| <!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="A multi-producer, single-consumer queue for sending values between asynchronous tasks."><meta name="keywords" content="rust, rustlang, rust-lang, mpsc"><title>tokio::sync::mpsc - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../normalize.css"><link rel="stylesheet" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../ayu.css" disabled><link rel="stylesheet" href="../../../dark.css" disabled><link rel="stylesheet" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script defer src="../../../main.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../favicon.svg"></head><body class="rustdoc mod"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../../../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Module mpsc</a></h2><div class="sidebar-elems"><section><ul class="block"><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li><li><a href="#functions">Functions</a></li></ul></section></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Module <a href="../../index.html">tokio</a>::<wbr><a href="../index.html">sync</a>::<wbr><a class="mod" href="#">mpsc</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../../../src/tokio/sync/mpsc/mod.rs.html#1-121">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A multi-producer, single-consumer queue for sending values between |
| asynchronous tasks.</p> |
| <p>This module provides two variants of the channel: bounded and unbounded. The |
| bounded variant has a limit on the number of messages that the channel can |
| store, and if this limit is reached, trying to send another message will |
| wait until a message is received from the channel. An unbounded channel has |
| an infinite capacity, so the <code>send</code> method will always complete immediately. |
| This makes the <a href="struct.UnboundedSender.html"><code>UnboundedSender</code></a> usable from both synchronous and |
| asynchronous code.</p> |
| <p>Similar to the <code>mpsc</code> channels provided by <code>std</code>, the channel constructor |
| functions provide separate send and receive handles, <a href="struct.Sender.html"><code>Sender</code></a> and |
| <a href="struct.Receiver.html"><code>Receiver</code></a> for the bounded channel, <a href="struct.UnboundedSender.html"><code>UnboundedSender</code></a> and |
| <a href="struct.UnboundedReceiver.html"><code>UnboundedReceiver</code></a> for the unbounded channel. If there is no message to read, |
| the current task will be notified when a new value is sent. <a href="struct.Sender.html"><code>Sender</code></a> and |
| <a href="struct.UnboundedSender.html"><code>UnboundedSender</code></a> allow sending values into the channel. If the bounded |
| channel is at capacity, the send is rejected and the task will be notified |
| when additional capacity is available. In other words, the channel provides |
| backpressure.</p> |
| <p>This channel is also suitable for the single-producer single-consumer |
| use-case. (Unless you only need to send one message, in which case you |
| should use the <a href="../oneshot/index.html">oneshot</a> channel.)</p> |
| <h2 id="disconnection"><a href="#disconnection">Disconnection</a></h2> |
| <p>When all <a href="struct.Sender.html"><code>Sender</code></a> handles have been dropped, it is no longer |
| possible to send values into the channel. This is considered the termination |
| event of the stream. As such, <code>Receiver::poll</code> returns <code>Ok(Ready(None))</code>.</p> |
| <p>If the <a href="struct.Receiver.html"><code>Receiver</code></a> handle is dropped, then messages can no longer |
| be read out of the channel. In this case, all further attempts to send will |
| result in an error.</p> |
| <h2 id="clean-shutdown"><a href="#clean-shutdown">Clean Shutdown</a></h2> |
| <p>When the <a href="struct.Receiver.html"><code>Receiver</code></a> is dropped, it is possible for unprocessed messages to |
| remain in the channel. Instead, it is usually desirable to perform a “clean” |
| shutdown. To do this, the receiver first calls <code>close</code>, which will prevent |
| any further messages to be sent into the channel. Then, the receiver |
| consumes the channel to completion, at which point the receiver can be |
| dropped.</p> |
| <h2 id="communicating-between-sync-and-async-code"><a href="#communicating-between-sync-and-async-code">Communicating between sync and async code</a></h2> |
| <p>When you want to communicate between synchronous and asynchronous code, there |
| are two situations to consider:</p> |
| <p><strong>Bounded channel</strong>: If you need a bounded channel, you should use a bounded |
| Tokio <code>mpsc</code> channel for both directions of communication. Instead of calling |
| the async <a href="struct.Sender.html#method.send"><code>send</code></a> or <a href="struct.Receiver.html#method.recv"><code>recv</code></a> methods, in |
| synchronous code you will need to use the <a href="struct.Sender.html#method.blocking_send"><code>blocking_send</code></a> or |
| <a href="struct.Receiver.html#method.blocking_recv"><code>blocking_recv</code></a> methods.</p> |
| <p><strong>Unbounded channel</strong>: You should use the kind of channel that matches where |
| the receiver is. So for sending a message <em>from async to sync</em>, you should |
| use <a href="std::sync::mpsc::channel">the standard library unbounded channel</a> or |
| <a href="https://docs.rs/crossbeam/*/crossbeam/channel/fn.unbounded.html">crossbeam</a>. Similarly, for sending a message <em>from sync |
| to async</em>, you should use an unbounded Tokio <code>mpsc</code> channel.</p> |
| <p>Please be aware that the above remarks were written with the <code>mpsc</code> channel |
| in mind, but they can also be generalized to other kinds of channels. In |
| general, any channel method that isn’t marked async can be called anywhere, |
| including outside of the runtime. For example, sending a message on a |
| <a href="../oneshot/index.html">oneshot</a> channel from outside the runtime is perfectly fine.</p> |
| <h2 id="multiple-runtimes"><a href="#multiple-runtimes">Multiple runtimes</a></h2> |
| <p>The mpsc channel does not care about which runtime you use it in, and can be |
| used to send messages from one runtime to another. It can also be used in |
| non-Tokio runtimes.</p> |
| <p>There is one exception to the above: the <a href="struct.Sender.html#method.send_timeout"><code>send_timeout</code></a> must be used from |
| within a Tokio runtime, however it is still not tied to one specific Tokio |
| runtime, and the sender may be moved from one Tokio runtime to another.</p> |
| </div></details><h2 id="modules" class="small-section-header"><a href="#modules">Modules</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="mod" href="error/index.html" title="tokio::sync::mpsc::error mod">error</a></div><div class="item-right docblock-short">Channel error types.</div></div></div><h2 id="structs" class="small-section-header"><a href="#structs">Structs</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.OwnedPermit.html" title="tokio::sync::mpsc::OwnedPermit struct">OwnedPermit</a></div><div class="item-right docblock-short">Owned permit to send one value into the channel.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Permit.html" title="tokio::sync::mpsc::Permit struct">Permit</a></div><div class="item-right docblock-short">Permits to send one value into the channel.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Receiver.html" title="tokio::sync::mpsc::Receiver struct">Receiver</a></div><div class="item-right docblock-short">Receives values from the associated <code>Sender</code>.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Sender.html" title="tokio::sync::mpsc::Sender struct">Sender</a></div><div class="item-right docblock-short">Sends values to the associated <code>Receiver</code>.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.UnboundedReceiver.html" title="tokio::sync::mpsc::UnboundedReceiver struct">UnboundedReceiver</a></div><div class="item-right docblock-short">Receive values from the associated <code>UnboundedSender</code>.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.UnboundedSender.html" title="tokio::sync::mpsc::UnboundedSender struct">UnboundedSender</a></div><div class="item-right docblock-short">Send values to the associated <code>UnboundedReceiver</code>.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.WeakSender.html" title="tokio::sync::mpsc::WeakSender struct">WeakSender</a></div><div class="item-right docblock-short">A sender that does not prevent the channel from being closed.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.WeakUnboundedSender.html" title="tokio::sync::mpsc::WeakUnboundedSender struct">WeakUnboundedSender</a></div><div class="item-right docblock-short">An unbounded sender that does not prevent the channel from being closed.</div></div></div><h2 id="functions" class="small-section-header"><a href="#functions">Functions</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.channel.html" title="tokio::sync::mpsc::channel fn">channel</a></div><div class="item-right docblock-short">Creates a bounded mpsc channel for communicating between asynchronous tasks |
| with backpressure.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.unbounded_channel.html" title="tokio::sync::mpsc::unbounded_channel fn">unbounded_channel</a></div><div class="item-right docblock-short">Creates an unbounded mpsc channel for communicating between asynchronous |
| tasks without backpressure.</div></div></div></section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="tokio" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
