<!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/oneshot.rs`."> <meta name="keywords" content="rust, rustlang, rust-lang"> <title>oneshot.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="../../../../main.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"> </div> </form> </nav> <section id='main' class="content"><pre class="line-numbers"><span id="1"> 1</span> <span id="2"> 2</span> <span id="3"> 3</span> <span id="4"> 4</span> <span id="5"> 5</span> <span id="6"> 6</span> <span id="7"> 7</span> <span id="8"> 8</span> <span id="9"> 9</span> <span id="10"> 10</span> <span id="11"> 11</span> <span 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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">/// Oneshot channels/ports</span> <span class="doccomment">///</span> <span class="doccomment">/// This is the initial flavor of channels/ports used for comm module. This is</span> <span class="doccomment">/// an optimization for the one-use case of a channel. The major optimization of</span> <span class="doccomment">/// this type is to have one and exactly one allocation when the chan/port pair</span> <span class="doccomment">/// is created.</span> <span class="doccomment">///</span> <span class="doccomment">/// Another possible optimization would be to not use an Arc box because</span> <span class="doccomment">/// in theory we know when the shared packet can be deallocated (no real need</span> <span class="doccomment">/// for the atomic reference counting), but I was having trouble how to destroy</span> <span class="doccomment">/// the data early in a drop of a Port.</span> <span class="doccomment">///</span> <span class="doccomment">/// # Implementation</span> <span class="doccomment">///</span> <span class="doccomment">/// Oneshots are implemented around one atomic usize variable. This variable</span> <span class="doccomment">/// indicates both the state of the port/chan but also contains any threads</span> <span class="doccomment">/// blocked on the port. All atomic operations happen on this one word.</span> <span class="doccomment">///</span> <span class="doccomment">/// In order to upgrade a oneshot channel, an upgrade is considered a disconnect</span> <span class="doccomment">/// on behalf of the channel side of things (it can be mentally thought of as</span> <span class="doccomment">/// consuming the port). This upgrade is then also stored in the shared packet.</span> <span class="doccomment">/// The one caveat to consider is that when a port sees a disconnected channel</span> <span class="doccomment">/// it must check for data because there is no "data plus upgrade" state.</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">MyUpgrade</span>::<span class="kw-2">*</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">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">Ordering</span>}; <span class="kw">use</span> <span class="ident">time</span>::<span class="ident">Instant</span>; <span class="comment">// Various states you can find a port in.</span> <span class="kw">const</span> <span class="ident">EMPTY</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">0</span>; <span class="comment">// initial state: no data, no blocked receiver</span> <span class="kw">const</span> <span class="ident">DATA</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">1</span>; <span class="comment">// data ready for receiver to take</span> <span class="kw">const</span> <span class="ident">DISCONNECTED</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">2</span>; <span class="comment">// channel is disconnected OR upgraded</span> <span class="comment">// Any other value represents a pointer to a SignalToken value. The</span> <span class="comment">// protocol ensures that when the state moves *to* a pointer,</span> <span class="comment">// ownership of the token is given to the packet, and when the state</span> <span class="comment">// moves *from* a pointer, ownership of the token is transferred to</span> <span class="comment">// whoever changed the state.</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 state of the chan/port pair (stores the blocked thread as well)</span> <span class="ident">state</span>: <span class="ident">AtomicUsize</span>, <span class="comment">// One-shot data slot location</span> <span class="ident">data</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>, <span class="comment">// when used for the second time, a oneshot channel must be upgraded, and</span> <span class="comment">// this contains the slot for the upgrade</span> <span class="ident">upgrade</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">MyUpgrade</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">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">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="ident">SelSuccess</span>, } <span class="kw">enum</span> <span class="ident">MyUpgrade</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="ident">NothingSent</span>, <span class="ident">SendUsed</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">data</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>), <span class="ident">upgrade</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">NothingSent</span>), <span class="ident">state</span>: <span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="ident">EMPTY</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="kw">unsafe</span> { <span class="comment">// Sanity check</span> <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>() { <span class="ident">NothingSent</span> <span class="op">=></span> {} _ <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(<span class="string">"sending on a oneshot that's already sent on "</span>), } <span class="macro">assert</span><span class="macro">!</span>((<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">is_none</span>()); <span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>(), <span class="prelude-val">Some</span>(<span class="ident">t</span>)); <span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">SendUsed</span>); <span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">DATA</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) { <span class="comment">// Sent the data, no one was waiting</span> <span class="ident">EMPTY</span> <span class="op">=></span> <span class="prelude-val">Ok</span>(()), <span class="comment">// Couldn't send the data, the port hung up first. Return the data</span> <span class="comment">// back up the stack.</span> <span class="ident">DISCONNECTED</span> <span class="op">=></span> { <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>); <span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">NothingSent</span>); <span class="prelude-val">Err</span>((<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">take</span>().<span class="ident">unwrap</span>()) } <span class="comment">// Not possible, these are one-use channels</span> <span class="ident">DATA</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(), <span class="comment">// There is a thread waiting on the other end. We leave the 'DATA'</span> <span class="comment">// state inside so it'll pick it up on the other end.</span> <span class="ident">ptr</span> <span class="op">=></span> { <span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>).<span class="ident">signal</span>(); <span class="prelude-val">Ok</span>(()) } } } } <span class="comment">// Just tests whether this channel has been sent on or not, this is only</span> <span class="comment">// safe to use from the sender.</span> <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">sent</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">bool</span> { <span class="kw">unsafe</span> { <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>() { <span class="ident">NothingSent</span> <span class="op">=></span> <span class="bool-val">false</span>, _ <span class="op">=></span> <span class="bool-val">true</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">// Attempt to not block the thread (it's a little expensive). If it looks</span> <span class="comment">// like we're not empty, then immediately go through to `try_recv`.</span> <span class="kw">if</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op">==</span> <span class="ident">EMPTY</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">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">signal_token</span>.<span class="ident">cast_to_usize</span>() }; <span class="comment">// race with senders to enter the blocking state</span> <span class="kw">if</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">compare_and_swap</span>(<span class="ident">EMPTY</span>, <span class="ident">ptr</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op">==</span> <span class="ident">EMPTY</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="comment">// Try to reset the state</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="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="macro">debug_assert</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op">!=</span> <span class="ident">EMPTY</span>); } } <span class="kw">else</span> { <span class="comment">// drop the signal token, since we never blocked</span> <span class="ident">drop</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="self">self</span>.<span class="ident">try_recv</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">unsafe</span> { <span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) { <span class="ident">EMPTY</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Empty</span>), <span class="comment">// We saw some data on the channel, but the channel can be used</span> <span class="comment">// again to send us an upgrade. As a result, we need to re-insert</span> <span class="comment">// into the channel that there's no data available (otherwise we'll</span> <span class="comment">// just see DATA next time). This is done as a cmpxchg because if</span> <span class="comment">// the state changes under our feet we'd rather just see that state</span> <span class="comment">// change.</span> <span class="ident">DATA</span> <span class="op">=></span> { <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">compare_and_swap</span>(<span class="ident">DATA</span>, <span class="ident">EMPTY</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>); <span class="kw">match</span> (<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">take</span>() { <span class="prelude-val">Some</span>(<span class="ident">data</span>) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">data</span>), <span class="prelude-val">None</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(), } } <span class="comment">// There's no guarantee that we receive before an upgrade happens,</span> <span class="comment">// and an upgrade flags the channel as disconnected, so when we see</span> <span class="comment">// this we first need to check if there's data available and *then*</span> <span class="comment">// we go through and process the upgrade.</span> <span class="ident">DISCONNECTED</span> <span class="op">=></span> { <span class="kw">match</span> (<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">take</span>() { <span class="prelude-val">Some</span>(<span class="ident">data</span>) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">data</span>), <span class="prelude-val">None</span> <span class="op">=></span> { <span class="kw">match</span> <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">SendUsed</span>) { <span class="ident">SendUsed</span> <span class="op">|</span> <span class="ident">NothingSent</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Disconnected</span>), <span class="ident">GoUp</span>(<span class="ident">upgrade</span>) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Upgraded</span>(<span class="ident">upgrade</span>)) } } } } <span class="comment">// We are the sole receiver; there cannot be a blocking</span> <span class="comment">// receiver already.</span> _ <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>() } } } <span class="comment">// Returns whether the upgrade was completed. If the upgrade wasn't</span> <span class="comment">// completed, then the port couldn't get sent to the other half (it will</span> <span class="comment">// never receive it).</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="kw">unsafe</span> { <span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>() { <span class="ident">NothingSent</span> <span class="op">=></span> <span class="ident">NothingSent</span>, <span class="ident">SendUsed</span> <span class="op">=></span> <span class="ident">SendUsed</span>, _ <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(<span class="string">"upgrading again"</span>), }; <span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">GoUp</span>(<span class="ident">up</span>)); <span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) { <span class="comment">// If the channel is empty or has data on it, then we're good to go.</span> <span class="comment">// Senders will check the data before the upgrade (in case we</span> <span class="comment">// plastered over the DATA state).</span> <span class="ident">DATA</span> <span class="op">|</span> <span class="ident">EMPTY</span> <span class="op">=></span> <span class="ident">UpSuccess</span>, <span class="comment">// If the other end is already disconnected, then we failed the</span> <span class="comment">// upgrade. Be sure to trash the port we were given.</span> <span class="ident">DISCONNECTED</span> <span class="op">=></span> { <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">prev</span>); <span class="ident">UpDisconnected</span> } <span class="comment">// If someone's waiting, we gotta wake them up</span> <span class="ident">ptr</span> <span class="op">=></span> <span class="ident">UpWoke</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">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">state</span>.<span class="ident">swap</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) { <span class="ident">DATA</span> <span class="op">|</span> <span class="ident">DISCONNECTED</span> <span class="op">|</span> <span class="ident">EMPTY</span> <span class="op">=></span> {} <span class="comment">// If someone's waiting, we gotta wake them up</span> <span class="ident">ptr</span> <span class="op">=></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="ident">signal</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="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) { <span class="comment">// An empty channel has nothing to do, and a remotely disconnected</span> <span class="comment">// channel also has nothing to do b/c we're about to run the drop</span> <span class="comment">// glue</span> <span class="ident">DISCONNECTED</span> <span class="op">|</span> <span class="ident">EMPTY</span> <span class="op">=></span> {} <span class="comment">// There's data on the channel, so make sure we destroy it promptly.</span> <span class="comment">// This is why not using an arc is a little difficult (need the box</span> <span class="comment">// to stay valid while we take the data).</span> <span class="ident">DATA</span> <span class="op">=></span> <span class="kw">unsafe</span> { (<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">take</span>().<span class="ident">unwrap</span>(); }, <span class="comment">// We're the only ones that can block on this port</span> _ <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>() } } <span class="comment">////////////////////////////////////////////////////////////////////////////</span> <span class="comment">// select implementation</span> <span class="comment">////////////////////////////////////////////////////////////////////////////</span> <span class="comment">// If Ok, the value is whether this port has data, if Err, then the upgraded</span> <span class="comment">// port needs to be checked instead of this one.</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="kw">unsafe</span> { <span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) { <span class="ident">EMPTY</span> <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">false</span>), <span class="comment">// Welp, we tried</span> <span class="ident">DATA</span> <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>), <span class="comment">// we have some un-acquired data</span> <span class="ident">DISCONNECTED</span> <span class="kw">if</span> (<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">is_some</span>() <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>), <span class="comment">// we have data</span> <span class="ident">DISCONNECTED</span> <span class="op">=></span> { <span class="kw">match</span> <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">SendUsed</span>) { <span class="comment">// The other end sent us an upgrade, so we need to</span> <span class="comment">// propagate upwards whether the upgrade can receive</span> <span class="comment">// data</span> <span class="ident">GoUp</span>(<span class="ident">upgrade</span>) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">upgrade</span>), <span class="comment">// If the other end disconnected without sending an</span> <span class="comment">// upgrade, then we have data to receive (the channel is</span> <span class="comment">// disconnected).</span> <span class="ident">up</span> <span class="op">=></span> { <span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">up</span>); <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>) } } } _ <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(), <span class="comment">// we're the "one blocker"</span> } } } <span class="comment">// Attempts to start selection on this port. This can either succeed, fail</span> <span class="comment">// because there is data, or fail because there is an upgrade 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">SelectionResult</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> { <span class="kw">unsafe</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="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">compare_and_swap</span>(<span class="ident">EMPTY</span>, <span class="ident">ptr</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) { <span class="ident">EMPTY</span> <span class="op">=></span> <span class="ident">SelSuccess</span>, <span class="ident">DATA</span> <span class="op">=></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">SelCanceled</span> } <span class="ident">DISCONNECTED</span> <span class="kw">if</span> (<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">is_some</span>() <span class="op">=></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">SelCanceled</span> } <span class="ident">DISCONNECTED</span> <span class="op">=></span> { <span class="kw">match</span> <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">SendUsed</span>) { <span class="comment">// The other end sent us an upgrade, so we need to</span> <span class="comment">// propagate upwards whether the upgrade can receive</span> <span class="comment">// data</span> <span class="ident">GoUp</span>(<span class="ident">upgrade</span>) <span class="op">=></span> { <span class="ident">SelUpgraded</span>(<span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>), <span class="ident">upgrade</span>) } <span class="comment">// If the other end disconnected without sending an</span> <span class="comment">// upgrade, then we have data to receive (the channel is</span> <span class="comment">// disconnected).</span> <span class="ident">up</span> <span class="op">=></span> { <span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">up</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">SelCanceled</span> } } } _ <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(), <span class="comment">// we're the "one blocker"</span> } } } <span class="comment">// Remove a previous selecting thread from this port. This ensures that the</span> <span class="comment">// blocked thread will no longer be visible to any other threads.</span> <span class="comment">//</span> <span class="comment">// The return value indicates whether there's data on 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="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="kw">let</span> <span class="ident">state</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) { <span class="comment">// Each of these states means that no further activity will happen</span> <span class="comment">// with regard to abortion selection</span> <span class="ident">s</span> @ <span class="ident">EMPTY</span> <span class="op">|</span> <span class="ident">s</span> @ <span class="ident">DATA</span> <span class="op">|</span> <span class="ident">s</span> @ <span class="ident">DISCONNECTED</span> <span class="op">=></span> <span class="ident">s</span>, <span class="comment">// If we've got a blocked thread, then use an atomic to gain ownership</span> <span class="comment">// of it (may fail)</span> <span class="ident">ptr</span> <span class="op">=></span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">compare_and_swap</span>(<span class="ident">ptr</span>, <span class="ident">EMPTY</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) }; <span class="comment">// Now that we've got ownership of our state, figure out what to do</span> <span class="comment">// about it.</span> <span class="kw">match</span> <span class="ident">state</span> { <span class="ident">EMPTY</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(), <span class="comment">// our thread used for select was stolen</span> <span class="ident">DATA</span> <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>), <span class="comment">// If the other end has hung up, then we have complete ownership</span> <span class="comment">// of the port. First, check if there was data waiting for us. This</span> <span class="comment">// is possible if the other end sent something and then hung up.</span> <span class="comment">//</span> <span class="comment">// We then need to check to see if there was an upgrade requested,</span> <span class="comment">// and if so, the upgraded port needs to have its selection aborted.</span> <span class="ident">DISCONNECTED</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">data</span>.<span class="ident">get</span>()).<span class="ident">is_some</span>() { <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>) } <span class="kw">else</span> { <span class="kw">match</span> <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">SendUsed</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="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>), } } }, <span class="comment">// We woke ourselves up from select.</span> <span class="ident">ptr</span> <span class="op">=></span> <span class="kw">unsafe</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="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="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>), <span class="ident">DISCONNECTED</span>); } } </pre> </section> <section id='search' class="content hidden"></section> <section class="footer"></section> <aside id="help" class="hidden"> <div> <h1 class="hidden">Help</h1> <div class="shortcuts"> <h2>Keyboard Shortcuts</h2> <dl> <dt><kbd>?</kbd></dt> <dd>Show this help dialog</dd> <dt><kbd>S</kbd></dt> <dd>Focus the search field</dd> <dt><kbd>↑</kbd></dt> <dd>Move up in search results</dd> <dt><kbd>↓</kbd></dt> <dd>Move down in search results</dd> <dt><kbd>↹</kbd></dt> <dd>Switch tab</dd> <dt><kbd>⏎</kbd></dt> <dd>Go to active search result</dd> <dt><kbd>+</kbd></dt> <dd>Expand all sections</dd> <dt><kbd>-</kbd></dt> <dd>Collapse all sections</dd> </dl> </div> <div class="infos"> <h2>Search Tricks</h2> <p> Prefix searches with a type followed by a colon (e.g. <code>fn:</code>) to restrict the search to a given type. </p> <p> Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>. </p> <p> Search functions by type signature (e.g. <code>vec -> usize</code> or <code>* -> vec</code>) </p> </div> </div> </aside> <script> window.rootPath = "../../../../"; window.currentCrate = "std"; </script> <script src="../../../../main.js"></script> <script defer src="../../../../search-index.js"></script> </body> </html>