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</pre><pre class="rust ">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cell</span>::<span class="ident">RefCell</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">mem</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">rc</span>::<span class="ident">Rc</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">atomic</span>::<span class="ident">Ordering</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">Arc</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">thread</span>;
<span class="kw">use</span> {<span class="ident">spawn_unsafe</span>, <span class="ident">FnBox</span>};
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">AtomicOption</span>;
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Scope</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">dtors</span>: <span class="ident">RefCell</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">DtorChain</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">>></span><span class="op">></span>
}
<span class="kw">struct</span> <span class="ident">DtorChain</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">dtor</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">FnBox</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span>,
<span class="ident">next</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="ident">DtorChain</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">>></span><span class="op">></span>
}
<span class="kw">enum</span> <span class="ident">JoinState</span> {
<span class="ident">Running</span>(<span class="ident">thread</span>::<span class="ident">JoinHandle</span><span class="op"><</span>()<span class="op">></span>),
<span class="ident">Joined</span>,
}
<span class="kw">impl</span> <span class="ident">JoinState</span> {
<span class="kw">fn</span> <span class="ident">join</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">state</span> <span class="op">=</span> <span class="ident">JoinState</span>::<span class="ident">Joined</span>;
<span class="ident">mem</span>::<span class="ident">swap</span>(<span class="self">self</span>, <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">state</span>);
<span class="kw">if</span> <span class="kw">let</span> <span class="ident">JoinState</span>::<span class="ident">Running</span>(<span class="ident">handle</span>) <span class="op">=</span> <span class="ident">state</span> {
<span class="kw">let</span> <span class="ident">res</span> <span class="op">=</span> <span class="ident">handle</span>.<span class="ident">join</span>();
<span class="kw">if</span> <span class="op">!</span><span class="ident">thread</span>::<span class="ident">panicking</span>() { <span class="ident">res</span>.<span class="ident">unwrap</span>(); }
}
}
}
<span class="doccomment">/// A handle to a scoped thread</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ScopedJoinHandle</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">inner</span>: <span class="ident">Rc</span><span class="op"><</span><span class="ident">RefCell</span><span class="op"><</span><span class="ident">JoinState</span><span class="op">>></span>,
<span class="ident">packet</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">AtomicOption</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="ident">thread</span>: <span class="ident">thread</span>::<span class="ident">Thread</span>,
}
<span class="doccomment">/// Create a new `scope`, for deferred destructors.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Scopes, in particular, support [*scoped thread spawning*](struct.Scope.html#method.spawn).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Creating and using a scope:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// crossbeam::scope(|scope| {</span>
<span class="doccomment">/// scope.defer(|| println!("Exiting scope"));</span>
<span class="doccomment">/// scope.spawn(|| println!("Running child thread in scope"))</span>
<span class="doccomment">/// });</span>
<span class="doccomment">/// // Prints messages in the reverse order written</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">scope</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">F</span>, <span class="ident">R</span><span class="op">></span>(<span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-></span> <span class="ident">R</span> <span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="ident">Scope</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>) <span class="op">-></span> <span class="ident">R</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">scope</span> <span class="op">=</span> <span class="ident">Scope</span> { <span class="ident">dtors</span>: <span class="ident">RefCell</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>) };
<span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="ident">f</span>(<span class="kw-2">&</span><span class="ident">scope</span>);
<span class="ident">scope</span>.<span class="ident">drop_all</span>();
<span class="ident">ret</span>
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">Scope</span><span class="op"><</span><span class="lifetime">'a</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="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">"Scope {{ ... }}"</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">ScopedJoinHandle</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="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">"ScopedJoinHandle {{ ... }}"</span>)
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="ident">Scope</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="comment">// This method is carefully written in a transactional style, so</span>
<span class="comment">// that it can be called directly and, if any dtor panics, can be</span>
<span class="comment">// resumed in the unwinding this causes. By initially running the</span>
<span class="comment">// method outside of any destructor, we avoid any leakage problems</span>
<span class="comment">// due to @rust-lang/rust#14875.</span>
<span class="kw">fn</span> <span class="ident">drop_all</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="kw">loop</span> {
<span class="comment">// use a separate scope to ensure that the RefCell borrow</span>
<span class="comment">// is relinquishe before running `dtor`</span>
<span class="kw">let</span> <span class="ident">dtor</span> <span class="op">=</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">dtors</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">dtors</span>.<span class="ident">borrow_mut</span>();
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="kw-2">mut</span> <span class="ident">node</span>) <span class="op">=</span> <span class="ident">dtors</span>.<span class="ident">take</span>() {
<span class="kw-2">*</span><span class="ident">dtors</span> <span class="op">=</span> <span class="ident">node</span>.<span class="ident">next</span>.<span class="ident">take</span>().<span class="ident">map</span>(<span class="op">|</span><span class="ident">b</span><span class="op">|</span> <span class="kw-2">*</span><span class="ident">b</span>);
<span class="ident">node</span>.<span class="ident">dtor</span>
} <span class="kw">else</span> {
<span class="kw">return</span>
}
};
<span class="ident">dtor</span>.<span class="ident">call_box</span>()
}
}
<span class="doccomment">/// Schedule code to be executed when exiting the scope.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is akin to having a destructor on the stack, except that it is</span>
<span class="doccomment">/// *guaranteed* to be run.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">defer</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="ident">F</span>) <span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">+</span> <span class="lifetime">'a</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">dtors</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">dtors</span>.<span class="ident">borrow_mut</span>();
<span class="kw-2">*</span><span class="ident">dtors</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">DtorChain</span> {
<span class="ident">dtor</span>: <span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">f</span>),
<span class="ident">next</span>: <span class="ident">dtors</span>.<span class="ident">take</span>().<span class="ident">map</span>(<span class="ident">Box</span>::<span class="ident">new</span>)
});
}
<span class="doccomment">/// Create a scoped thread.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `spawn` is similar to the [`spawn`][spawn] function in Rust's standard library. The</span>
<span class="doccomment">/// difference is that this thread is scoped, meaning that it's guaranteed to terminate</span>
<span class="doccomment">/// before the current stack frame goes away, allowing you to reference the parent stack frame</span>
<span class="doccomment">/// directly. This is ensured by having the parent thread join on the child thread before the</span>
<span class="doccomment">/// scope exits.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [spawn]: http://doc.rust-lang.org/std/thread/fn.spawn.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A basic scoped thread:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// crossbeam::scope(|scope| {</span>
<span class="doccomment">/// scope.spawn(|| {</span>
<span class="doccomment">/// println!("Hello from a scoped thread!");</span>
<span class="doccomment">/// });</span>
<span class="doccomment">/// });</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When writing concurrent Rust programs, you'll sometimes see a pattern like this, using</span>
<span class="doccomment">/// [`std::thread::spawn`][spawn]:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```ignore</span>
<span class="doccomment">/// let array = [1, 2, 3];</span>
<span class="doccomment">/// let mut guards = vec![];</span>
<span class="doccomment">///</span>
<span class="doccomment">/// for i in &array {</span>
<span class="doccomment">/// let guard = std::thread::spawn(move || {</span>
<span class="doccomment">/// println!("element: {}", i);</span>
<span class="doccomment">/// });</span>
<span class="doccomment">///</span>
<span class="doccomment">/// guards.push(guard);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// for guard in guards {</span>
<span class="doccomment">/// guard.join().unwrap();</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The basic pattern is:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// 1. Iterate over some collection.</span>
<span class="doccomment">/// 2. Spin up a thread to operate on each part of the collection.</span>
<span class="doccomment">/// 3. Join all the threads.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// However, this code actually gives an error:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```text</span>
<span class="doccomment">/// error: `array` does not live long enough</span>
<span class="doccomment">/// for i in &array {</span>
<span class="doccomment">/// ^~~~~</span>
<span class="doccomment">/// in expansion of for loop expansion</span>
<span class="doccomment">/// note: expansion site</span>
<span class="doccomment">/// note: reference must be valid for the static lifetime...</span>
<span class="doccomment">/// note: ...but borrowed value is only valid for the block suffix following statement 0 at ...</span>
<span class="doccomment">/// let array = [1, 2, 3];</span>
<span class="doccomment">/// let mut guards = vec![];</span>
<span class="doccomment">///</span>
<span class="doccomment">/// for i in &array {</span>
<span class="doccomment">/// let guard = std::thread::spawn(move || {</span>
<span class="doccomment">/// println!("element: {}", i);</span>
<span class="doccomment">/// ...</span>
<span class="doccomment">/// error: aborting due to previous error</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Because [`std::thread::spawn`][spawn] doesn't know about this scope, it requires a</span>
<span class="doccomment">/// `'static` lifetime. One way of giving it a proper lifetime is to use an [`Arc`][arc]:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [arc]: http://doc.rust-lang.org/stable/std/sync/struct.Arc.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::sync::Arc;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let array = Arc::new([1, 2, 3]);</span>
<span class="doccomment">/// let mut guards = vec![];</span>
<span class="doccomment">///</span>
<span class="doccomment">/// for i in (0..array.len()) {</span>
<span class="doccomment">/// let a = array.clone();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let guard = std::thread::spawn(move || {</span>
<span class="doccomment">/// println!("element: {}", a[i]);</span>
<span class="doccomment">/// });</span>
<span class="doccomment">///</span>
<span class="doccomment">/// guards.push(guard);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// for guard in guards {</span>
<span class="doccomment">/// guard.join().unwrap();</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// But this introduces unnecessary allocation, as `Arc<T>` puts its data on the heap, and we</span>
<span class="doccomment">/// also end up dealing with reference counts. We know that we're joining the threads before</span>
<span class="doccomment">/// our function returns, so just taking a reference _should_ be safe. Rust can't know that,</span>
<span class="doccomment">/// though.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Enter scoped threads. Here's our original example, using `spawn` from crossbeam rather</span>
<span class="doccomment">/// than from `std::thread`:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// let array = [1, 2, 3];</span>
<span class="doccomment">///</span>
<span class="doccomment">/// crossbeam::scope(|scope| {</span>
<span class="doccomment">/// for i in &array {</span>
<span class="doccomment">/// scope.spawn(move || {</span>
<span class="doccomment">/// println!("element: {}", i);</span>
<span class="doccomment">/// });</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// });</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Much more straightforward.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">spawn</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">T</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-></span> <span class="ident">ScopedJoinHandle</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">where</span>
<span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">-></span> <span class="ident">T</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'a</span>, <span class="ident">T</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'a</span>
{
<span class="kw">let</span> <span class="ident">their_packet</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">AtomicOption</span>::<span class="ident">new</span>());
<span class="kw">let</span> <span class="ident">my_packet</span> <span class="op">=</span> <span class="ident">their_packet</span>.<span class="ident">clone</span>();
<span class="kw">let</span> <span class="ident">join_handle</span> <span class="op">=</span> <span class="kw">unsafe</span> {
<span class="ident">spawn_unsafe</span>(<span class="kw">move</span> <span class="op">||</span> {
<span class="ident">their_packet</span>.<span class="ident">swap</span>(<span class="ident">f</span>(), <span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
})
};
<span class="kw">let</span> <span class="ident">thread</span> <span class="op">=</span> <span class="ident">join_handle</span>.<span class="ident">thread</span>().<span class="ident">clone</span>();
<span class="kw">let</span> <span class="ident">deferred_handle</span> <span class="op">=</span> <span class="ident">Rc</span>::<span class="ident">new</span>(<span class="ident">RefCell</span>::<span class="ident">new</span>(<span class="ident">JoinState</span>::<span class="ident">Running</span>(<span class="ident">join_handle</span>)));
<span class="kw">let</span> <span class="ident">my_handle</span> <span class="op">=</span> <span class="ident">deferred_handle</span>.<span class="ident">clone</span>();
<span class="self">self</span>.<span class="ident">defer</span>(<span class="kw">move</span> <span class="op">||</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">state</span> <span class="op">=</span> <span class="ident">deferred_handle</span>.<span class="ident">borrow_mut</span>();
<span class="ident">state</span>.<span class="ident">join</span>();
});
<span class="ident">ScopedJoinHandle</span> {
<span class="ident">inner</span>: <span class="ident">my_handle</span>,
<span class="ident">packet</span>: <span class="ident">my_packet</span>,
<span class="ident">thread</span>: <span class="ident">thread</span>,
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">ScopedJoinHandle</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Join the scoped thread, returning the result it produced.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">join</span>(<span class="self">self</span>) <span class="op">-></span> <span class="ident">T</span> {
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">borrow_mut</span>().<span class="ident">join</span>();
<span class="self">self</span>.<span class="ident">packet</span>.<span class="ident">take</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>).<span class="ident">unwrap</span>()
}
<span class="doccomment">/// Get the underlying thread handle.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">thread</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">thread</span>::<span class="ident">Thread</span> {
<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">thread</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">Scope</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="self">self</span>.<span class="ident">drop_all</span>()
}
}
</pre>
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