| <!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."><meta name="keywords" content="rust, rustlang, rust-lang, crossbeam_epoch"><title>crossbeam_epoch - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../normalize.css"><link rel="stylesheet" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../ayu.css" disabled><link rel="stylesheet" href="../dark.css" disabled><link rel="stylesheet" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script defer src="../crates.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../favicon.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><a class="sidebar-logo" href="../crossbeam_epoch/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../crossbeam_epoch/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Crate crossbeam_epoch</a></h2><div class="sidebar-elems"><ul class="block"><li class="version">Version 0.9.14</li><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 Definitions</a></li></ul></section></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Crate <a class="mod" href="#">crossbeam_epoch</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../src/crossbeam_epoch/lib.rs.html#1-169">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Epoch-based memory reclamation.</p> |
| <p>An interesting problem concurrent collections deal with comes from the remove operation. |
| Suppose that a thread removes an element from a lock-free map, while another thread is reading |
| that same element at the same time. The first thread must wait until the second thread stops |
| reading the element. Only then it is safe to destruct it.</p> |
| <p>Programming languages that come with garbage collectors solve this problem trivially. The |
| garbage collector will destruct the removed element when no thread can hold a reference to it |
| anymore.</p> |
| <p>This crate implements a basic memory reclamation mechanism, which is based on epochs. When an |
| element gets removed from a concurrent collection, it is inserted into a pile of garbage and |
| marked with the current epoch. Every time a thread accesses a collection, it checks the current |
| epoch, attempts to increment it, and destructs some garbage that became so old that no thread |
| can be referencing it anymore.</p> |
| <p>That is the general mechanism behind epoch-based memory reclamation, but the details are a bit |
| more complicated. Anyhow, memory reclamation is designed to be fully automatic and something |
| users of concurrent collections don’t have to worry much about.</p> |
| <h2 id="pointers"><a href="#pointers">Pointers</a></h2> |
| <p>Concurrent collections are built using atomic pointers. This module provides <a href="struct.Atomic.html" title="Atomic"><code>Atomic</code></a>, which |
| is just a shared atomic pointer to a heap-allocated object. Loading an <a href="struct.Atomic.html" title="Atomic"><code>Atomic</code></a> yields a |
| <a href="struct.Shared.html" title="Shared"><code>Shared</code></a>, which is an epoch-protected pointer through which the loaded object can be safely |
| read.</p> |
| <h2 id="pinning"><a href="#pinning">Pinning</a></h2> |
| <p>Before an <a href="struct.Atomic.html" title="Atomic"><code>Atomic</code></a> can be loaded, a participant must be <a href="fn.pin.html" title="pin"><code>pin</code></a>ned. By pinning a participant |
| we declare that any object that gets removed from now on must not be destructed just |
| yet. Garbage collection of newly removed objects is suspended until the participant gets |
| unpinned.</p> |
| <h2 id="garbage"><a href="#garbage">Garbage</a></h2> |
| <p>Objects that get removed from concurrent collections must be stashed away until all currently |
| pinned participants get unpinned. Such objects can be stored into a thread-local or global |
| storage, where they are kept until the right time for their destruction comes.</p> |
| <p>There is a global shared instance of garbage queue. You can <a href="struct.Guard.html#method.defer"><code>defer</code></a> the execution of an |
| arbitrary function until the global epoch is advanced enough. Most notably, concurrent data |
| structures may defer the deallocation of an object.</p> |
| <h2 id="apis"><a href="#apis">APIs</a></h2> |
| <p>For majority of use cases, just use the default garbage collector by invoking <a href="fn.pin.html" title="pin"><code>pin</code></a>. If you |
| want to create your own garbage collector, use the <a href="struct.Collector.html" title="Collector"><code>Collector</code></a> API.</p> |
| </div></details><h2 id="structs" class="small-section-header"><a href="#structs">Structs</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Atomic.html" title="crossbeam_epoch::Atomic struct">Atomic</a></div><div class="item-right docblock-short">An atomic pointer that can be safely shared between threads.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Collector.html" title="crossbeam_epoch::Collector struct">Collector</a></div><div class="item-right docblock-short">An epoch-based garbage collector.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.CompareExchangeError.html" title="crossbeam_epoch::CompareExchangeError struct">CompareExchangeError</a></div><div class="item-right docblock-short">The error returned on failed compare-and-swap operation.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Guard.html" title="crossbeam_epoch::Guard struct">Guard</a></div><div class="item-right docblock-short">A guard that keeps the current thread pinned.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.LocalHandle.html" title="crossbeam_epoch::LocalHandle struct">LocalHandle</a></div><div class="item-right docblock-short">A handle to a garbage collector.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Owned.html" title="crossbeam_epoch::Owned struct">Owned</a></div><div class="item-right docblock-short">An owned heap-allocated object.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Shared.html" title="crossbeam_epoch::Shared struct">Shared</a></div><div class="item-right docblock-short">A pointer to an object protected by the epoch GC.</div></div></div><h2 id="traits" class="small-section-header"><a href="#traits">Traits</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="trait" href="trait.CompareAndSetOrdering.html" title="crossbeam_epoch::CompareAndSetOrdering trait">CompareAndSetOrdering</a><span class="stab deprecated" title="">Deprecated</span></div><div class="item-right docblock-short">Memory orderings for compare-and-set operations.</div></div><div class="item-row"><div class="item-left module-item"><a class="trait" href="trait.Pointable.html" title="crossbeam_epoch::Pointable trait">Pointable</a></div><div class="item-right docblock-short">Types that are pointed to by a single word.</div></div><div class="item-row"><div class="item-left module-item"><a class="trait" href="trait.Pointer.html" title="crossbeam_epoch::Pointer trait">Pointer</a></div><div class="item-right docblock-short">A trait for either <code>Owned</code> or <code>Shared</code> pointers.</div></div></div><h2 id="functions" class="small-section-header"><a href="#functions">Functions</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.default_collector.html" title="crossbeam_epoch::default_collector fn">default_collector</a></div><div class="item-right docblock-short">Returns the default global collector.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.is_pinned.html" title="crossbeam_epoch::is_pinned fn">is_pinned</a></div><div class="item-right docblock-short">Returns <code>true</code> if the current thread is pinned.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.pin.html" title="crossbeam_epoch::pin fn">pin</a></div><div class="item-right docblock-short">Pins the current thread.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.unprotected.html" title="crossbeam_epoch::unprotected fn">unprotected</a><sup title="unsafe function">⚠</sup></div><div class="item-right docblock-short">Returns a reference to a dummy guard that allows unprotected access to <a href="struct.Atomic.html"><code>Atomic</code></a>s.</div></div></div><h2 id="types" class="small-section-header"><a href="#types">Type Definitions</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="type" href="type.CompareAndSetError.html" title="crossbeam_epoch::CompareAndSetError type">CompareAndSetError</a><span class="stab deprecated" title="">Deprecated</span></div><div class="item-right docblock-short">The error returned on failed compare-and-set operation.</div></div></div></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="crossbeam_epoch" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
