<!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/sangenya/.cargo/registry/src/github.com-1ecc6299db9ec823/crossbeam-channel-0.5.1/src/utils.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>utils.rs - source</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../../ayu.css" disabled ><script id="default-settings"></script><script src="../../storage.js"></script><script src="../../crates.js"></script><noscript><link rel="stylesheet" href="../../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../../favicon.svg">
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</pre><pre class="rust">
<span class="doccomment">//! Miscellaneous utilities.</span>
<span class="kw">use</span> <span class="ident">std::cell</span>::{<span class="ident">Cell</span>, <span class="ident">UnsafeCell</span>};
<span class="kw">use</span> <span class="ident">std::num::Wrapping</span>;
<span class="kw">use</span> <span class="ident">std::ops</span>::{<span class="ident">Deref</span>, <span class="ident">DerefMut</span>};
<span class="kw">use</span> <span class="ident">std::sync::atomic</span>::{<span class="ident">AtomicBool</span>, <span class="ident">Ordering</span>};
<span class="kw">use</span> <span class="ident">std::thread</span>;
<span class="kw">use</span> <span class="ident">std::time</span>::{<span class="ident">Duration</span>, <span class="ident">Instant</span>};
<span class="kw">use</span> <span class="ident">crossbeam_utils::Backoff</span>;
<span class="doccomment">/// Randomly shuffles a slice.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">shuffle</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">v</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> [<span class="ident">T</span>]) {
<span class="kw">let</span> <span class="ident">len</span> <span class="op">=</span> <span class="ident">v</span>.<span class="ident">len</span>();
<span class="kw">if</span> <span class="ident">len</span> <span class="op"><</span><span class="op">=</span> <span class="number">1</span> {
<span class="kw">return</span>;
}
<span class="macro">thread_local!</span> {
<span class="kw">static</span> <span class="ident">RNG</span>: <span class="ident">Cell</span><span class="op"><</span><span class="ident">Wrapping</span><span class="op"><</span><span class="ident">u32</span><span class="op">></span><span class="op">></span> <span class="op">=</span> <span class="ident">Cell::new</span>(<span class="ident">Wrapping</span>(<span class="number">1_406_868_647</span>));
}
<span class="kw">let</span> <span class="kw">_</span> <span class="op">=</span> <span class="ident">RNG</span>.<span class="ident">try_with</span>(<span class="op">|</span><span class="ident">rng</span><span class="op">|</span> {
<span class="kw">for</span> <span class="ident">i</span> <span class="kw">in</span> <span class="number">1</span>..<span class="ident">len</span> {
<span class="comment">// This is the 32-bit variant of Xorshift.</span>
<span class="comment">//</span>
<span class="comment">// Source: https://en.wikipedia.org/wiki/Xorshift</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">x</span> <span class="op">=</span> <span class="ident">rng</span>.<span class="ident">get</span>();
<span class="ident">x</span> <span class="op">^</span><span class="op">=</span> <span class="ident">x</span> <span class="op"><</span><span class="op"><</span> <span class="number">13</span>;
<span class="ident">x</span> <span class="op">^</span><span class="op">=</span> <span class="ident">x</span> <span class="op">></span><span class="op">></span> <span class="number">17</span>;
<span class="ident">x</span> <span class="op">^</span><span class="op">=</span> <span class="ident">x</span> <span class="op"><</span><span class="op"><</span> <span class="number">5</span>;
<span class="ident">rng</span>.<span class="ident">set</span>(<span class="ident">x</span>);
<span class="kw">let</span> <span class="ident">x</span> <span class="op">=</span> <span class="ident">x</span>.<span class="number">0</span>;
<span class="kw">let</span> <span class="ident">n</span> <span class="op">=</span> <span class="ident">i</span> <span class="op">+</span> <span class="number">1</span>;
<span class="comment">// This is a fast alternative to `let j = x % n`.</span>
<span class="comment">//</span>
<span class="comment">// Author: Daniel Lemire</span>
<span class="comment">// Source: https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/</span>
<span class="kw">let</span> <span class="ident">j</span> <span class="op">=</span> ((<span class="ident">x</span> <span class="kw">as</span> <span class="ident">u64</span>).<span class="ident">wrapping_mul</span>(<span class="ident">n</span> <span class="kw">as</span> <span class="ident">u64</span>) <span class="op">></span><span class="op">></span> <span class="number">32</span>) <span class="kw">as</span> <span class="ident">u32</span> <span class="kw">as</span> <span class="ident">usize</span>;
<span class="ident">v</span>.<span class="ident">swap</span>(<span class="ident">i</span>, <span class="ident">j</span>);
}
});
}
<span class="doccomment">/// Sleeps until the deadline, or forever if the deadline isn't specified.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">sleep_until</span>(<span class="ident">deadline</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Instant</span><span class="op">></span>) {
<span class="kw">loop</span> {
<span class="kw">match</span> <span class="ident">deadline</span> {
<span class="prelude-val">None</span> <span class="op">=</span><span class="op">></span> <span class="ident">thread::sleep</span>(<span class="ident">Duration::from_secs</span>(<span class="number">1000</span>)),
<span class="prelude-val">Some</span>(<span class="ident">d</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">now</span> <span class="op">=</span> <span class="ident">Instant::now</span>();
<span class="kw">if</span> <span class="ident">now</span> <span class="op">></span><span class="op">=</span> <span class="ident">d</span> {
<span class="kw">break</span>;
}
<span class="ident">thread::sleep</span>(<span class="ident">d</span> <span class="op">-</span> <span class="ident">now</span>);
}
}
}
}
<span class="doccomment">/// A simple spinlock.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct</span> <span class="ident">Spinlock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">flag</span>: <span class="ident">AtomicBool</span>,
<span class="ident">value</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Spinlock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Returns a new spinlock initialized with `value`.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">value</span>: <span class="ident">T</span>) <span class="op">-</span><span class="op">></span> <span class="ident">Spinlock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Spinlock</span> {
<span class="ident">flag</span>: <span class="ident">AtomicBool::new</span>(<span class="bool-val">false</span>),
<span class="ident">value</span>: <span class="ident">UnsafeCell::new</span>(<span class="ident">value</span>),
}
}
<span class="doccomment">/// Locks the spinlock.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">lock</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">SpinlockGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">backoff</span> <span class="op">=</span> <span class="ident">Backoff::new</span>();
<span class="kw">while</span> <span class="self">self</span>.<span class="ident">flag</span>.<span class="ident">swap</span>(<span class="bool-val">true</span>, <span class="ident">Ordering::Acquire</span>) {
<span class="ident">backoff</span>.<span class="ident">snooze</span>();
}
<span class="ident">SpinlockGuard</span> { <span class="ident">parent</span>: <span class="self">self</span> }
}
}
<span class="doccomment">/// A guard holding a spinlock locked.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct</span> <span class="ident">SpinlockGuard</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> {
<span class="ident">parent</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">Spinlock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">SpinlockGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="self">self</span>.<span class="ident">parent</span>.<span class="ident">flag</span>.<span class="ident">store</span>(<span class="bool-val">false</span>, <span class="ident">Ordering::Release</span>);
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">SpinlockGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">T</span>;
<span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">T</span> {
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">parent</span>.<span class="ident">value</span>.<span class="ident">get</span>() }
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">DerefMut</span> <span class="kw">for</span> <span class="ident">SpinlockGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">deref_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span> {
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">parent</span>.<span class="ident">value</span>.<span class="ident">get</span>() }
}
}
</pre></div>
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