<!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/stream.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>stream.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">/// Stream channels</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is the flavor of channels which are optimized for one sender and one</span>
<span class="doccomment">/// receiver. The sender will be upgraded to a shared channel if the channel is</span>
<span class="doccomment">/// cloned.</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.</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">pub</span> <span class="kw">use</span> <span class="self">self</span>::<span class="ident">UpgradeResult</span>::<span class="kw-2">*</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="self">self</span>::<span class="ident">SelectionResult</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="self">self</span>::<span class="ident">Message</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="ident">cell</span>::<span class="ident">UnsafeCell</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">isize</span>;
<span class="kw">use</span> <span class="ident">ptr</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">use</span> <span class="ident">sync</span>::<span class="ident">atomic</span>::{<span class="ident">AtomicIsize</span>, <span class="ident">AtomicUsize</span>, <span class="ident">Ordering</span>, <span class="ident">AtomicBool</span>};
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">mpsc</span>::<span class="ident">Receiver</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">spsc_queue</span> <span class="kw">as</span> <span class="ident">spsc</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="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="comment">// internal queue for all messages</span>
<span class="ident">queue</span>: <span class="ident">spsc</span>::<span class="ident">Queue</span><span class="op"><</span><span class="ident">Message</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">ProducerAddition</span>, <span class="ident">ConsumerAddition</span><span class="op">></span>,
}
<span class="kw">struct</span> <span class="ident">ProducerAddition</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">to_wake</span>: <span class="ident">AtomicUsize</span>, <span class="comment">// SignalToken for the blocked thread to wake up</span>
<span class="ident">port_dropped</span>: <span class="ident">AtomicBool</span>, <span class="comment">// flag if the channel has been destroyed.</span>
}
<span class="kw">struct</span> <span class="ident">ConsumerAddition</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="kw">pub</span> <span class="kw">enum</span> <span class="ident">Failure</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Empty</span>,
<span class="ident">Disconnected</span>,
<span class="ident">Upgraded</span>(<span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>),
}
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">UpgradeResult</span> {
<span class="ident">UpSuccess</span>,
<span class="ident">UpDisconnected</span>,
<span class="ident">UpWoke</span>(<span class="ident">SignalToken</span>),
}
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SelectionResult</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">SelSuccess</span>,
<span class="ident">SelCanceled</span>,
<span class="ident">SelUpgraded</span>(<span class="ident">SignalToken</span>, <span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>),
}
<span class="comment">// Any message could contain an "upgrade request" to a new shared port, so the</span>
<span class="comment">// internal queue it's a queue of T, but rather Message<T></span>
<span class="kw">enum</span> <span class="ident">Message</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Data</span>(<span class="ident">T</span>),
<span class="ident">GoUp</span>(<span class="ident">Receiver</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">Packet</span><span class="op"><</span><span class="ident">T</span><span class="op">></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="kw">unsafe</span> { <span class="ident">spsc</span>::<span class="ident">Queue</span>::<span class="ident">with_additions</span>(
<span class="number">128</span>,
<span class="ident">ProducerAddition</span> {
<span class="ident">cnt</span>: <span class="ident">AtomicIsize</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">port_dropped</span>: <span class="ident">AtomicBool</span>::<span class="ident">new</span>(<span class="bool-val">false</span>),
},
<span class="ident">ConsumerAddition</span> {
<span class="ident">steals</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="number">0</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">// If the other port has deterministically gone away, then definitely</span>
<span class="comment">// must return the data back up the stack. Otherwise, the data is</span>
<span class="comment">// considered as being sent.</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">producer_addition</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="kw">match</span> <span class="self">self</span>.<span class="ident">do_send</span>(<span class="ident">Data</span>(<span class="ident">t</span>)) {
<span class="ident">UpSuccess</span> <span class="op">|</span> <span class="ident">UpDisconnected</span> <span class="op">=></span> {},
<span class="ident">UpWoke</span>(<span class="ident">token</span>) <span class="op">=></span> { <span class="ident">token</span>.<span class="ident">signal</span>(); }
}
<span class="prelude-val">Ok</span>(())
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">upgrade</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">up</span>: <span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">UpgradeResult</span> {
<span class="comment">// If the port has gone away, then there's no need to proceed any</span>
<span class="comment">// further.</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">producer_addition</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="ident">UpDisconnected</span>
}
<span class="self">self</span>.<span class="ident">do_send</span>(<span class="ident">GoUp</span>(<span class="ident">up</span>))
}
<span class="kw">fn</span> <span class="ident">do_send</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">t</span>: <span class="ident">Message</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">UpgradeResult</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">queue</span>.<span class="ident">producer_addition</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="comment">// As described in the mod's doc comment, -1 == wakeup</span>
<span class="op">-</span><span class="number">1</span> <span class="op">=></span> <span class="ident">UpWoke</span>(<span class="self">self</span>.<span class="ident">take_to_wake</span>()),
<span class="comment">// As as described before, SPSC queues must be >= -2</span>
<span class="op">-</span><span class="number">2</span> <span class="op">=></span> <span class="ident">UpSuccess</span>,
<span class="comment">// Be sure to preserve the disconnected state, and the return value</span>
<span class="comment">// in this case is going to be whether our data was received or not.</span>
<span class="comment">// This manifests itself on whether we have an empty queue or not.</span>
<span class="comment">//</span>
<span class="comment">// Primarily, are required to drain the queue here because the port</span>
<span class="comment">// will never remove this data. We can only have at most one item to</span>
<span class="comment">// drain (the port drains the rest).</span>
<span class="ident">DISCONNECTED</span> <span class="op">=></span> {
<span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">producer_addition</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">let</span> <span class="ident">first</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">pop</span>();
<span class="kw">let</span> <span class="ident">second</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">pop</span>();
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">second</span>.<span class="ident">is_none</span>());
<span class="kw">match</span> <span class="ident">first</span> {
<span class="prelude-val">Some</span>(..) <span class="op">=></span> <span class="ident">UpSuccess</span>, <span class="comment">// we failed to send the data</span>
<span class="prelude-val">None</span> <span class="op">=></span> <span class="ident">UpDisconnected</span>, <span class="comment">// we successfully sent data</span>
}
}
<span class="comment">// Otherwise we just sent some data on a non-waiting queue, so just</span>
<span class="comment">// make sure the world is sane and carry on!</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="ident">UpSuccess</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">queue</span>.<span class="ident">producer_addition</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">queue</span>.<span class="ident">producer_addition</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">// Decrements the count on the channel for a sleeper, returning the sleeper</span>
<span class="comment">// back if it shouldn't sleep. Note that this is the location where we take</span>
<span class="comment">// steals into account.</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="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">SignalToken</span><span class="op">></span> {
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">producer_addition</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="kw">unsafe</span> { <span class="ident">token</span>.<span class="ident">cast_to_usize</span>() };
<span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">producer_addition</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="kw">unsafe</span> { <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">consumer_addition</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">queue</span>.<span class="ident">producer_addition</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">queue</span>.<span class="ident">producer_addition</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="prelude-val">Ok</span>(()) }
}
}
<span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">producer_addition</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="prelude-val">Err</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="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="ident">T</span><span class="op">>></span> {
<span class="comment">// Optimistic preflight check (scheduling is expensive).</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="comment">// Welp, our channel has no data. Deschedule the current thread and</span>
<span class="comment">// initiate the blocking protocol.</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="ident">is_ok</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="comment">/* was_upgrade = */</span> <span class="bool-val">false</span>).<span class="ident">map_err</span>(<span class="ident">Upgraded</span>)<span class="question-mark">?</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="comment">// Messages which actually popped from the queue shouldn't count as</span>
<span class="comment">// a steal, so offset the decrement here (we already have our</span>
<span class="comment">// "steal" factored into the channel count above).</span>
<span class="ident">data</span> @ <span class="prelude-val">Ok</span>(..) <span class="op">|</span>
<span class="ident">data</span> @ <span class="prelude-val">Err</span>(<span class="ident">Upgraded</span>(..)) <span class="op">=></span> <span class="kw">unsafe</span> {
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">consumer_addition</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="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="ident">T</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="comment">// If we stole some data, record to that effect (this will be</span>
<span class="comment">// factored into cnt later on).</span>
<span class="comment">//</span>
<span class="comment">// Note that we don't allow steals to grow without bound in order to</span>
<span class="comment">// prevent eventual overflow of either steals or cnt as an overflow</span>
<span class="comment">// would have catastrophic results. Sometimes, steals > cnt, but</span>
<span class="comment">// other times cnt > steals, so we don't know the relation between</span>
<span class="comment">// steals and cnt. This code path is executed only rarely, so we do</span>
<span class="comment">// a pretty slow operation, of swapping 0 into cnt, taking steals</span>
<span class="comment">// down as much as possible (without going negative), and then</span>
<span class="comment">// adding back in whatever we couldn't factor into 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">queue</span>.<span class="ident">consumer_addition</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">queue</span>.<span class="ident">producer_addition</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">queue</span>.<span class="ident">producer_addition</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">queue</span>.<span class="ident">consumer_addition</span>().<span class="ident">steals</span>.<span class="ident">get</span>());
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">consumer_addition</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">queue</span>.<span class="ident">consumer_addition</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">queue</span>.<span class="ident">consumer_addition</span>().<span class="ident">steals</span>.<span class="ident">get</span>() <span class="op">+=</span> <span class="number">1</span>;
<span class="kw">match</span> <span class="ident">data</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">GoUp</span>(<span class="ident">up</span>) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Upgraded</span>(<span class="ident">up</span>)),
}
},
<span class="prelude-val">None</span> <span class="op">=></span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">producer_addition</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="comment">// This is a little bit of a tricky case. We failed to pop</span>
<span class="comment">// data above, and then we have viewed that the channel is</span>
<span class="comment">// disconnected. In this window more data could have been</span>
<span class="comment">// sent on the channel. It doesn't really make sense to</span>
<span class="comment">// return that the channel is disconnected when there's</span>
<span class="comment">// actually data on it, so be extra sure there's no data by</span>
<span class="comment">// popping one more time.</span>
<span class="comment">//</span>
<span class="comment">// We can ignore steals because the other end is</span>
<span class="comment">// disconnected and we'll never need to really factor in our</span>
<span class="comment">// steals again.</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="prelude-val">Some</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="prelude-val">Some</span>(<span class="ident">GoUp</span>(<span class="ident">up</span>)) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Upgraded</span>(<span class="ident">up</span>)),
<span class="prelude-val">None</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">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="comment">// Dropping a channel is pretty simple, we just flag it as disconnected</span>
<span class="comment">// and then wakeup a blocker if there is one.</span>
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">producer_addition</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="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="comment">// Dropping a port seems like a fairly trivial thing. In theory all we</span>
<span class="comment">// need to do is flag that we're disconnected and then everything else</span>
<span class="comment">// can take over (we don't have anyone to wake up).</span>
<span class="comment">//</span>
<span class="comment">// The catch for Ports is that we want to drop the entire contents of</span>
<span class="comment">// the queue. There are multiple reasons for having this property, the</span>
<span class="comment">// largest of which is that if another chan is waiting in this channel</span>
<span class="comment">// (but not received yet), then waiting on that port will cause a</span>
<span class="comment">// deadlock.</span>
<span class="comment">//</span>
<span class="comment">// So if we accept that we must now destroy the entire contents of the</span>
<span class="comment">// queue, this code may make a bit more sense. The tricky part is that</span>
<span class="comment">// we can't let any in-flight sends go un-dropped, we have to make sure</span>
<span class="comment">// *everything* is dropped and nothing new will come onto the channel.</span>
<span class="comment">// The first thing we do is set a flag saying that we're done for. All</span>
<span class="comment">// sends are gated on this flag, so we're immediately guaranteed that</span>
<span class="comment">// there are a bounded number of active sends that we'll have to deal</span>
<span class="comment">// with.</span>
<span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">producer_addition</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="comment">// Now that we're guaranteed to deal with a bounded number of senders,</span>
<span class="comment">// we need to drain the queue. This draining process happens atomically</span>
<span class="comment">// with respect to the "count" of the channel. If the count is nonzero</span>
<span class="comment">// (with steals taken into account), then there must be data on the</span>
<span class="comment">// channel. In this case we drain everything and then try again. We will</span>
<span class="comment">// continue to fail while active senders send data while we're dropping</span>
<span class="comment">// data, but eventually we're guaranteed to break out of this loop</span>
<span class="comment">// (because there is a bounded number of senders).</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">queue</span>.<span class="ident">consumer_addition</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">queue</span>.<span class="ident">producer_addition</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="kw">while</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="kw">_</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">pop</span>() { <span class="ident">steals</span> <span class="op">+=</span> <span class="number">1</span>; }
}
<span class="comment">// At this point in time, we have gated all future senders from sending,</span>
<span class="comment">// and we have flagged the channel as being disconnected. The senders</span>
<span class="comment">// still have some responsibility, however, because some sends may not</span>
<span class="comment">// complete until after we flag the disconnection. There are more</span>
<span class="comment">// details in the sending methods that see DISCONNECTED</span>
}
<span class="comment">////////////////////////////////////////////////////////////////////////////</span>
<span class="comment">// select implementation</span>
<span class="comment">////////////////////////////////////////////////////////////////////////////</span>
<span class="comment">// Tests to see whether this port can receive without blocking. If Ok is</span>
<span class="comment">// returned, then that's the answer. If Err is returned, then the returned</span>
<span class="comment">// port needs to be queried instead (an upgrade happened)</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="prelude-ty">Result</span><span class="op"><</span><span class="ident">bool</span>, <span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="comment">// We peek at the queue to see if there's anything on it, and we use</span>
<span class="comment">// this return value to determine if we should pop from the queue and</span>
<span class="comment">// upgrade this channel immediately. If it looks like we've got an</span>
<span class="comment">// upgrade pending, then go through the whole recv rigamarole to update</span>
<span class="comment">// the internal state.</span>
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">peek</span>() {
<span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">GoUp</span>(..)) <span class="op">=></span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">recv</span>(<span class="prelude-val">None</span>) {
<span class="prelude-val">Err</span>(<span class="ident">Upgraded</span>(<span class="ident">port</span>)) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">port</span>),
<span class="kw">_</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(),
}
}
<span class="prelude-val">Some</span>(..) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>),
<span class="prelude-val">None</span> <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">false</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">queue</span>.<span class="ident">producer_addition</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">queue</span>.<span class="ident">producer_addition</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">// Attempts to start selecting on this port. Like a oneshot, this can fail</span>
<span class="comment">// immediately because of an upgrade.</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">SelectionResult</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">decrement</span>(<span class="ident">token</span>) {
<span class="prelude-val">Ok</span>(()) <span class="op">=></span> <span class="ident">SelSuccess</span>,
<span class="prelude-val">Err</span>(<span class="ident">token</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">peek</span>() {
<span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">GoUp</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="prelude-val">Some</span>(<span class="ident">GoUp</span>(<span class="ident">port</span>)) <span class="op">=></span> <span class="ident">SelUpgraded</span>(<span class="ident">token</span>, <span class="ident">port</span>),
<span class="kw">_</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(),
}
}
<span class="prelude-val">Some</span>(..) <span class="op">=></span> <span class="ident">SelCanceled</span>,
<span class="prelude-val">None</span> <span class="op">=></span> <span class="ident">SelCanceled</span>,
};
<span class="comment">// Undo our decrement above, and we should be guaranteed that the</span>
<span class="comment">// previous value is positive because we're not going to sleep</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">ret</span>
}
}
}
<span class="comment">// Removes a previous thread from being blocked in this port</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="prelude-ty">Result</span><span class="op"><</span><span class="ident">bool</span>, <span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="comment">// If we're aborting selection after upgrading from a oneshot, then</span>
<span class="comment">// we're guarantee that no one is waiting. The only way that we could</span>
<span class="comment">// have seen the upgrade is if data was actually sent on the channel</span>
<span class="comment">// half again. For us, this means that there is guaranteed to be data on</span>
<span class="comment">// this channel. Furthermore, we're guaranteed that there was no</span>
<span class="comment">// start_selection previously, so there's no need to modify `self.cnt`</span>
<span class="comment">// at all.</span>
<span class="comment">//</span>
<span class="comment">// Hence, because of these invariants, we immediately return `Ok(true)`.</span>
<span class="comment">// Note that the data may not actually be sent on the channel just yet.</span>
<span class="comment">// The other end could have flagged the upgrade but not sent data to</span>
<span class="comment">// this end. This is fine because we know it's a small bounded windows</span>
<span class="comment">// of time until the data is actually sent.</span>
<span class="kw">if</span> <span class="ident">was_upgrade</span> {
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="kw">unsafe</span> { <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">consumer_addition</span>().<span class="ident">steals</span>.<span class="ident">get</span>() }, <span class="number">0</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">producer_addition</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">return</span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>)
}
<span class="comment">// We want to make sure that the count on the channel goes non-negative,</span>
<span class="comment">// and in the stream case we can have at most one steal, so just assume</span>
<span class="comment">// that we had one steal.</span>
<span class="kw">let</span> <span class="ident">steals</span> <span class="op">=</span> <span class="number">1</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="comment">// If we were previously disconnected, then we know for sure that there</span>
<span class="comment">// is no thread in to_wake, so just keep going</span>
<span class="kw">let</span> <span class="ident">has_data</span> <span class="op">=</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">queue</span>.<span class="ident">producer_addition</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="comment">// there is data, that data is that we're disconnected</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="comment">// If the previous count was negative, then we just made things go</span>
<span class="comment">// positive, hence we passed the -1 boundary and we're responsible</span>
<span class="comment">// for removing the to_wake() field and trashing it.</span>
<span class="comment">//</span>
<span class="comment">// If the previous count was positive then we're in a tougher</span>
<span class="comment">// situation. A possible race is that a sender just incremented</span>
<span class="comment">// through -1 (meaning it's going to try to wake a thread up), but it</span>
<span class="comment">// hasn't yet read the to_wake. In order to prevent a future recv()</span>
<span class="comment">// from waking up too early (this sender picking up the plastered</span>
<span class="comment">// over to_wake), we spin loop here waiting for to_wake to be 0.</span>
<span class="comment">// Note that this entire select() implementation needs an overhaul,</span>
<span class="comment">// and this is *not* the worst part of it, so this is not done as a</span>
<span class="comment">// final solution but rather out of necessity for now to get</span>
<span class="comment">// something working.</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">queue</span>.<span class="ident">producer_addition</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="macro">assert_eq</span><span class="macro">!</span>(<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">consumer_addition</span>().<span class="ident">steals</span>.<span class="ident">get</span>(), <span class="number">0</span>);
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">consumer_addition</span>().<span class="ident">steals</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">steals</span>;
}
<span class="comment">// if we were previously positive, then there's surely data to</span>
<span class="comment">// receive</span>
<span class="ident">prev</span> <span class="op">>=</span> <span class="number">0</span>
};
<span class="comment">// Now that we've determined that this queue "has data", we peek at the</span>
<span class="comment">// queue to see if the data is an upgrade or not. If it's an upgrade,</span>
<span class="comment">// then we need to destroy this port and abort selection on the</span>
<span class="comment">// upgraded port.</span>
<span class="kw">if</span> <span class="ident">has_data</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">peek</span>() {
<span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">GoUp</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="prelude-val">Some</span>(<span class="ident">GoUp</span>(<span class="ident">port</span>)) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">port</span>),
<span class="kw">_</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(),
}
}
<span class="kw">_</span> <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>),
}
} <span class="kw">else</span> {
<span class="prelude-val">Ok</span>(<span class="bool-val">false</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">queue</span>.<span class="ident">producer_addition</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">queue</span>.<span class="ident">producer_addition</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>);
}
}
</pre>
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