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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="Source of the Rust file `/home/pico/.local/share/cargo/registry/src/github.com-1ecc6299db9ec823/getrandom-0.2.8/src/util.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>util.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="icon" href="https://www.rust-lang.org/favicon.ico"></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"></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../getrandom/index.html">
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</pre><pre class="rust"><code><span class="comment">// Copyright 2019 Developers of the Rand project.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
</span><span class="attribute">#![allow(dead_code)]
</span><span class="kw">use </span>core::sync::atomic::{AtomicUsize, Ordering::Relaxed};
<span class="comment">// This structure represents a lazily initialized static usize value. Useful
// when it is preferable to just rerun initialization instead of locking.
// Both unsync_init and sync_init will invoke an init() function until it
// succeeds, then return the cached value for future calls.
//
// Both methods support init() "failing". If the init() method returns UNINIT,
// that value will be returned as normal, but will not be cached.
//
// Users should only depend on the _value_ returned by init() functions.
// Specifically, for the following init() function:
// fn init() -> usize {
// a();
// let v = b();
// c();
// v
// }
// the effects of c() or writes to shared memory will not necessarily be
// observed and additional synchronization methods with be needed.
</span><span class="kw">pub struct </span>LazyUsize(AtomicUsize);
<span class="kw">impl </span>LazyUsize {
<span class="kw">pub const fn </span>new() -> <span class="self">Self </span>{
<span class="self">Self</span>(AtomicUsize::new(<span class="self">Self</span>::UNINIT))
}
<span class="comment">// The initialization is not completed.
</span><span class="kw">pub const </span>UNINIT: usize = usize::max_value();
<span class="comment">// Runs the init() function at least once, returning the value of some run
// of init(). Multiple callers can run their init() functions in parallel.
// init() should always return the same value, if it succeeds.
</span><span class="kw">pub fn </span>unsync_init(<span class="kw-2">&</span><span class="self">self</span>, init: <span class="kw">impl </span>FnOnce() -> usize) -> usize {
<span class="comment">// Relaxed ordering is fine, as we only have a single atomic variable.
</span><span class="kw">let </span><span class="kw-2">mut </span>val = <span class="self">self</span>.<span class="number">0</span>.load(Relaxed);
<span class="kw">if </span>val == <span class="self">Self</span>::UNINIT {
val = init();
<span class="self">self</span>.<span class="number">0</span>.store(val, Relaxed);
}
val
}
}
<span class="comment">// Identical to LazyUsize except with bool instead of usize.
</span><span class="kw">pub struct </span>LazyBool(LazyUsize);
<span class="kw">impl </span>LazyBool {
<span class="kw">pub const fn </span>new() -> <span class="self">Self </span>{
<span class="self">Self</span>(LazyUsize::new())
}
<span class="kw">pub fn </span>unsync_init(<span class="kw-2">&</span><span class="self">self</span>, init: <span class="kw">impl </span>FnOnce() -> bool) -> bool {
<span class="self">self</span>.<span class="number">0</span>.unsync_init(|| init() <span class="kw">as </span>usize) != <span class="number">0
</span>}
}
</code></pre></div>
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