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<title>thread_local - Rust</title>
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<p class='location'>Crate thread_local</p><div class="block items"><ul><li><a href="#structs">Structs</a></li><li><a href="#types">Type Definitions</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'thread_local', ty: 'mod', relpath: '../'};</script>
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<section id='main' class="content">
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<h1 class='fqn'><span class='in-band'>Crate <a class="mod" href=''>thread_local</a></span><span class='out-of-band'><span id='render-detail'>
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<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
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[<span class='inner'>−</span>]
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</span><a class='srclink' href='../src/thread_local/lib.rs.html#8-773' title='goto source code'>[src]</a></span></h1>
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<div class='docblock'><p>Per-object thread-local storage</p>
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<p>This library provides the <code>ThreadLocal</code> type which allows a separate copy of
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an object to be used for each thread. This allows for per-object
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thread-local storage, unlike the standard library's <code>thread_local!</code> macro
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which only allows static thread-local storage.</p>
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<p>Per-thread objects are not destroyed when a thread exits. Instead, objects
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are only destroyed when the <code>ThreadLocal</code> containing them is destroyed.</p>
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<p>You can also iterate over the thread-local values of all thread in a
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<code>ThreadLocal</code> object using the <code>iter_mut</code> and <code>into_iter</code> methods. This can
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only be done if you have mutable access to the <code>ThreadLocal</code> object, which
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guarantees that you are the only thread currently accessing it.</p>
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<p>A <code>CachedThreadLocal</code> type is also provided which wraps a <code>ThreadLocal</code> but
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also uses a special fast path for the first thread that writes into it. The
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fast path has very low overhead (<1ns per access) while keeping the same
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performance as <code>ThreadLocal</code> for other threads.</p>
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<p>Note that since thread IDs are recycled when a thread exits, it is possible
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for one thread to retrieve the object of another thread. Since this can only
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occur after a thread has exited this does not lead to any race conditions.</p>
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<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
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<p>Basic usage of <code>ThreadLocal</code>:</p>
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<pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">thread_local</span>::<span class="ident">ThreadLocal</span>;
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<span class="kw">let</span> <span class="ident">tls</span>: <span class="ident">ThreadLocal</span><span class="op"><</span><span class="ident">u32</span><span class="op">></span> <span class="op">=</span> <span class="ident">ThreadLocal</span>::<span class="ident">new</span>();
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">tls</span>.<span class="ident">get</span>(), <span class="prelude-val">None</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">tls</span>.<span class="ident">get_or</span>(<span class="op">||</span> <span class="ident">Box</span>::<span class="ident">new</span>(<span class="number">5</span>)), <span class="kw-2">&</span><span class="number">5</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">tls</span>.<span class="ident">get</span>(), <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="number">5</span>));</pre>
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<p>Combining thread-local values into a single result:</p>
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<pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">thread_local</span>::<span class="ident">ThreadLocal</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">Arc</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cell</span>::<span class="ident">Cell</span>;
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">thread</span>;
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<span class="kw">let</span> <span class="ident">tls</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">ThreadLocal</span>::<span class="ident">new</span>());
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<span class="comment">// Create a bunch of threads to do stuff</span>
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<span class="kw">for</span> _ <span class="kw">in</span> <span class="number">0</span>..<span class="number">5</span> {
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<span class="kw">let</span> <span class="ident">tls2</span> <span class="op">=</span> <span class="ident">tls</span>.<span class="ident">clone</span>();
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<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span> <span class="op">||</span> {
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<span class="comment">// Increment a counter to count some event...</span>
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<span class="kw">let</span> <span class="ident">cell</span> <span class="op">=</span> <span class="ident">tls2</span>.<span class="ident">get_or</span>(<span class="op">||</span> <span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">Cell</span>::<span class="ident">new</span>(<span class="number">0</span>)));
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<span class="ident">cell</span>.<span class="ident">set</span>(<span class="ident">cell</span>.<span class="ident">get</span>() <span class="op">+</span> <span class="number">1</span>);
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}).<span class="ident">join</span>().<span class="ident">unwrap</span>();
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}
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<span class="comment">// Once all threads are done, collect the counter values and return the</span>
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<span class="comment">// sum of all thread-local counter values.</span>
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<span class="kw">let</span> <span class="ident">tls</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">try_unwrap</span>(<span class="ident">tls</span>).<span class="ident">unwrap</span>();
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<span class="kw">let</span> <span class="ident">total</span> <span class="op">=</span> <span class="ident">tls</span>.<span class="ident">into_iter</span>().<span class="ident">fold</span>(<span class="number">0</span>, <span class="op">|</span><span class="ident">x</span>, <span class="ident">y</span><span class="op">|</span> <span class="ident">x</span> <span class="op">+</span> <span class="ident">y</span>.<span class="ident">get</span>());
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">total</span>, <span class="number">5</span>);</pre>
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</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.CachedThreadLocal.html"
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title='struct thread_local::CachedThreadLocal'>CachedThreadLocal</a></td>
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<td class='docblock-short'>
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<p>Wrapper around <code>ThreadLocal</code> which adds a fast path for a single thread.</p>
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</td>
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</tr>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.IntoIter.html"
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title='struct thread_local::IntoIter'>IntoIter</a></td>
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<td class='docblock-short'>
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<p>An iterator that moves out of a <code>ThreadLocal</code>.</p>
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</td>
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</tr>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.IterMut.html"
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title='struct thread_local::IterMut'>IterMut</a></td>
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<td class='docblock-short'>
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<p>Mutable iterator over the contents of a <code>ThreadLocal</code>.</p>
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</td>
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</tr>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.ThreadLocal.html"
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title='struct thread_local::ThreadLocal'>ThreadLocal</a></td>
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<td class='docblock-short'>
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<p>Thread-local variable wrapper</p>
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</td>
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</tr></table><h2 id='types' class='section-header'><a href="#types">Type Definitions</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="type" href="type.CachedIntoIter.html"
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title='type thread_local::CachedIntoIter'>CachedIntoIter</a></td>
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<td class='docblock-short'>
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<p>An iterator that moves out of a <code>CachedThreadLocal</code>.</p>
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</td>
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</tr>
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<tr class=' module-item'>
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<td><a class="type" href="type.CachedIterMut.html"
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title='type thread_local::CachedIterMut'>CachedIterMut</a></td>
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<td class='docblock-short'>
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<p>Mutable iterator over the contents of a <code>CachedThreadLocal</code>.</p>
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</td>
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