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37 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="Epoch-based memory reclamation."><title>crossbeam_epoch - 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="crossbeam_epoch" 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="../crates.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 mod crate"><!--[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="#">Crate crossbeam_epoch</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../crossbeam_epoch/index.html">crossbeam_<wbr>epoch</a><span class="version">0.9.18</span></h2></div><div class="sidebar-elems"><ul class="block"><li><a id="all-types" href="all.html">All Items</a></li></ul><section id="rustdoc-toc"><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#pointers" title="Pointers">Pointers</a></li><li><a href="#pinning" title="Pinning">Pinning</a></li><li><a href="#garbage" title="Garbage">Garbage</a></li><li><a href="#apis" title="APIs">APIs</a></li></ul><h3><a href="#structs">Crate Items</a></h3><ul class="block"><li><a href="#structs" title="Structs">Structs</a></li><li><a href="#traits" title="Traits">Traits</a></li><li><a href="#functions" title="Functions">Functions</a></li><li><a href="#types" title="Type Aliases">Type Aliases</a></li></ul></section><div id="rustdoc-modnav"></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"><h1>Crate <span>crossbeam_<wbr>epoch</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/crossbeam_epoch/lib.rs.html#1-166">Source</a> </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 class="doc-anchor" href="#pointers">§</a>Pointers</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 class="doc-anchor" href="#pinning">§</a>Pinning</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 class="doc-anchor" href="#garbage">§</a>Garbage</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 class="doc-anchor" href="#apis">§</a>APIs</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">Structs<a href="#structs" class="anchor">§</a></h2><dl class="item-table"><dt><a class="struct" href="struct.Atomic.html" title="struct crossbeam_epoch::Atomic">Atomic</a></dt><dd>An atomic pointer that can be safely shared between threads.</dd><dt><a class="struct" href="struct.Collector.html" title="struct crossbeam_epoch::Collector">Collector</a></dt><dd>An epoch-based garbage collector.</dd><dt><a class="struct" href="struct.CompareExchangeError.html" title="struct crossbeam_epoch::CompareExchangeError">Compare<wbr>Exchange<wbr>Error</a></dt><dd>The error returned on failed compare-and-swap operation.</dd><dt><a class="struct" href="struct.Guard.html" title="struct crossbeam_epoch::Guard">Guard</a></dt><dd>A guard that keeps the current thread pinned.</dd><dt><a class="struct" href="struct.LocalHandle.html" title="struct crossbeam_epoch::LocalHandle">Local<wbr>Handle</a></dt><dd>A handle to a garbage collector.</dd><dt><a class="struct" href="struct.Owned.html" title="struct crossbeam_epoch::Owned">Owned</a></dt><dd>An owned heap-allocated object.</dd><dt><a class="struct" href="struct.Shared.html" title="struct crossbeam_epoch::Shared">Shared</a></dt><dd>A pointer to an object protected by the epoch GC.</dd></dl><h2 id="traits" class="section-header">Traits<a href="#traits" class="anchor">§</a></h2><dl class="item-table"><dt><a class="trait" href="trait.CompareAndSetOrdering.html" title="trait crossbeam_epoch::CompareAndSetOrdering">Compare<wbr>AndSet<wbr>Ordering</a><wbr><span class="stab deprecated" title="">Deprecated</span></dt><dd>Memory orderings for compare-and-set operations.</dd><dt><a class="trait" href="trait.Pointable.html" title="trait crossbeam_epoch::Pointable">Pointable</a></dt><dd>Types that are pointed to by a single word.</dd><dt><a class="trait" href="trait.Pointer.html" title="trait crossbeam_epoch::Pointer">Pointer</a></dt><dd>A trait for either <code>Owned</code> or <code>Shared</code> pointers.</dd></dl><h2 id="functions" class="section-header">Functions<a href="#functions" class="anchor">§</a></h2><dl class="item-table"><dt><a class="fn" href="fn.default_collector.html" title="fn crossbeam_epoch::default_collector">default_<wbr>collector</a></dt><dd>Returns the default global collector.</dd><dt><a class="fn" href="fn.is_pinned.html" title="fn crossbeam_epoch::is_pinned">is_<wbr>pinned</a></dt><dd>Returns <code>true</code> if the current thread is pinned.</dd><dt><a class="fn" href="fn.pin.html" title="fn crossbeam_epoch::pin">pin</a></dt><dd>Pins the current thread.</dd><dt><a class="fn" href="fn.unprotected.html" title="fn crossbeam_epoch::unprotected">unprotected</a><sup title="unsafe function">⚠</sup></dt><dd>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.</dd></dl><h2 id="types" class="section-header">Type Aliases<a href="#types" class="anchor">§</a></h2><dl class="item-table"><dt><a class="type" href="type.CompareAndSetError.html" title="type crossbeam_epoch::CompareAndSetError">Compare<wbr>AndSet<wbr>Error</a><wbr><span class="stab deprecated" title="">Deprecated</span></dt><dd>The error returned on failed compare-and-set operation.</dd></dl></section></div></main></body></html> |