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</pre><pre class="rust ">
<span class="comment">// Copyright 2013 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="doccomment">//! A lock-free concurrent work-stealing deque</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! This module contains a hybrid implementation of the Chase-Lev work stealing deque</span>
<span class="doccomment">//! described in ["Dynamic Circular Work-Stealing Deque"][chase_lev] and the improved version</span>
<span class="doccomment">//! described in ["Correct and Efficient Work-Stealing for Weak Memory Models"][weak_chase_lev].</span>
<span class="doccomment">//! The implementation is heavily based on the pseudocode found in the papers.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Example</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! use crossbeam::sync::chase_lev;</span>
<span class="doccomment">//! let (worker, stealer) = chase_lev::deque();</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Only the worker may push/try_pop</span>
<span class="doccomment">//! worker.push(1);</span>
<span class="doccomment">//! worker.try_pop();</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Stealers take data from the other end of the deque</span>
<span class="doccomment">//! worker.push(1);</span>
<span class="doccomment">//! stealer.steal();</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! // Stealers can be cloned to have many stealers stealing in parallel</span>
<span class="doccomment">//! worker.push(1);</span>
<span class="doccomment">//! let stealer2 = stealer.clone();</span>
<span class="doccomment">//! stealer2.steal();</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [chase_lev]: http://neteril.org/~jeremie/Dynamic_Circular_Work_Queue.pdf</span>
<span class="doccomment">//! [weak_chase_lev]: http://www.di.ens.fr/~zappa/readings/ppopp13.pdf</span>
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cell</span>::<span class="ident">UnsafeCell</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">ptr</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="ident">Acquire</span>, <span class="ident">Relaxed</span>, <span class="ident">Release</span>, <span class="ident">SeqCst</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">atomic</span>::{<span class="ident">AtomicIsize</span>, <span class="ident">fence</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">marker</span>::<span class="ident">PhantomData</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cell</span>::<span class="ident">Cell</span>;
<span class="kw">use</span> <span class="ident">epoch</span>::{<span class="self">self</span>, <span class="ident">Atomic</span>, <span class="ident">Shared</span>, <span class="ident">Owned</span>};
<span class="comment">// Once the queue is less than 1/K full, then it will be downsized. Note that</span>
<span class="comment">// the deque requires that this number be less than 2.</span>
<span class="kw">const</span> <span class="ident">K</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="number">4</span>;
<span class="comment">// Minimum number of bits that a buffer size should be. No buffer will resize to</span>
<span class="comment">// under this value, and all deques will initially contain a buffer of this</span>
<span class="comment">// size.</span>
<span class="comment">//</span>
<span class="comment">// The size in question is 1 << MIN_BITS</span>
<span class="kw">const</span> <span class="ident">MIN_BITS</span>: <span class="ident">u32</span> <span class="op">=</span> <span class="number">7</span>;
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">struct</span> <span class="ident">Deque</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">bottom</span>: <span class="ident">AtomicIsize</span>,
<span class="ident">top</span>: <span class="ident">AtomicIsize</span>,
<span class="ident">array</span>: <span class="ident">Atomic</span><span class="op"><</span><span class="ident">Buffer</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
}
<span class="comment">// FIXME: can these constraints be relaxed?</span>
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Send</span><span class="op">></span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">Deque</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Send</span><span class="op">></span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">Deque</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="doccomment">/// Worker half of the work-stealing deque. This worker has exclusive access to</span>
<span class="doccomment">/// one side of the deque, and uses `push` and `try_pop` method to manipulate it.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// There may only be one worker per deque, so `Worker` does not implement</span>
<span class="doccomment">/// `Clone` or `Copy`.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Worker</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">deque</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">Deque</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="comment">// Marker so that the Worker is Send but not Sync. The worker can only be</span>
<span class="comment">// accessed from a single thread at once. Ideally we would use a negative</span>
<span class="comment">// impl here but these are not stable yet.</span>
<span class="ident">marker</span>: <span class="ident">PhantomData</span><span class="op"><</span><span class="ident">Cell</span><span class="op"><</span>()<span class="op">>></span>,
}
<span class="doccomment">/// The stealing half of the work-stealing deque. Stealers have access to the</span>
<span class="doccomment">/// opposite end of the deque from the worker, and they only have access to the</span>
<span class="doccomment">/// `steal` method.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Stealers can be cloned to have more than one handle active at a time.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Stealer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">deque</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">Deque</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
}
<span class="doccomment">/// When stealing some data, this is an enumeration of the possible outcomes.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">PartialEq</span>, <span class="ident">Eq</span>, <span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">Steal</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// The deque was empty at the time of stealing</span>
<span class="ident">Empty</span>,
<span class="doccomment">/// The stealer lost the race for stealing data, and a retry may return more</span>
<span class="doccomment">/// data.</span>
<span class="ident">Abort</span>,
<span class="doccomment">/// The stealer has successfully stolen some data.</span>
<span class="ident">Data</span>(<span class="ident">T</span>),
}
<span class="comment">// An internal buffer used by the chase-lev deque. This structure is actually</span>
<span class="comment">// implemented as a circular buffer, and is used as the intermediate storage of</span>
<span class="comment">// the data in the deque.</span>
<span class="comment">//</span>
<span class="comment">// This Vec<T> always has a length of 0, the backing buffer is just used by the</span>
<span class="comment">// code below.</span>
<span class="kw">struct</span> <span class="ident">Buffer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">storage</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">Vec</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="ident">log_size</span>: <span class="ident">u32</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">Buffer</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">"Buffer {{ ... }}"</span>)
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Worker</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Pushes data onto the front of this work queue.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">push</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">t</span>: <span class="ident">T</span>) {
<span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">deque</span>.<span class="ident">push</span>(<span class="ident">t</span>) }
}
<span class="doccomment">/// Pops data off the front of the work queue, returning `None` on an empty</span>
<span class="doccomment">/// queue.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">try_pop</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">deque</span>.<span class="ident">try_pop</span>() }
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Stealer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Steals work off the end of the queue (opposite of the worker's end)</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">steal</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Steal</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="self">self</span>.<span class="ident">deque</span>.<span class="ident">steal</span>()
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">Stealer</span><span class="op"><</span><span class="ident">T</span><span class="op">></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="ident">Stealer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Stealer</span> { <span class="ident">deque</span>: <span class="self">self</span>.<span class="ident">deque</span>.<span class="ident">clone</span>() }
}
}
<span class="doccomment">/// Creates a new empty deque</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">deque</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>() <span class="op">-></span> (<span class="ident">Worker</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">Stealer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) {
<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">Deque</span>::<span class="ident">new</span>());
<span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="ident">a</span>.<span class="ident">clone</span>();
(<span class="ident">Worker</span> { <span class="ident">deque</span>: <span class="ident">a</span>, <span class="ident">marker</span>: <span class="ident">PhantomData</span> }, <span class="ident">Stealer</span> { <span class="ident">deque</span>: <span class="ident">b</span> })
}
<span class="comment">// Almost all of this code can be found directly in the paper so I'm not</span>
<span class="comment">// personally going to heavily comment what's going on here.</span>
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Deque</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-></span> <span class="ident">Deque</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">array</span> <span class="op">=</span> <span class="ident">Atomic</span>::<span class="ident">null</span>();
<span class="ident">array</span>.<span class="ident">store</span>(<span class="prelude-val">Some</span>(<span class="ident">Owned</span>::<span class="ident">new</span>(<span class="ident">Buffer</span>::<span class="ident">new</span>(<span class="ident">MIN_BITS</span>))), <span class="ident">SeqCst</span>);
<span class="ident">Deque</span> {
<span class="ident">bottom</span>: <span class="ident">AtomicIsize</span>::<span class="ident">new</span>(<span class="number">0</span>),
<span class="ident">top</span>: <span class="ident">AtomicIsize</span>::<span class="ident">new</span>(<span class="number">0</span>),
<span class="ident">array</span>: <span class="ident">array</span>,
}
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">push</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">data</span>: <span class="ident">T</span>) {
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">epoch</span>::<span class="ident">pin</span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">b</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">bottom</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>);
<span class="kw">let</span> <span class="ident">t</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">top</span>.<span class="ident">load</span>(<span class="ident">Acquire</span>);
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">a</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">array</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>, <span class="kw-2">&</span><span class="ident">guard</span>).<span class="ident">unwrap</span>();
<span class="kw">let</span> <span class="ident">size</span> <span class="op">=</span> <span class="ident">b</span> <span class="op">-</span> <span class="ident">t</span>;
<span class="kw">if</span> <span class="ident">size</span> <span class="op">>=</span> (<span class="ident">a</span>.<span class="ident">size</span>() <span class="kw">as</span> <span class="ident">isize</span>) <span class="op">-</span> <span class="number">1</span> {
<span class="comment">// You won't find this code in the chase-lev deque paper. This is</span>
<span class="comment">// alluded to in a small footnote, however. We always free a buffer</span>
<span class="comment">// when growing in order to prevent leaks.</span>
<span class="ident">a</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">swap_buffer</span>(<span class="ident">a</span>, <span class="ident">a</span>.<span class="ident">resize</span>(<span class="ident">b</span>, <span class="ident">t</span>, <span class="number">1</span>), <span class="kw-2">&</span><span class="ident">guard</span>);
<span class="comment">// reload the bottom counter, since swap_buffer modifies it.</span>
<span class="ident">b</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">bottom</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>);
}
<span class="ident">a</span>.<span class="ident">put</span>(<span class="ident">b</span>, <span class="ident">data</span>);
<span class="ident">fence</span>(<span class="ident">Release</span>);
<span class="self">self</span>.<span class="ident">bottom</span>.<span class="ident">store</span>(<span class="ident">b</span> <span class="op">+</span> <span class="number">1</span>, <span class="ident">Relaxed</span>);
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">try_pop</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">epoch</span>::<span class="ident">pin</span>();
<span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">bottom</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>);
<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">array</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>, <span class="kw-2">&</span><span class="ident">guard</span>).<span class="ident">unwrap</span>();
<span class="self">self</span>.<span class="ident">bottom</span>.<span class="ident">store</span>(<span class="ident">b</span> <span class="op">-</span> <span class="number">1</span>, <span class="ident">Relaxed</span>);
<span class="ident">fence</span>(<span class="ident">SeqCst</span>); <span class="comment">// the store to bottom must occur before loading top.</span>
<span class="kw">let</span> <span class="ident">t</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">top</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>);
<span class="kw">let</span> <span class="ident">size</span> <span class="op">=</span> <span class="ident">b</span> <span class="op">-</span> <span class="ident">t</span>;
<span class="kw">if</span> <span class="ident">size</span> <span class="op"><=</span> <span class="number">0</span> {
<span class="comment">// empty queue. revert the decrement of bottom.</span>
<span class="self">self</span>.<span class="ident">bottom</span>.<span class="ident">store</span>(<span class="ident">b</span>, <span class="ident">Relaxed</span>);
<span class="prelude-val">None</span>
} <span class="kw">else</span> <span class="kw">if</span> <span class="ident">size</span> <span class="op">>=</span> <span class="number">2</span> {
<span class="comment">// non-racy case. return the data</span>
<span class="kw">let</span> <span class="ident">data</span> <span class="op">=</span> <span class="ident">a</span>.<span class="ident">get</span>(<span class="ident">b</span> <span class="op">-</span> <span class="number">1</span>);
<span class="self">self</span>.<span class="ident">maybe_shrink</span>(<span class="ident">b</span> <span class="op">-</span> <span class="number">1</span>, <span class="ident">t</span>, <span class="kw-2">&</span><span class="ident">guard</span>);
<span class="prelude-val">Some</span>(<span class="ident">data</span>)
} <span class="kw">else</span> {
<span class="comment">// racy case. race against steals.</span>
<span class="kw">let</span> <span class="ident">success</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">top</span>.<span class="ident">compare_and_swap</span>(<span class="ident">t</span>, <span class="ident">t</span> <span class="op">+</span> <span class="number">1</span>, <span class="ident">SeqCst</span>) <span class="op">==</span> <span class="ident">t</span>;
<span class="comment">// set the queue to a canonically empty state.</span>
<span class="self">self</span>.<span class="ident">bottom</span>.<span class="ident">store</span>(<span class="ident">b</span>, <span class="ident">Relaxed</span>);
<span class="kw">if</span> <span class="ident">success</span> {
<span class="prelude-val">Some</span>(<span class="ident">a</span>.<span class="ident">get</span>(<span class="ident">t</span>))
} <span class="kw">else</span> {
<span class="prelude-val">None</span>
}
}
}
<span class="kw">fn</span> <span class="ident">steal</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Steal</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">epoch</span>::<span class="ident">pin</span>();
<span class="kw">let</span> <span class="ident">t</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">top</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>);
<span class="ident">fence</span>(<span class="ident">SeqCst</span>); <span class="comment">// top must be loaded before bottom.</span>
<span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">bottom</span>.<span class="ident">load</span>(<span class="ident">Acquire</span>);
<span class="kw">let</span> <span class="ident">size</span> <span class="op">=</span> <span class="ident">b</span> <span class="op">-</span> <span class="ident">t</span>;
<span class="kw">if</span> <span class="ident">size</span> <span class="op"><=</span> <span class="number">0</span> {
<span class="kw">return</span> <span class="ident">Steal</span>::<span class="ident">Empty</span>
}
<span class="kw">unsafe</span> {
<span class="comment">// while the paper uses a "consume" ordering here, the closest thing we have</span>
<span class="comment">// available is Acquire, which is strictly stronger.</span>
<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">array</span>.<span class="ident">load</span>(<span class="ident">Acquire</span>, <span class="kw-2">&</span><span class="ident">guard</span>).<span class="ident">unwrap</span>();
<span class="kw">let</span> <span class="ident">data</span> <span class="op">=</span> <span class="ident">a</span>.<span class="ident">get</span>(<span class="ident">t</span>);
<span class="comment">// we may be racing against other steals and a pop.</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">top</span>.<span class="ident">compare_and_swap</span>(<span class="ident">t</span>, <span class="ident">t</span> <span class="op">+</span> <span class="number">1</span>, <span class="ident">SeqCst</span>) <span class="op">==</span> <span class="ident">t</span> {
<span class="ident">Steal</span>::<span class="ident">Data</span>(<span class="ident">data</span>)
} <span class="kw">else</span> {
<span class="ident">mem</span>::<span class="ident">forget</span>(<span class="ident">data</span>); <span class="comment">// someone else stole this value</span>
<span class="ident">Steal</span>::<span class="ident">Abort</span>
}
}
}
<span class="comment">// potentially shrink the array. This can be called only from the worker.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">maybe_shrink</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">b</span>: <span class="ident">isize</span>, <span class="ident">t</span>: <span class="ident">isize</span>, <span class="ident">guard</span>: <span class="kw-2">&</span><span class="ident">epoch</span>::<span class="ident">Guard</span>) {
<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">array</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>, <span class="ident">guard</span>).<span class="ident">unwrap</span>();
<span class="kw">let</span> <span class="ident">size</span> <span class="op">=</span> <span class="ident">b</span> <span class="op">-</span> <span class="ident">t</span>;
<span class="kw">if</span> <span class="ident">size</span> <span class="op"><</span> (<span class="ident">a</span>.<span class="ident">size</span>() <span class="kw">as</span> <span class="ident">isize</span>) <span class="op">/</span> <span class="ident">K</span> <span class="op">&&</span> <span class="ident">size</span> <span class="op">></span> (<span class="number">1</span> <span class="op"><<</span> <span class="ident">MIN_BITS</span>) {
<span class="self">self</span>.<span class="ident">swap_buffer</span>(<span class="ident">a</span>, <span class="ident">a</span>.<span class="ident">resize</span>(<span class="ident">b</span>, <span class="ident">t</span>, <span class="op">-</span><span class="number">1</span>), <span class="ident">guard</span>);
}
}
<span class="comment">// Helper routine not mentioned in the paper which is used in growing and</span>
<span class="comment">// shrinking buffers to swap in a new buffer into place.</span>
<span class="comment">//</span>
<span class="comment">// As a bit of a recap, stealers can continue using buffers after this</span>
<span class="comment">// method has called 'unlinked' on it. The continued usage is simply a read</span>
<span class="comment">// followed by a forget, but we must make sure that the memory can continue</span>
<span class="comment">// to be read after we flag this buffer for reclamation. All stealers,</span>
<span class="comment">// however, have their own epoch pinned during this time so the buffer will</span>
<span class="comment">// just naturally be free'd once all concurrent stealers have exited.</span>
<span class="comment">//</span>
<span class="comment">// This method may only be called safely from the workers due to the way it modifies</span>
<span class="comment">// the array pointer.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">swap_buffer</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>,
<span class="ident">old</span>: <span class="ident">Shared</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">Buffer</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="ident">buf</span>: <span class="ident">Buffer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
<span class="ident">guard</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">epoch</span>::<span class="ident">Guard</span>)
<span class="op">-></span> <span class="ident">Shared</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">Buffer</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="kw">let</span> <span class="ident">newbuf</span> <span class="op">=</span> <span class="ident">Owned</span>::<span class="ident">new</span>(<span class="ident">buf</span>);
<span class="kw">let</span> <span class="ident">newbuf</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">array</span>.<span class="ident">store_and_ref</span>(<span class="ident">newbuf</span>, <span class="ident">Release</span>, <span class="kw-2">&</span><span class="ident">guard</span>);
<span class="ident">guard</span>.<span class="ident">unlinked</span>(<span class="ident">old</span>);
<span class="ident">newbuf</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">Deque</span><span class="op"><</span><span class="ident">T</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="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">epoch</span>::<span class="ident">pin</span>();
<span class="comment">// Arc enforces that we have truly exclusive access here.</span>
<span class="kw">let</span> <span class="ident">t</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">top</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>);
<span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">bottom</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>);
<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">array</span>.<span class="ident">swap</span>(<span class="prelude-val">None</span>, <span class="ident">Relaxed</span>, <span class="kw-2">&</span><span class="ident">guard</span>).<span class="ident">unwrap</span>();
<span class="comment">// Free whatever is leftover in the dequeue, then free the backing</span>
<span class="comment">// memory itself</span>
<span class="kw">unsafe</span> {
<span class="kw">for</span> <span class="ident">i</span> <span class="kw">in</span> <span class="ident">t</span>..<span class="ident">b</span> {
<span class="ident">drop</span>(<span class="ident">a</span>.<span class="ident">get</span>(<span class="ident">i</span>));
}
<span class="ident">guard</span>.<span class="ident">unlinked</span>(<span class="ident">a</span>);
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Buffer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">log_size</span>: <span class="ident">u32</span>) <span class="op">-></span> <span class="ident">Buffer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Buffer</span> {
<span class="ident">storage</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">Vec</span>::<span class="ident">with_capacity</span>(<span class="number">1</span> <span class="op"><<</span> <span class="ident">log_size</span>)),
<span class="ident">log_size</span>: <span class="ident">log_size</span>,
}
}
<span class="kw">fn</span> <span class="ident">size</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">usize</span> {
<span class="kw">unsafe</span> { (<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">storage</span>.<span class="ident">get</span>()).<span class="ident">capacity</span>() }
}
<span class="kw">fn</span> <span class="ident">mask</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">isize</span> {
<span class="kw">unsafe</span> {
((<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">storage</span>.<span class="ident">get</span>()).<span class="ident">capacity</span>() <span class="op">-</span> <span class="number">1</span>) <span class="kw">as</span> <span class="ident">isize</span>
}
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">elem</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">i</span>: <span class="ident">isize</span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span> {
(<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">storage</span>.<span class="ident">get</span>()).<span class="ident">as_mut_ptr</span>().<span class="ident">offset</span>(<span class="ident">i</span> <span class="op">&</span> <span class="self">self</span>.<span class="ident">mask</span>())
}
<span class="comment">// This does not protect against loading duplicate values of the same cell,</span>
<span class="comment">// nor does this clear out the contents contained within. Hence, this is a</span>
<span class="comment">// very unsafe method which the caller needs to treat specially in case a</span>
<span class="comment">// race is lost.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">get</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">i</span>: <span class="ident">isize</span>) <span class="op">-></span> <span class="ident">T</span> {
<span class="ident">ptr</span>::<span class="ident">read</span>(<span class="self">self</span>.<span class="ident">elem</span>(<span class="ident">i</span>))
}
<span class="comment">// Unsafe because this unsafely overwrites possibly uninitialized or</span>
<span class="comment">// initialized data.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">put</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">i</span>: <span class="ident">isize</span>, <span class="ident">t</span>: <span class="ident">T</span>) {
<span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">elem</span>(<span class="ident">i</span>), <span class="ident">t</span>);
}
<span class="comment">// Again, unsafe because this has incredibly dubious ownership violations.</span>
<span class="comment">// It is assumed that this buffer is immediately dropped.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">resize</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">b</span>: <span class="ident">isize</span>, <span class="ident">t</span>: <span class="ident">isize</span>, <span class="ident">delta</span>: <span class="ident">i32</span>) <span class="op">-></span> <span class="ident">Buffer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">buf</span> <span class="op">=</span> <span class="ident">Buffer</span>::<span class="ident">new</span>(((<span class="self">self</span>.<span class="ident">log_size</span> <span class="kw">as</span> <span class="ident">i32</span>) <span class="op">+</span> <span class="ident">delta</span>) <span class="kw">as</span> <span class="ident">u32</span>);
<span class="kw">for</span> <span class="ident">i</span> <span class="kw">in</span> <span class="ident">t</span>..<span class="ident">b</span> {
<span class="ident">buf</span>.<span class="ident">put</span>(<span class="ident">i</span>, <span class="self">self</span>.<span class="ident">get</span>(<span class="ident">i</span>));
}
<span class="kw">return</span> <span class="ident">buf</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">extern</span> <span class="kw">crate</span> <span class="ident">rand</span>;
<span class="kw">use</span> <span class="kw">super</span>::{<span class="ident">deque</span>, <span class="ident">Worker</span>, <span class="ident">Stealer</span>, <span class="ident">Steal</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">thread</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">sync</span>::<span class="ident">atomic</span>::{<span class="ident">AtomicBool</span>, <span class="ident">ATOMIC_BOOL_INIT</span>,
<span class="ident">AtomicUsize</span>, <span class="ident">ATOMIC_USIZE_INIT</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="ident">SeqCst</span>;
<span class="kw">use</span> <span class="self">self</span>::<span class="ident">rand</span>::<span class="ident">Rng</span>;
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">smoke</span>() {
<span class="kw">let</span> (<span class="ident">w</span>, <span class="ident">s</span>) <span class="op">=</span> <span class="ident">deque</span>();
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">w</span>.<span class="ident">try_pop</span>(), <span class="prelude-val">None</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">s</span>.<span class="ident">steal</span>(), <span class="ident">Steal</span>::<span class="ident">Empty</span>);
<span class="ident">w</span>.<span class="ident">push</span>(<span class="number">1</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">w</span>.<span class="ident">try_pop</span>(), <span class="prelude-val">Some</span>(<span class="number">1</span>));
<span class="ident">w</span>.<span class="ident">push</span>(<span class="number">1</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">s</span>.<span class="ident">steal</span>(), <span class="ident">Steal</span>::<span class="ident">Data</span>(<span class="number">1</span>));
<span class="ident">w</span>.<span class="ident">push</span>(<span class="number">1</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">s</span>.<span class="ident">clone</span>().<span class="ident">steal</span>(), <span class="ident">Steal</span>::<span class="ident">Data</span>(<span class="number">1</span>));
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">stealpush</span>() {
<span class="kw">static</span> <span class="ident">AMT</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="number">100000</span>;
<span class="kw">let</span> (<span class="ident">w</span>, <span class="ident">s</span>) <span class="op">=</span> <span class="ident">deque</span>();
<span class="kw">let</span> <span class="ident">t</span> <span class="op">=</span> <span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span> <span class="op">||</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">left</span> <span class="op">=</span> <span class="ident">AMT</span>;
<span class="kw">while</span> <span class="ident">left</span> <span class="op">></span> <span class="number">0</span> {
<span class="kw">match</span> <span class="ident">s</span>.<span class="ident">steal</span>() {
<span class="ident">Steal</span>::<span class="ident">Data</span>(<span class="ident">i</span>) <span class="op">=></span> {
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">i</span>, <span class="number">1</span>);
<span class="ident">left</span> <span class="op">-=</span> <span class="number">1</span>;
}
<span class="ident">Steal</span>::<span class="ident">Abort</span> <span class="op">|</span> <span class="ident">Steal</span>::<span class="ident">Empty</span> <span class="op">=></span> {}
}
}
});
<span class="kw">for</span> _ <span class="kw">in</span> <span class="number">0</span>..<span class="ident">AMT</span> {
<span class="ident">w</span>.<span class="ident">push</span>(<span class="number">1</span>);
}
<span class="ident">t</span>.<span class="ident">join</span>().<span class="ident">unwrap</span>();
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">stealpush_large</span>() {
<span class="kw">static</span> <span class="ident">AMT</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="number">100000</span>;
<span class="kw">let</span> (<span class="ident">w</span>, <span class="ident">s</span>) <span class="op">=</span> <span class="ident">deque</span>();
<span class="kw">let</span> <span class="ident">t</span> <span class="op">=</span> <span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="kw">move</span> <span class="op">||</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">left</span> <span class="op">=</span> <span class="ident">AMT</span>;
<span class="kw">while</span> <span class="ident">left</span> <span class="op">></span> <span class="number">0</span> {
<span class="kw">match</span> <span class="ident">s</span>.<span class="ident">steal</span>() {
<span class="ident">Steal</span>::<span class="ident">Data</span>((<span class="number">1</span>, <span class="number">10</span>)) <span class="op">=></span> { <span class="ident">left</span> <span class="op">-=</span> <span class="number">1</span>; }
<span class="ident">Steal</span>::<span class="ident">Data</span>(..) <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(),
<span class="ident">Steal</span>::<span class="ident">Abort</span> <span class="op">|</span> <span class="ident">Steal</span>::<span class="ident">Empty</span> <span class="op">=></span> {}
}
}
});
<span class="kw">for</span> _ <span class="kw">in</span> <span class="number">0</span>..<span class="ident">AMT</span> {
<span class="ident">w</span>.<span class="ident">push</span>((<span class="number">1</span>, <span class="number">10</span>));
}
<span class="ident">t</span>.<span class="ident">join</span>().<span class="ident">unwrap</span>();
}
<span class="kw">fn</span> <span class="ident">stampede</span>(<span class="ident">w</span>: <span class="ident">Worker</span><span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="ident">isize</span><span class="op">>></span>,
<span class="ident">s</span>: <span class="ident">Stealer</span><span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="ident">isize</span><span class="op">>></span>,
<span class="ident">nthreads</span>: <span class="ident">isize</span>,
<span class="ident">amt</span>: <span class="ident">usize</span>) {
<span class="kw">for</span> _ <span class="kw">in</span> <span class="number">0</span>..<span class="ident">amt</span> {
<span class="ident">w</span>.<span class="ident">push</span>(<span class="ident">Box</span>::<span class="ident">new</span>(<span class="number">20</span>));
}
<span class="kw">let</span> <span class="ident">remaining</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="ident">amt</span>));
<span class="kw">let</span> <span class="ident">threads</span> <span class="op">=</span> (<span class="number">0</span>..<span class="ident">nthreads</span>).<span class="ident">map</span>(<span class="op">|</span>_<span class="op">|</span> {
<span class="kw">let</span> <span class="ident">remaining</span> <span class="op">=</span> <span class="ident">remaining</span>.<span class="ident">clone</span>();
<span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="ident">s</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="kw">while</span> <span class="ident">remaining</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) <span class="op">></span> <span class="number">0</span> {
<span class="kw">match</span> <span class="ident">s</span>.<span class="ident">steal</span>() {
<span class="ident">Steal</span>::<span class="ident">Data</span>(<span class="ident">val</span>) <span class="op">=></span> {
<span class="kw">if</span> <span class="kw-2">*</span><span class="ident">val</span> <span class="op">==</span> <span class="number">20</span> {
<span class="ident">remaining</span>.<span class="ident">fetch_sub</span>(<span class="number">1</span>, <span class="ident">SeqCst</span>);
} <span class="kw">else</span> {
<span class="macro">panic</span><span class="macro">!</span>()
}
}
<span class="ident">Steal</span>::<span class="ident">Abort</span> <span class="op">|</span> <span class="ident">Steal</span>::<span class="ident">Empty</span> <span class="op">=></span> {}
}
}
})
}).<span class="ident">collect</span>::<span class="op"><</span><span class="ident">Vec</span><span class="op"><</span>_<span class="op">>></span>();
<span class="kw">while</span> <span class="ident">remaining</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) <span class="op">></span> <span class="number">0</span> {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">val</span>) <span class="op">=</span> <span class="ident">w</span>.<span class="ident">try_pop</span>() {
<span class="kw">if</span> <span class="kw-2">*</span><span class="ident">val</span> <span class="op">==</span> <span class="number">20</span> {
<span class="ident">remaining</span>.<span class="ident">fetch_sub</span>(<span class="number">1</span>, <span class="ident">SeqCst</span>);
} <span class="kw">else</span> {
<span class="macro">panic</span><span class="macro">!</span>()
}
}
}
<span class="kw">for</span> <span class="ident">thread</span> <span class="kw">in</span> <span class="ident">threads</span>.<span class="ident">into_iter</span>() {
<span class="ident">thread</span>.<span class="ident">join</span>().<span class="ident">unwrap</span>();
}
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">run_stampede</span>() {
<span class="kw">let</span> (<span class="ident">w</span>, <span class="ident">s</span>) <span class="op">=</span> <span class="ident">deque</span>();
<span class="ident">stampede</span>(<span class="ident">w</span>, <span class="ident">s</span>, <span class="number">8</span>, <span class="number">10000</span>);
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">many_stampede</span>() {
<span class="kw">static</span> <span class="ident">AMT</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">4</span>;
<span class="kw">let</span> <span class="ident">threads</span> <span class="op">=</span> (<span class="number">0</span>..<span class="ident">AMT</span>).<span class="ident">map</span>(<span class="op">|</span>_<span class="op">|</span> {
<span class="kw">let</span> (<span class="ident">w</span>, <span class="ident">s</span>) <span class="op">=</span> <span class="ident">deque</span>();
<span class="ident">thread</span>::<span class="ident">spawn</span>(<span class="op">||</span> {
<span class="ident">stampede</span>(<span class="ident">w</span>, <span class="ident">s</span>, <span class="number">4</span>, <span class="number">10000</span>);
})
}).<span class="ident">collect</span>::<span class="op"><</span><span class="ident">Vec</span><span class="op"><</span>_<span class="op">>></span>();
<span class="kw">for</span> <span class="ident">thread</span> <span class="kw">in</span> <span class="ident">threads</span>.<span class="ident">into_iter</span>() {
<span class="ident">thread</span>.<span class="ident">join</span>().<span class="ident">unwrap</span>();
}
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">stress</span>() {
<span class="kw">static</span> <span class="ident">AMT</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="number">100000</span>;
<span class="kw">static</span> <span class="ident">NTHREADS</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="number">8</span>;
<span class="kw">static</span> <span class="ident">DONE</span>: <span class="ident">AtomicBool</span> <span class="op">=</span> <span class="ident">ATOMIC_BOOL_INIT</span>;
<span class="kw">static</span> <span class="ident">HITS</span>: <span class="ident">AtomicUsize</span> <span class="op">=</span> <span class="ident">ATOMIC_USIZE_INIT</span>;
<span class="kw">let</span> (<span class="ident">w</span>, <span class="ident">s</span>) <span class="op">=</span> <span class="ident">deque</span>();
<span class="kw">let</span> <span class="ident">threads</span> <span class="op">=</span> (<span class="number">0</span>..<span class="ident">NTHREADS</span>).<span class="ident">map</span>(<span class="op">|</span>_<span class="op">|</span> {
<span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="ident">s</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="kw">loop</span> {
<span class="kw">match</span> <span class="ident">s</span>.<span class="ident">steal</span>() {
<span class="ident">Steal</span>::<span class="ident">Data</span>(<span class="number">2</span>) <span class="op">=></span> { <span class="ident">HITS</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">SeqCst</span>); }
<span class="ident">Steal</span>::<span class="ident">Data</span>(..) <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(),
_ <span class="kw">if</span> <span class="ident">DONE</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) <span class="op">=></span> <span class="kw">break</span>,
_ <span class="op">=></span> {}
}
}
})
}).<span class="ident">collect</span>::<span class="op"><</span><span class="ident">Vec</span><span class="op"><</span>_<span class="op">>></span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">rng</span> <span class="op">=</span> <span class="ident">rand</span>::<span class="ident">thread_rng</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">while</span> <span class="ident">expected</span> <span class="op"><</span> <span class="ident">AMT</span> {
<span class="kw">if</span> <span class="ident">rng</span>.<span class="ident">gen_range</span>(<span class="number">0</span>, <span class="number">3</span>) <span class="op">==</span> <span class="number">2</span> {
<span class="kw">match</span> <span class="ident">w</span>.<span class="ident">try_pop</span>() {
<span class="prelude-val">None</span> <span class="op">=></span> {}
<span class="prelude-val">Some</span>(<span class="number">2</span>) <span class="op">=></span> { <span class="ident">HITS</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">SeqCst</span>); },
<span class="prelude-val">Some</span>(_) <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(),
}
} <span class="kw">else</span> {
<span class="ident">expected</span> <span class="op">+=</span> <span class="number">1</span>;
<span class="ident">w</span>.<span class="ident">push</span>(<span class="number">2</span>);
}
}
<span class="kw">while</span> <span class="ident">HITS</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) <span class="op"><</span> <span class="ident">AMT</span> <span class="kw">as</span> <span class="ident">usize</span> {
<span class="kw">match</span> <span class="ident">w</span>.<span class="ident">try_pop</span>() {
<span class="prelude-val">None</span> <span class="op">=></span> {}
<span class="prelude-val">Some</span>(<span class="number">2</span>) <span class="op">=></span> { <span class="ident">HITS</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">SeqCst</span>); },
<span class="prelude-val">Some</span>(_) <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(),
}
}
<span class="ident">DONE</span>.<span class="ident">store</span>(<span class="bool-val">true</span>, <span class="ident">SeqCst</span>);
<span class="kw">for</span> <span class="ident">thread</span> <span class="kw">in</span> <span class="ident">threads</span>.<span class="ident">into_iter</span>() {
<span class="ident">thread</span>.<span class="ident">join</span>().<span class="ident">unwrap</span>();
}
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">HITS</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>), <span class="ident">expected</span> <span class="kw">as</span> <span class="ident">usize</span>);
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">no_starvation</span>() {
<span class="kw">static</span> <span class="ident">AMT</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="number">10000</span>;
<span class="kw">static</span> <span class="ident">NTHREADS</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="number">4</span>;
<span class="kw">static</span> <span class="ident">DONE</span>: <span class="ident">AtomicBool</span> <span class="op">=</span> <span class="ident">ATOMIC_BOOL_INIT</span>;
<span class="kw">let</span> (<span class="ident">w</span>, <span class="ident">s</span>) <span class="op">=</span> <span class="ident">deque</span>();
<span class="kw">let</span> (<span class="ident">threads</span>, <span class="ident">hits</span>): (<span class="ident">Vec</span><span class="op"><</span>_<span class="op">></span>, <span class="ident">Vec</span><span class="op"><</span>_<span class="op">></span>) <span class="op">=</span> (<span class="number">0</span>..<span class="ident">NTHREADS</span>).<span class="ident">map</span>(<span class="op">|</span>_<span class="op">|</span> {
<span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="ident">s</span>.<span class="ident">clone</span>();
<span class="kw">let</span> <span class="ident">ctr</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="number">0</span>));
<span class="kw">let</span> <span class="ident">ctr2</span> <span class="op">=</span> <span class="ident">ctr</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="kw">loop</span> {
<span class="kw">match</span> <span class="ident">s</span>.<span class="ident">steal</span>() {
<span class="ident">Steal</span>::<span class="ident">Data</span>((<span class="number">1</span>, <span class="number">2</span>)) <span class="op">=></span> { <span class="ident">ctr</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">SeqCst</span>); }
<span class="ident">Steal</span>::<span class="ident">Data</span>(..) <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(),
_ <span class="kw">if</span> <span class="ident">DONE</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) <span class="op">=></span> <span class="kw">break</span>,
_ <span class="op">=></span> {}
}
}
}), <span class="ident">ctr2</span>)
}).<span class="ident">unzip</span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">rng</span> <span class="op">=</span> <span class="ident">rand</span>::<span class="ident">thread_rng</span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">myhit</span> <span class="op">=</span> <span class="bool-val">false</span>;
<span class="lifetime">'outer</span>: <span class="kw">loop</span> {
<span class="kw">for</span> _ <span class="kw">in</span> <span class="number">0</span>..<span class="ident">rng</span>.<span class="ident">gen_range</span>(<span class="number">0</span>, <span class="ident">AMT</span>) {
<span class="kw">if</span> <span class="op">!</span><span class="ident">myhit</span> <span class="op">&&</span> <span class="ident">rng</span>.<span class="ident">gen_range</span>(<span class="number">0</span>, <span class="number">3</span>) <span class="op">==</span> <span class="number">2</span> {
<span class="kw">match</span> <span class="ident">w</span>.<span class="ident">try_pop</span>() {
<span class="prelude-val">None</span> <span class="op">=></span> {}
<span class="prelude-val">Some</span>((<span class="number">1</span>, <span class="number">2</span>)) <span class="op">=></span> <span class="ident">myhit</span> <span class="op">=</span> <span class="bool-val">true</span>,
<span class="prelude-val">Some</span>(_) <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(),
}
} <span class="kw">else</span> {
<span class="ident">w</span>.<span class="ident">push</span>((<span class="number">1</span>, <span class="number">2</span>));
}
}
<span class="kw">for</span> <span class="ident">slot</span> <span class="kw">in</span> <span class="ident">hits</span>.<span class="ident">iter</span>() {
<span class="kw">let</span> <span class="ident">amt</span> <span class="op">=</span> <span class="ident">slot</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>);
<span class="kw">if</span> <span class="ident">amt</span> <span class="op">==</span> <span class="number">0</span> { <span class="kw">continue</span> <span class="lifetime">'outer</span>; }
}
<span class="kw">if</span> <span class="ident">myhit</span> {
<span class="kw">break</span>
}
}
<span class="ident">DONE</span>.<span class="ident">store</span>(<span class="bool-val">true</span>, <span class="ident">SeqCst</span>);
<span class="kw">for</span> <span class="ident">thread</span> <span class="kw">in</span> <span class="ident">threads</span>.<span class="ident">into_iter</span>() {
<span class="ident">thread</span>.<span class="ident">join</span>().<span class="ident">unwrap</span>();
}
}
}
</pre>
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