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</pre><pre class="rust ">
<span class="comment">/* Copyright (c) 2010-2011 Dmitry Vyukov. All rights reserved.
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY DMITRY VYUKOV "AS IS" AND ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
* SHALL DMITRY VYUKOV OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
* OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
* ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* The views and conclusions contained in the software and documentation are
* those of the authors and should not be interpreted as representing official
* policies, either expressed or implied, of Dmitry Vyukov.
*/</span>
<span class="doccomment">//! A mostly lock-free multi-producer, single consumer queue.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! This module contains an implementation of a concurrent MPSC queue. This</span>
<span class="doccomment">//! queue can be used to share data between threads, and is also used as the</span>
<span class="doccomment">//! building block of channels in rust.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Note that the current implementation of this queue has a caveat of the `pop`</span>
<span class="doccomment">//! method, and see the method for more information about it. Due to this</span>
<span class="doccomment">//! caveat, this queue may not be appropriate for all use-cases.</span>
<span class="comment">// http://www.1024cores.net/home/lock-free-algorithms</span>
<span class="comment">// /queues/non-intrusive-mpsc-node-based-queue</span>
<span class="comment">// NOTE: this implementation is lifted from the standard library and only</span>
<span class="comment">// slightly modified</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="self">self</span>::<span class="ident">PopResult</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">prelude</span>::<span class="ident">v1</span>::<span class="kw-2">*</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">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">AtomicPtr</span>, <span class="ident">Ordering</span>};
<span class="doccomment">/// A result of the `pop` function.</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">PopResult</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Some data has been popped</span>
<span class="ident">Data</span>(<span class="ident">T</span>),
<span class="doccomment">/// The queue is empty</span>
<span class="ident">Empty</span>,
<span class="doccomment">/// The queue is in an inconsistent state. Popping data should succeed, but</span>
<span class="doccomment">/// some pushers have yet to make enough progress in order allow a pop to</span>
<span class="doccomment">/// succeed. It is recommended that a pop() occur "in the near future" in</span>
<span class="doccomment">/// order to see if the sender has made progress or not</span>
<span class="ident">Inconsistent</span>,
}
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">struct</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">next</span>: <span class="ident">AtomicPtr</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="ident">value</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
}
<span class="doccomment">/// The multi-producer single-consumer structure. This is not cloneable, but it</span>
<span class="doccomment">/// may be safely shared so long as it is guaranteed that there is only one</span>
<span class="doccomment">/// popper at a time (many pushers are allowed).</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">Queue</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">head</span>: <span class="ident">AtomicPtr</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="ident">tail</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Node</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">Send</span> <span class="kw">for</span> <span class="ident">Queue</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">Queue</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { }
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">v</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Box</span>::<span class="ident">into_raw</span>(<span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">Node</span> {
<span class="ident">next</span>: <span class="ident">AtomicPtr</span>::<span class="ident">new</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>()),
<span class="ident">value</span>: <span class="ident">v</span>,
}))
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Queue</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Creates a new queue that is safe to share among multiple producers and</span>
<span class="doccomment">/// one consumer.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-></span> <span class="ident">Queue</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">stub</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">Node</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>) };
<span class="ident">Queue</span> {
<span class="ident">head</span>: <span class="ident">AtomicPtr</span>::<span class="ident">new</span>(<span class="ident">stub</span>),
<span class="ident">tail</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">stub</span>),
}
}
<span class="doccomment">/// Pushes a new value onto this 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="kw">let</span> <span class="ident">n</span> <span class="op">=</span> <span class="ident">Node</span>::<span class="ident">new</span>(<span class="prelude-val">Some</span>(<span class="ident">t</span>));
<span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">head</span>.<span class="ident">swap</span>(<span class="ident">n</span>, <span class="ident">Ordering</span>::<span class="ident">AcqRel</span>);
(<span class="kw-2">*</span><span class="ident">prev</span>).<span class="ident">next</span>.<span class="ident">store</span>(<span class="ident">n</span>, <span class="ident">Ordering</span>::<span class="ident">Release</span>);
}
}
<span class="doccomment">/// Pops some data from this queue.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that the current implementation means that this function cannot</span>
<span class="doccomment">/// return `Option<T>`. It is possible for this queue to be in an</span>
<span class="doccomment">/// inconsistent state where many pushes have succeeded and completely</span>
<span class="doccomment">/// finished, but pops cannot return `Some(t)`. This inconsistent state</span>
<span class="doccomment">/// happens when a pusher is pre-empted at an inopportune moment.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This inconsistent state means that this queue does indeed have data, but</span>
<span class="doccomment">/// it does not currently have access to it at this time.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because only one thread can call it at a time.</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">pop</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">PopResult</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">tail</span> <span class="op">=</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">tail</span>.<span class="ident">get</span>();
<span class="kw">let</span> <span class="ident">next</span> <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">tail</span>).<span class="ident">next</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Acquire</span>);
<span class="kw">if</span> <span class="op">!</span><span class="ident">next</span>.<span class="ident">is_null</span>() {
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">tail</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">next</span>;
<span class="macro">assert</span><span class="macro">!</span>((<span class="kw-2">*</span><span class="ident">tail</span>).<span class="ident">value</span>.<span class="ident">is_none</span>());
<span class="macro">assert</span><span class="macro">!</span>((<span class="kw-2">*</span><span class="ident">next</span>).<span class="ident">value</span>.<span class="ident">is_some</span>());
<span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">next</span>).<span class="ident">value</span>.<span class="ident">take</span>().<span class="ident">unwrap</span>();
<span class="ident">drop</span>(<span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">tail</span>));
<span class="kw">return</span> <span class="ident">Data</span>(<span class="ident">ret</span>);
}
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">head</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Acquire</span>) <span class="op">==</span> <span class="ident">tail</span> {<span class="ident">Empty</span>} <span class="kw">else</span> {<span class="ident">Inconsistent</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">Queue</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">unsafe</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cur</span> <span class="op">=</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">tail</span>.<span class="ident">get</span>();
<span class="kw">while</span> <span class="op">!</span><span class="ident">cur</span>.<span class="ident">is_null</span>() {
<span class="kw">let</span> <span class="ident">next</span> <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">cur</span>).<span class="ident">next</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="ident">drop</span>(<span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">cur</span>));
<span class="ident">cur</span> <span class="op">=</span> <span class="ident">next</span>;
}
}
}
}
</pre>
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