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<div class="sidebar-menu">☰</div>
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<p class='location'>Struct Scope</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#methods">Methods</a><div class="sidebar-links"><a href="#method.defer">defer</a><a href="#method.spawn">spawn</a><a href="#method.builder">builder</a></div><a class="sidebar-title" href="#implementations">Trait Implementations</a><div class="sidebar-links"><a href="#impl-Debug">Debug</a><a href="#impl-Drop">Drop</a></div></div><p class='location'><a href='index.html'>crossbeam</a></p><script>window.sidebarCurrent = {name: 'Scope', ty: 'struct', relpath: ''};</script><script defer src="sidebar-items.js"></script></div>
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<h1 class='fqn'><span class='in-band'>Struct <a href='index.html'>crossbeam</a>::<wbr><a class="struct" href=''>Scope</a></span><span class='out-of-band'><span id='render-detail'>
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[<span class='inner'>−</span>]
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</span><a class='srclink' href='../src/crossbeam/scoped.rs.html#13-15' title='goto source code'>[src]</a></span></h1>
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<pre class='rust struct'>pub struct Scope<'a> { /* fields omitted */ }</pre>
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<h2 id='methods' class='small-section-header'>
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Methods<a href='#methods' class='anchor'></a>
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</h2>
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<h3 id='impl' class='impl'><span class='in-band'><code>impl<'a> <a class="struct" href="../crossbeam/struct.Scope.html" title="struct crossbeam::Scope">Scope</a><'a></code><a href='#impl' class='anchor'></a></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/crossbeam/scoped.rs.html#80-244' title='goto source code'>[src]</a></span></h3>
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<div class='impl-items'><h4 id='method.defer' class="method"><span id='defer.v' class='invisible'><code>pub fn <a href='#method.defer' class='fnname'>defer</a><F>(&self, f: F) <span class="where fmt-newline">where<br> F: <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/function/trait.FnOnce.html" title="trait core::ops::function::FnOnce">FnOnce</a>() + 'a, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/crossbeam/scoped.rs.html#107-113' title='goto source code'>[src]</a></span></h4>
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<div class='docblock'><p>Schedule code to be executed when exiting the scope.</p>
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<p>This is akin to having a destructor on the stack, except that it is
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<em>guaranteed</em> to be run.</p>
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</div><h4 id='method.spawn' class="method"><span id='spawn.v' class='invisible'><code>pub fn <a href='#method.spawn' class='fnname'>spawn</a><F, T>(&self, f: F) -> <a class="struct" href="../crossbeam/struct.ScopedJoinHandle.html" title="struct crossbeam::ScopedJoinHandle">ScopedJoinHandle</a><T> <span class="where fmt-newline">where<br> F: <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/function/trait.FnOnce.html" title="trait core::ops::function::FnOnce">FnOnce</a>() -> T + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a> + 'a,<br> T: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a> + 'a, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/crossbeam/scoped.rs.html#230-234' title='goto source code'>[src]</a></span></h4>
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<div class='docblock'><p>Create a scoped thread.</p>
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<p><code>spawn</code> is similar to the <a href="http://doc.rust-lang.org/std/thread/fn.spawn.html"><code>spawn</code></a> function in Rust's standard library. The
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difference is that this thread is scoped, meaning that it's guaranteed to terminate
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before the current stack frame goes away, allowing you to reference the parent stack frame
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directly. This is ensured by having the parent thread join on the child thread before the
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scope exits.</p>
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<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
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<p>A basic scoped thread:</p>
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<pre class="rust rust-example-rendered">
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<span class="ident">crossbeam</span>::<span class="ident">scope</span>(<span class="op">|</span><span class="ident">scope</span><span class="op">|</span> {
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<span class="ident">scope</span>.<span class="ident">spawn</span>(<span class="op">||</span> {
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"Hello from a scoped thread!"</span>);
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});
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});</pre>
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<p>When writing concurrent Rust programs, you'll sometimes see a pattern like this, using
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<a href="http://doc.rust-lang.org/std/thread/fn.spawn.html"><code>std::thread::spawn</code></a>:</p>
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<div class='information'><div class='tooltip ignore'>ⓘ<span class='tooltiptext'>This example is not tested</span></div></div><pre class="rust rust-example-rendered ignore">
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<span class="kw">let</span> <span class="ident">array</span> <span class="op">=</span> [<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>];
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">guards</span> <span class="op">=</span> <span class="macro">vec</span><span class="macro">!</span>[];
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<span class="kw">for</span> <span class="ident">i</span> <span class="kw">in</span> <span class="kw-2">&</span><span class="ident">array</span> {
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<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">std</span>::<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="macro">println</span><span class="macro">!</span>(<span class="string">"element: {}"</span>, <span class="ident">i</span>);
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});
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<span class="ident">guards</span>.<span class="ident">push</span>(<span class="ident">guard</span>);
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}
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<span class="kw">for</span> <span class="ident">guard</span> <span class="kw">in</span> <span class="ident">guards</span> {
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<span class="ident">guard</span>.<span class="ident">join</span>().<span class="ident">unwrap</span>();
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}</pre>
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<p>The basic pattern is:</p>
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<ol>
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<li>Iterate over some collection.</li>
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<li>Spin up a thread to operate on each part of the collection.</li>
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<li>Join all the threads.</li>
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</ol>
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<p>However, this code actually gives an error:</p>
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<pre><code class="language-text">error: `array` does not live long enough
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for i in &array {
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^~~~~
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in expansion of for loop expansion
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note: expansion site
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note: reference must be valid for the static lifetime...
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note: ...but borrowed value is only valid for the block suffix following statement 0 at ...
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let array = [1, 2, 3];
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let mut guards = vec![];
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for i in &array {
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let guard = std::thread::spawn(move || {
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println!("element: {}", i);
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...
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error: aborting due to previous error
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</code></pre>
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<p>Because <a href="http://doc.rust-lang.org/std/thread/fn.spawn.html"><code>std::thread::spawn</code></a> doesn't know about this scope, it requires a
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<code>'static</code> lifetime. One way of giving it a proper lifetime is to use an <a href="http://doc.rust-lang.org/stable/std/sync/struct.Arc.html"><code>Arc</code></a>:</p>
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<pre class="rust rust-example-rendered">
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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">let</span> <span class="ident">array</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>([<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>]);
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">guards</span> <span class="op">=</span> <span class="macro">vec</span><span class="macro">!</span>[];
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<span class="kw">for</span> <span class="ident">i</span> <span class="kw">in</span> <span class="number">0</span>..<span class="ident">array</span>.<span class="ident">len</span>() {
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<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="ident">array</span>.<span class="ident">clone</span>();
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<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">std</span>::<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="macro">println</span><span class="macro">!</span>(<span class="string">"element: {}"</span>, <span class="ident">a</span>[<span class="ident">i</span>]);
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});
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<span class="ident">guards</span>.<span class="ident">push</span>(<span class="ident">guard</span>);
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}
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<span class="kw">for</span> <span class="ident">guard</span> <span class="kw">in</span> <span class="ident">guards</span> {
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<span class="ident">guard</span>.<span class="ident">join</span>().<span class="ident">unwrap</span>();
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}</pre>
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<p>But this introduces unnecessary allocation, as <code>Arc<T></code> puts its data on the heap, and we
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also end up dealing with reference counts. We know that we're joining the threads before
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our function returns, so just taking a reference <em>should</em> be safe. Rust can't know that,
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though.</p>
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<p>Enter scoped threads. Here's our original example, using <code>spawn</code> from crossbeam rather
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than from <code>std::thread</code>:</p>
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<pre class="rust rust-example-rendered">
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<span class="kw">let</span> <span class="ident">array</span> <span class="op">=</span> [<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>];
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<span class="ident">crossbeam</span>::<span class="ident">scope</span>(<span class="op">|</span><span class="ident">scope</span><span class="op">|</span> {
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<span class="kw">for</span> <span class="ident">i</span> <span class="kw">in</span> <span class="kw-2">&</span><span class="ident">array</span> {
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<span class="ident">scope</span>.<span class="ident">spawn</span>(<span class="kw">move</span> <span class="op">||</span> {
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<span class="macro">println</span><span class="macro">!</span>(<span class="string">"element: {}"</span>, <span class="ident">i</span>);
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});
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}
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});</pre>
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<p>Much more straightforward.</p>
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</div><h4 id='method.builder' class="method"><span id='builder.v' class='invisible'><code>pub fn <a href='#method.builder' class='fnname'>builder</a><'s>(&'s self) -> ScopedThreadBuilder<'s, 'a></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/crossbeam/scoped.rs.html#238-243' title='goto source code'>[src]</a></span></h4>
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<div class='docblock'><p>Generates the base configuration for spawning a scoped thread, from which configuration
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methods can be chained.</p>
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</div></div>
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<h2 id='implementations' class='small-section-header'>
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Trait Implementations<a href='#implementations' class='anchor'></a>
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<h3 id='impl-Debug' class='impl'><span class='in-band'><code>impl<'a> <a class="trait" href="https://doc.rust-lang.org/nightly/core/fmt/trait.Debug.html" title="trait core::fmt::Debug">Debug</a> for <a class="struct" href="../crossbeam/struct.Scope.html" title="struct crossbeam::Scope">Scope</a><'a></code><a href='#impl-Debug' class='anchor'></a></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/crossbeam/scoped.rs.html#68-72' title='goto source code'>[src]</a></span></h3>
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<div class='impl-items'><h4 id='method.fmt' class="method"><span id='fmt.v' class='invisible'><code>fn <a href='https://doc.rust-lang.org/nightly/core/fmt/trait.Debug.html#tymethod.fmt' class='fnname'>fmt</a>(&self, f: &mut <a class="struct" href="https://doc.rust-lang.org/nightly/core/fmt/struct.Formatter.html" title="struct core::fmt::Formatter">Formatter</a>) -> <a class="type" href="https://doc.rust-lang.org/nightly/core/fmt/type.Result.html" title="type core::fmt::Result">Result</a></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/crossbeam/scoped.rs.html#69-71' title='goto source code'>[src]</a></span></h4>
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<div class='docblock'><p>Formats the value using the given formatter. <a href="https://doc.rust-lang.org/nightly/core/fmt/trait.Debug.html#tymethod.fmt">Read more</a></p>
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</div></div><h3 id='impl-Drop' class='impl'><span class='in-band'><code>impl<'a> <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/drop/trait.Drop.html" title="trait core::ops::drop::Drop">Drop</a> for <a class="struct" href="../crossbeam/struct.Scope.html" title="struct crossbeam::Scope">Scope</a><'a></code><a href='#impl-Drop' class='anchor'></a></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/crossbeam/scoped.rs.html#310-314' title='goto source code'>[src]</a></span></h3>
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<div class='impl-items'><h4 id='method.drop' class="method"><span id='drop.v' class='invisible'><code>fn <a href='https://doc.rust-lang.org/nightly/core/ops/drop/trait.Drop.html#tymethod.drop' class='fnname'>drop</a>(&mut self)</code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/crossbeam/scoped.rs.html#311-313' title='goto source code'>[src]</a></span></h4>
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<div class='docblock'><p>Executes the destructor for this type. <a href="https://doc.rust-lang.org/nightly/core/ops/drop/trait.Drop.html#tymethod.drop">Read more</a></p>
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