| <!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="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/crossbeam-utils-0.8.15/src/atomic/seq_lock.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>seq_lock.rs - source</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="../../../source-script.js"></script><script defer src="../../../source-files.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 source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../crossbeam_utils/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../crossbeam_utils/index.html"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></a><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="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="kw">use </span>core::mem; |
| <span class="kw">use </span>core::sync::atomic::{<span class="self">self</span>, AtomicUsize, Ordering}; |
| |
| <span class="kw">use </span><span class="kw">crate</span>::Backoff; |
| |
| <span class="doccomment">/// A simple stamped lock. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>SeqLock { |
| <span class="doccomment">/// The current state of the lock. |
| /// |
| /// All bits except the least significant one hold the current stamp. When locked, the state |
| /// equals 1 and doesn't contain a valid stamp. |
| </span>state: AtomicUsize, |
| } |
| |
| <span class="kw">impl </span>SeqLock { |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">const fn </span>new() -> <span class="self">Self </span>{ |
| <span class="self">Self </span>{ |
| state: AtomicUsize::new(<span class="number">0</span>), |
| } |
| } |
| |
| <span class="doccomment">/// If not locked, returns the current stamp. |
| /// |
| /// This method should be called before optimistic reads. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>optimistic_read(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><usize> { |
| <span class="kw">let </span>state = <span class="self">self</span>.state.load(Ordering::Acquire); |
| <span class="kw">if </span>state == <span class="number">1 </span>{ |
| <span class="prelude-val">None |
| </span>} <span class="kw">else </span>{ |
| <span class="prelude-val">Some</span>(state) |
| } |
| } |
| |
| <span class="doccomment">/// Returns `true` if the current stamp is equal to `stamp`. |
| /// |
| /// This method should be called after optimistic reads to check whether they are valid. The |
| /// argument `stamp` should correspond to the one returned by method `optimistic_read`. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>validate_read(<span class="kw-2">&</span><span class="self">self</span>, stamp: usize) -> bool { |
| atomic::fence(Ordering::Acquire); |
| <span class="self">self</span>.state.load(Ordering::Relaxed) == stamp |
| } |
| |
| <span class="doccomment">/// Grabs the lock for writing. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>write(<span class="kw-2">&</span><span class="lifetime">'static </span><span class="self">self</span>) -> SeqLockWriteGuard { |
| <span class="kw">let </span>backoff = Backoff::new(); |
| <span class="kw">loop </span>{ |
| <span class="kw">let </span>previous = <span class="self">self</span>.state.swap(<span class="number">1</span>, Ordering::Acquire); |
| |
| <span class="kw">if </span>previous != <span class="number">1 </span>{ |
| atomic::fence(Ordering::Release); |
| |
| <span class="kw">return </span>SeqLockWriteGuard { |
| lock: <span class="self">self</span>, |
| state: previous, |
| }; |
| } |
| |
| backoff.snooze(); |
| } |
| } |
| } |
| |
| <span class="doccomment">/// An RAII guard that releases the lock and increments the stamp when dropped. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>SeqLockWriteGuard { |
| <span class="doccomment">/// The parent lock. |
| </span>lock: <span class="kw-2">&</span><span class="lifetime">'static </span>SeqLock, |
| |
| <span class="doccomment">/// The stamp before locking. |
| </span>state: usize, |
| } |
| |
| <span class="kw">impl </span>SeqLockWriteGuard { |
| <span class="doccomment">/// Releases the lock without incrementing the stamp. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>abort(<span class="self">self</span>) { |
| <span class="self">self</span>.lock.state.store(<span class="self">self</span>.state, Ordering::Release); |
| |
| <span class="comment">// We specifically don't want to call drop(), since that's |
| // what increments the stamp. |
| </span>mem::forget(<span class="self">self</span>); |
| } |
| } |
| |
| <span class="kw">impl </span>Drop <span class="kw">for </span>SeqLockWriteGuard { |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="comment">// Release the lock and increment the stamp. |
| </span><span class="self">self</span>.lock |
| .state |
| .store(<span class="self">self</span>.state.wrapping_add(<span class="number">2</span>), Ordering::Release); |
| } |
| } |
| |
| <span class="attribute">#[cfg(test)] |
| </span><span class="kw">mod </span>tests { |
| <span class="kw">use </span><span class="kw">super</span>::SeqLock; |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_abort() { |
| <span class="kw">static </span>LK: SeqLock = SeqLock::new(); |
| <span class="kw">let </span>before = LK.optimistic_read().unwrap(); |
| { |
| <span class="kw">let </span>guard = LK.write(); |
| guard.abort(); |
| } |
| <span class="kw">let </span>after = LK.optimistic_read().unwrap(); |
| <span class="macro">assert_eq!</span>(before, after, <span class="string">"aborted write does not update the stamp"</span>); |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="crossbeam_utils" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |