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</pre><pre class="rust">
<span class="comment">// Necessary for using `Mutex<usize>` for conditional variables</span>
<span class="attribute">#![<span class="ident">allow</span>(<span class="ident">clippy::mutex_atomic</span>)]</span>
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::primitive::sync</span>::{<span class="ident">Arc</span>, <span class="ident">Condvar</span>, <span class="ident">Mutex</span>};
<span class="kw">use</span> <span class="ident">std::fmt</span>;
<span class="doccomment">/// Enables threads to synchronize the beginning or end of some computation.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Wait groups vs barriers</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `WaitGroup` is very similar to [`Barrier`], but there are a few differences:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * [`Barrier`] needs to know the number of threads at construction, while `WaitGroup` is cloned to</span>
<span class="doccomment">/// register more threads.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * A [`Barrier`] can be reused even after all threads have synchronized, while a `WaitGroup`</span>
<span class="doccomment">/// synchronizes threads only once.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * All threads wait for others to reach the [`Barrier`]. With `WaitGroup`, each thread can choose</span>
<span class="doccomment">/// to either wait for other threads or to continue without blocking.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::WaitGroup;</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Create a new wait group.</span>
<span class="doccomment">/// let wg = WaitGroup::new();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// for _ in 0..4 {</span>
<span class="doccomment">/// // Create another reference to the wait group.</span>
<span class="doccomment">/// let wg = wg.clone();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// thread::spawn(move || {</span>
<span class="doccomment">/// // Do some work.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Drop the reference to the wait group.</span>
<span class="doccomment">/// drop(wg);</span>
<span class="doccomment">/// });</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Block until all threads have finished their work.</span>
<span class="doccomment">/// wg.wait();</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Barrier`]: std::sync::Barrier</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">WaitGroup</span> {
<span class="ident">inner</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">Inner</span><span class="op">></span>,
}
<span class="doccomment">/// Inner state of a `WaitGroup`.</span>
<span class="kw">struct</span> <span class="ident">Inner</span> {
<span class="ident">cvar</span>: <span class="ident">Condvar</span>,
<span class="ident">count</span>: <span class="ident">Mutex</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>,
}
<span class="kw">impl</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">WaitGroup</span> {
<span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="self">Self</span> {
<span class="ident">inner</span>: <span class="ident">Arc::new</span>(<span class="ident">Inner</span> {
<span class="ident">cvar</span>: <span class="ident">Condvar::new</span>(),
<span class="ident">count</span>: <span class="ident">Mutex::new</span>(<span class="number">1</span>),
}),
}
}
}
<span class="kw">impl</span> <span class="ident">WaitGroup</span> {
<span class="doccomment">/// Creates a new wait group and returns the single reference to it.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::WaitGroup;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let wg = WaitGroup::new();</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="self">Self</span><span class="ident">::default</span>()
}
<span class="doccomment">/// Drops this reference and waits until all other references are dropped.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::WaitGroup;</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let wg = WaitGroup::new();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// thread::spawn({</span>
<span class="doccomment">/// let wg = wg.clone();</span>
<span class="doccomment">/// move || {</span>
<span class="doccomment">/// // Block until both threads have reached `wait()`.</span>
<span class="doccomment">/// wg.wait();</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// });</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Block until both threads have reached `wait()`.</span>
<span class="doccomment">/// wg.wait();</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">wait</span>(<span class="self">self</span>) {
<span class="kw">if</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">count</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>() <span class="op">=</span><span class="op">=</span> <span class="number">1</span> {
<span class="kw">return</span>;
}
<span class="kw">let</span> <span class="ident">inner</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">clone</span>();
<span class="ident">drop</span>(<span class="self">self</span>);
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">count</span> <span class="op">=</span> <span class="ident">inner</span>.<span class="ident">count</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="kw">while</span> <span class="kw-2">*</span><span class="ident">count</span> <span class="op">></span> <span class="number">0</span> {
<span class="ident">count</span> <span class="op">=</span> <span class="ident">inner</span>.<span class="ident">cvar</span>.<span class="ident">wait</span>(<span class="ident">count</span>).<span class="ident">unwrap</span>();
}
}
}
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">WaitGroup</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="kw">let</span> <span class="kw-2">mut</span> <span class="ident">count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">count</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="kw-2">*</span><span class="ident">count</span> <span class="op">-</span><span class="op">=</span> <span class="number">1</span>;
<span class="kw">if</span> <span class="kw-2">*</span><span class="ident">count</span> <span class="op">=</span><span class="op">=</span> <span class="number">0</span> {
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">cvar</span>.<span class="ident">notify_all</span>();
}
}
}
<span class="kw">impl</span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">WaitGroup</span> {
<span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">WaitGroup</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">count</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="kw-2">*</span><span class="ident">count</span> <span class="op">+</span><span class="op">=</span> <span class="number">1</span>;
<span class="ident">WaitGroup</span> {
<span class="ident">inner</span>: <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">clone</span>(),
}
}
}
<span class="kw">impl</span> <span class="ident">fmt::Debug</span> <span class="kw">for</span> <span class="ident">WaitGroup</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::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::Result</span> {
<span class="kw">let</span> <span class="ident">count</span>: <span class="kw-2">&</span><span class="ident">usize</span> <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">count</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">"WaitGroup"</span>).<span class="ident">field</span>(<span class="string">"count"</span>, <span class="ident">count</span>).<span class="ident">finish</span>()
}
}
</pre></div>
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