<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source to the Rust file `libstd/sync/mpsc/spsc_queue.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>spsc_queue.rs.html -- source</title><link rel="stylesheet" type="text/css" href="../../../../normalize.css"><link rel="stylesheet" type="text/css" href="../../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../../../dark.css"><link rel="stylesheet" type="text/css" href="../../../../light.css" id="themeStyle"><script src="../../../../storage.js"></script><link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"></head><body class="rustdoc source"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../../../std/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><a id="settings-menu" href="../../../../settings.html"><img src="../../../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><pre class="line-numbers"><span id="1"> 1</span>
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</pre><pre class="rust ">
<span class="comment">// Copyright 2017 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 single-producer single-consumer concurrent queue</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! This module contains the implementation of an SPSC queue which can be used</span>
<span class="doccomment">//! concurrently between two threads. This data structure is safe to use and</span>
<span class="doccomment">//! enforces the semantics that there is one pusher and one popper.</span>
<span class="comment">// http://www.1024cores.net/home/lock-free-algorithms/queues/unbounded-spsc-queue</span>
<span class="kw">use</span> <span class="ident">boxed</span>::<span class="ident">Box</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">ptr</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">cell</span>::<span class="ident">UnsafeCell</span>;
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">atomic</span>::{<span class="ident">AtomicPtr</span>, <span class="ident">AtomicUsize</span>, <span class="ident">Ordering</span>};
<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">cache_aligned</span>::<span class="ident">CacheAligned</span>;
<span class="comment">// Node within the linked list queue of messages to send</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="comment">// FIXME: this could be an uninitialized T if we're careful enough, and</span>
<span class="comment">// that would reduce memory usage (and be a bit faster).</span>
<span class="comment">// is it worth it?</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="comment">// nullable for re-use of nodes</span>
<span class="ident">cached</span>: <span class="ident">bool</span>, <span class="comment">// This node goes into the node cache</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="comment">// next node in the queue</span>
}
<span class="doccomment">/// The single-producer single-consumer queue. This structure is not cloneable,</span>
<span class="doccomment">/// but it can be safely shared in an Arc if it is guaranteed that there</span>
<span class="doccomment">/// is only one popper and one pusher touching the queue at any one point in</span>
<span class="doccomment">/// time.</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="ident">ProducerAddition</span><span class="op">=</span>(), <span class="ident">ConsumerAddition</span><span class="op">=</span>()<span class="op">></span> {
<span class="comment">// consumer fields</span>
<span class="ident">consumer</span>: <span class="ident">CacheAligned</span><span class="op"><</span><span class="ident">Consumer</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">ConsumerAddition</span><span class="op">>></span>,
<span class="comment">// producer fields</span>
<span class="ident">producer</span>: <span class="ident">CacheAligned</span><span class="op"><</span><span class="ident">Producer</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">ProducerAddition</span><span class="op">>></span>,
}
<span class="kw">struct</span> <span class="ident">Consumer</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">Addition</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="comment">// where to pop from</span>
<span class="ident">tail_prev</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="comment">// where to pop from</span>
<span class="ident">cache_bound</span>: <span class="ident">usize</span>, <span class="comment">// maximum cache size</span>
<span class="ident">cached_nodes</span>: <span class="ident">AtomicUsize</span>, <span class="comment">// number of nodes marked as cachable</span>
<span class="ident">addition</span>: <span class="ident">Addition</span>,
}
<span class="kw">struct</span> <span class="ident">Producer</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">Addition</span><span class="op">></span> {
<span class="ident">head</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="comment">// where to push to</span>
<span class="ident">first</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="comment">// where to get new nodes from</span>
<span class="ident">tail_copy</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="comment">// between first/tail</span>
<span class="ident">addition</span>: <span class="ident">Addition</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="ident">P</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span>, <span class="ident">C</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</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="ident">P</span>, <span class="ident">C</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="ident">P</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span>, <span class="ident">C</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</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="ident">P</span>, <span class="ident">C</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">fn</span> <span class="ident">new</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="kw">box</span> <span class="ident">Node</span> {
<span class="ident">value</span>: <span class="prelude-val">None</span>,
<span class="ident">cached</span>: <span class="bool-val">false</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="op"><</span><span class="ident">Node</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="ident">ProducerAddition</span>, <span class="ident">ConsumerAddition</span><span class="op">></span> <span class="ident">Queue</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">ProducerAddition</span>, <span class="ident">ConsumerAddition</span><span class="op">></span> {
<span class="doccomment">/// Creates a new queue. With given additional elements in the producer and</span>
<span class="doccomment">/// consumer portions of the queue.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Due to the performance implications of cache-contention,</span>
<span class="doccomment">/// we wish to keep fields used mainly by the producer on a separate cache</span>
<span class="doccomment">/// line than those used by the consumer.</span>
<span class="doccomment">/// Since cache lines are usually 64 bytes, it is unreasonably expensive to</span>
<span class="doccomment">/// allocate one for small fields, so we allow users to insert additional</span>
<span class="doccomment">/// fields into the cache lines already allocated by this for the producer</span>
<span class="doccomment">/// and consumer.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is unsafe as the type system doesn't enforce a single</span>
<span class="doccomment">/// consumer-producer relationship. It also allows the consumer to `pop`</span>
<span class="doccomment">/// items while there is a `peek` active due to all methods having a</span>
<span class="doccomment">/// non-mutable receiver.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Arguments</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `bound` - This queue implementation is implemented with a linked</span>
<span class="doccomment">/// list, and this means that a push is always a malloc. In</span>
<span class="doccomment">/// order to amortize this cost, an internal cache of nodes is</span>
<span class="doccomment">/// maintained to prevent a malloc from always being</span>
<span class="doccomment">/// necessary. This bound is the limit on the size of the</span>
<span class="doccomment">/// cache (if desired). If the value is 0, then the cache has</span>
<span class="doccomment">/// no bound. Otherwise, the cache will never grow larger than</span>
<span class="doccomment">/// `bound` (although the queue itself could be much larger.</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">with_additions</span>(
<span class="ident">bound</span>: <span class="ident">usize</span>,
<span class="ident">producer_addition</span>: <span class="ident">ProducerAddition</span>,
<span class="ident">consumer_addition</span>: <span class="ident">ConsumerAddition</span>,
) <span class="op">-></span> <span class="self">Self</span> {
<span class="kw">let</span> <span class="ident">n1</span> <span class="op">=</span> <span class="ident">Node</span>::<span class="ident">new</span>();
<span class="kw">let</span> <span class="ident">n2</span> <span class="op">=</span> <span class="ident">Node</span>::<span class="ident">new</span>();
(<span class="kw-2">*</span><span class="ident">n1</span>).<span class="ident">next</span>.<span class="ident">store</span>(<span class="ident">n2</span>, <span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="ident">Queue</span> {
<span class="ident">consumer</span>: <span class="ident">CacheAligned</span>::<span class="ident">new</span>(<span class="ident">Consumer</span> {
<span class="ident">tail</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">n2</span>),
<span class="ident">tail_prev</span>: <span class="ident">AtomicPtr</span>::<span class="ident">new</span>(<span class="ident">n1</span>),
<span class="ident">cache_bound</span>: <span class="ident">bound</span>,
<span class="ident">cached_nodes</span>: <span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="number">0</span>),
<span class="ident">addition</span>: <span class="ident">consumer_addition</span>
}),
<span class="ident">producer</span>: <span class="ident">CacheAligned</span>::<span class="ident">new</span>(<span class="ident">Producer</span> {
<span class="ident">head</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">n2</span>),
<span class="ident">first</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">n1</span>),
<span class="ident">tail_copy</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">n1</span>),
<span class="ident">addition</span>: <span class="ident">producer_addition</span>
}),
}
}
<span class="doccomment">/// Pushes a new value onto this queue. Note that to use this function</span>
<span class="doccomment">/// safely, it must be externally guaranteed that there is only one pusher.</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="comment">// Acquire a node (which either uses a cached one or allocates a new</span>
<span class="comment">// one), and then append this to the 'head' node.</span>
<span class="kw">let</span> <span class="ident">n</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">alloc</span>();
<span class="macro">assert</span><span class="macro">!</span>((<span class="kw-2">*</span><span class="ident">n</span>).<span class="ident">value</span>.<span class="ident">is_none</span>());
(<span class="kw-2">*</span><span class="ident">n</span>).<span class="ident">value</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">t</span>);
(<span class="kw-2">*</span><span class="ident">n</span>).<span class="ident">next</span>.<span class="ident">store</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>(), <span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
(<span class="kw-2">*</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="ident">head</span>.<span class="ident">get</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="kw-2">*</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="ident">head</span>).<span class="ident">get</span>() <span class="op">=</span> <span class="ident">n</span>;
}
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">alloc</span>(<span class="kw-2">&</span><span class="self">self</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="comment">// First try to see if we can consume the 'first' node for our uses.</span>
<span class="kw">if</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="ident">first</span>.<span class="ident">get</span>() <span class="op">!=</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="ident">tail_copy</span>.<span class="ident">get</span>() {
<span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="ident">first</span>.<span class="ident">get</span>();
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="number">0</span>.<span class="ident">first</span>.<span class="ident">get</span>() <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">ret</span>).<span class="ident">next</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="kw">return</span> <span class="ident">ret</span>;
}
<span class="comment">// If the above fails, then update our copy of the tail and try</span>
<span class="comment">// again.</span>
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="number">0</span>.<span class="ident">tail_copy</span>.<span class="ident">get</span>() <span class="op">=</span>
<span class="self">self</span>.<span class="ident">consumer</span>.<span class="ident">tail_prev</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Acquire</span>);
<span class="kw">if</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="ident">first</span>.<span class="ident">get</span>() <span class="op">!=</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="ident">tail_copy</span>.<span class="ident">get</span>() {
<span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="ident">first</span>.<span class="ident">get</span>();
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="number">0</span>.<span class="ident">first</span>.<span class="ident">get</span>() <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">ret</span>).<span class="ident">next</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="kw">return</span> <span class="ident">ret</span>;
}
<span class="comment">// If all of that fails, then we have to allocate a new node</span>
<span class="comment">// (there's nothing in the node cache).</span>
<span class="ident">Node</span>::<span class="ident">new</span>()
}
<span class="doccomment">/// Attempts to pop a value from this queue. Remember that to use this type</span>
<span class="doccomment">/// safely you must ensure that there is only one popper at a time.</span>
<span class="kw">pub</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="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">unsafe</span> {
<span class="comment">// The `tail` node is not actually a used node, but rather a</span>
<span class="comment">// sentinel from where we should start popping from. Hence, look at</span>
<span class="comment">// tail's next field and see if we can use it. If we do a pop, then</span>
<span class="comment">// the current tail node is a candidate for going into the cache.</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">consumer</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="ident">next</span>.<span class="ident">is_null</span>() { <span class="kw">return</span> <span class="prelude-val">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="kw-2">*</span><span class="self">self</span>.<span class="ident">consumer</span>.<span class="number">0</span>.<span class="ident">tail</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">next</span>;
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">consumer</span>.<span class="ident">cache_bound</span> <span class="op">==</span> <span class="number">0</span> {
<span class="self">self</span>.<span class="ident">consumer</span>.<span class="ident">tail_prev</span>.<span class="ident">store</span>(<span class="ident">tail</span>, <span class="ident">Ordering</span>::<span class="ident">Release</span>);
} <span class="kw">else</span> {
<span class="kw">let</span> <span class="ident">cached_nodes</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">consumer</span>.<span class="ident">cached_nodes</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="kw">if</span> <span class="ident">cached_nodes</span> <span class="op"><</span> <span class="self">self</span>.<span class="ident">consumer</span>.<span class="ident">cache_bound</span> <span class="op">&&</span> <span class="op">!</span>(<span class="kw-2">*</span><span class="ident">tail</span>).<span class="ident">cached</span> {
<span class="self">self</span>.<span class="ident">consumer</span>.<span class="ident">cached_nodes</span>.<span class="ident">store</span>(<span class="ident">cached_nodes</span>, <span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
(<span class="kw-2">*</span><span class="ident">tail</span>).<span class="ident">cached</span> <span class="op">=</span> <span class="bool-val">true</span>;
}
<span class="kw">if</span> (<span class="kw-2">*</span><span class="ident">tail</span>).<span class="ident">cached</span> {
<span class="self">self</span>.<span class="ident">consumer</span>.<span class="ident">tail_prev</span>.<span class="ident">store</span>(<span class="ident">tail</span>, <span class="ident">Ordering</span>::<span class="ident">Release</span>);
} <span class="kw">else</span> {
(<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">consumer</span>.<span class="ident">tail_prev</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>))
.<span class="ident">next</span>.<span class="ident">store</span>(<span class="ident">next</span>, <span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
<span class="comment">// We have successfully erased all references to 'tail', so</span>
<span class="comment">// now we can safely drop it.</span>
<span class="kw">let</span> <span class="kw">_</span>: <span class="ident">Box</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="op">=</span> <span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">tail</span>);
}
}
<span class="ident">ret</span>
}
}
<span class="doccomment">/// Attempts to peek at the head of the queue, returning `None` if the queue</span>
<span class="doccomment">/// has no data currently</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Warning</span>
<span class="doccomment">/// The reference returned is invalid if it is not used before the consumer</span>
<span class="doccomment">/// pops the value off the queue. If the producer then pushes another value</span>
<span class="doccomment">/// onto the queue, it will overwrite the value pointed to by the reference.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">peek</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="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span><span class="op">></span> {
<span class="comment">// This is essentially the same as above with all the popping bits</span>
<span class="comment">// stripped out.</span>
<span class="kw">unsafe</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">consumer</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="ident">next</span>.<span class="ident">is_null</span>() { <span class="prelude-val">None</span> } <span class="kw">else</span> { (<span class="kw-2">*</span><span class="ident">next</span>).<span class="ident">value</span>.<span class="ident">as_mut</span>() }
}
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">producer_addition</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">ProducerAddition</span> {
<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">producer</span>.<span class="ident">addition</span>
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">consumer_addition</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">ConsumerAddition</span> {
<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">consumer</span>.<span class="ident">addition</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">ProducerAddition</span>, <span class="ident">ConsumerAddition</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="ident">ProducerAddition</span>, <span class="ident">ConsumerAddition</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">producer</span>.<span class="ident">first</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="kw">let</span> <span class="ident">_n</span>: <span class="ident">Box</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="op">=</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>;
}
}
}
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">all</span>(<span class="ident">test</span>, <span class="ident">not</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">"emscripten"</span>)))]</span>
<span class="kw">mod</span> <span class="ident">tests</span> {
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">Arc</span>;
<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">Queue</span>;
<span class="kw">use</span> <span class="ident">thread</span>;
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">mpsc</span>::<span class="ident">channel</span>;
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">smoke</span>() {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">queue</span> <span class="op">=</span> <span class="ident">Queue</span>::<span class="ident">with_additions</span>(<span class="number">0</span>, (), ());
<span class="ident">queue</span>.<span class="ident">push</span>(<span class="number">1</span>);
<span class="ident">queue</span>.<span class="ident">push</span>(<span class="number">2</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">queue</span>.<span class="ident">pop</span>(), <span class="prelude-val">Some</span>(<span class="number">1</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">queue</span>.<span class="ident">pop</span>(), <span class="prelude-val">Some</span>(<span class="number">2</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">queue</span>.<span class="ident">pop</span>(), <span class="prelude-val">None</span>);
<span class="ident">queue</span>.<span class="ident">push</span>(<span class="number">3</span>);
<span class="ident">queue</span>.<span class="ident">push</span>(<span class="number">4</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">queue</span>.<span class="ident">pop</span>(), <span class="prelude-val">Some</span>(<span class="number">3</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">queue</span>.<span class="ident">pop</span>(), <span class="prelude-val">Some</span>(<span class="number">4</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">queue</span>.<span class="ident">pop</span>(), <span class="prelude-val">None</span>);
}
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">peek</span>() {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">queue</span> <span class="op">=</span> <span class="ident">Queue</span>::<span class="ident">with_additions</span>(<span class="number">0</span>, (), ());
<span class="ident">queue</span>.<span class="ident">push</span>(<span class="macro">vec</span><span class="macro">!</span>[<span class="number">1</span>]);
<span class="comment">// Ensure the borrowchecker works</span>
<span class="kw">match</span> <span class="ident">queue</span>.<span class="ident">peek</span>() {
<span class="prelude-val">Some</span>(<span class="ident">vec</span>) <span class="op">=></span> {
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">vec</span>, <span class="kw-2">&</span>[<span class="number">1</span>]);
},
<span class="prelude-val">None</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>()
}
<span class="kw">match</span> <span class="ident">queue</span>.<span class="ident">pop</span>() {
<span class="prelude-val">Some</span>(<span class="ident">vec</span>) <span class="op">=></span> {
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">vec</span>, <span class="kw-2">&</span>[<span class="number">1</span>]);
},
<span class="prelude-val">None</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>()
}
}
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">drop_full</span>() {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">q</span>: <span class="ident">Queue</span><span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="kw">_</span><span class="op">>></span> <span class="op">=</span> <span class="ident">Queue</span>::<span class="ident">with_additions</span>(<span class="number">0</span>, (), ());
<span class="ident">q</span>.<span class="ident">push</span>(<span class="kw">box</span> <span class="number">1</span>);
<span class="ident">q</span>.<span class="ident">push</span>(<span class="kw">box</span> <span class="number">2</span>);
}
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">smoke_bound</span>() {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">q</span> <span class="op">=</span> <span class="ident">Queue</span>::<span class="ident">with_additions</span>(<span class="number">0</span>, (), ());
<span class="ident">q</span>.<span class="ident">push</span>(<span class="number">1</span>);
<span class="ident">q</span>.<span class="ident">push</span>(<span class="number">2</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">q</span>.<span class="ident">pop</span>(), <span class="prelude-val">Some</span>(<span class="number">1</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">q</span>.<span class="ident">pop</span>(), <span class="prelude-val">Some</span>(<span class="number">2</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">q</span>.<span class="ident">pop</span>(), <span class="prelude-val">None</span>);
<span class="ident">q</span>.<span class="ident">push</span>(<span class="number">3</span>);
<span class="ident">q</span>.<span class="ident">push</span>(<span class="number">4</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">q</span>.<span class="ident">pop</span>(), <span class="prelude-val">Some</span>(<span class="number">3</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">q</span>.<span class="ident">pop</span>(), <span class="prelude-val">Some</span>(<span class="number">4</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">q</span>.<span class="ident">pop</span>(), <span class="prelude-val">None</span>);
}
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">stress</span>() {
<span class="kw">unsafe</span> {
<span class="ident">stress_bound</span>(<span class="number">0</span>);
<span class="ident">stress_bound</span>(<span class="number">1</span>);
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">stress_bound</span>(<span class="ident">bound</span>: <span class="ident">usize</span>) {
<span class="kw">let</span> <span class="ident">q</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">Queue</span>::<span class="ident">with_additions</span>(<span class="ident">bound</span>, (), ()));
<span class="kw">let</span> (<span class="ident">tx</span>, <span class="ident">rx</span>) <span class="op">=</span> <span class="ident">channel</span>();
<span class="kw">let</span> <span class="ident">q2</span> <span class="op">=</span> <span class="ident">q</span>.<span class="ident">clone</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">for</span> <span class="kw">_</span> <span class="kw">in</span> <span class="number">0</span>..<span class="number">100000</span> {
<span class="kw">loop</span> {
<span class="kw">match</span> <span class="ident">q2</span>.<span class="ident">pop</span>() {
<span class="prelude-val">Some</span>(<span class="number">1</span>) <span class="op">=></span> <span class="kw">break</span>,
<span class="prelude-val">Some</span>(<span class="kw">_</span>) <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(),
<span class="prelude-val">None</span> <span class="op">=></span> {}
}
}
}
<span class="ident">tx</span>.<span class="ident">send</span>(()).<span class="ident">unwrap</span>();
});
<span class="kw">for</span> <span class="kw">_</span> <span class="kw">in</span> <span class="number">0</span>..<span class="number">100000</span> {
<span class="ident">q</span>.<span class="ident">push</span>(<span class="number">1</span>);
}
<span class="ident">rx</span>.<span class="ident">recv</span>().<span class="ident">unwrap</span>();
}
}
}
</pre>
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