<!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 to the Rust file `src/libstd/sys_common/at_exit_imp.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>at_exit_imp.rs.html -- source</title><link rel="stylesheet" type="text/css" href="../../../normalize1.35.0.css"><link rel="stylesheet" type="text/css" href="../../../rustdoc1.35.0.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../../dark1.35.0.css"><link rel="stylesheet" type="text/css" href="../../../light1.35.0.css" id="themeStyle"><script src="../../../storage1.35.0.js"></script><noscript><link rel="stylesheet" href="../../../noscript1.35.0.css"></noscript><link rel="shortcut icon" href="../../../favicon1.35.0.ico"><style type="text/css">#crate-search{background-image:url("../../../down-arrow1.35.0.svg");}</style></head><body class="rustdoc source"><!--[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='../../../std/index.html'><img src='../../../rust-logo1.35.0.png' alt='logo' width='100'></a></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../../brush1.35.0.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../../theme1.35.0.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../../../settings.html"><img src="../../../wheel1.35.0.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><pre class="line-numbers"><span id="1"> 1</span>
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</pre><div class="example-wrap"><pre class="rust ">
<span class="doccomment">//! Implementation of running at_exit routines</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Documentation can be found on the `rt::at_exit` function.</span>
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">boxed</span>::<span class="ident">FnBox</span>;
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">ptr</span>;
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">mem</span>;
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">sys_common</span>::<span class="ident">mutex</span>::<span class="ident">Mutex</span>;
<span class="kw">type</span> <span class="ident">Queue</span> <span class="op">=</span> <span class="ident">Vec</span><span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="kw">dyn</span> <span class="ident">FnBox</span>()<span class="op">>></span>;
<span class="comment">// NB these are specifically not types from `std::sync` as they currently rely</span>
<span class="comment">// on poisoning and this module needs to operate at a lower level than requiring</span>
<span class="comment">// the thread infrastructure to be in place (useful on the borders of</span>
<span class="comment">// initialization/destruction).</span>
<span class="comment">// We never call `LOCK.init()`, so it is UB to attempt to</span>
<span class="comment">// acquire this mutex reentrantly!</span>
<span class="kw">static</span> <span class="ident">LOCK</span>: <span class="ident">Mutex</span> <span class="op">=</span> <span class="ident">Mutex</span>::<span class="ident">new</span>();
<span class="kw">static</span> <span class="kw-2">mut</span> <span class="ident">QUEUE</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Queue</span> <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">null_mut</span>();
<span class="kw">const</span> <span class="ident">DONE</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Queue</span> <span class="op">=</span> <span class="number">1_usize</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="kw">_</span>;
<span class="comment">// The maximum number of times the cleanup routines will be run. While running</span>
<span class="comment">// the at_exit closures new ones may be registered, and this count is the number</span>
<span class="comment">// of times the new closures will be allowed to register successfully. After</span>
<span class="comment">// this number of iterations all new registrations will return `false`.</span>
<span class="kw">const</span> <span class="ident">ITERS</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">10</span>;
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">init</span>() <span class="op">-></span> <span class="ident">bool</span> {
<span class="kw">if</span> <span class="ident">QUEUE</span>.<span class="ident">is_null</span>() {
<span class="kw">let</span> <span class="ident">state</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">Queue</span><span class="op">></span> <span class="op">=</span> <span class="kw">box</span> <span class="ident">Vec</span>::<span class="ident">new</span>();
<span class="ident">QUEUE</span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">into_raw</span>(<span class="ident">state</span>);
} <span class="kw">else</span> <span class="kw">if</span> <span class="ident">QUEUE</span> <span class="op">==</span> <span class="ident">DONE</span> {
<span class="comment">// can't re-init after a cleanup</span>
<span class="kw">return</span> <span class="bool-val">false</span>
}
<span class="bool-val">true</span>
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">cleanup</span>() {
<span class="kw">for</span> <span class="ident">i</span> <span class="kw">in</span> <span class="number">1</span>..=<span class="ident">ITERS</span> {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">queue</span> <span class="op">=</span> {
<span class="kw">let</span> <span class="ident">_guard</span> <span class="op">=</span> <span class="ident">LOCK</span>.<span class="ident">lock</span>();
<span class="ident">mem</span>::<span class="ident">replace</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">QUEUE</span>, <span class="kw">if</span> <span class="ident">i</span> <span class="op">==</span> <span class="ident">ITERS</span> { <span class="ident">DONE</span> } <span class="kw">else</span> { <span class="ident">ptr</span>::<span class="ident">null_mut</span>() })
};
<span class="comment">// make sure we're not recursively cleaning up</span>
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">queue</span> <span class="op">!=</span> <span class="ident">DONE</span>);
<span class="comment">// If we never called init, not need to cleanup!</span>
<span class="kw">if</span> <span class="op">!</span><span class="ident">queue</span>.<span class="ident">is_null</span>() {
<span class="kw">let</span> <span class="ident">queue</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">Queue</span><span class="op">></span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">queue</span>);
<span class="kw">for</span> <span class="ident">to_run</span> <span class="kw">in</span> <span class="kw-2">*</span><span class="ident">queue</span> {
<span class="comment">// We are not holding any lock, so reentrancy is fine.</span>
<span class="ident">to_run</span>();
}
}
}
}
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">push</span>(<span class="ident">f</span>: <span class="ident">Box</span><span class="op"><</span><span class="kw">dyn</span> <span class="ident">FnBox</span>()<span class="op">></span>) <span class="op">-></span> <span class="ident">bool</span> {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">_guard</span> <span class="op">=</span> <span class="ident">LOCK</span>.<span class="ident">lock</span>();
<span class="kw">if</span> <span class="ident">init</span>() {
<span class="comment">// We are just moving `f` around, not calling it.</span>
<span class="comment">// There is no possibility of reentrancy here.</span>
(<span class="kw-2">*</span><span class="ident">QUEUE</span>).<span class="ident">push</span>(<span class="ident">f</span>);
<span class="bool-val">true</span>
} <span class="kw">else</span> {
<span class="bool-val">false</span>
}
}
}
</pre></div>
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