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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="A fixed capacity Multiple-Producer Multiple-Consumer (MPMC) lock-free queue"><title>heapless::mpmc - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../static.files/rustdoc-492a78a4a87dcc01.css"><meta name="rustdoc-vars" data-root-path="../../" data-static-root-path="../../static.files/" data-current-crate="heapless" data-themes="" data-resource-suffix="" data-rustdoc-version="1.82.0 (f6e511eec 2024-10-15)" data-channel="1.82.0" data-search-js="search-a99f1315e7cc5121.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../static.files/storage-118b08c4c78b968e.js"></script><script defer src="../sidebar-items.js"></script><script defer src="../../static.files/main-921df33f47b8780c.js"></script><noscript><link rel="stylesheet" href="../../static.files/noscript-3b12f09e550e0385.css"></noscript><link rel="alternate icon" type="image/png" href="../../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc mod"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../heapless/index.html">heapless</a><span class="version">0.7.17</span></h2></div><h2 class="location"><a href="#">Module mpmc</a></h2><div class="sidebar-elems"><section><ul class="block"><li><a href="#structs">Structs</a></li><li><a href="#types">Type Aliases</a></li></ul></section><h2><a href="../index.html">In crate heapless</a></h2></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><h1>Module <a href="../index.html">heapless</a>::<wbr><a class="mod" href="#">mpmc</a><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><span class="out-of-band"><a class="src" href="../../src/heapless/mpmc.rs.html#1-329">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A fixed capacity Multiple-Producer Multiple-Consumer (MPMC) lock-free queue</p>
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<p>NOTE: This module is not available on targets that do <em>not</em> support CAS operations and are not
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emulated by the <a href="https://crates.io/crates/atomic-polyfill"><code>atomic_polyfill</code></a> crate (e.g.,
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MSP430).</p>
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<h2 id="example"><a class="doc-anchor" href="#example">§</a>Example</h2>
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<p>This queue can be constructed in “const context”. Placing it in a <code>static</code> variable lets <em>all</em>
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contexts (interrupts / threads / <code>main</code>) safely enqueue and dequeue items from it.</p>
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<div class="example-wrap ignore"><a href="#" class="tooltip" title="This example is not tested">ⓘ</a><pre class="rust rust-example-rendered"><code><span class="attr">#![no_main]
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#![no_std]
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</span><span class="kw">use </span>panic_semihosting <span class="kw">as _</span>;
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<span class="kw">use </span>cortex_m::{asm, peripheral::syst::SystClkSource};
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<span class="kw">use </span>cortex_m_rt::{entry, exception};
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<span class="kw">use </span>cortex_m_semihosting::hprintln;
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<span class="kw">use </span>heapless::mpmc::Q2;
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<span class="kw">static </span>Q: Q2<u8> = Q2::new();
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<span class="attr">#[entry]
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</span><span class="kw">fn </span>main() -> ! {
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<span class="kw">if let </span><span class="prelude-val">Some</span>(p) = cortex_m::Peripherals::take() {
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<span class="kw">let </span><span class="kw-2">mut </span>syst = p.SYST;
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<span class="comment">// configures the system timer to trigger a SysTick exception every second
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</span>syst.set_clock_source(SystClkSource::Core);
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syst.set_reload(<span class="number">12_000_000</span>);
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syst.enable_counter();
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syst.enable_interrupt();
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}
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<span class="kw">loop </span>{
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<span class="kw">if let </span><span class="prelude-val">Some</span>(x) = Q.dequeue() {
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<span class="macro">hprintln!</span>(<span class="string">"{}"</span>, x).ok();
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} <span class="kw">else </span>{
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asm::wfi();
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}
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}
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}
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<span class="attr">#[exception]
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</span><span class="kw">fn </span>SysTick() {
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<span class="kw">static </span><span class="kw-2">mut </span>COUNT: u8 = <span class="number">0</span>;
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Q.enqueue(<span class="kw-2">*</span>COUNT).ok();
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<span class="kw-2">*</span>COUNT += <span class="number">1</span>;
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}</code></pre></div>
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<h2 id="benchmark"><a class="doc-anchor" href="#benchmark">§</a>Benchmark</h2>
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<p>Measured on a ARM Cortex-M3 core running at 8 MHz and with zero Flash wait cycles</p>
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<div><table><thead><tr><th>N</th><th><code>Q8::<u8>::enqueue().ok()</code> (<code>z</code>)</th><th><code>Q8::<u8>::dequeue()</code> (<code>z</code>)</th></tr></thead><tbody>
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<tr><td>0</td><td>34</td><td>35</td></tr>
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<tr><td>1</td><td>52</td><td>53</td></tr>
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<tr><td>2</td><td>69</td><td>71</td></tr>
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</tbody></table>
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</div>
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<ul>
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<li><code>N</code> denotes the number of <em>interruptions</em>. On Cortex-M, an interruption consists of an
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interrupt handler preempting the would-be atomic section of the <code>enqueue</code> / <code>dequeue</code>
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operation. Note that it does <em>not</em> matter if the higher priority handler uses the queue or
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not.</li>
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<li>All execution times are in clock cycles. 1 clock cycle = 125 ns.</li>
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<li>Execution time is <em>dependent</em> of <code>mem::size_of::<T>()</code>. Both operations include one
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<code>memcpy(T)</code> in their successful path.</li>
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<li>The optimization level is indicated in parentheses.</li>
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<li>The numbers reported correspond to the successful path (i.e. <code>Some</code> is returned by <code>dequeue</code>
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and <code>Ok</code> is returned by <code>enqueue</code>).</li>
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</ul>
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<h2 id="portability"><a class="doc-anchor" href="#portability">§</a>Portability</h2>
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<p>This module requires CAS atomic instructions which are not available on all architectures
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(e.g. ARMv6-M (<code>thumbv6m-none-eabi</code>) and MSP430 (<code>msp430-none-elf</code>)). These atomics can be
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emulated however with <a href="https://crates.io/crates/atomic-polyfill"><code>atomic_polyfill</code></a>, which is
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enabled with the <code>cas</code> feature and is enabled by default for <code>thumbv6m-none-eabi</code> and <code>riscv32</code>
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targets. MSP430 is currently not supported by
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<a href="https://crates.io/crates/atomic-polyfill"><code>atomic_polyfill</code></a>.</p>
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<h2 id="references"><a class="doc-anchor" href="#references">§</a>References</h2>
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<p>This is an implementation of Dmitry Vyukov’s <a href="http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue">“Bounded MPMC queue”</a> minus the cache padding.</p>
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</div></details><h2 id="structs" class="section-header">Structs<a href="#structs" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="struct" href="struct.MpMcQueue.html" title="struct heapless::mpmc::MpMcQueue">MpMc<wbr>Queue</a></div><div class="desc docblock-short">MPMC queue with a capacity for N elements
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N must be a power of 2
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The max value of N is u8::MAX - 1 if <code>mpmc_large</code> feature is not enabled.</div></li></ul><h2 id="types" class="section-header">Type Aliases<a href="#types" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="type" href="type.Q2.html" title="type heapless::mpmc::Q2">Q2</a></div><div class="desc docblock-short">MPMC queue with a capability for 2 elements.</div></li><li><div class="item-name"><a class="type" href="type.Q4.html" title="type heapless::mpmc::Q4">Q4</a></div><div class="desc docblock-short">MPMC queue with a capability for 4 elements.</div></li><li><div class="item-name"><a class="type" href="type.Q8.html" title="type heapless::mpmc::Q8">Q8</a></div><div class="desc docblock-short">MPMC queue with a capability for 8 elements.</div></li><li><div class="item-name"><a class="type" href="type.Q16.html" title="type heapless::mpmc::Q16">Q16</a></div><div class="desc docblock-short">MPMC queue with a capability for 16 elements.</div></li><li><div class="item-name"><a class="type" href="type.Q32.html" title="type heapless::mpmc::Q32">Q32</a></div><div class="desc docblock-short">MPMC queue with a capability for 32 elements.</div></li><li><div class="item-name"><a class="type" href="type.Q64.html" title="type heapless::mpmc::Q64">Q64</a></div><div class="desc docblock-short">MPMC queue with a capability for 64 elements.</div></li></ul></section></div></main></body></html> |