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</pre><pre class="rust ">
<span class="comment">// Copyright 2014 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="kw">use</span> <span class="ident">fmt</span>;
<span class="kw">use</span> <span class="ident">sync</span>::{<span class="ident">Mutex</span>, <span class="ident">Condvar</span>};
<span class="doccomment">/// A barrier enables multiple threads to synchronize the beginning</span>
<span class="doccomment">/// of some computation.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::sync::{Arc, Barrier};</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let mut handles = Vec::with_capacity(10);</span>
<span class="doccomment">/// let barrier = Arc::new(Barrier::new(10));</span>
<span class="doccomment">/// for _ in 0..10 {</span>
<span class="doccomment">/// let c = barrier.clone();</span>
<span class="doccomment">/// // The same messages will be printed together.</span>
<span class="doccomment">/// // You will NOT see any interleaving.</span>
<span class="doccomment">/// handles.push(thread::spawn(move|| {</span>
<span class="doccomment">/// println!("before wait");</span>
<span class="doccomment">/// c.wait();</span>
<span class="doccomment">/// println!("after wait");</span>
<span class="doccomment">/// }));</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// // Wait for other threads to finish.</span>
<span class="doccomment">/// for handle in handles {</span>
<span class="doccomment">/// handle.join().unwrap();</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Barrier</span> {
<span class="ident">lock</span>: <span class="ident">Mutex</span><span class="op"><</span><span class="ident">BarrierState</span><span class="op">></span>,
<span class="ident">cvar</span>: <span class="ident">Condvar</span>,
<span class="ident">num_threads</span>: <span class="ident">usize</span>,
}
<span class="comment">// The inner state of a double barrier</span>
<span class="kw">struct</span> <span class="ident">BarrierState</span> {
<span class="ident">count</span>: <span class="ident">usize</span>,
<span class="ident">generation_id</span>: <span class="ident">usize</span>,
}
<span class="doccomment">/// A `BarrierWaitResult` is returned by [`wait`] when all threads in the [`Barrier`]</span>
<span class="doccomment">/// have rendezvoused.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`wait`]: struct.Barrier.html#method.wait</span>
<span class="doccomment">/// [`Barrier`]: struct.Barrier.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::sync::Barrier;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let barrier = Barrier::new(1);</span>
<span class="doccomment">/// let barrier_wait_result = barrier.wait();</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">BarrierWaitResult</span>(<span class="ident">bool</span>);
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std_debug"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.16.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">Barrier</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">"Barrier { .. }"</span>)
}
}
<span class="kw">impl</span> <span class="ident">Barrier</span> {
<span class="doccomment">/// Creates a new barrier that can block a given number of threads.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A barrier will block `n`-1 threads which call [`wait`] and then wake up</span>
<span class="doccomment">/// all threads at once when the `n`th thread calls [`wait`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`wait`]: #method.wait</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::sync::Barrier;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let barrier = Barrier::new(10);</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">n</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="ident">Barrier</span> {
<span class="ident">Barrier</span> {
<span class="ident">lock</span>: <span class="ident">Mutex</span>::<span class="ident">new</span>(<span class="ident">BarrierState</span> {
<span class="ident">count</span>: <span class="number">0</span>,
<span class="ident">generation_id</span>: <span class="number">0</span>,
}),
<span class="ident">cvar</span>: <span class="ident">Condvar</span>::<span class="ident">new</span>(),
<span class="ident">num_threads</span>: <span class="ident">n</span>,
}
}
<span class="doccomment">/// Blocks the current thread until all threads have rendezvoused here.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Barriers are re-usable after all threads have rendezvoused once, and can</span>
<span class="doccomment">/// be used continuously.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A single (arbitrary) thread will receive a [`BarrierWaitResult`] that</span>
<span class="doccomment">/// returns `true` from [`is_leader`] when returning from this function, and</span>
<span class="doccomment">/// all other threads will receive a result that will return `false` from</span>
<span class="doccomment">/// [`is_leader`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`BarrierWaitResult`]: struct.BarrierWaitResult.html</span>
<span class="doccomment">/// [`is_leader`]: struct.BarrierWaitResult.html#method.is_leader</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::sync::{Arc, Barrier};</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let mut handles = Vec::with_capacity(10);</span>
<span class="doccomment">/// let barrier = Arc::new(Barrier::new(10));</span>
<span class="doccomment">/// for _ in 0..10 {</span>
<span class="doccomment">/// let c = barrier.clone();</span>
<span class="doccomment">/// // The same messages will be printed together.</span>
<span class="doccomment">/// // You will NOT see any interleaving.</span>
<span class="doccomment">/// handles.push(thread::spawn(move|| {</span>
<span class="doccomment">/// println!("before wait");</span>
<span class="doccomment">/// c.wait();</span>
<span class="doccomment">/// println!("after wait");</span>
<span class="doccomment">/// }));</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// // Wait for other threads to finish.</span>
<span class="doccomment">/// for handle in handles {</span>
<span class="doccomment">/// handle.join().unwrap();</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">wait</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">BarrierWaitResult</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">lock</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">lock</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="kw">let</span> <span class="ident">local_gen</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">generation_id</span>;
<span class="ident">lock</span>.<span class="ident">count</span> <span class="op">+=</span> <span class="number">1</span>;
<span class="kw">if</span> <span class="ident">lock</span>.<span class="ident">count</span> <span class="op"><</span> <span class="self">self</span>.<span class="ident">num_threads</span> {
<span class="comment">// We need a while loop to guard against spurious wakeups.</span>
<span class="comment">// http://en.wikipedia.org/wiki/Spurious_wakeup</span>
<span class="kw">while</span> <span class="ident">local_gen</span> <span class="op">==</span> <span class="ident">lock</span>.<span class="ident">generation_id</span> <span class="op">&&</span>
<span class="ident">lock</span>.<span class="ident">count</span> <span class="op"><</span> <span class="self">self</span>.<span class="ident">num_threads</span> {
<span class="ident">lock</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">cvar</span>.<span class="ident">wait</span>(<span class="ident">lock</span>).<span class="ident">unwrap</span>();
}
<span class="ident">BarrierWaitResult</span>(<span class="bool-val">false</span>)
} <span class="kw">else</span> {
<span class="ident">lock</span>.<span class="ident">count</span> <span class="op">=</span> <span class="number">0</span>;
<span class="ident">lock</span>.<span class="ident">generation_id</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">generation_id</span>.<span class="ident">wrapping_add</span>(<span class="number">1</span>);
<span class="self">self</span>.<span class="ident">cvar</span>.<span class="ident">notify_all</span>();
<span class="ident">BarrierWaitResult</span>(<span class="bool-val">true</span>)
}
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std_debug"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.16.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">BarrierWaitResult</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">debug_struct</span>(<span class="string">"BarrierWaitResult"</span>)
.<span class="ident">field</span>(<span class="string">"is_leader"</span>, <span class="kw-2">&</span><span class="self">self</span>.<span class="ident">is_leader</span>())
.<span class="ident">finish</span>()
}
}
<span class="kw">impl</span> <span class="ident">BarrierWaitResult</span> {
<span class="doccomment">/// Returns whether this thread from [`wait`] is the "leader thread".</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Only one thread will have `true` returned from their result, all other</span>
<span class="doccomment">/// threads will have `false` returned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`wait`]: struct.Barrier.html#method.wait</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::sync::Barrier;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let barrier = Barrier::new(1);</span>
<span class="doccomment">/// let barrier_wait_result = barrier.wait();</span>
<span class="doccomment">/// println!("{:?}", barrier_wait_result.is_leader());</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">is_leader</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="self">self</span>.<span class="number">0</span> }
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">mod</span> <span class="ident">tests</span> {
<span class="kw">use</span> <span class="ident">sync</span>::{<span class="ident">Arc</span>, <span class="ident">Barrier</span>};
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">mpsc</span>::{<span class="ident">channel</span>, <span class="ident">TryRecvError</span>};
<span class="kw">use</span> <span class="ident">thread</span>;
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="attribute">#[<span class="ident">cfg_attr</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"emscripten"</span>, <span class="ident">ignore</span>)]</span>
<span class="kw">fn</span> <span class="ident">test_barrier</span>() {
<span class="kw">const</span> <span class="ident">N</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">10</span>;
<span class="kw">let</span> <span class="ident">barrier</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">Barrier</span>::<span class="ident">new</span>(<span class="ident">N</span>));
<span class="kw">let</span> (<span class="ident">tx</span>, <span class="ident">rx</span>) <span class="op">=</span> <span class="ident">channel</span>();
<span class="kw">for</span> <span class="kw">_</span> <span class="kw">in</span> <span class="number">0</span>..<span class="ident">N</span> <span class="op">-</span> <span class="number">1</span> {
<span class="kw">let</span> <span class="ident">c</span> <span class="op">=</span> <span class="ident">barrier</span>.<span class="ident">clone</span>();
<span class="kw">let</span> <span class="ident">tx</span> <span class="op">=</span> <span class="ident">tx</span>.<span class="ident">clone</span>();
<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span><span class="op">||</span> {
<span class="ident">tx</span>.<span class="ident">send</span>(<span class="ident">c</span>.<span class="ident">wait</span>().<span class="ident">is_leader</span>()).<span class="ident">unwrap</span>();
});
}
<span class="comment">// At this point, all spawned threads should be blocked,</span>
<span class="comment">// so we shouldn't get anything from the port</span>
<span class="macro">assert</span><span class="macro">!</span>(<span class="kw">match</span> <span class="ident">rx</span>.<span class="ident">try_recv</span>() {
<span class="prelude-val">Err</span>(<span class="ident">TryRecvError</span>::<span class="ident">Empty</span>) <span class="op">=></span> <span class="bool-val">true</span>,
<span class="kw">_</span> <span class="op">=></span> <span class="bool-val">false</span>,
});
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">leader_found</span> <span class="op">=</span> <span class="ident">barrier</span>.<span class="ident">wait</span>().<span class="ident">is_leader</span>();
<span class="comment">// Now, the barrier is cleared and we should get data.</span>
<span class="kw">for</span> <span class="kw">_</span> <span class="kw">in</span> <span class="number">0</span>..<span class="ident">N</span> <span class="op">-</span> <span class="number">1</span> {
<span class="kw">if</span> <span class="ident">rx</span>.<span class="ident">recv</span>().<span class="ident">unwrap</span>() {
<span class="macro">assert</span><span class="macro">!</span>(<span class="op">!</span><span class="ident">leader_found</span>);
<span class="ident">leader_found</span> <span class="op">=</span> <span class="bool-val">true</span>;
}
}
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">leader_found</span>);
}
}
</pre>
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