| <!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-epoch-0.9.14/src/sync/once_lock.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>once_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_epoch/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_epoch/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> |
| <span id="2">2</span> |
| <span id="3">3</span> |
| <span id="4">4</span> |
| <span id="5">5</span> |
| <span id="6">6</span> |
| <span id="7">7</span> |
| <span id="8">8</span> |
| <span id="9">9</span> |
| <span id="10">10</span> |
| <span id="11">11</span> |
| <span id="12">12</span> |
| <span id="13">13</span> |
| <span id="14">14</span> |
| <span id="15">15</span> |
| <span id="16">16</span> |
| <span id="17">17</span> |
| <span id="18">18</span> |
| <span id="19">19</span> |
| <span id="20">20</span> |
| <span id="21">21</span> |
| <span id="22">22</span> |
| <span id="23">23</span> |
| <span id="24">24</span> |
| <span id="25">25</span> |
| <span id="26">26</span> |
| <span id="27">27</span> |
| <span id="28">28</span> |
| <span id="29">29</span> |
| <span id="30">30</span> |
| <span id="31">31</span> |
| <span id="32">32</span> |
| <span id="33">33</span> |
| <span id="34">34</span> |
| <span id="35">35</span> |
| <span id="36">36</span> |
| <span id="37">37</span> |
| <span id="38">38</span> |
| <span id="39">39</span> |
| <span id="40">40</span> |
| <span id="41">41</span> |
| <span id="42">42</span> |
| <span id="43">43</span> |
| <span id="44">44</span> |
| <span id="45">45</span> |
| <span id="46">46</span> |
| <span id="47">47</span> |
| <span id="48">48</span> |
| <span id="49">49</span> |
| <span id="50">50</span> |
| <span id="51">51</span> |
| <span id="52">52</span> |
| <span id="53">53</span> |
| <span id="54">54</span> |
| <span id="55">55</span> |
| <span id="56">56</span> |
| <span id="57">57</span> |
| <span id="58">58</span> |
| <span id="59">59</span> |
| <span id="60">60</span> |
| <span id="61">61</span> |
| <span id="62">62</span> |
| <span id="63">63</span> |
| <span id="64">64</span> |
| <span id="65">65</span> |
| <span id="66">66</span> |
| <span id="67">67</span> |
| <span id="68">68</span> |
| <span id="69">69</span> |
| <span id="70">70</span> |
| <span id="71">71</span> |
| <span id="72">72</span> |
| <span id="73">73</span> |
| <span id="74">74</span> |
| <span id="75">75</span> |
| <span id="76">76</span> |
| <span id="77">77</span> |
| <span id="78">78</span> |
| <span id="79">79</span> |
| <span id="80">80</span> |
| <span id="81">81</span> |
| <span id="82">82</span> |
| <span id="83">83</span> |
| <span id="84">84</span> |
| <span id="85">85</span> |
| <span id="86">86</span> |
| <span id="87">87</span> |
| <span id="88">88</span> |
| <span id="89">89</span> |
| <span id="90">90</span> |
| <span id="91">91</span> |
| <span id="92">92</span> |
| <span id="93">93</span> |
| <span id="94">94</span> |
| <span id="95">95</span> |
| <span id="96">96</span> |
| <span id="97">97</span> |
| <span id="98">98</span> |
| <span id="99">99</span> |
| <span id="100">100</span> |
| <span id="101">101</span> |
| <span id="102">102</span> |
| <span id="103">103</span> |
| </pre><pre class="rust"><code><span class="comment">// Based on unstable std::sync::OnceLock. |
| // |
| // Source: https://github.com/rust-lang/rust/blob/8e9c93df464b7ada3fc7a1c8ccddd9dcb24ee0a0/library/std/src/sync/once_lock.rs |
| |
| </span><span class="kw">use </span>core::cell::UnsafeCell; |
| <span class="kw">use </span>core::mem::MaybeUninit; |
| <span class="kw">use </span>core::sync::atomic::{AtomicBool, Ordering}; |
| <span class="kw">use </span>std::sync::Once; |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>OnceLock<T> { |
| once: Once, |
| <span class="comment">// Once::is_completed requires Rust 1.43, so use this to track of whether they have been initialized. |
| </span>is_initialized: AtomicBool, |
| value: UnsafeCell<MaybeUninit<T>>, |
| <span class="comment">// Unlike std::sync::OnceLock, we don't need PhantomData here because |
| // we don't use #[may_dangle]. |
| </span>} |
| |
| <span class="kw">unsafe impl</span><T: Sync + Send> Sync <span class="kw">for </span>OnceLock<T> {} |
| <span class="kw">unsafe impl</span><T: Send> Send <span class="kw">for </span>OnceLock<T> {} |
| |
| <span class="kw">impl</span><T> OnceLock<T> { |
| <span class="doccomment">/// Creates a new empty cell. |
| </span><span class="attribute">#[must_use] |
| </span><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>{ |
| once: Once::new(), |
| is_initialized: AtomicBool::new(<span class="bool-val">false</span>), |
| value: UnsafeCell::new(MaybeUninit::uninit()), |
| } |
| } |
| |
| <span class="doccomment">/// Gets the contents of the cell, initializing it with `f` if the cell |
| /// was empty. |
| /// |
| /// Many threads may call `get_or_init` concurrently with different |
| /// initializing functions, but it is guaranteed that only one function |
| /// will be executed. |
| /// |
| /// # Panics |
| /// |
| /// If `f` panics, the panic is propagated to the caller, and the cell |
| /// remains uninitialized. |
| /// |
| /// It is an error to reentrantly initialize the cell from `f`. The |
| /// exact outcome is unspecified. Current implementation deadlocks, but |
| /// this may be changed to a panic in the future. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>get_or_init<F>(<span class="kw-2">&</span><span class="self">self</span>, f: F) -> <span class="kw-2">&</span>T |
| <span class="kw">where |
| </span>F: FnOnce() -> T, |
| { |
| <span class="comment">// Fast path check |
| </span><span class="kw">if </span><span class="self">self</span>.is_initialized() { |
| <span class="comment">// SAFETY: The inner value has been initialized |
| </span><span class="kw">return unsafe </span>{ <span class="self">self</span>.get_unchecked() }; |
| } |
| <span class="self">self</span>.initialize(f); |
| |
| <span class="macro">debug_assert!</span>(<span class="self">self</span>.is_initialized()); |
| |
| <span class="comment">// SAFETY: The inner value has been initialized |
| </span><span class="kw">unsafe </span>{ <span class="self">self</span>.get_unchecked() } |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>is_initialized(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="self">self</span>.is_initialized.load(Ordering::Acquire) |
| } |
| |
| <span class="attribute">#[cold] |
| </span><span class="kw">fn </span>initialize<F>(<span class="kw-2">&</span><span class="self">self</span>, f: F) |
| <span class="kw">where |
| </span>F: FnOnce() -> T, |
| { |
| <span class="kw">let </span>slot = <span class="self">self</span>.value.get().cast::<T>(); |
| <span class="kw">let </span>is_initialized = <span class="kw-2">&</span><span class="self">self</span>.is_initialized; |
| |
| <span class="self">self</span>.once.call_once(|| { |
| <span class="kw">let </span>value = f(); |
| <span class="kw">unsafe </span>{ |
| slot.write(value); |
| } |
| is_initialized.store(<span class="bool-val">true</span>, Ordering::Release); |
| }); |
| } |
| |
| <span class="doccomment">/// # Safety |
| /// |
| /// The value must be initialized |
| </span><span class="kw">unsafe fn </span>get_unchecked(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>T { |
| <span class="macro">debug_assert!</span>(<span class="self">self</span>.is_initialized()); |
| <span class="kw-2">&*</span><span class="self">self</span>.value.get().cast::<T>() |
| } |
| } |
| |
| <span class="kw">impl</span><T> Drop <span class="kw">for </span>OnceLock<T> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="kw">if </span><span class="self">self</span>.is_initialized() { |
| <span class="comment">// SAFETY: The inner value has been initialized |
| </span><span class="kw">unsafe </span>{ <span class="self">self</span>.value.get().cast::<T>().drop_in_place() }; |
| } |
| } |
| } |
| </code></pre></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> |
