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</pre><div class="example-wrap"><pre class="rust ">
<span class="comment">// Copyright 2020 Shin Yoshida</span>
<span class="comment">//</span>
<span class="comment">// "LGPL-3.0-or-later OR Apache-2.0 OR BSD-2-Clause"</span>
<span class="comment">//</span>
<span class="comment">// This is part of spin-sync</span>
<span class="comment">//</span>
<span class="comment">// spin-sync is free software: you can redistribute it and/or modify</span>
<span class="comment">// it under the terms of the GNU Lesser General Public License as published by</span>
<span class="comment">// the Free Software Foundation, either version 3 of the License, or</span>
<span class="comment">// (at your option) any later version.</span>
<span class="comment">//</span>
<span class="comment">// spin-sync is distributed in the hope that it will be useful,</span>
<span class="comment">// but WITHOUT ANY WARRANTY; without even the implied warranty of</span>
<span class="comment">// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the</span>
<span class="comment">// GNU Lesser General Public License for more details.</span>
<span class="comment">//</span>
<span class="comment">// You should have received a copy of the GNU Lesser General Public License</span>
<span class="comment">// along with spin-sync. If not, see <http://www.gnu.org/licenses/>.</span>
<span class="comment">//</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 (the "License");</span>
<span class="comment">// you may not use this file except in compliance with the License.</span>
<span class="comment">// You may obtain a copy of the License at</span>
<span class="comment">//</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0</span>
<span class="comment">//</span>
<span class="comment">// Unless required by applicable law or agreed to in writing, software</span>
<span class="comment">// distributed under the License is distributed on an "AS IS" BASIS,</span>
<span class="comment">// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.</span>
<span class="comment">// See the License for the specific language governing permissions and</span>
<span class="comment">// limitations under the License.</span>
<span class="comment">//</span>
<span class="comment">//</span>
<span class="comment">// Redistribution and use in source and binary forms, with or without modification, are permitted</span>
<span class="comment">// provided that the following conditions are met:</span>
<span class="comment">//</span>
<span class="comment">// 1. Redistributions of source code must retain the above copyright notice, this list of</span>
<span class="comment">// conditions and the following disclaimer.</span>
<span class="comment">// 2. Redistributions in binary form must reproduce the above copyright notice, this</span>
<span class="comment">// list of conditions and the following disclaimer in the documentation and/or other</span>
<span class="comment">// materials provided with the distribution.</span>
<span class="comment">//</span>
<span class="comment">// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND</span>
<span class="comment">// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED</span>
<span class="comment">// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.</span>
<span class="comment">// IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,</span>
<span class="comment">// INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT</span>
<span class="comment">// NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR</span>
<span class="comment">// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,</span>
<span class="comment">// WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)</span>
<span class="comment">// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE</span>
<span class="comment">// POSSIBILITY OF SUCH DAMAGE.</span>
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">misc</span>::{<span class="ident">PhantomBarrier</span>, <span class="ident">PhantomBarrierWaitResult</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">sync</span>::<span class="ident">atomic</span>::{<span class="ident">AtomicUsize</span>, <span class="ident">Ordering</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">/// The behavior is same to `std::sync::Barrier` except for this uses spinlock.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Unlike to `std::sync::Barrier::new`, the constructor [`Barrier.new`] is a const function;</span>
<span class="doccomment">/// i.e. static [`Barrier`] variable can be declared.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Barrier`]: struct.Barrier.html</span>
<span class="doccomment">/// [`Barrier.new`]: #method.new</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use spin_sync::Barrier;</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// static NUM_THREADS: usize = 10;</span>
<span class="doccomment">/// static BARRIER: Barrier = Barrier::new(NUM_THREADS);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let mut handles = Vec::with_capacity(10);</span>
<span class="doccomment">/// for _ in 0..10 {</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">/// BARRIER.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="doccomment">///</span>
<span class="doccomment">/// Once all the threads have finished to wait, `Barrier` is reinitialized.</span>
<span class="doccomment">/// The same instance can be used again.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use spin_sync::Barrier;</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// static NUM_THREADS: usize = 10;</span>
<span class="doccomment">/// static BARRIER: Barrier = Barrier::new(NUM_THREADS);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn wait_and_reinitialize() {</span>
<span class="doccomment">/// let mut handles = Vec::with_capacity(10);</span>
<span class="doccomment">/// for _ in 0..10 {</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">/// BARRIER.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="doccomment">///</span>
<span class="doccomment">/// fn main() {</span>
<span class="doccomment">/// // First use.</span>
<span class="doccomment">/// wait_and_reinitialize();</span>
<span class="doccomment">/// // Second use.</span>
<span class="doccomment">/// wait_and_reinitialize();</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If 0 or 1 is passed to `Barrier::new`, the instance will never block.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use spin_sync::Barrier;</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// static BARRIER0: Barrier = Barrier::new(0);</span>
<span class="doccomment">/// static BARRIER1: Barrier = Barrier::new(1);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// BARRIER0.wait();</span>
<span class="doccomment">/// BARRIER1.wait();</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Barrier</span> {
<span class="ident">num_threads</span>: <span class="ident">usize</span>, <span class="comment">// immutable</span>
<span class="ident">count</span>: <span class="ident">AtomicUsize</span>,
<span class="ident">generation_id</span>: <span class="ident">AtomicUsize</span>, <span class="comment">// MSB plays lock flag role.</span>
<span class="ident">_phantom</span>: <span class="ident">PhantomBarrier</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">/// Unlike to `std::sync::Barrier::new`, this function is const; i.e.</span>
<span class="doccomment">/// static [`Barrier`] variable can be declared.</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">/// [`Barrier`]: struct.Barrier.html</span>
<span class="doccomment">/// [`wait`]: #method.wait</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Declaring [`Barrier`] instance as a local variable.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use spin_sync::Barrier;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let barrier = Barrier::new(10);</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Declaring static [`Barrier`] variable.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use spin_sync::Barrier;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// static BARRIER: Barrier = Barrier::new(5);</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">const</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="op">></span> <span class="self">Self</span> {
<span class="self">Self</span> {
<span class="ident">num_threads</span>: <span class="ident">n</span>,
<span class="ident">count</span>: <span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="number">0</span>),
<span class="ident">generation_id</span>: <span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="number">0</span>),
<span class="ident">_phantom</span>: <span class="ident">PhantomBarrier</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 spin_sync::Barrier;</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// static NUM_THREADS: usize = 10;</span>
<span class="doccomment">/// static BARRIER: Barrier = Barrier::new(NUM_THREADS);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let mut handles = Vec::with_capacity(10);</span>
<span class="doccomment">/// for _ in 0..10 {</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">/// BARRIER.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="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="op">></span> <span class="ident">BarrierWaitResult</span> {
<span class="kw">let</span> (<span class="ident">guard</span>, <span class="ident">generation_id</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">lock</span>();
<span class="kw">let</span> <span class="ident">count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">count</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>) <span class="op">+</span> <span class="number">1</span>;
<span class="self">self</span>.<span class="ident">count</span>.<span class="ident">store</span>(<span class="ident">count</span>, <span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="kw">if</span> <span class="ident">count</span> <span class="op"><</span> <span class="self">self</span>.<span class="ident">num_threads</span> {
<span class="comment">// Unlock and waiting for the leader reinitialize self.</span>
<span class="ident">drop</span>(<span class="ident">guard</span>);
<span class="kw">loop</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">current_id</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">generation_id</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="kw">if</span> (<span class="ident">current_id</span> <span class="op">&</span> <span class="ident">BarrierLockGuard</span>::<span class="ident">MSB</span>) <span class="op">!</span><span class="op">=</span> <span class="number">0</span> {
<span class="ident">current_id</span> <span class="op">=</span> <span class="ident">current_id</span> <span class="op">-</span> <span class="ident">BarrierLockGuard</span>::<span class="ident">MSB</span>;
}
<span class="kw">if</span> <span class="ident">generation_id</span> <span class="op">!</span><span class="op">=</span> <span class="ident">current_id</span> {
<span class="kw">return</span> <span class="ident">BarrierWaitResult</span>(<span class="bool-val">false</span>, <span class="ident">PhantomBarrierWaitResult</span> {});
} <span class="kw">else</span> {
<span class="ident">std</span>::<span class="ident">thread</span>::<span class="ident">yield_now</span>();
}
}
} <span class="kw">else</span> {
<span class="comment">// This thread will be the leader.</span>
<span class="comment">// Reinitialize self and return immediately.</span>
<span class="self">self</span>.<span class="ident">count</span>.<span class="ident">store</span>(<span class="number">0</span>, <span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="comment">// The other waiting threads judge whether reinitialized or not from generation_id.</span>
<span class="comment">// After generation_id was updated, they stop to block and return.</span>
<span class="comment">// However, the next wait() won't be started because this thread still owns the lock.</span>
<span class="kw">let</span> <span class="ident">generation_id</span> <span class="op">=</span> (<span class="ident">generation_id</span> <span class="op">+</span> <span class="number">1</span>) <span class="op">|</span> <span class="ident">BarrierLockGuard</span>::<span class="ident">MSB</span>;
<span class="self">self</span>.<span class="ident">generation_id</span>.<span class="ident">store</span>(<span class="ident">generation_id</span>, <span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="comment">// Release the lock.</span>
<span class="ident">drop</span>(<span class="ident">guard</span>);
<span class="ident">BarrierWaitResult</span>(<span class="bool-val">true</span>, <span class="ident">PhantomBarrierWaitResult</span> {})
}
}
<span class="kw">fn</span> <span class="ident">lock</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> (<span class="ident">BarrierLockGuard</span>, <span class="ident">usize</span>) {
<span class="comment">// Acquire lock</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">expected</span> <span class="op">=</span> <span class="number">0</span>;
<span class="kw">loop</span> {
<span class="kw">let</span> <span class="ident">desired</span> <span class="op">=</span> <span class="ident">expected</span> <span class="op">+</span> <span class="ident">BarrierLockGuard</span>::<span class="ident">MSB</span>;
<span class="kw">let</span> <span class="ident">current</span> <span class="op">=</span> <span class="self">self</span>
.<span class="ident">generation_id</span>
.<span class="ident">compare_and_swap</span>(<span class="ident">expected</span>, <span class="ident">desired</span>, <span class="ident">Ordering</span>::<span class="ident">Acquire</span>);
<span class="kw">if</span> <span class="ident">current</span> <span class="op">=</span><span class="op">=</span> <span class="ident">expected</span> {
<span class="comment">// Succeeded to lock</span>
<span class="kw">break</span>;
} <span class="kw">else</span> {
<span class="comment">// Failed to lock.</span>
<span class="comment">// Retry.</span>
<span class="kw">if</span> (<span class="ident">current</span> <span class="op">&</span> <span class="ident">BarrierLockGuard</span>::<span class="ident">MSB</span>) <span class="op">!</span><span class="op">=</span> <span class="number">0</span> {
<span class="comment">// Another thread is holding the lock.</span>
<span class="comment">// Wait for a while and retry.</span>
<span class="ident">expected</span> <span class="op">=</span> <span class="ident">current</span> <span class="op">-</span> <span class="ident">BarrierLockGuard</span>::<span class="ident">MSB</span>;
<span class="ident">std</span>::<span class="ident">thread</span>::<span class="ident">yield_now</span>();
} <span class="kw">else</span> {
<span class="comment">// Just the first assumption was wrong.</span>
<span class="comment">// Retry immediately.</span>
<span class="ident">expected</span> <span class="op">=</span> <span class="ident">current</span>;
}
}
}
(
<span class="ident">BarrierLockGuard</span> {
<span class="ident">generation_id</span>: <span class="kw-2">&</span><span class="self">self</span>.<span class="ident">generation_id</span>,
},
<span class="ident">expected</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="lifetime">'_</span><span class="op">></span>) <span class="op">-</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">pub</span> <span class="kw">struct</span> <span class="ident">BarrierWaitResult</span>(<span class="ident">bool</span>, <span class="ident">PhantomBarrierWaitResult</span>);
<span class="kw">impl</span> <span class="ident">BarrierWaitResult</span> {
<span class="doccomment">/// Returns `true` if 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">/// assert!(barrier_wait_result.is_leader());</span>
<span class="doccomment">/// ```</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="op">></span> <span class="ident">bool</span> {
<span class="self">self</span>.<span class="number">0</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="lifetime">'_</span><span class="op">></span>) <span class="op">-</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">struct</span> <span class="ident">BarrierLockGuard</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">generation_id</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">AtomicUsize</span>,
}
<span class="kw">impl</span> <span class="ident">BarrierLockGuard</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span> {
<span class="kw">pub</span> <span class="kw">const</span> <span class="ident">MSB</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="ident">usize</span>::<span class="ident">MAX</span> <span class="op">/</span> <span class="number">2</span> <span class="op">+</span> <span class="number">1</span>;
}
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">BarrierLockGuard</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span> {
<span class="comment">// Make sure to unlock</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="ident">current</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">generation_id</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="macro">debug_assert_eq</span><span class="macro">!</span>(<span class="self">Self</span>::<span class="ident">MSB</span>, <span class="ident">current</span> <span class="op">&</span> <span class="self">Self</span>::<span class="ident">MSB</span>);
<span class="kw">let</span> <span class="ident">desired</span> <span class="op">=</span> <span class="ident">current</span> <span class="op">-</span> <span class="self">Self</span>::<span class="ident">MSB</span>;
<span class="self">self</span>.<span class="ident">generation_id</span>.<span class="ident">store</span>(<span class="ident">desired</span>, <span class="ident">Ordering</span>::<span class="ident">Release</span>);
}
}
</pre></div>
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