a class="fn" href="fn.default_collector.html" title="fn crossbeam_epoch::default_collector">default_collector</a></div><div class="desc docblock-short">Returns the default global collector.</div></li><li><div class="item-name"><a class="fn" href="fn.is_pinned.html" title="fn crossbeam_epoch::is_pinned">is_pinned</a></div><div class="desc docblock-short">Returns <code>true</code> if the current thread is pinned.</div></li><li><div class="item-name"><a class="fn" href="fn.pin.html" title="fn crossbeam_epoch::pin">pin</a></div><div class="desc docblock-short">Pins the current thread.</div></li><li><div class="item-name"><a class="fn" href="fn.unprotected.html" title="fn crossbeam_epoch::unprotected">unprotected</a><sup title="unsafe function">⚠</sup></div><div class="desc docblock-short">Returns a reference to a dummy guard that allows unprotected access to <a href="struct.Atomic.html" title="struct crossbeam_epoch::Atomic"><code>Atomic</code></a>s.</div></li></ul><h2 id="types" class="section-header"><a href="#types">Type Aliases</a></h2><ul class="item-table"><li><div class="item-name"><a class="type" href="type.CompareAndSetError.html" title="type crossbeam_epoch::CompareAndSetError">CompareAndSetError</a><span class="stab deprecated" title="">Deprecated</span></div><div class="desc docblock-short">The error returned on failed compare-and-set operation.</div></li></ul></section></div></main></body></html> |