| <!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/spin-0.5.2/src/once.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>once.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="../../spin/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="../../spin/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::cell::UnsafeCell; |
| <span class="kw">use </span>core::sync::atomic::{AtomicUsize, Ordering, spin_loop_hint <span class="kw">as </span>cpu_relax}; |
| <span class="kw">use </span>core::fmt; |
| |
| <span class="doccomment">/// A synchronization primitive which can be used to run a one-time global |
| /// initialization. Unlike its std equivalent, this is generalized so that the |
| /// closure returns a value and it is stored. Once therefore acts something like |
| /// a future, too. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use spin; |
| /// |
| /// static START: spin::Once<()> = spin::Once::new(); |
| /// |
| /// START.call_once(|| { |
| /// // run initialization here |
| /// }); |
| /// ``` |
| </span><span class="kw">pub struct </span>Once<T> { |
| state: AtomicUsize, |
| data: UnsafeCell<<span class="prelude-ty">Option</span><T>>, <span class="comment">// TODO remove option and use mem::uninitialized |
| </span>} |
| |
| <span class="kw">impl</span><T: fmt::Debug> fmt::Debug <span class="kw">for </span>Once<T> { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter) -> fmt::Result { |
| <span class="kw">match </span><span class="self">self</span>.<span class="kw">try</span>() { |
| <span class="prelude-val">Some</span>(s) => <span class="macro">write!</span>(f, <span class="string">"Once {{ data: "</span>) |
| .and_then(|()| s.fmt(f)) |
| .and_then(|()| <span class="macro">write!</span>(f, <span class="string">"}}"</span>)), |
| <span class="prelude-val">None </span>=> <span class="macro">write!</span>(f, <span class="string">"Once {{ <uninitialized> }}"</span>) |
| } |
| } |
| } |
| |
| <span class="comment">// Same unsafe impls as `std::sync::RwLock`, because this also allows for |
| // concurrent reads. |
| </span><span class="kw">unsafe impl</span><T: Send + Sync> Sync <span class="kw">for </span>Once<T> {} |
| <span class="kw">unsafe impl</span><T: Send> Send <span class="kw">for </span>Once<T> {} |
| |
| <span class="comment">// Four states that a Once can be in, encoded into the lower bits of `state` in |
| // the Once structure. |
| </span><span class="kw">const </span>INCOMPLETE: usize = <span class="number">0x0</span>; |
| <span class="kw">const </span>RUNNING: usize = <span class="number">0x1</span>; |
| <span class="kw">const </span>COMPLETE: usize = <span class="number">0x2</span>; |
| <span class="kw">const </span>PANICKED: usize = <span class="number">0x3</span>; |
| |
| <span class="kw">use </span>core::hint::unreachable_unchecked <span class="kw">as </span>unreachable; |
| |
| <span class="kw">impl</span><T> Once<T> { |
| <span class="doccomment">/// Initialization constant of `Once`. |
| </span><span class="kw">pub const </span>INIT: <span class="self">Self </span>= Once { |
| state: AtomicUsize::new(INCOMPLETE), |
| data: UnsafeCell::new(<span class="prelude-val">None</span>), |
| }; |
| |
| <span class="doccomment">/// Creates a new `Once` value. |
| </span><span class="kw">pub const fn </span>new() -> Once<T> { |
| <span class="self">Self</span>::INIT |
| } |
| |
| <span class="kw">fn </span>force_get<<span class="lifetime">'a</span>>(<span class="kw-2">&</span><span class="lifetime">'a </span><span class="self">self</span>) -> <span class="kw-2">&</span><span class="lifetime">'a </span>T { |
| <span class="kw">match unsafe </span>{ <span class="kw-2">&*</span><span class="self">self</span>.data.get() }.as_ref() { |
| <span class="prelude-val">None </span>=> <span class="kw">unsafe </span>{ unreachable() }, |
| <span class="prelude-val">Some</span>(p) => p, |
| } |
| } |
| |
| <span class="doccomment">/// Performs an initialization routine once and only once. The given closure |
| /// will be executed if this is the first time `call_once` has been called, |
| /// and otherwise the routine will *not* be invoked. |
| /// |
| /// This method will block the calling thread if another initialization |
| /// routine is currently running. |
| /// |
| /// When this function returns, it is guaranteed that some initialization |
| /// has run and completed (it may not be the closure specified). The |
| /// returned pointer will point to the result from the closure that was |
| /// run. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use spin; |
| /// |
| /// static INIT: spin::Once<usize> = spin::Once::new(); |
| /// |
| /// fn get_cached_val() -> usize { |
| /// *INIT.call_once(expensive_computation) |
| /// } |
| /// |
| /// fn expensive_computation() -> usize { |
| /// // ... |
| /// # 2 |
| /// } |
| /// ``` |
| </span><span class="kw">pub fn </span>call_once<<span class="lifetime">'a</span>, F>(<span class="kw-2">&</span><span class="lifetime">'a </span><span class="self">self</span>, builder: F) -> <span class="kw-2">&</span><span class="lifetime">'a </span>T |
| <span class="kw">where </span>F: FnOnce() -> T |
| { |
| <span class="kw">let </span><span class="kw-2">mut </span>status = <span class="self">self</span>.state.load(Ordering::SeqCst); |
| |
| <span class="kw">if </span>status == INCOMPLETE { |
| status = <span class="self">self</span>.state.compare_and_swap(INCOMPLETE, |
| RUNNING, |
| Ordering::SeqCst); |
| <span class="kw">if </span>status == INCOMPLETE { <span class="comment">// We init |
| // We use a guard (Finish) to catch panics caused by builder |
| </span><span class="kw">let </span><span class="kw-2">mut </span>finish = Finish { state: <span class="kw-2">&</span><span class="self">self</span>.state, panicked: <span class="bool-val">true </span>}; |
| <span class="kw">unsafe </span>{ <span class="kw-2">*</span><span class="self">self</span>.data.get() = <span class="prelude-val">Some</span>(builder()) }; |
| finish.panicked = <span class="bool-val">false</span>; |
| |
| status = COMPLETE; |
| <span class="self">self</span>.state.store(status, Ordering::SeqCst); |
| |
| <span class="comment">// This next line is strictly an optimization |
| </span><span class="kw">return </span><span class="self">self</span>.force_get(); |
| } |
| } |
| |
| <span class="kw">loop </span>{ |
| <span class="kw">match </span>status { |
| INCOMPLETE => <span class="macro">unreachable!</span>(), |
| RUNNING => { <span class="comment">// We spin |
| </span>cpu_relax(); |
| status = <span class="self">self</span>.state.load(Ordering::SeqCst) |
| }, |
| PANICKED => <span class="macro">panic!</span>(<span class="string">"Once has panicked"</span>), |
| COMPLETE => <span class="kw">return </span><span class="self">self</span>.force_get(), |
| <span class="kw">_ </span>=> <span class="kw">unsafe </span>{ unreachable() }, |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Returns a pointer iff the `Once` was previously initialized |
| </span><span class="kw">pub fn try</span><<span class="lifetime">'a</span>>(<span class="kw-2">&</span><span class="lifetime">'a </span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><<span class="kw-2">&</span><span class="lifetime">'a </span>T> { |
| <span class="kw">match </span><span class="self">self</span>.state.load(Ordering::SeqCst) { |
| COMPLETE => <span class="prelude-val">Some</span>(<span class="self">self</span>.force_get()), |
| <span class="kw">_ </span>=> <span class="prelude-val">None</span>, |
| } |
| } |
| |
| <span class="doccomment">/// Like try, but will spin if the `Once` is in the process of being |
| /// initialized |
| </span><span class="kw">pub fn </span>wait<<span class="lifetime">'a</span>>(<span class="kw-2">&</span><span class="lifetime">'a </span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><<span class="kw-2">&</span><span class="lifetime">'a </span>T> { |
| <span class="kw">loop </span>{ |
| <span class="kw">match </span><span class="self">self</span>.state.load(Ordering::SeqCst) { |
| INCOMPLETE => <span class="kw">return </span><span class="prelude-val">None</span>, |
| RUNNING => cpu_relax(), <span class="comment">// We spin |
| </span>COMPLETE => <span class="kw">return </span><span class="prelude-val">Some</span>(<span class="self">self</span>.force_get()), |
| PANICKED => <span class="macro">panic!</span>(<span class="string">"Once has panicked"</span>), |
| <span class="kw">_ </span>=> <span class="kw">unsafe </span>{ unreachable() }, |
| } |
| } |
| } |
| } |
| |
| <span class="kw">struct </span>Finish<<span class="lifetime">'a</span>> { |
| state: <span class="kw-2">&</span><span class="lifetime">'a </span>AtomicUsize, |
| panicked: bool, |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>> Drop <span class="kw">for </span>Finish<<span class="lifetime">'a</span>> { |
| <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>.panicked { |
| <span class="self">self</span>.state.store(PANICKED, Ordering::SeqCst); |
| } |
| } |
| } |
| |
| <span class="attribute">#[cfg(test)] |
| </span><span class="kw">mod </span>tests { |
| <span class="kw">use </span>std::prelude::v1::<span class="kw-2">*</span>; |
| |
| <span class="kw">use </span>std::sync::mpsc::channel; |
| <span class="kw">use </span>std::thread; |
| <span class="kw">use </span><span class="kw">super</span>::Once; |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>smoke_once() { |
| <span class="kw">static </span>O: Once<()> = Once::new(); |
| <span class="kw">let </span><span class="kw-2">mut </span>a = <span class="number">0</span>; |
| O.call_once(|| a += <span class="number">1</span>); |
| <span class="macro">assert_eq!</span>(a, <span class="number">1</span>); |
| O.call_once(|| a += <span class="number">1</span>); |
| <span class="macro">assert_eq!</span>(a, <span class="number">1</span>); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>smoke_once_value() { |
| <span class="kw">static </span>O: Once<usize> = Once::new(); |
| <span class="kw">let </span>a = O.call_once(|| <span class="number">1</span>); |
| <span class="macro">assert_eq!</span>(<span class="kw-2">*</span>a, <span class="number">1</span>); |
| <span class="kw">let </span>b = O.call_once(|| <span class="number">2</span>); |
| <span class="macro">assert_eq!</span>(<span class="kw-2">*</span>b, <span class="number">1</span>); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>stampede_once() { |
| <span class="kw">static </span>O: Once<()> = Once::new(); |
| <span class="kw">static </span><span class="kw-2">mut </span>RUN: bool = <span class="bool-val">false</span>; |
| |
| <span class="kw">let </span>(tx, rx) = channel(); |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">10 </span>{ |
| <span class="kw">let </span>tx = tx.clone(); |
| thread::spawn(<span class="kw">move</span>|| { |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">4 </span>{ thread::yield_now() } |
| <span class="kw">unsafe </span>{ |
| O.call_once(|| { |
| <span class="macro">assert!</span>(!RUN); |
| RUN = <span class="bool-val">true</span>; |
| }); |
| <span class="macro">assert!</span>(RUN); |
| } |
| tx.send(()).unwrap(); |
| }); |
| } |
| |
| <span class="kw">unsafe </span>{ |
| O.call_once(|| { |
| <span class="macro">assert!</span>(!RUN); |
| RUN = <span class="bool-val">true</span>; |
| }); |
| <span class="macro">assert!</span>(RUN); |
| } |
| |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">10 </span>{ |
| rx.recv().unwrap(); |
| } |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn try</span>() { |
| <span class="kw">static </span>INIT: Once<usize> = Once::new(); |
| |
| <span class="macro">assert!</span>(INIT.<span class="kw">try</span>().is_none()); |
| INIT.call_once(|| <span class="number">2</span>); |
| <span class="macro">assert_eq!</span>(INIT.<span class="kw">try</span>().map(|r| <span class="kw-2">*</span>r), <span class="prelude-val">Some</span>(<span class="number">2</span>)); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>try_no_wait() { |
| <span class="kw">static </span>INIT: Once<usize> = Once::new(); |
| |
| <span class="macro">assert!</span>(INIT.<span class="kw">try</span>().is_none()); |
| thread::spawn(<span class="kw">move</span>|| { |
| INIT.call_once(|| <span class="kw">loop </span>{ }); |
| }); |
| <span class="macro">assert!</span>(INIT.<span class="kw">try</span>().is_none()); |
| } |
| |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>wait() { |
| <span class="kw">static </span>INIT: Once<usize> = Once::new(); |
| |
| <span class="macro">assert!</span>(INIT.wait().is_none()); |
| INIT.call_once(|| <span class="number">3</span>); |
| <span class="macro">assert_eq!</span>(INIT.wait().map(|r| <span class="kw-2">*</span>r), <span class="prelude-val">Some</span>(<span class="number">3</span>)); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>panic() { |
| <span class="kw">use </span>::std::panic; |
| |
| <span class="kw">static </span>INIT: Once<()> = Once::new(); |
| |
| <span class="comment">// poison the once |
| </span><span class="kw">let </span>t = panic::catch_unwind(|| { |
| INIT.call_once(|| <span class="macro">panic!</span>()); |
| }); |
| <span class="macro">assert!</span>(t.is_err()); |
| |
| <span class="comment">// poisoning propagates |
| </span><span class="kw">let </span>t = panic::catch_unwind(|| { |
| INIT.call_once(|| {}); |
| }); |
| <span class="macro">assert!</span>(t.is_err()); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>init_constant() { |
| <span class="kw">static </span>O: Once<()> = Once::INIT; |
| <span class="kw">let </span><span class="kw-2">mut </span>a = <span class="number">0</span>; |
| O.call_once(|| a += <span class="number">1</span>); |
| <span class="macro">assert_eq!</span>(a, <span class="number">1</span>); |
| O.call_once(|| a += <span class="number">1</span>); |
| <span class="macro">assert_eq!</span>(a, <span class="number">1</span>); |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="spin" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
