build: 2026-06-22
This commit is contained in:
626
build/ch17-03-more-futures.html
Normal file
626
build/ch17-03-more-futures.html
Normal file
@@ -0,0 +1,626 @@
|
||||
<!DOCTYPE HTML>
|
||||
<html lang="en" class="light sidebar-visible" dir="ltr">
|
||||
<head>
|
||||
<!-- Book generated using mdBook -->
|
||||
<meta charset="UTF-8">
|
||||
<title>Working With Any Number of Futures - The Rust Programming Language</title>
|
||||
|
||||
|
||||
<!-- Custom HTML head -->
|
||||
|
||||
<meta name="description" content="">
|
||||
<meta name="viewport" content="width=device-width, initial-scale=1">
|
||||
<meta name="theme-color" content="#ffffff">
|
||||
|
||||
<link rel="icon" href="favicon-de23e50b.svg">
|
||||
<link rel="shortcut icon" href="favicon-8114d1fc.png">
|
||||
<link rel="stylesheet" href="css/variables-8adf115d.css">
|
||||
<link rel="stylesheet" href="css/general-0392ca55.css">
|
||||
<link rel="stylesheet" href="css/chrome-fc474251.css">
|
||||
<link rel="stylesheet" href="css/print-9e4910d8.css" media="print">
|
||||
|
||||
<!-- Fonts -->
|
||||
<link rel="stylesheet" href="fonts/fonts-9644e21d.css">
|
||||
|
||||
<!-- Highlight.js Stylesheets -->
|
||||
<link rel="stylesheet" id="mdbook-highlight-css" href="highlight-493f70e1.css">
|
||||
<link rel="stylesheet" id="mdbook-tomorrow-night-css" href="tomorrow-night-4c0ae647.css">
|
||||
<link rel="stylesheet" id="mdbook-ayu-highlight-css" href="ayu-highlight-3fdfc3ac.css">
|
||||
|
||||
<!-- Custom theme stylesheets -->
|
||||
<link rel="stylesheet" href="ferris-d33b75bf.css">
|
||||
<link rel="stylesheet" href="theme/2018-edition-4e126c62.css">
|
||||
<link rel="stylesheet" href="theme/semantic-notes-9b5766c0.css">
|
||||
<link rel="stylesheet" href="theme/listing-cab26221.css">
|
||||
|
||||
|
||||
<!-- Provide site root and default themes to javascript -->
|
||||
<script>
|
||||
const path_to_root = "";
|
||||
const default_light_theme = "light";
|
||||
const default_dark_theme = "navy";
|
||||
window.path_to_searchindex_js = "searchindex-6a1da8cc.js";
|
||||
</script>
|
||||
<!-- Start loading toc.js asap -->
|
||||
<script src="toc-0e4ce700.js"></script>
|
||||
</head>
|
||||
<body>
|
||||
<div id="mdbook-help-container">
|
||||
<div id="mdbook-help-popup">
|
||||
<h2 class="mdbook-help-title">Keyboard shortcuts</h2>
|
||||
<div>
|
||||
<p>Press <kbd>←</kbd> or <kbd>→</kbd> to navigate between chapters</p>
|
||||
<p>Press <kbd>S</kbd> or <kbd>/</kbd> to search in the book</p>
|
||||
<p>Press <kbd>?</kbd> to show this help</p>
|
||||
<p>Press <kbd>Esc</kbd> to hide this help</p>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
<div id="mdbook-body-container">
|
||||
<!-- Work around some values being stored in localStorage wrapped in quotes -->
|
||||
<script>
|
||||
try {
|
||||
let theme = localStorage.getItem('mdbook-theme');
|
||||
let sidebar = localStorage.getItem('mdbook-sidebar');
|
||||
|
||||
if (theme.startsWith('"') && theme.endsWith('"')) {
|
||||
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
|
||||
}
|
||||
|
||||
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
|
||||
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
|
||||
}
|
||||
} catch (e) { }
|
||||
</script>
|
||||
|
||||
<!-- Set the theme before any content is loaded, prevents flash -->
|
||||
<script>
|
||||
const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme;
|
||||
let theme;
|
||||
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
|
||||
if (theme === null || theme === undefined) { theme = default_theme; }
|
||||
const html = document.documentElement;
|
||||
html.classList.remove('light')
|
||||
html.classList.add(theme);
|
||||
html.classList.add("js");
|
||||
</script>
|
||||
|
||||
<input type="checkbox" id="mdbook-sidebar-toggle-anchor" class="hidden">
|
||||
|
||||
<!-- Hide / unhide sidebar before it is displayed -->
|
||||
<script>
|
||||
let sidebar = null;
|
||||
const sidebar_toggle = document.getElementById("mdbook-sidebar-toggle-anchor");
|
||||
if (document.body.clientWidth >= 1080) {
|
||||
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
|
||||
sidebar = sidebar || 'visible';
|
||||
} else {
|
||||
sidebar = 'hidden';
|
||||
sidebar_toggle.checked = false;
|
||||
}
|
||||
if (sidebar === 'visible') {
|
||||
sidebar_toggle.checked = true;
|
||||
} else {
|
||||
html.classList.remove('sidebar-visible');
|
||||
}
|
||||
</script>
|
||||
|
||||
<nav id="mdbook-sidebar" class="sidebar" aria-label="Table of contents">
|
||||
<!-- populated by js -->
|
||||
<mdbook-sidebar-scrollbox class="sidebar-scrollbox"></mdbook-sidebar-scrollbox>
|
||||
<noscript>
|
||||
<iframe class="sidebar-iframe-outer" src="toc.html"></iframe>
|
||||
</noscript>
|
||||
<div id="mdbook-sidebar-resize-handle" class="sidebar-resize-handle">
|
||||
<div class="sidebar-resize-indicator"></div>
|
||||
</div>
|
||||
</nav>
|
||||
|
||||
<div id="mdbook-page-wrapper" class="page-wrapper">
|
||||
|
||||
<div class="page">
|
||||
<div id="mdbook-menu-bar-hover-placeholder"></div>
|
||||
<div id="mdbook-menu-bar" class="menu-bar sticky">
|
||||
<div class="left-buttons">
|
||||
<label id="mdbook-sidebar-toggle" class="icon-button" for="mdbook-sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="mdbook-sidebar">
|
||||
<span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M0 96C0 78.3 14.3 64 32 64H416c17.7 0 32 14.3 32 32s-14.3 32-32 32H32C14.3 128 0 113.7 0 96zM0 256c0-17.7 14.3-32 32-32H416c17.7 0 32 14.3 32 32s-14.3 32-32 32H32c-17.7 0-32-14.3-32-32zM448 416c0 17.7-14.3 32-32 32H32c-17.7 0-32-14.3-32-32s14.3-32 32-32H416c17.7 0 32 14.3 32 32z"/></svg></span>
|
||||
</label>
|
||||
<button id="mdbook-theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="mdbook-theme-list">
|
||||
<span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 576 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M371.3 367.1c27.3-3.9 51.9-19.4 67.2-42.9L600.2 74.1c12.6-19.5 9.4-45.3-7.6-61.2S549.7-4.4 531.1 9.6L294.4 187.2c-24 18-38.2 46.1-38.4 76.1L371.3 367.1zm-19.6 25.4l-116-104.4C175.9 290.3 128 339.6 128 400c0 3.9 .2 7.8 .6 11.6c1.8 17.5-10.2 36.4-27.8 36.4H96c-17.7 0-32 14.3-32 32s14.3 32 32 32H240c61.9 0 112-50.1 112-112c0-2.5-.1-5-.2-7.5z"/></svg></span>
|
||||
</button>
|
||||
<ul id="mdbook-theme-list" class="theme-popup" aria-label="Themes" role="menu">
|
||||
<li role="none"><button role="menuitem" class="theme" id="mdbook-theme-default_theme">Auto</button></li>
|
||||
<li role="none"><button role="menuitem" class="theme" id="mdbook-theme-light">Light</button></li>
|
||||
<li role="none"><button role="menuitem" class="theme" id="mdbook-theme-rust">Rust</button></li>
|
||||
<li role="none"><button role="menuitem" class="theme" id="mdbook-theme-coal">Coal</button></li>
|
||||
<li role="none"><button role="menuitem" class="theme" id="mdbook-theme-navy">Navy</button></li>
|
||||
<li role="none"><button role="menuitem" class="theme" id="mdbook-theme-ayu">Ayu</button></li>
|
||||
</ul>
|
||||
<button id="mdbook-search-toggle" class="icon-button" type="button" title="Search (`/`)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="/ s" aria-controls="mdbook-searchbar">
|
||||
<span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M416 208c0 45.9-14.9 88.3-40 122.7L502.6 457.4c12.5 12.5 12.5 32.8 0 45.3s-32.8 12.5-45.3 0L330.7 376c-34.4 25.2-76.8 40-122.7 40C93.1 416 0 322.9 0 208S93.1 0 208 0S416 93.1 416 208zM208 352c79.5 0 144-64.5 144-144s-64.5-144-144-144S64 128.5 64 208s64.5 144 144 144z"/></svg></span>
|
||||
</button>
|
||||
</div>
|
||||
|
||||
<h1 class="menu-title">The Rust Programming Language</h1>
|
||||
|
||||
<div class="right-buttons">
|
||||
<a href="print.html" title="Print this book" aria-label="Print this book">
|
||||
<span class=fa-svg id="print-button"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M128 0C92.7 0 64 28.7 64 64v96h64V64H354.7L384 93.3V160h64V93.3c0-17-6.7-33.3-18.7-45.3L400 18.7C388 6.7 371.7 0 354.7 0H128zM384 352v32 64H128V384 368 352H384zm64 32h32c17.7 0 32-14.3 32-32V256c0-35.3-28.7-64-64-64H64c-35.3 0-64 28.7-64 64v96c0 17.7 14.3 32 32 32H64v64c0 35.3 28.7 64 64 64H384c35.3 0 64-28.7 64-64V384zm-16-88c-13.3 0-24-10.7-24-24s10.7-24 24-24s24 10.7 24 24s-10.7 24-24 24z"/></svg></span>
|
||||
</a>
|
||||
<a href="https://github.com/rust-lang/book" title="Git repository" aria-label="Git repository">
|
||||
<span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 496 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M165.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6zm-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3zm44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9zM244.8 8C106.1 8 0 113.3 0 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8zM97.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1zm-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7zm32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1zm-11.4-14.7c-1.6 1-1.6 3.6 0 5.9 1.6 2.3 4.3 3.3 5.6 2.3 1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2z"/></svg></span>
|
||||
</a>
|
||||
|
||||
</div>
|
||||
</div>
|
||||
|
||||
<div id="mdbook-search-wrapper" class="hidden">
|
||||
<form id="mdbook-searchbar-outer" class="searchbar-outer">
|
||||
<div class="search-wrapper">
|
||||
<input type="search" id="mdbook-searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="mdbook-searchresults-outer" aria-describedby="searchresults-header">
|
||||
<div class="spinner-wrapper">
|
||||
<span class=fa-svg id="fa-spin"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M304 48c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zm0 416c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zM48 304c26.5 0 48-21.5 48-48s-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48zm464-48c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zM142.9 437c18.7-18.7 18.7-49.1 0-67.9s-49.1-18.7-67.9 0s-18.7 49.1 0 67.9s49.1 18.7 67.9 0zm0-294.2c18.7-18.7 18.7-49.1 0-67.9S93.7 56.2 75 75s-18.7 49.1 0 67.9s49.1 18.7 67.9 0zM369.1 437c18.7 18.7 49.1 18.7 67.9 0s18.7-49.1 0-67.9s-49.1-18.7-67.9 0s-18.7 49.1 0 67.9z"/></svg></span>
|
||||
</div>
|
||||
</div>
|
||||
</form>
|
||||
<div id="mdbook-searchresults-outer" class="searchresults-outer hidden">
|
||||
<div id="mdbook-searchresults-header" class="searchresults-header"></div>
|
||||
<ul id="mdbook-searchresults">
|
||||
</ul>
|
||||
</div>
|
||||
</div>
|
||||
|
||||
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
|
||||
<script>
|
||||
document.getElementById('mdbook-sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
|
||||
document.getElementById('mdbook-sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
|
||||
Array.from(document.querySelectorAll('#mdbook-sidebar a')).forEach(function(link) {
|
||||
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
|
||||
});
|
||||
</script>
|
||||
|
||||
<div id="mdbook-content" class="content">
|
||||
<main>
|
||||
<!-- Old headings. Do not remove or links may break. -->
|
||||
<p><a id="yielding"></a></p>
|
||||
<h3 id="yielding-control-to-the-runtime"><a class="header" href="#yielding-control-to-the-runtime">Yielding Control to the Runtime</a></h3>
|
||||
<p>Recall from the <a href="ch17-01-futures-and-syntax.html#our-first-async-program">“Our First Async Program”</a><!-- ignore -->
|
||||
section that at each await point, Rust gives a runtime a chance to pause the
|
||||
task and switch to another one if the future being awaited isn’t ready. The
|
||||
inverse is also true: Rust <em>only</em> pauses async blocks and hands control back to
|
||||
a runtime at an await point. Everything between await points is synchronous.</p>
|
||||
<p>That means if you do a bunch of work in an async block without an await point,
|
||||
that future will block any other futures from making progress. You may sometimes
|
||||
hear this referred to as one future <em>starving</em> other futures. In some cases,
|
||||
that may not be a big deal. However, if you are doing some kind of expensive
|
||||
setup or long-running work, or if you have a future that will keep doing some
|
||||
particular task indefinitely, you’ll need to think about when and where to hand
|
||||
control back to the runtime.</p>
|
||||
<p>Let’s simulate a long-running operation to illustrate the starvation problem,
|
||||
then explore how to solve it. Listing 17-14 introduces a <code>slow</code> function.</p>
|
||||
<figure class="listing" id="listing-17-14">
|
||||
<span class="file-name">Filename: src/main.rs</span>
|
||||
<pre class="playground"><code class="language-rust edition2024"><span class="boring">extern crate trpl; // required for mdbook test
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">use std::{thread, time::Duration};
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">fn main() {
|
||||
</span><span class="boring"> trpl::block_on(async {
|
||||
</span><span class="boring"> // We will call `slow` here later
|
||||
</span><span class="boring"> });
|
||||
</span><span class="boring">}
|
||||
</span><span class="boring">
|
||||
</span>fn slow(name: &str, ms: u64) {
|
||||
thread::sleep(Duration::from_millis(ms));
|
||||
println!("'{name}' ran for {ms}ms");
|
||||
}</code></pre>
|
||||
<figcaption><a href="#listing-17-14">Listing 17-14</a>: Using <code>thread::sleep</code> to simulate slow operations</figcaption>
|
||||
</figure>
|
||||
<p>This code uses <code>std::thread::sleep</code> instead of <code>trpl::sleep</code> so that calling
|
||||
<code>slow</code> will block the current thread for some number of milliseconds. We can
|
||||
use <code>slow</code> to stand in for real-world operations that are both long-running and
|
||||
blocking.</p>
|
||||
<p>In Listing 17-15, we use <code>slow</code> to emulate doing this kind of CPU-bound work in
|
||||
a pair of futures.</p>
|
||||
<figure class="listing" id="listing-17-15">
|
||||
<span class="file-name">Filename: src/main.rs</span>
|
||||
<pre class="playground"><code class="language-rust edition2024"><span class="boring">extern crate trpl; // required for mdbook test
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">use std::{thread, time::Duration};
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">fn main() {
|
||||
</span><span class="boring"> trpl::block_on(async {
|
||||
</span> let a = async {
|
||||
println!("'a' started.");
|
||||
slow("a", 30);
|
||||
slow("a", 10);
|
||||
slow("a", 20);
|
||||
trpl::sleep(Duration::from_millis(50)).await;
|
||||
println!("'a' finished.");
|
||||
};
|
||||
|
||||
let b = async {
|
||||
println!("'b' started.");
|
||||
slow("b", 75);
|
||||
slow("b", 10);
|
||||
slow("b", 15);
|
||||
slow("b", 350);
|
||||
trpl::sleep(Duration::from_millis(50)).await;
|
||||
println!("'b' finished.");
|
||||
};
|
||||
|
||||
trpl::select(a, b).await;
|
||||
<span class="boring"> });
|
||||
</span><span class="boring">}
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">fn slow(name: &str, ms: u64) {
|
||||
</span><span class="boring"> thread::sleep(Duration::from_millis(ms));
|
||||
</span><span class="boring"> println!("'{name}' ran for {ms}ms");
|
||||
</span><span class="boring">}</span></code></pre>
|
||||
<figcaption><a href="#listing-17-15">Listing 17-15</a>: Calling the <code>slow</code> function to simulate slow operations</figcaption>
|
||||
</figure>
|
||||
<p>Each future hands control back to the runtime only <em>after</em> carrying out a bunch
|
||||
of slow operations. If you run this code, you will see this output:</p>
|
||||
<!-- manual-regeneration
|
||||
cd listings/ch17-async-await/listing-17-15/
|
||||
cargo run
|
||||
copy just the output
|
||||
-->
|
||||
<pre><code class="language-text">'a' started.
|
||||
'a' ran for 30ms
|
||||
'a' ran for 10ms
|
||||
'a' ran for 20ms
|
||||
'b' started.
|
||||
'b' ran for 75ms
|
||||
'b' ran for 10ms
|
||||
'b' ran for 15ms
|
||||
'b' ran for 350ms
|
||||
'a' finished.
|
||||
</code></pre>
|
||||
<p>As with Listing 17-5 where we used <code>trpl::select</code> to race futures fetching two
|
||||
URLs, <code>select</code> still finishes as soon as <code>a</code> is done. There’s no interleaving
|
||||
between the calls to <code>slow</code> in the two futures, though. The <code>a</code> future does all
|
||||
of its work until the <code>trpl::sleep</code> call is awaited, then the <code>b</code> future does
|
||||
all of its work until its own <code>trpl::sleep</code> call is awaited, and finally the
|
||||
<code>a</code> future completes. To allow both futures to make progress between their slow
|
||||
tasks, we need await points so we can hand control back to the runtime. That
|
||||
means we need something we can await!</p>
|
||||
<p>We can already see this kind of handoff happening in Listing 17-15: if we
|
||||
removed the <code>trpl::sleep</code> at the end of the <code>a</code> future, it would complete
|
||||
without the <code>b</code> future running <em>at all</em>. Let’s try using the <code>trpl::sleep</code>
|
||||
function as a starting point for letting operations switch off making progress,
|
||||
as shown in Listing 17-16.</p>
|
||||
<figure class="listing" id="listing-17-16">
|
||||
<span class="file-name">Filename: src/main.rs</span>
|
||||
<pre class="playground"><code class="language-rust edition2024"><span class="boring">extern crate trpl; // required for mdbook test
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">use std::{thread, time::Duration};
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">fn main() {
|
||||
</span><span class="boring"> trpl::block_on(async {
|
||||
</span> let one_ms = Duration::from_millis(1);
|
||||
|
||||
let a = async {
|
||||
println!("'a' started.");
|
||||
slow("a", 30);
|
||||
trpl::sleep(one_ms).await;
|
||||
slow("a", 10);
|
||||
trpl::sleep(one_ms).await;
|
||||
slow("a", 20);
|
||||
trpl::sleep(one_ms).await;
|
||||
println!("'a' finished.");
|
||||
};
|
||||
|
||||
let b = async {
|
||||
println!("'b' started.");
|
||||
slow("b", 75);
|
||||
trpl::sleep(one_ms).await;
|
||||
slow("b", 10);
|
||||
trpl::sleep(one_ms).await;
|
||||
slow("b", 15);
|
||||
trpl::sleep(one_ms).await;
|
||||
slow("b", 350);
|
||||
trpl::sleep(one_ms).await;
|
||||
println!("'b' finished.");
|
||||
};
|
||||
<span class="boring">
|
||||
</span><span class="boring"> trpl::select(a, b).await;
|
||||
</span><span class="boring"> });
|
||||
</span><span class="boring">}
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">fn slow(name: &str, ms: u64) {
|
||||
</span><span class="boring"> thread::sleep(Duration::from_millis(ms));
|
||||
</span><span class="boring"> println!("'{name}' ran for {ms}ms");
|
||||
</span><span class="boring">}</span></code></pre>
|
||||
<figcaption><a href="#listing-17-16">Listing 17-16</a>: Using <code>trpl::sleep</code> to let operations switch off making progress</figcaption>
|
||||
</figure>
|
||||
<p>We’ve added <code>trpl::sleep</code> calls with await points between each call to <code>slow</code>.
|
||||
Now the two futures’ work is interleaved:</p>
|
||||
<!-- manual-regeneration
|
||||
cd listings/ch17-async-await/listing-17-16
|
||||
cargo run
|
||||
copy just the output
|
||||
-->
|
||||
<pre><code class="language-text">'a' started.
|
||||
'a' ran for 30ms
|
||||
'b' started.
|
||||
'b' ran for 75ms
|
||||
'a' ran for 10ms
|
||||
'b' ran for 10ms
|
||||
'a' ran for 20ms
|
||||
'b' ran for 15ms
|
||||
'a' finished.
|
||||
</code></pre>
|
||||
<p>The <code>a</code> future still runs for a bit before handing off control to <code>b</code>, because
|
||||
it calls <code>slow</code> before ever calling <code>trpl::sleep</code>, but after that the futures
|
||||
swap back and forth each time one of them hits an await point. In this case, we
|
||||
have done that after every call to <code>slow</code>, but we could break up the work in
|
||||
whatever way makes the most sense to us.</p>
|
||||
<p>We don’t really want to <em>sleep</em> here, though: we want to make progress as fast
|
||||
as we can. We just need to hand back control to the runtime. We can do that
|
||||
directly, using the <code>trpl::yield_now</code> function. In Listing 17-17, we replace
|
||||
all those <code>trpl::sleep</code> calls with <code>trpl::yield_now</code>.</p>
|
||||
<figure class="listing" id="listing-17-17">
|
||||
<span class="file-name">Filename: src/main.rs</span>
|
||||
<pre class="playground"><code class="language-rust edition2024"><span class="boring">extern crate trpl; // required for mdbook test
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">use std::{thread, time::Duration};
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">fn main() {
|
||||
</span><span class="boring"> trpl::block_on(async {
|
||||
</span> let a = async {
|
||||
println!("'a' started.");
|
||||
slow("a", 30);
|
||||
trpl::yield_now().await;
|
||||
slow("a", 10);
|
||||
trpl::yield_now().await;
|
||||
slow("a", 20);
|
||||
trpl::yield_now().await;
|
||||
println!("'a' finished.");
|
||||
};
|
||||
|
||||
let b = async {
|
||||
println!("'b' started.");
|
||||
slow("b", 75);
|
||||
trpl::yield_now().await;
|
||||
slow("b", 10);
|
||||
trpl::yield_now().await;
|
||||
slow("b", 15);
|
||||
trpl::yield_now().await;
|
||||
slow("b", 350);
|
||||
trpl::yield_now().await;
|
||||
println!("'b' finished.");
|
||||
};
|
||||
<span class="boring">
|
||||
</span><span class="boring"> trpl::select(a, b).await;
|
||||
</span><span class="boring"> });
|
||||
</span><span class="boring">}
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">fn slow(name: &str, ms: u64) {
|
||||
</span><span class="boring"> thread::sleep(Duration::from_millis(ms));
|
||||
</span><span class="boring"> println!("'{name}' ran for {ms}ms");
|
||||
</span><span class="boring">}</span></code></pre>
|
||||
<figcaption><a href="#listing-17-17">Listing 17-17</a>: Using <code>yield_now</code> to let operations switch off making progress</figcaption>
|
||||
</figure>
|
||||
<p>This code is both clearer about the actual intent and can be significantly
|
||||
faster than using <code>sleep</code>, because timers such as the one used by <code>sleep</code> often
|
||||
have limits on how granular they can be. The version of <code>sleep</code> we are using,
|
||||
for example, will always sleep for at least a millisecond, even if we pass it a
|
||||
<code>Duration</code> of one nanosecond. Again, modern computers are <em>fast</em>: they can do a
|
||||
lot in one millisecond!</p>
|
||||
<p>This means that async can be useful even for compute-bound tasks, depending on
|
||||
what else your program is doing, because it provides a useful tool for
|
||||
structuring the relationships between different parts of the program (but at a
|
||||
cost of the overhead of the async state machine). This is a form of
|
||||
<em>cooperative multitasking</em>, where each future has the power to determine when
|
||||
it hands over control via await points. Each future therefore also has the
|
||||
responsibility to avoid blocking for too long. In some Rust-based embedded
|
||||
operating systems, this is the <em>only</em> kind of multitasking!</p>
|
||||
<p>In real-world code, you won’t usually be alternating function calls with await
|
||||
points on every single line, of course. While yielding control in this way is
|
||||
relatively inexpensive, it’s not free. In many cases, trying to break up a
|
||||
compute-bound task might make it significantly slower, so sometimes it’s better
|
||||
for <em>overall</em> performance to let an operation block briefly. Always
|
||||
measure to see what your code’s actual performance bottlenecks are. The
|
||||
underlying dynamic is important to keep in mind, though, if you <em>are</em> seeing a
|
||||
lot of work happening in serial that you expected to happen concurrently!</p>
|
||||
<h3 id="building-our-own-async-abstractions"><a class="header" href="#building-our-own-async-abstractions">Building Our Own Async Abstractions</a></h3>
|
||||
<p>We can also compose futures together to create new patterns. For example, we can
|
||||
build a <code>timeout</code> function with async building blocks we already have. When
|
||||
we’re done, the result will be another building block we could use to create
|
||||
still more async abstractions.</p>
|
||||
<p>Listing 17-18 shows how we would expect this <code>timeout</code> to work with a slow
|
||||
future.</p>
|
||||
<figure class="listing" id="listing-17-18">
|
||||
<span class="file-name">Filename: src/main.rs</span>
|
||||
<pre><code class="language-rust ignore does_not_compile"><span class="boring">extern crate trpl; // required for mdbook test
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">use std::time::Duration;
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">fn main() {
|
||||
</span><span class="boring"> trpl::block_on(async {
|
||||
</span> let slow = async {
|
||||
trpl::sleep(Duration::from_secs(5)).await;
|
||||
"Finally finished"
|
||||
};
|
||||
|
||||
match timeout(slow, Duration::from_secs(2)).await {
|
||||
Ok(message) => println!("Succeeded with '{message}'"),
|
||||
Err(duration) => {
|
||||
println!("Failed after {} seconds", duration.as_secs())
|
||||
}
|
||||
}
|
||||
<span class="boring"> });
|
||||
</span><span class="boring">}</span></code></pre>
|
||||
<figcaption><a href="#listing-17-18">Listing 17-18</a>: Using our imagined <code>timeout</code> to run a slow operation with a time limit</figcaption>
|
||||
</figure>
|
||||
<p>Let’s implement this! To begin, let’s think about the API for <code>timeout</code>:</p>
|
||||
<ul>
|
||||
<li>It needs to be an async function itself so we can await it.</li>
|
||||
<li>Its first parameter should be a future to run. We can make it generic to allow
|
||||
it to work with any future.</li>
|
||||
<li>Its second parameter will be the maximum time to wait. If we use a <code>Duration</code>,
|
||||
that will make it easy to pass along to <code>trpl::sleep</code>.</li>
|
||||
<li>It should return a <code>Result</code>. If the future completes successfully, the
|
||||
<code>Result</code> will be <code>Ok</code> with the value produced by the future. If the timeout
|
||||
elapses first, the <code>Result</code> will be <code>Err</code> with the duration that the timeout
|
||||
waited for.</li>
|
||||
</ul>
|
||||
<p>Listing 17-19 shows this declaration.</p>
|
||||
<!-- This is not tested because it intentionally does not compile. -->
|
||||
<figure class="listing" id="listing-17-19">
|
||||
<span class="file-name">Filename: src/main.rs</span>
|
||||
<pre><code class="language-rust ignore does_not_compile"><span class="boring">extern crate trpl; // required for mdbook test
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">use std::time::Duration;
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">fn main() {
|
||||
</span><span class="boring"> trpl::block_on(async {
|
||||
</span><span class="boring"> let slow = async {
|
||||
</span><span class="boring"> trpl::sleep(Duration::from_secs(5)).await;
|
||||
</span><span class="boring"> "Finally finished"
|
||||
</span><span class="boring"> };
|
||||
</span><span class="boring">
|
||||
</span><span class="boring"> match timeout(slow, Duration::from_secs(2)).await {
|
||||
</span><span class="boring"> Ok(message) => println!("Succeeded with '{message}'"),
|
||||
</span><span class="boring"> Err(duration) => {
|
||||
</span><span class="boring"> println!("Failed after {} seconds", duration.as_secs())
|
||||
</span><span class="boring"> }
|
||||
</span><span class="boring"> }
|
||||
</span><span class="boring"> });
|
||||
</span><span class="boring">}
|
||||
</span><span class="boring">
|
||||
</span>async fn timeout<F: Future>(
|
||||
future_to_try: F,
|
||||
max_time: Duration,
|
||||
) -> Result<F::Output, Duration> {
|
||||
// Here is where our implementation will go!
|
||||
}</code></pre>
|
||||
<figcaption><a href="#listing-17-19">Listing 17-19</a>: Defining the signature of <code>timeout</code></figcaption>
|
||||
</figure>
|
||||
<p>That satisfies our goals for the types. Now let’s think about the <em>behavior</em> we
|
||||
need: we want to race the future passed in against the duration. We can use
|
||||
<code>trpl::sleep</code> to make a timer future from the duration, and use <code>trpl::select</code>
|
||||
to run that timer with the future the caller passes in.</p>
|
||||
<p>In Listing 17-20, we implement <code>timeout</code> by matching on the result of awaiting
|
||||
<code>trpl::select</code>.</p>
|
||||
<figure class="listing" id="listing-17-20">
|
||||
<span class="file-name">Filename: src/main.rs</span>
|
||||
<pre class="playground"><code class="language-rust edition2024"><span class="boring">extern crate trpl; // required for mdbook test
|
||||
</span><span class="boring">
|
||||
</span><span class="boring">use std::time::Duration;
|
||||
</span><span class="boring">
|
||||
</span>use trpl::Either;
|
||||
|
||||
// --snip--
|
||||
|
||||
<span class="boring">fn main() {
|
||||
</span><span class="boring"> trpl::block_on(async {
|
||||
</span><span class="boring"> let slow = async {
|
||||
</span><span class="boring"> trpl::sleep(Duration::from_secs(5)).await;
|
||||
</span><span class="boring"> "Finally finished"
|
||||
</span><span class="boring"> };
|
||||
</span><span class="boring">
|
||||
</span><span class="boring"> match timeout(slow, Duration::from_secs(2)).await {
|
||||
</span><span class="boring"> Ok(message) => println!("Succeeded with '{message}'"),
|
||||
</span><span class="boring"> Err(duration) => {
|
||||
</span><span class="boring"> println!("Failed after {} seconds", duration.as_secs())
|
||||
</span><span class="boring"> }
|
||||
</span><span class="boring"> }
|
||||
</span><span class="boring"> });
|
||||
</span><span class="boring">}
|
||||
</span><span class="boring">
|
||||
</span>async fn timeout<F: Future>(
|
||||
future_to_try: F,
|
||||
max_time: Duration,
|
||||
) -> Result<F::Output, Duration> {
|
||||
match trpl::select(future_to_try, trpl::sleep(max_time)).await {
|
||||
Either::Left(output) => Ok(output),
|
||||
Either::Right(_) => Err(max_time),
|
||||
}
|
||||
}</code></pre>
|
||||
<figcaption><a href="#listing-17-20">Listing 17-20</a>: Defining <code>timeout</code> with <code>select</code> and <code>sleep</code></figcaption>
|
||||
</figure>
|
||||
<p>The implementation of <code>trpl::select</code> is not fair: it always polls arguments in
|
||||
the order in which they are passed (other <code>select</code> implementations will
|
||||
randomly choose which argument to poll first). Thus, we pass <code>future_to_try</code> to
|
||||
<code>select</code> first so it gets a chance to complete even if <code>max_time</code> is a very
|
||||
short duration. If <code>future_to_try</code> finishes first, <code>select</code> will return <code>Left</code>
|
||||
with the output from <code>future_to_try</code>. If <code>timer</code> finishes first, <code>select</code> will
|
||||
return <code>Right</code> with the timer’s output of <code>()</code>.</p>
|
||||
<p>If the <code>future_to_try</code> succeeds and we get a <code>Left(output)</code>, we return
|
||||
<code>Ok(output)</code>. If the sleep timer elapses instead and we get a <code>Right(())</code>, we
|
||||
ignore the <code>()</code> with <code>_</code> and return <code>Err(max_time)</code> instead.</p>
|
||||
<p>With that, we have a working <code>timeout</code> built out of two other async helpers. If
|
||||
we run our code, it will print the failure mode after the timeout:</p>
|
||||
<pre><code class="language-text">Failed after 2 seconds
|
||||
</code></pre>
|
||||
<p>Because futures compose with other futures, you can build really powerful tools
|
||||
using smaller async building blocks. For example, you can use this same
|
||||
approach to combine timeouts with retries, and in turn use those with
|
||||
operations such as network calls (such as those in Listing 17-5).</p>
|
||||
<p>In practice, you’ll usually work directly with <code>async</code> and <code>await</code>, and
|
||||
secondarily with functions such as <code>select</code> and macros such as the <code>join!</code>
|
||||
macro to control how the outermost futures are executed.</p>
|
||||
<p>We’ve now seen a number of ways to work with multiple futures at the same time.
|
||||
Up next, we’ll look at how we can work with multiple futures in a sequence over
|
||||
time with <em>streams</em>.</p>
|
||||
|
||||
</main>
|
||||
|
||||
<nav class="nav-wrapper" aria-label="Page navigation">
|
||||
<!-- Mobile navigation buttons -->
|
||||
<a rel="prev" href="ch17-02-concurrency-with-async.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
||||
<span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 320 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M41.4 233.4c-12.5 12.5-12.5 32.8 0 45.3l160 160c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 256 246.6 118.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-160 160z"/></svg></span>
|
||||
</a>
|
||||
|
||||
<a rel="next prefetch" href="ch17-04-streams.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
||||
<span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 320 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M278.6 233.4c12.5 12.5 12.5 32.8 0 45.3l-160 160c-12.5 12.5-32.8 12.5-45.3 0s-12.5-32.8 0-45.3L210.7 256 73.4 118.6c-12.5-12.5-12.5-32.8 0-45.3s32.8-12.5 45.3 0l160 160z"/></svg></span>
|
||||
</a>
|
||||
|
||||
<div style="clear: both"></div>
|
||||
</nav>
|
||||
</div>
|
||||
</div>
|
||||
|
||||
<nav class="nav-wide-wrapper" aria-label="Page navigation">
|
||||
<a rel="prev" href="ch17-02-concurrency-with-async.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
|
||||
<span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 320 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M41.4 233.4c-12.5 12.5-12.5 32.8 0 45.3l160 160c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 256 246.6 118.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-160 160z"/></svg></span>
|
||||
</a>
|
||||
|
||||
<a rel="next prefetch" href="ch17-04-streams.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
|
||||
<span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 320 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M278.6 233.4c12.5 12.5 12.5 32.8 0 45.3l-160 160c-12.5 12.5-32.8 12.5-45.3 0s-12.5-32.8 0-45.3L210.7 256 73.4 118.6c-12.5-12.5-12.5-32.8 0-45.3s32.8-12.5 45.3 0l160 160z"/></svg></span>
|
||||
</a>
|
||||
</nav>
|
||||
|
||||
</div>
|
||||
|
||||
<template id=fa-eye><span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 576 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M288 32c-80.8 0-145.5 36.8-192.6 80.6C48.6 156 17.3 208 2.5 243.7c-3.3 7.9-3.3 16.7 0 24.6C17.3 304 48.6 356 95.4 399.4C142.5 443.2 207.2 480 288 480s145.5-36.8 192.6-80.6c46.8-43.5 78.1-95.4 93-131.1c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C433.5 68.8 368.8 32 288 32zM432 256c0 79.5-64.5 144-144 144s-144-64.5-144-144s64.5-144 144-144s144 64.5 144 144zM288 192c0 35.3-28.7 64-64 64c-11.5 0-22.3-3-31.6-8.4c-.2 2.8-.4 5.5-.4 8.4c0 53 43 96 96 96s96-43 96-96s-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6z"/></svg></span></template>
|
||||
<template id=fa-eye-slash><span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 640 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M38.8 5.1C28.4-3.1 13.3-1.2 5.1 9.2S-1.2 34.7 9.2 42.9l592 464c10.4 8.2 25.5 6.3 33.7-4.1s6.3-25.5-4.1-33.7L525.6 386.7c39.6-40.6 66.4-86.1 79.9-118.4c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C465.5 68.8 400.8 32 320 32c-68.2 0-125 26.3-169.3 60.8L38.8 5.1zM223.1 149.5C248.6 126.2 282.7 112 320 112c79.5 0 144 64.5 144 144c0 24.9-6.3 48.3-17.4 68.7L408 294.5c5.2-11.8 8-24.8 8-38.5c0-53-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6c0 10.2-2.4 19.8-6.6 28.3l-90.3-70.8zm223.1 298L373 389.9c-16.4 6.5-34.3 10.1-53 10.1c-79.5 0-144-64.5-144-144c0-6.9 .5-13.6 1.4-20.2L83.1 161.5C60.3 191.2 44 220.8 34.5 243.7c-3.3 7.9-3.3 16.7 0 24.6c14.9 35.7 46.2 87.7 93 131.1C174.5 443.2 239.2 480 320 480c47.8 0 89.9-12.9 126.2-32.5z"/></svg></span></template>
|
||||
<template id=fa-copy><span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M502.6 70.63l-61.25-61.25C435.4 3.371 427.2 0 418.7 0H255.1c-35.35 0-64 28.66-64 64l.0195 256C192 355.4 220.7 384 256 384h192c35.2 0 64-28.8 64-64V93.25C512 84.77 508.6 76.63 502.6 70.63zM464 320c0 8.836-7.164 16-16 16H255.1c-8.838 0-16-7.164-16-16L239.1 64.13c0-8.836 7.164-16 16-16h128L384 96c0 17.67 14.33 32 32 32h47.1V320zM272 448c0 8.836-7.164 16-16 16H63.1c-8.838 0-16-7.164-16-16L47.98 192.1c0-8.836 7.164-16 16-16H160V128H63.99c-35.35 0-64 28.65-64 64l.0098 256C.002 483.3 28.66 512 64 512h192c35.2 0 64-28.8 64-64v-32h-47.1L272 448z"/></svg></span></template>
|
||||
<template id=fa-play><span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 384 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M73 39c-14.8-9.1-33.4-9.4-48.5-.9S0 62.6 0 80V432c0 17.4 9.4 33.4 24.5 41.9s33.7 8.1 48.5-.9L361 297c14.3-8.7 23-24.2 23-41s-8.7-32.2-23-41L73 39z"/></svg></span></template>
|
||||
<template id=fa-clock-rotate-left><span class=fa-svg><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512"><!--! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --><path d="M75 75L41 41C25.9 25.9 0 36.6 0 57.9V168c0 13.3 10.7 24 24 24H134.1c21.4 0 32.1-25.9 17-41l-30.8-30.8C155 85.5 203 64 256 64c106 0 192 86 192 192s-86 192-192 192c-40.8 0-78.6-12.7-109.7-34.4c-14.5-10.1-34.4-6.6-44.6 7.9s-6.6 34.4 7.9 44.6C151.2 495 201.7 512 256 512c141.4 0 256-114.6 256-256S397.4 0 256 0C185.3 0 121.3 28.7 75 75zm181 53c-13.3 0-24 10.7-24 24V256c0 6.4 2.5 12.5 7 17l72 72c9.4 9.4 24.6 9.4 33.9 0s9.4-24.6 0-33.9l-65-65V152c0-13.3-10.7-24-24-24z"/></svg></span></template>
|
||||
|
||||
|
||||
|
||||
<script>
|
||||
window.playground_copyable = true;
|
||||
</script>
|
||||
|
||||
|
||||
<script src="elasticlunr-ef4e11c1.min.js"></script>
|
||||
<script src="mark-09e88c2c.min.js"></script>
|
||||
<script src="searcher-09f2665d.js"></script>
|
||||
|
||||
<script src="clipboard-1626706a.min.js"></script>
|
||||
<script src="highlight-abc7f01d.js"></script>
|
||||
<script src="book-c22b7243.js"></script>
|
||||
|
||||
<!-- Custom JS scripts -->
|
||||
<script src="ferris-2317480c.js"></script>
|
||||
|
||||
|
||||
|
||||
</div>
|
||||
</body>
|
||||
</html>
|
||||
Reference in New Issue
Block a user