<!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/unix/fast_thread_local.rs`."> <meta name="keywords" content="rust, rustlang, rust-lang"> <title>fast_thread_local.rs.html -- source</title> <link rel="stylesheet" type="text/css" href="../../../../normalize.css"> <link rel="stylesheet" type="text/css" href="../../../../rustdoc.css"> <link rel="stylesheet" type="text/css" href="../../../../main.css"> <link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"> </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"> <a href='../../../../std/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a> </nav> <nav class="sub"> <form class="search-form js-only"> <div class="search-container"> <input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"> </div> </form> </nav> <section id='main' class="content"><pre class="line-numbers"><span id="1"> 1</span> <span id="2"> 2</span> <span id="3"> 3</span> <span id="4"> 4</span> <span id="5"> 5</span> <span id="6"> 6</span> <span id="7"> 7</span> <span id="8"> 8</span> <span id="9"> 9</span> <span id="10"> 10</span> <span id="11"> 11</span> <span id="12"> 12</span> <span id="13"> 13</span> <span id="14"> 14</span> <span id="15"> 15</span> <span id="16"> 16</span> <span id="17"> 17</span> <span id="18"> 18</span> <span id="19"> 19</span> <span id="20"> 20</span> <span id="21"> 21</span> <span id="22"> 22</span> <span id="23"> 23</span> <span id="24"> 24</span> <span id="25"> 25</span> <span id="26"> 26</span> <span id="27"> 27</span> <span 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id="145">145</span> <span id="146">146</span> <span id="147">147</span> <span id="148">148</span> <span id="149">149</span> <span id="150">150</span> <span id="151">151</span> <span id="152">152</span> <span id="153">153</span> <span id="154">154</span> <span id="155">155</span> <span id="156">156</span> <span id="157">157</span> <span id="158">158</span> <span id="159">159</span> <span id="160">160</span> <span id="161">161</span> <span id="162">162</span> <span id="163">163</span> <span id="164">164</span> <span id="165">165</span> <span id="166">166</span> <span id="167">167</span> <span id="168">168</span> <span id="169">169</span> <span id="170">170</span> <span id="171">171</span> <span id="172">172</span> <span id="173">173</span> <span id="174">174</span> </pre><pre class="rust "> <span class="comment">// Copyright 2014-2015 The Rust Project Developers. See the COPYRIGHT</span> <span class="comment">// file at the top-level directory of this distribution and at</span> <span class="comment">// http://rust-lang.org/COPYRIGHT.</span> <span class="comment">//</span> <span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span> <span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span> <span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your</span> <span class="comment">// option. This file may not be copied, modified, or distributed</span> <span class="comment">// except according to those terms.</span> <span class="attribute">#<span class="op">!</span>[<span class="ident">cfg</span>(<span class="ident">target_thread_local</span>)]</span> <span class="attribute">#<span class="op">!</span>[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"thread_local_internals"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"0"</span>)]</span> <span class="kw">use</span> <span class="ident">cell</span>::{<span class="ident">Cell</span>, <span class="ident">UnsafeCell</span>}; <span class="kw">use</span> <span class="ident">fmt</span>; <span class="kw">use</span> <span class="ident">mem</span>; <span class="kw">use</span> <span class="ident">ptr</span>; <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Key</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">inner</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>, <span class="comment">// Metadata to keep track of the state of the destructor. Remember that</span> <span class="comment">// these variables are thread-local, not global.</span> <span class="ident">dtor_registered</span>: <span class="ident">Cell</span><span class="op"><</span><span class="ident">bool</span><span class="op">></span>, <span class="ident">dtor_running</span>: <span class="ident">Cell</span><span class="op"><</span><span class="ident">bool</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">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">Key</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> { <span class="ident">f</span>.<span class="ident">pad</span>(<span class="string">"Key { .. }"</span>) } } <span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> ::<span class="ident">marker</span>::<span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">Key</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">Key</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">pub</span> <span class="kw">const</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-></span> <span class="ident">Key</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">Key</span> { <span class="ident">inner</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>), <span class="ident">dtor_registered</span>: <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="bool-val">false</span>), <span class="ident">dtor_running</span>: <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="bool-val">false</span>) } } <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get</span>(<span class="kw-2">&</span><span class="lifetime">'static</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'static</span> <span class="ident">UnsafeCell</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span><span class="op">></span> { <span class="kw">unsafe</span> { <span class="kw">if</span> <span class="ident">mem</span>::<span class="ident">needs_drop</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>() <span class="op">&&</span> <span class="self">self</span>.<span class="ident">dtor_running</span>.<span class="ident">get</span>() { <span class="kw">return</span> <span class="prelude-val">None</span> } <span class="self">self</span>.<span class="ident">register_dtor</span>(); } <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">inner</span>) } <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">register_dtor</span>(<span class="kw-2">&</span><span class="self">self</span>) { <span class="kw">if</span> <span class="op">!</span><span class="ident">mem</span>::<span class="ident">needs_drop</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>() <span class="op">||</span> <span class="self">self</span>.<span class="ident">dtor_registered</span>.<span class="ident">get</span>() { <span class="kw">return</span> } <span class="ident">register_dtor</span>(<span class="self">self</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> _ <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">destroy_value</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>); <span class="self">self</span>.<span class="ident">dtor_registered</span>.<span class="ident">set</span>(<span class="bool-val">true</span>); } } <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"linux"</span>, <span class="ident">target_os</span> <span class="op">=</span> <span class="string">"fuchsia"</span>))]</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">register_dtor_fallback</span>(<span class="ident">t</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>)) { <span class="comment">// The fallback implementation uses a vanilla OS-based TLS key to track</span> <span class="comment">// the list of destructors that need to be run for this thread. The key</span> <span class="comment">// then has its own destructor which runs all the other destructors.</span> <span class="comment">//</span> <span class="comment">// The destructor for DTORS is a little special in that it has a `while`</span> <span class="comment">// loop to continuously drain the list of registered destructors. It</span> <span class="comment">// *should* be the case that this loop always terminates because we</span> <span class="comment">// provide the guarantee that a TLS key cannot be set after it is</span> <span class="comment">// flagged for destruction.</span> <span class="kw">use</span> <span class="ident">sys_common</span>::<span class="ident">thread_local</span> <span class="kw">as</span> <span class="ident">os</span>; <span class="kw">static</span> <span class="ident">DTORS</span>: <span class="ident">os</span>::<span class="ident">StaticKey</span> <span class="op">=</span> <span class="ident">os</span>::<span class="ident">StaticKey</span>::<span class="ident">new</span>(<span class="prelude-val">Some</span>(<span class="ident">run_dtors</span>)); <span class="kw">type</span> <span class="ident">List</span> <span class="op">=</span> <span class="ident">Vec</span><span class="op"><</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>))<span class="op">></span>; <span class="kw">if</span> <span class="ident">DTORS</span>.<span class="ident">get</span>().<span class="ident">is_null</span>() { <span class="kw">let</span> <span class="ident">v</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">List</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">DTORS</span>.<span class="ident">set</span>(<span class="ident">Box</span>::<span class="ident">into_raw</span>(<span class="ident">v</span>) <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>); } <span class="kw">let</span> <span class="ident">list</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">List</span> <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span>(<span class="ident">DTORS</span>.<span class="ident">get</span>() <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">List</span>); <span class="ident">list</span>.<span class="ident">push</span>((<span class="ident">t</span>, <span class="ident">dtor</span>)); <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span> <span class="ident">run_dtors</span>(<span class="kw-2">mut</span> <span class="ident">ptr</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>) { <span class="kw">while</span> <span class="op">!</span><span class="ident">ptr</span>.<span class="ident">is_null</span>() { <span class="kw">let</span> <span class="ident">list</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">List</span><span class="op">></span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">ptr</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">List</span>); <span class="kw">for</span> <span class="kw-2">&</span>(<span class="ident">ptr</span>, <span class="ident">dtor</span>) <span class="kw">in</span> <span class="ident">list</span>.<span class="ident">iter</span>() { <span class="ident">dtor</span>(<span class="ident">ptr</span>); } <span class="ident">ptr</span> <span class="op">=</span> <span class="ident">DTORS</span>.<span class="ident">get</span>(); <span class="ident">DTORS</span>.<span class="ident">set</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>()); } } } <span class="comment">// Since what appears to be glibc 2.18 this symbol has been shipped which</span> <span class="comment">// GCC and clang both use to invoke destructors in thread_local globals, so</span> <span class="comment">// let's do the same!</span> <span class="comment">//</span> <span class="comment">// Note, however, that we run on lots older linuxes, as well as cross</span> <span class="comment">// compiling from a newer linux to an older linux, so we also have a</span> <span class="comment">// fallback implementation to use as well.</span> <span class="comment">//</span> <span class="comment">// Due to rust-lang/rust#18804, make sure this is not generic!</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"linux"</span>)]</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">register_dtor</span>(<span class="ident">t</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>)) { <span class="kw">use</span> <span class="ident">mem</span>; <span class="kw">use</span> <span class="ident">libc</span>; <span class="kw">extern</span> { <span class="attribute">#[<span class="ident">linkage</span> <span class="op">=</span> <span class="string">"extern_weak"</span>]</span> <span class="kw">static</span> <span class="ident">__dso_handle</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>; <span class="attribute">#[<span class="ident">linkage</span> <span class="op">=</span> <span class="string">"extern_weak"</span>]</span> <span class="kw">static</span> <span class="ident">__cxa_thread_atexit_impl</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">libc</span>::<span class="ident">c_void</span>; } <span class="kw">if</span> <span class="op">!</span><span class="ident">__cxa_thread_atexit_impl</span>.<span class="ident">is_null</span>() { <span class="kw">type</span> <span class="ident">F</span> <span class="op">=</span> <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>), <span class="ident">arg</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">dso_handle</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>) <span class="op">-></span> <span class="ident">libc</span>::<span class="ident">c_int</span>; <span class="ident">mem</span>::<span class="ident">transmute</span>::<span class="op"><</span><span class="kw-2">*</span><span class="kw">const</span> <span class="ident">libc</span>::<span class="ident">c_void</span>, <span class="ident">F</span><span class="op">></span>(<span class="ident">__cxa_thread_atexit_impl</span>) (<span class="ident">dtor</span>, <span class="ident">t</span>, <span class="kw-2">&</span><span class="ident">__dso_handle</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> _ <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> _); <span class="kw">return</span> } <span class="ident">register_dtor_fallback</span>(<span class="ident">t</span>, <span class="ident">dtor</span>); } <span class="comment">// macOS's analog of the above linux function is this _tlv_atexit function.</span> <span class="comment">// The disassembly of thread_local globals in C++ (at least produced by</span> <span class="comment">// clang) will have this show up in the output.</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"macos"</span>)]</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">register_dtor</span>(<span class="ident">t</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>)) { <span class="kw">extern</span> { <span class="kw">fn</span> <span class="ident">_tlv_atexit</span>(<span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>), <span class="ident">arg</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>); } <span class="ident">_tlv_atexit</span>(<span class="ident">dtor</span>, <span class="ident">t</span>); } <span class="comment">// Just use the thread_local fallback implementation, at least until there's</span> <span class="comment">// a more direct implementation.</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"fuchsia"</span>)]</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">register_dtor</span>(<span class="ident">t</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>)) { <span class="ident">register_dtor_fallback</span>(<span class="ident">t</span>, <span class="ident">dtor</span>); } <span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span> <span class="ident">destroy_value</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">ptr</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>) { <span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="ident">ptr</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Key</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>; <span class="comment">// Right before we run the user destructor be sure to flag the</span> <span class="comment">// destructor as running for this thread so calls to `get` will return</span> <span class="comment">// `None`.</span> (<span class="kw-2">*</span><span class="ident">ptr</span>).<span class="ident">dtor_running</span>.<span class="ident">set</span>(<span class="bool-val">true</span>); <span class="comment">// The macOS implementation of TLS apparently had an odd aspect to it</span> <span class="comment">// where the pointer we have may be overwritten while this destructor</span> <span class="comment">// is running. Specifically if a TLS destructor re-accesses TLS it may</span> <span class="comment">// trigger a re-initialization of all TLS variables, paving over at</span> <span class="comment">// least some destroyed ones with initial values.</span> <span class="comment">//</span> <span class="comment">// This means that if we drop a TLS value in place on macOS that we could</span> <span class="comment">// revert the value to its original state halfway through the</span> <span class="comment">// destructor, which would be bad!</span> <span class="comment">//</span> <span class="comment">// Hence, we use `ptr::read` on macOS (to move to a "safe" location)</span> <span class="comment">// instead of drop_in_place.</span> <span class="kw">if</span> <span class="macro">cfg</span><span class="macro">!</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"macos"</span>) { <span class="ident">ptr</span>::<span class="ident">read</span>((<span class="kw-2">*</span><span class="ident">ptr</span>).<span class="ident">inner</span>.<span class="ident">get</span>()); } <span class="kw">else</span> { <span class="ident">ptr</span>::<span class="ident">drop_in_place</span>((<span class="kw-2">*</span><span class="ident">ptr</span>).<span class="ident">inner</span>.<span class="ident">get</span>()); } } </pre> </section> <section id='search' class="content hidden"></section> <section class="footer"></section> <aside id="help" class="hidden"> <div> <h1 class="hidden">Help</h1> <div class="shortcuts"> <h2>Keyboard Shortcuts</h2> <dl> <dt>?</dt> <dd>Show this help dialog</dd> <dt>S</dt> <dd>Focus the search field</dd> <dt>⇤</dt> <dd>Move up in search results</dd> <dt>⇥</dt> <dd>Move down in search results</dd> <dt>⏎</dt> <dd>Go to active search result</dd> <dt>+</dt> <dd>Collapse/expand all sections</dd> </dl> </div> <div class="infos"> <h2>Search Tricks</h2> <p> Prefix searches with a type followed by a colon (e.g. <code>fn:</code>) to restrict the search to a given type. </p> <p> Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>. </p> <p> Search functions by type signature (e.g. <code>vec -> usize</code> or <code>* -> vec</code>) </p> </div> </div> </aside> <script> window.rootPath = "../../../../"; window.currentCrate = "std"; </script> <script src="../../../../main.js"></script> <script defer src="../../../../search-index.js"></script> </body> </html>