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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="API documentation for the Rust `try_enqueue` fn in crate `delog`."><meta name="keywords" content="rust, rustlang, rust-lang, try_enqueue"><title>delog::try_enqueue - Rust</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><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../favicon.svg">
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<link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc fn"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../delog/index.html'><div class='logo-container rust-logo'><img src='../rust-logo.png' alt='logo'></div></a><div class="sidebar-elems"><p class="location"><a href="index.html">delog</a></p><script>window.sidebarCurrent = {name: "try_enqueue", ty: "fn", relpath: ""};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu"><img src="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices" role="menu"></div></div><script src="../theme.js"></script><nav class="sub"><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" disabled autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" class="help-button">?</button>
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<a id="settings-menu" href="../settings.html"><img src="../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class="fqn"><span class="out-of-band"><span id="render-detail"><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span><a class="srclink" href="../src/delog/logger.rs.html#433-524" title="goto source code">[src]</a></span><span class="in-band">Function <a href="index.html">delog</a>::<wbr><a class="fn" href="">try_enqueue</a></span></h1><pre class="rust fn">pub unsafe fn try_enqueue(<br> delogger: impl <a class="trait" href="../delog/trait.Delogger.html" title="trait delog::Delogger">Delogger</a>, <br> record: &<a class="struct" href="../delog/struct.Record.html" title="struct delog::Record">Record</a><'_><br>) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><(), ()></pre><div class="docblock"><p>The fallible "write to circular buffer" method. Marked unsafe to discourage use!</p>
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<h1 id="safety" class="section-header"><a href="#safety">Safety</a></h1>
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<p>Unfortunately exposed for all to see, as the <code>delog!</code> macro needs access to it to
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implement the logger at call site. Hence marked as unsafe.</p>
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<p>This implementation needs some HEAVY testing. It is unsound on PC, where the OS
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can schedule threads in any manner, but assumed to be sound in ARM Cortex-M NVIC
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situations, where interrupts are "nested", in the sense that one may be interrupted,
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then the interrupter can, ..., then the interrupter hands back control, ..., and finally
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the original caller of this function regains control.</p>
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<p>In this situation, we keep track of three counters <code>(read, written, claimed)</code>, with
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invariants <code>read <= written <= claimed</code>. Each writer pessimistically gauges sufficient
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capacity for its log by checking <code>claimed + size <= read + capacity</code>, accounting for the
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wraparound. If so, the writer <strong>atomically advances the claim counter</strong>, and starts copying
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its data in this newly claimed space. At the end, it is the duty of the "first" caller
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to advance the <code>written</code> counter to the correct state.</p>
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