<!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/shared.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>shared.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 2014 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">/// Shared channels</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is the flavor of channels which are not necessarily optimized for any</span>
<span class="doccomment">/// particular use case, but are the most general in how they are used. Shared</span>
<span class="doccomment">/// channels are cloneable allowing for multiple senders.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// High level implementation details can be found in the comment of the parent</span>
<span class="doccomment">/// module. You'll also note that the implementation of the shared and stream</span>
<span class="doccomment">/// channels are quite similar, and this is no coincidence!</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="self">self</span>::<span class="ident">Failure</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">cmp</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">intrinsics</span>::<span class="ident">abort</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">isize</span>;
<span class="kw">use</span> <span class="ident">cell</span>::<span class="ident">UnsafeCell</span>;
<span class="kw">use</span> <span class="ident">ptr</span>;
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">atomic</span>::{<span class="ident">AtomicUsize</span>, <span class="ident">AtomicIsize</span>, <span class="ident">AtomicBool</span>, <span class="ident">Ordering</span>};
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">mpsc</span>::<span class="ident">blocking</span>::{<span class="self">self</span>, <span class="ident">SignalToken</span>};
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">mpsc</span>::<span class="ident">mpsc_queue</span> <span class="kw">as</span> <span class="ident">mpsc</span>;
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">mpsc</span>::<span class="ident">select</span>::<span class="ident">StartResult</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">mpsc</span>::<span class="ident">select</span>::<span class="ident">StartResult</span>;
<span class="kw">use</span> <span class="ident">sync</span>::{<span class="ident">Mutex</span>, <span class="ident">MutexGuard</span>};
<span class="kw">use</span> <span class="ident">thread</span>;
<span class="kw">use</span> <span class="ident">time</span>::<span class="ident">Instant</span>;
<span class="kw">const</span> <span class="ident">DISCONNECTED</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="ident">isize</span>::<span class="ident">MIN</span>;
<span class="kw">const</span> <span class="ident">FUDGE</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="number">1024</span>;
<span class="kw">const</span> <span class="ident">MAX_REFCOUNT</span>: <span class="ident">usize</span> <span class="op">=</span> (<span class="ident">isize</span>::<span class="ident">MAX</span>) <span class="kw">as</span> <span class="ident">usize</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">const</span> <span class="ident">MAX_STEALS</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="number">5</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">test</span>))]</span>
<span class="kw">const</span> <span class="ident">MAX_STEALS</span>: <span class="ident">isize</span> <span class="op">=</span> <span class="number">1</span> <span class="op"><<</span> <span class="number">20</span>;
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Packet</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">queue</span>: <span class="ident">mpsc</span>::<span class="ident">Queue</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
<span class="ident">cnt</span>: <span class="ident">AtomicIsize</span>, <span class="comment">// How many items are on this channel</span>
<span class="ident">steals</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">isize</span><span class="op">></span>, <span class="comment">// How many times has a port received without blocking?</span>
<span class="ident">to_wake</span>: <span class="ident">AtomicUsize</span>, <span class="comment">// SignalToken for wake up</span>
<span class="comment">// The number of channels which are currently using this packet.</span>
<span class="ident">channels</span>: <span class="ident">AtomicUsize</span>,
<span class="comment">// See the discussion in Port::drop and the channel send methods for what</span>
<span class="comment">// these are used for</span>
<span class="ident">port_dropped</span>: <span class="ident">AtomicBool</span>,
<span class="ident">sender_drain</span>: <span class="ident">AtomicIsize</span>,
<span class="comment">// this lock protects various portions of this implementation during</span>
<span class="comment">// select()</span>
<span class="ident">select_lock</span>: <span class="ident">Mutex</span><span class="op"><</span>()<span class="op">></span>,
}
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">Failure</span> {
<span class="ident">Empty</span>,
<span class="ident">Disconnected</span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Packet</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="comment">// Creation of a packet *must* be followed by a call to postinit_lock</span>
<span class="comment">// and later by inherit_blocker</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-></span> <span class="ident">Packet</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Packet</span> {
<span class="ident">queue</span>: <span class="ident">mpsc</span>::<span class="ident">Queue</span>::<span class="ident">new</span>(),
<span class="ident">cnt</span>: <span class="ident">AtomicIsize</span>::<span class="ident">new</span>(<span class="number">0</span>),
<span class="ident">steals</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="number">0</span>),
<span class="ident">to_wake</span>: <span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="number">0</span>),
<span class="ident">channels</span>: <span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="number">2</span>),
<span class="ident">port_dropped</span>: <span class="ident">AtomicBool</span>::<span class="ident">new</span>(<span class="bool-val">false</span>),
<span class="ident">sender_drain</span>: <span class="ident">AtomicIsize</span>::<span class="ident">new</span>(<span class="number">0</span>),
<span class="ident">select_lock</span>: <span class="ident">Mutex</span>::<span class="ident">new</span>(()),
}
}
<span class="comment">// This function should be used after newly created Packet</span>
<span class="comment">// was wrapped with an Arc</span>
<span class="comment">// In other case mutex data will be duplicated while cloning</span>
<span class="comment">// and that could cause problems on platforms where it is</span>
<span class="comment">// represented by opaque data structure</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">postinit_lock</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">MutexGuard</span><span class="op"><</span>()<span class="op">></span> {
<span class="self">self</span>.<span class="ident">select_lock</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>()
}
<span class="comment">// This function is used at the creation of a shared packet to inherit a</span>
<span class="comment">// previously blocked thread. This is done to prevent spurious wakeups of</span>
<span class="comment">// threads in select().</span>
<span class="comment">//</span>
<span class="comment">// This can only be called at channel-creation time</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">inherit_blocker</span>(<span class="kw-2">&</span><span class="self">self</span>,
<span class="ident">token</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">SignalToken</span><span class="op">></span>,
<span class="ident">guard</span>: <span class="ident">MutexGuard</span><span class="op"><</span>()<span class="op">></span>) {
<span class="ident">token</span>.<span class="ident">map</span>(<span class="op">|</span><span class="ident">token</span><span class="op">|</span> {
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>), <span class="number">0</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">to_wake</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>), <span class="number">0</span>);
<span class="self">self</span>.<span class="ident">to_wake</span>.<span class="ident">store</span>(<span class="kw">unsafe</span> { <span class="ident">token</span>.<span class="ident">cast_to_usize</span>() }, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">store</span>(<span class="op">-</span><span class="number">1</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="comment">// This store is a little sketchy. What's happening here is that</span>
<span class="comment">// we're transferring a blocker from a oneshot or stream channel to</span>
<span class="comment">// this shared channel. In doing so, we never spuriously wake them</span>
<span class="comment">// up and rather only wake them up at the appropriate time. This</span>
<span class="comment">// implementation of shared channels assumes that any blocking</span>
<span class="comment">// recv() will undo the increment of steals performed in try_recv()</span>
<span class="comment">// once the recv is complete. This thread that we're inheriting,</span>
<span class="comment">// however, is not in the middle of recv. Hence, the first time we</span>
<span class="comment">// wake them up, they're going to wake up from their old port, move</span>
<span class="comment">// on to the upgraded port, and then call the block recv() function.</span>
<span class="comment">//</span>
<span class="comment">// When calling this function, they'll find there's data immediately</span>
<span class="comment">// available, counting it as a steal. This in fact wasn't a steal</span>
<span class="comment">// because we appropriately blocked them waiting for data.</span>
<span class="comment">//</span>
<span class="comment">// To offset this bad increment, we initially set the steal count to</span>
<span class="comment">// -1. You'll find some special code in abort_selection() as well to</span>
<span class="comment">// ensure that this -1 steal count doesn't escape too far.</span>
<span class="kw">unsafe</span> { <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="op">-</span><span class="number">1</span>; }
});
<span class="comment">// When the shared packet is constructed, we grabbed this lock. The</span>
<span class="comment">// purpose of this lock is to ensure that abort_selection() doesn't</span>
<span class="comment">// interfere with this method. After we unlock this lock, we're</span>
<span class="comment">// signifying that we're done modifying self.cnt and self.to_wake and</span>
<span class="comment">// the port is ready for the world to continue using it.</span>
<span class="ident">drop</span>(<span class="ident">guard</span>);
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">send</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">t</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">T</span><span class="op">></span> {
<span class="comment">// See Port::drop for what's going on</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">port_dropped</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) { <span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">t</span>) }
<span class="comment">// Note that the multiple sender case is a little trickier</span>
<span class="comment">// semantically than the single sender case. The logic for</span>
<span class="comment">// incrementing is "add and if disconnected store disconnected".</span>
<span class="comment">// This could end up leading some senders to believe that there</span>
<span class="comment">// wasn't a disconnect if in fact there was a disconnect. This means</span>
<span class="comment">// that while one thread is attempting to re-store the disconnected</span>
<span class="comment">// states, other threads could walk through merrily incrementing</span>
<span class="comment">// this very-negative disconnected count. To prevent senders from</span>
<span class="comment">// spuriously attempting to send when the channels is actually</span>
<span class="comment">// disconnected, the count has a ranged check here.</span>
<span class="comment">//</span>
<span class="comment">// This is also done for another reason. Remember that the return</span>
<span class="comment">// value of this function is:</span>
<span class="comment">//</span>
<span class="comment">// `true` == the data *may* be received, this essentially has no</span>
<span class="comment">// meaning</span>
<span class="comment">// `false` == the data will *never* be received, this has a lot of</span>
<span class="comment">// meaning</span>
<span class="comment">//</span>
<span class="comment">// In the SPSC case, we have a check of 'queue.is_empty()' to see</span>
<span class="comment">// whether the data was actually received, but this same condition</span>
<span class="comment">// means nothing in a multi-producer context. As a result, this</span>
<span class="comment">// preflight check serves as the definitive "this will never be</span>
<span class="comment">// received". Once we get beyond this check, we have permanently</span>
<span class="comment">// entered the realm of "this may be received"</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op"><</span> <span class="ident">DISCONNECTED</span> <span class="op">+</span> <span class="ident">FUDGE</span> {
<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">t</span>)
}
<span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">push</span>(<span class="ident">t</span>);
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="op">-</span><span class="number">1</span> <span class="op">=></span> {
<span class="self">self</span>.<span class="ident">take_to_wake</span>().<span class="ident">signal</span>();
}
<span class="comment">// In this case, we have possibly failed to send our data, and</span>
<span class="comment">// we need to consider re-popping the data in order to fully</span>
<span class="comment">// destroy it. We must arbitrate among the multiple senders,</span>
<span class="comment">// however, because the queues that we're using are</span>
<span class="comment">// single-consumer queues. In order to do this, all exiting</span>
<span class="comment">// pushers will use an atomic count in order to count those</span>
<span class="comment">// flowing through. Pushers who see 0 are required to drain as</span>
<span class="comment">// much as possible, and then can only exit when they are the</span>
<span class="comment">// only pusher (otherwise they must try again).</span>
<span class="ident">n</span> <span class="kw">if</span> <span class="ident">n</span> <span class="op"><</span> <span class="ident">DISCONNECTED</span> <span class="op">+</span> <span class="ident">FUDGE</span> <span class="op">=></span> {
<span class="comment">// see the comment in 'try' for a shared channel for why this</span>
<span class="comment">// window of "not disconnected" is ok.</span>
<span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">store</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">sender_drain</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op">==</span> <span class="number">0</span> {
<span class="kw">loop</span> {
<span class="comment">// drain the queue, for info on the thread yield see the</span>
<span class="comment">// discussion in try_recv</span>
<span class="kw">loop</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">pop</span>() {
<span class="ident">mpsc</span>::<span class="ident">Data</span>(..) <span class="op">=></span> {}
<span class="ident">mpsc</span>::<span class="ident">Empty</span> <span class="op">=></span> <span class="kw">break</span>,
<span class="ident">mpsc</span>::<span class="ident">Inconsistent</span> <span class="op">=></span> <span class="ident">thread</span>::<span class="ident">yield_now</span>(),
}
}
<span class="comment">// maybe we're done, if we're not the last ones</span>
<span class="comment">// here, then we need to go try again.</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">sender_drain</span>.<span class="ident">fetch_sub</span>(<span class="number">1</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op">==</span> <span class="number">1</span> {
<span class="kw">break</span>
}
}
<span class="comment">// At this point, there may still be data on the queue,</span>
<span class="comment">// but only if the count hasn't been incremented and</span>
<span class="comment">// some other sender hasn't finished pushing data just</span>
<span class="comment">// yet. That sender in question will drain its own data.</span>
}
}
<span class="comment">// Can't make any assumptions about this case like in the SPSC case.</span>
<span class="kw">_</span> <span class="op">=></span> {}
}
<span class="prelude-val">Ok</span>(())
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">recv</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">deadline</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Instant</span><span class="op">></span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">Failure</span><span class="op">></span> {
<span class="comment">// This code is essentially the exact same as that found in the stream</span>
<span class="comment">// case (see stream.rs)</span>
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">try_recv</span>() {
<span class="prelude-val">Err</span>(<span class="ident">Empty</span>) <span class="op">=></span> {}
<span class="ident">data</span> <span class="op">=></span> <span class="kw">return</span> <span class="ident">data</span>,
}
<span class="kw">let</span> (<span class="ident">wait_token</span>, <span class="ident">signal_token</span>) <span class="op">=</span> <span class="ident">blocking</span>::<span class="ident">tokens</span>();
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">decrement</span>(<span class="ident">signal_token</span>) <span class="op">==</span> <span class="ident">Installed</span> {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">deadline</span>) <span class="op">=</span> <span class="ident">deadline</span> {
<span class="kw">let</span> <span class="ident">timed_out</span> <span class="op">=</span> <span class="op">!</span><span class="ident">wait_token</span>.<span class="ident">wait_max_until</span>(<span class="ident">deadline</span>);
<span class="kw">if</span> <span class="ident">timed_out</span> {
<span class="self">self</span>.<span class="ident">abort_selection</span>(<span class="bool-val">false</span>);
}
} <span class="kw">else</span> {
<span class="ident">wait_token</span>.<span class="ident">wait</span>();
}
}
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">try_recv</span>() {
<span class="ident">data</span> @ <span class="prelude-val">Ok</span>(..) <span class="op">=></span> <span class="kw">unsafe</span> { <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>() <span class="op">-=</span> <span class="number">1</span>; <span class="ident">data</span> },
<span class="ident">data</span> <span class="op">=></span> <span class="ident">data</span>,
}
}
<span class="comment">// Essentially the exact same thing as the stream decrement function.</span>
<span class="comment">// Returns true if blocking should proceed.</span>
<span class="kw">fn</span> <span class="ident">decrement</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">token</span>: <span class="ident">SignalToken</span>) <span class="op">-></span> <span class="ident">StartResult</span> {
<span class="kw">unsafe</span> {
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">to_wake</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>), <span class="number">0</span>);
<span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="ident">token</span>.<span class="ident">cast_to_usize</span>();
<span class="self">self</span>.<span class="ident">to_wake</span>.<span class="ident">store</span>(<span class="ident">ptr</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="kw">let</span> <span class="ident">steals</span> <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>(), <span class="number">0</span>);
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">fetch_sub</span>(<span class="number">1</span> <span class="op">+</span> <span class="ident">steals</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="ident">DISCONNECTED</span> <span class="op">=></span> { <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">store</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>); }
<span class="comment">// If we factor in our steals and notice that the channel has no</span>
<span class="comment">// data, we successfully sleep</span>
<span class="ident">n</span> <span class="op">=></span> {
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">n</span> <span class="op">>=</span> <span class="number">0</span>);
<span class="kw">if</span> <span class="ident">n</span> <span class="op">-</span> <span class="ident">steals</span> <span class="op"><=</span> <span class="number">0</span> { <span class="kw">return</span> <span class="ident">Installed</span> }
}
}
<span class="self">self</span>.<span class="ident">to_wake</span>.<span class="ident">store</span>(<span class="number">0</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="ident">drop</span>(<span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>));
<span class="ident">Abort</span>
}
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">try_recv</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">Failure</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">pop</span>() {
<span class="ident">mpsc</span>::<span class="ident">Data</span>(<span class="ident">t</span>) <span class="op">=></span> <span class="prelude-val">Some</span>(<span class="ident">t</span>),
<span class="ident">mpsc</span>::<span class="ident">Empty</span> <span class="op">=></span> <span class="prelude-val">None</span>,
<span class="comment">// This is a bit of an interesting case. The channel is reported as</span>
<span class="comment">// having data available, but our pop() has failed due to the queue</span>
<span class="comment">// being in an inconsistent state. This means that there is some</span>
<span class="comment">// pusher somewhere which has yet to complete, but we are guaranteed</span>
<span class="comment">// that a pop will eventually succeed. In this case, we spin in a</span>
<span class="comment">// yield loop because the remote sender should finish their enqueue</span>
<span class="comment">// operation "very quickly".</span>
<span class="comment">//</span>
<span class="comment">// Avoiding this yield loop would require a different queue</span>
<span class="comment">// abstraction which provides the guarantee that after M pushes have</span>
<span class="comment">// succeeded, at least M pops will succeed. The current queues</span>
<span class="comment">// guarantee that if there are N active pushes, you can pop N times</span>
<span class="comment">// once all N have finished.</span>
<span class="ident">mpsc</span>::<span class="ident">Inconsistent</span> <span class="op">=></span> {
<span class="kw">let</span> <span class="ident">data</span>;
<span class="kw">loop</span> {
<span class="ident">thread</span>::<span class="ident">yield_now</span>();
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">pop</span>() {
<span class="ident">mpsc</span>::<span class="ident">Data</span>(<span class="ident">t</span>) <span class="op">=></span> { <span class="ident">data</span> <span class="op">=</span> <span class="ident">t</span>; <span class="kw">break</span> }
<span class="ident">mpsc</span>::<span class="ident">Empty</span> <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(<span class="string">"inconsistent => empty"</span>),
<span class="ident">mpsc</span>::<span class="ident">Inconsistent</span> <span class="op">=></span> {}
}
}
<span class="prelude-val">Some</span>(<span class="ident">data</span>)
}
};
<span class="kw">match</span> <span class="ident">ret</span> {
<span class="comment">// See the discussion in the stream implementation for why we</span>
<span class="comment">// might decrement steals.</span>
<span class="prelude-val">Some</span>(<span class="ident">data</span>) <span class="op">=></span> <span class="kw">unsafe</span> {
<span class="kw">if</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>() <span class="op">></span> <span class="ident">MAX_STEALS</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">swap</span>(<span class="number">0</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="ident">DISCONNECTED</span> <span class="op">=></span> {
<span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">store</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
}
<span class="ident">n</span> <span class="op">=></span> {
<span class="kw">let</span> <span class="ident">m</span> <span class="op">=</span> <span class="ident">cmp</span>::<span class="ident">min</span>(<span class="ident">n</span>, <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>());
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>() <span class="op">-=</span> <span class="ident">m</span>;
<span class="self">self</span>.<span class="ident">bump</span>(<span class="ident">n</span> <span class="op">-</span> <span class="ident">m</span>);
}
}
<span class="macro">assert</span><span class="macro">!</span>(<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>() <span class="op">>=</span> <span class="number">0</span>);
}
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>() <span class="op">+=</span> <span class="number">1</span>;
<span class="prelude-val">Ok</span>(<span class="ident">data</span>)
},
<span class="comment">// See the discussion in the stream implementation for why we try</span>
<span class="comment">// again.</span>
<span class="prelude-val">None</span> <span class="op">=></span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="ident">n</span> <span class="kw">if</span> <span class="ident">n</span> <span class="op">!=</span> <span class="ident">DISCONNECTED</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Empty</span>),
<span class="kw">_</span> <span class="op">=></span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">pop</span>() {
<span class="ident">mpsc</span>::<span class="ident">Data</span>(<span class="ident">t</span>) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">t</span>),
<span class="ident">mpsc</span>::<span class="ident">Empty</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Disconnected</span>),
<span class="comment">// with no senders, an inconsistency is impossible.</span>
<span class="ident">mpsc</span>::<span class="ident">Inconsistent</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(),
}
}
}
}
}
}
<span class="comment">// Prepares this shared packet for a channel clone, essentially just bumping</span>
<span class="comment">// a refcount.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">clone_chan</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">let</span> <span class="ident">old_count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">channels</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="comment">// See comments on Arc::clone() on why we do this (for `mem::forget`).</span>
<span class="kw">if</span> <span class="ident">old_count</span> <span class="op">></span> <span class="ident">MAX_REFCOUNT</span> {
<span class="kw">unsafe</span> {
<span class="ident">abort</span>();
}
}
}
<span class="comment">// Decrement the reference count on a channel. This is called whenever a</span>
<span class="comment">// Chan is dropped and may end up waking up a receiver. It's the receiver's</span>
<span class="comment">// responsibility on the other end to figure out that we've disconnected.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">drop_chan</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">channels</span>.<span class="ident">fetch_sub</span>(<span class="number">1</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="number">1</span> <span class="op">=></span> {}
<span class="ident">n</span> <span class="kw">if</span> <span class="ident">n</span> <span class="op">></span> <span class="number">1</span> <span class="op">=></span> <span class="kw">return</span>,
<span class="ident">n</span> <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(<span class="string">"bad number of channels left {}"</span>, <span class="ident">n</span>),
}
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">swap</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="op">-</span><span class="number">1</span> <span class="op">=></span> { <span class="self">self</span>.<span class="ident">take_to_wake</span>().<span class="ident">signal</span>(); }
<span class="ident">DISCONNECTED</span> <span class="op">=></span> {}
<span class="ident">n</span> <span class="op">=></span> { <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">n</span> <span class="op">>=</span> <span class="number">0</span>); }
}
}
<span class="comment">// See the long discussion inside of stream.rs for why the queue is drained,</span>
<span class="comment">// and why it is done in this fashion.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">drop_port</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="self">self</span>.<span class="ident">port_dropped</span>.<span class="ident">store</span>(<span class="bool-val">true</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">steals</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>() };
<span class="kw">while</span> {
<span class="kw">let</span> <span class="ident">cnt</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">compare_and_swap</span>(<span class="ident">steals</span>, <span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="ident">cnt</span> <span class="op">!=</span> <span class="ident">DISCONNECTED</span> <span class="op">&&</span> <span class="ident">cnt</span> <span class="op">!=</span> <span class="ident">steals</span>
} {
<span class="comment">// See the discussion in 'try_recv' for why we yield</span>
<span class="comment">// control of this thread.</span>
<span class="kw">loop</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">pop</span>() {
<span class="ident">mpsc</span>::<span class="ident">Data</span>(..) <span class="op">=></span> { <span class="ident">steals</span> <span class="op">+=</span> <span class="number">1</span>; }
<span class="ident">mpsc</span>::<span class="ident">Empty</span> <span class="op">|</span> <span class="ident">mpsc</span>::<span class="ident">Inconsistent</span> <span class="op">=></span> <span class="kw">break</span>,
}
}
}
}
<span class="comment">// Consumes ownership of the 'to_wake' field.</span>
<span class="kw">fn</span> <span class="ident">take_to_wake</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">SignalToken</span> {
<span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">to_wake</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="self">self</span>.<span class="ident">to_wake</span>.<span class="ident">store</span>(<span class="number">0</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">ptr</span> <span class="op">!=</span> <span class="number">0</span>);
<span class="kw">unsafe</span> { <span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>) }
}
<span class="comment">////////////////////////////////////////////////////////////////////////////</span>
<span class="comment">// select implementation</span>
<span class="comment">////////////////////////////////////////////////////////////////////////////</span>
<span class="comment">// Helper function for select, tests whether this port can receive without</span>
<span class="comment">// blocking (obviously not an atomic decision).</span>
<span class="comment">//</span>
<span class="comment">// This is different than the stream version because there's no need to peek</span>
<span class="comment">// at the queue, we can just look at the local count.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">can_recv</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">bool</span> {
<span class="kw">let</span> <span class="ident">cnt</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="ident">cnt</span> <span class="op">==</span> <span class="ident">DISCONNECTED</span> <span class="op">||</span> <span class="ident">cnt</span> <span class="op">-</span> <span class="kw">unsafe</span> { <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>() } <span class="op">></span> <span class="number">0</span>
}
<span class="comment">// increment the count on the channel (used for selection)</span>
<span class="kw">fn</span> <span class="ident">bump</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">amt</span>: <span class="ident">isize</span>) <span class="op">-></span> <span class="ident">isize</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">fetch_add</span>(<span class="ident">amt</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="ident">DISCONNECTED</span> <span class="op">=></span> {
<span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">store</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="ident">DISCONNECTED</span>
}
<span class="ident">n</span> <span class="op">=></span> <span class="ident">n</span>
}
}
<span class="comment">// Inserts the signal token for selection on this port, returning true if</span>
<span class="comment">// blocking should proceed.</span>
<span class="comment">//</span>
<span class="comment">// The code here is the same as in stream.rs, except that it doesn't need to</span>
<span class="comment">// peek at the channel to see if an upgrade is pending.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">start_selection</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">token</span>: <span class="ident">SignalToken</span>) <span class="op">-></span> <span class="ident">StartResult</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">decrement</span>(<span class="ident">token</span>) {
<span class="ident">Installed</span> <span class="op">=></span> <span class="ident">Installed</span>,
<span class="ident">Abort</span> <span class="op">=></span> {
<span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">bump</span>(<span class="number">1</span>);
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">prev</span> <span class="op">==</span> <span class="ident">DISCONNECTED</span> <span class="op">||</span> <span class="ident">prev</span> <span class="op">>=</span> <span class="number">0</span>);
<span class="ident">Abort</span>
}
}
}
<span class="comment">// Cancels a previous thread waiting on this port, returning whether there's</span>
<span class="comment">// data on the port.</span>
<span class="comment">//</span>
<span class="comment">// This is similar to the stream implementation (hence fewer comments), but</span>
<span class="comment">// uses a different value for the "steals" variable.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">abort_selection</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">_was_upgrade</span>: <span class="ident">bool</span>) <span class="op">-></span> <span class="ident">bool</span> {
<span class="comment">// Before we do anything else, we bounce on this lock. The reason for</span>
<span class="comment">// doing this is to ensure that any upgrade-in-progress is gone and</span>
<span class="comment">// done with. Without this bounce, we can race with inherit_blocker</span>
<span class="comment">// about looking at and dealing with to_wake. Once we have acquired the</span>
<span class="comment">// lock, we are guaranteed that inherit_blocker is done.</span>
{
<span class="kw">let</span> <span class="ident">_guard</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">select_lock</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
}
<span class="comment">// Like the stream implementation, we want to make sure that the count</span>
<span class="comment">// on the channel goes non-negative. We don't know how negative the</span>
<span class="comment">// stream currently is, so instead of using a steal value of 1, we load</span>
<span class="comment">// the channel count and figure out what we should do to make it</span>
<span class="comment">// positive.</span>
<span class="kw">let</span> <span class="ident">steals</span> <span class="op">=</span> {
<span class="kw">let</span> <span class="ident">cnt</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="kw">if</span> <span class="ident">cnt</span> <span class="op"><</span> <span class="number">0</span> <span class="op">&&</span> <span class="ident">cnt</span> <span class="op">!=</span> <span class="ident">DISCONNECTED</span> {<span class="op">-</span><span class="ident">cnt</span>} <span class="kw">else</span> {<span class="number">0</span>}
};
<span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">bump</span>(<span class="ident">steals</span> <span class="op">+</span> <span class="number">1</span>);
<span class="kw">if</span> <span class="ident">prev</span> <span class="op">==</span> <span class="ident">DISCONNECTED</span> {
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">to_wake</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>), <span class="number">0</span>);
<span class="bool-val">true</span>
} <span class="kw">else</span> {
<span class="kw">let</span> <span class="ident">cur</span> <span class="op">=</span> <span class="ident">prev</span> <span class="op">+</span> <span class="ident">steals</span> <span class="op">+</span> <span class="number">1</span>;
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">cur</span> <span class="op">>=</span> <span class="number">0</span>);
<span class="kw">if</span> <span class="ident">prev</span> <span class="op"><</span> <span class="number">0</span> {
<span class="ident">drop</span>(<span class="self">self</span>.<span class="ident">take_to_wake</span>());
} <span class="kw">else</span> {
<span class="kw">while</span> <span class="self">self</span>.<span class="ident">to_wake</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op">!=</span> <span class="number">0</span> {
<span class="ident">thread</span>::<span class="ident">yield_now</span>();
}
}
<span class="kw">unsafe</span> {
<span class="comment">// if the number of steals is -1, it was the pre-emptive -1 steal</span>
<span class="comment">// count from when we inherited a blocker. This is fine because</span>
<span class="comment">// we're just going to overwrite it with a real value.</span>
<span class="kw">let</span> <span class="ident">old</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">steals</span>.<span class="ident">get</span>();
<span class="macro">assert</span><span class="macro">!</span>(<span class="kw-2">*</span><span class="ident">old</span> <span class="op">==</span> <span class="number">0</span> <span class="op">||</span> <span class="kw-2">*</span><span class="ident">old</span> <span class="op">==</span> <span class="op">-</span><span class="number">1</span>);
<span class="kw-2">*</span><span class="ident">old</span> <span class="op">=</span> <span class="ident">steals</span>;
<span class="ident">prev</span> <span class="op">>=</span> <span class="number">0</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">Packet</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="comment">// Note that this load is not only an assert for correctness about</span>
<span class="comment">// disconnection, but also a proper fence before the read of</span>
<span class="comment">// `to_wake`, so this assert cannot be removed with also removing</span>
<span class="comment">// the `to_wake` assert.</span>
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">cnt</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>), <span class="ident">DISCONNECTED</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">to_wake</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>), <span class="number">0</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">channels</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>), <span class="number">0</span>);
}
}
</pre>
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