rust
/
rust-course
mirror of https://github.com/sunface/rust-course
5
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity
You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
Branches Tags
${ item.name }
Create tag ${ searchTerm }
Create branch ${ searchTerm }
from 'gh-pages'
${ noResults }
rust-course/advance-practice/async.html

806 lines
89 KiB
Raw Permalink Blame History Escape

This file contains ambiguous Unicode characters!

This file contains ambiguous Unicode characters that may be confused with others in your current locale. If your use case is intentional and legitimate, you can safely ignore this warning. Use the Escape button to highlight these characters.

<!DOCTYPE HTML>
<html lang="zh-CN" class="light" dir="ltr">
<head>
<!-- Book generated using mdBook -->
<meta charset="UTF-8">
<title>深入 async - Rust语言圣经(Rust Course)</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.svg">
<link rel="shortcut icon" href="../favicon.png">
<link rel="stylesheet" href="../css/variables.css">
<link rel="stylesheet" href="../css/general.css">
<link rel="stylesheet" href="../css/chrome.css">
<link rel="stylesheet" href="../css/print.css" media="print">
<!-- Fonts -->
<link rel="stylesheet" href="../FontAwesome/css/font-awesome.css">
<link rel="stylesheet" href="../fonts/fonts.css">
<!-- Highlight.js Stylesheets -->
<link rel="stylesheet" href="../highlight.css">
<link rel="stylesheet" href="../tomorrow-night.css">
<link rel="stylesheet" href="../ayu-highlight.css">
<!-- Custom theme stylesheets -->
<link rel="stylesheet" href="../theme/style.css">
</head>
<body class="sidebar-visible no-js">
<div id="body-container">
<!-- Provide site root to javascript -->
<script>
var path_to_root = "../";
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
</script>
<!-- Work around some values being stored in localStorage wrapped in quotes -->
<script>
try {
var theme = localStorage.getItem('mdbook-theme');
var 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>
var theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
var html = document.querySelector('html');
html.classList.remove('light')
html.classList.add(theme);
var body = document.querySelector('body');
body.classList.remove('no-js')
body.classList.add('js');
</script>
<input type="checkbox" id="sidebar-toggle-anchor" class="hidden">
<!-- Hide / unhide sidebar before it is displayed -->
<script>
var body = document.querySelector('body');
var sidebar = null;
var sidebar_toggle = document.getElementById("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 = sidebar === 'visible';
body.classList.remove('sidebar-visible');
body.classList.add("sidebar-" + sidebar);
</script>
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
<div class="sidebar-scrollbox">
<ol class="chapter"><li class="chapter-item affix "><a href="../about-book.html">关于本书</a></li><li class="chapter-item affix "><a href="../into-rust.html">进入 Rust 编程世界</a></li><li class="chapter-item affix "><a href="../first-try/sth-you-should-not-do.html">避免从入门到放弃</a></li><li class="chapter-item affix "><a href="../community.html">社区和锈书</a></li><li class="spacer"></li><li class="chapter-item affix "><a href="../some-thoughts.html">Xobserve: 一切皆可观测</a></li><li class="chapter-item affix "><a href="../beat-ai.html">BeatAI: 工程师 AI 入门圣经</a></li><li class="chapter-item affix "><li class="part-title">Rust 语言基础学习</li><li class="spacer"></li><li class="chapter-item "><a href="../first-try/intro.html"><strong aria-hidden="true">1.</strong> 寻找牛刀，以便小试</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../first-try/installation.html"><strong aria-hidden="true">1.1.</strong> 安装 Rust 环境</a></li><li class="chapter-item "><a href="../first-try/editor.html"><strong aria-hidden="true">1.2.</strong> 墙推 VSCode!</a></li><li class="chapter-item "><a href="../first-try/cargo.html"><strong aria-hidden="true">1.3.</strong> 认识 Cargo</a></li><li class="chapter-item "><a href="../first-try/hello-world.html"><strong aria-hidden="true">1.4.</strong> 不仅仅是 Hello world</a></li><li class="chapter-item "><a href="../first-try/slowly-downloading.html"><strong aria-hidden="true">1.5.</strong> 下载依赖太慢了？</a></li></ol></li><li class="chapter-item "><a href="../basic/intro.html"><strong aria-hidden="true">2.</strong> Rust 基础入门</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../basic/variable.html"><strong aria-hidden="true">2.1.</strong> 变量绑定与解构</a></li><li class="chapter-item "><a href="../basic/base-type/index.html"><strong aria-hidden="true">2.2.</strong> 基本类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../basic/base-type/numbers.html"><strong aria-hidden="true">2.2.1.</strong> 数值类型</a></li><li class="chapter-item "><a href="../basic/base-type/char-bool.html"><strong aria-hidden="true">2.2.2.</strong> 字符、布尔、单元类型</a></li><li class="chapter-item "><a href="../basic/base-type/statement-expression.html"><strong aria-hidden="true">2.2.3.</strong> 语句与表达式</a></li><li class="chapter-item "><a href="../basic/base-type/function.html"><strong aria-hidden="true">2.2.4.</strong> 函数</a></li></ol></li><li class="chapter-item "><a href="../basic/ownership/index.html"><strong aria-hidden="true">2.3.</strong> 所有权和借用</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../basic/ownership/ownership.html"><strong aria-hidden="true">2.3.1.</strong> 所有权</a></li><li class="chapter-item "><a href="../basic/ownership/borrowing.html"><strong aria-hidden="true">2.3.2.</strong> 引用与借用</a></li></ol></li><li class="chapter-item "><a href="../basic/compound-type/intro.html"><strong aria-hidden="true">2.4.</strong> 复合类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../basic/compound-type/string-slice.html"><strong aria-hidden="true">2.4.1.</strong> 字符串与切片</a></li><li class="chapter-item "><a href="../basic/compound-type/tuple.html"><strong aria-hidden="true">2.4.2.</strong> 元组</a></li><li class="chapter-item "><a href="../basic/compound-type/struct.html"><strong aria-hidden="true">2.4.3.</strong> 结构体</a></li><li class="chapter-item "><a href="../basic/compound-type/enum.html"><strong aria-hidden="true">2.4.4.</strong> 枚举</a></li><li class="chapter-item "><a href="../basic/compound-type/array.html"><strong aria-hidden="true">2.4.5.</strong> 数组</a></li></ol></li><li class="chapter-item "><a href="../basic/flow-control.html"><strong aria-hidden="true">2.5.</strong> 流程控制</a></li><li class="chapter-item "><a href="../basic/match-pattern/intro.html"><strong aria-hidden="true">2.6.</strong> 模式匹配</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../basic/match-pattern/match-if-let.html"><strong aria-hidden="true">2.6.1.</strong> match 和 if let</a></li><li class="chapter-item "><a href="../basic/match-pattern/option.html"><strong aria-hidden="true">2.6.2.</strong> 解构 Option</a></li><li class="chapter-item "><a href="../basic/match-pattern/pattern-match.html"><strong aria-hidden="true">2.6.3.</strong> 模式适用场景</a></li><li class="chapter-item "><a href="../basic/match-pattern/all-patterns.html"><strong aria-hidden="true">2.6.4.</strong> 全模式列表</a></li></ol></li><li class="chapter-item "><a href="../basic/method.html"><strong aria-hidden="true">2.7.</strong> 方法 Method</a></li><li class="chapter-item "><a href="../basic/trait/intro.html"><strong aria-hidden="true">2.8.</strong> 泛型和特征</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../basic/trait/generic.html"><strong aria-hidden="true">2.8.1.</strong> 泛型 Generics</a></li><li class="chapter-item "><a href="../basic/trait/trait.html"><strong aria-hidden="true">2.8.2.</strong> 特征 Trait</a></li><li class="chapter-item "><a href="../basic/trait/trait-object.html"><strong aria-hidden="true">2.8.3.</strong> 特征对象</a></li><li class="chapter-item "><a href="../basic/trait/advance-trait.html"><strong aria-hidden="true">2.8.4.</strong> 进一步深入特征</a></li></ol></li><li class="chapter-item "><a href="../basic/collections/intro.html"><strong aria-hidden="true">2.9.</strong> 集合类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../basic/collections/vector.html"><strong aria-hidden="true">2.9.1.</strong> 动态数组 Vector</a></li><li class="chapter-item "><a href="../basic/collections/hashmap.html"><strong aria-hidden="true">2.9.2.</strong> KV 存储 HashMap</a></li></ol></li><li class="chapter-item "><a href="../basic/lifetime.html"><strong aria-hidden="true">2.10.</strong> 认识生命周期</a></li><li class="chapter-item "><a href="../basic/result-error/intro.html"><strong aria-hidden="true">2.11.</strong> 返回值和错误处理</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../basic/result-error/panic.html"><strong aria-hidden="true">2.11.1.</strong> panic! 深入剖析</a></li><li class="chapter-item "><a href="../basic/result-error/result.html"><strong aria-hidden="true">2.11.2.</strong> 返回值 Result 和?</a></li></ol></li><li class="chapter-item "><a href="../basic/crate-module/intro.html"><strong aria-hidden="true">2.12.</strong> 包和模块</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../basic/crate-module/crate.html"><strong aria-hidden="true">2.12.1.</strong> 包 Crate</a></li><li class="chapter-item "><a href="../basic/crate-module/module.html"><strong aria-hidden="true">2.12.2.</strong> 模块 Module</a></li><li class="chapter-item "><a href="../basic/crate-module/use.html"><strong aria-hidden="true">2.12.3.</strong> 使用 use 引入模块及受限可见性</a></li></ol></li><li class="chapter-item "><a href="../basic/comment.html"><strong aria-hidden="true">2.13.</strong> 注释和文档</a></li><li class="chapter-item "><a href="../basic/formatted-output.html"><strong aria-hidden="true">2.14.</strong> 格式化输出</a></li></ol></li><li class="chapter-item "><a href="../basic-practice/intro.html"><strong aria-hidden="true">3.</strong> 入门实战：文件搜索工具</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../basic-practice/base-features.html"><strong aria-hidden="true">3.1.</strong> 基本功能</a></li><li class="chapter-item "><a href="../basic-practice/refactoring.html"><strong aria-hidden="true">3.2.</strong> 增加模块化和错误处理</a></li><li class="chapter-item "><a href="../basic-practice/tests.html"><strong aria-hidden="true">3.3.</strong> 测试驱动开发</a></li><li class="chapter-item "><a href="../basic-practice/envs.html"><strong aria-hidden="true">3.4.</strong> 使用环境变量</a></li><li class="chapter-item "><a href="../basic-practice/stderr.html"><strong aria-hidden="true">3.5.</strong> 重定向错误信息的输出</a></li><li class="chapter-item "><a href="../basic-practice/iterators.html"><strong aria-hidden="true">3.6.</strong> 使用迭代器来改进程序(可选)</a></li></ol></li><li class="chapter-item "><li class="part-title">Rust 语言进阶学习</li><li class="spacer"></li><li class="chapter-item "><a href="../advance/intro.html"><strong aria-hidden="true">4.</strong> Rust 高级进阶</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance/lifetime/intro.html"><strong aria-hidden="true">4.1.</strong> 生命周期</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance/lifetime/advance.html"><strong aria-hidden="true">4.1.1.</strong> 深入生命周期</a></li><li class="chapter-item "><a href="../advance/lifetime/static.html"><strong aria-hidden="true">4.1.2.</strong> &'static 和 T: 'static</a></li></ol></li><li class="chapter-item "><a href="../advance/functional-programing/intro.html"><strong aria-hidden="true">4.2.</strong> 函数式编程: 闭包、迭代器</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance/functional-programing/closure.html"><strong aria-hidden="true">4.2.1.</strong> 闭包 Closure</a></li><li class="chapter-item "><a href="../advance/functional-programing/iterator.html"><strong aria-hidden="true">4.2.2.</strong> 迭代器 Iterator</a></li></ol></li><li class="chapter-item "><a href="../advance/into-types/intro.html"><strong aria-hidden="true">4.3.</strong> 深入类型</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance/into-types/converse.html"><strong aria-hidden="true">4.3.1.</strong> 类型转换</a></li><li class="chapter-item "><a href="../advance/into-types/custom-type.html"><strong aria-hidden="true">4.3.2.</strong> newtype 和 类型别名</a></li><li class="chapter-item "><a href="../advance/into-types/sized.html"><strong aria-hidden="true">4.3.3.</strong> Sized 和不定长类型 DST</a></li><li class="chapter-item "><a href="../advance/into-types/enum-int.html"><strong aria-hidden="true">4.3.4.</strong> 枚举和整数</a></li></ol></li><li class="chapter-item "><a href="../advance/smart-pointer/intro.html"><strong aria-hidden="true">4.4.</strong> 智能指针</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance/smart-pointer/box.html"><strong aria-hidden="true">4.4.1.</strong> Box堆对象分配</a></li><li class="chapter-item "><a href="../advance/smart-pointer/deref.html"><strong aria-hidden="true">4.4.2.</strong> Deref 解引用</a></li><li class="chapter-item "><a href="../advance/smart-pointer/drop.html"><strong aria-hidden="true">4.4.3.</strong> Drop 释放资源</a></li><li class="chapter-item "><a href="../advance/smart-pointer/rc-arc.html"><strong aria-hidden="true">4.4.4.</strong> Rc 与 Arc 实现 1vN 所有权机制</a></li><li class="chapter-item "><a href="../advance/smart-pointer/cell-refcell.html"><strong aria-hidden="true">4.4.5.</strong> Cell 与 RefCell 内部可变性</a></li></ol></li><li class="chapter-item "><a href="../advance/circle-self-ref/intro.html"><strong aria-hidden="true">4.5.</strong> 循环引用与自引用</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance/circle-self-ref/circle-reference.html"><strong aria-hidden="true">4.5.1.</strong> Weak 与循环引用</a></li><li class="chapter-item "><a href="../advance/circle-self-ref/self-referential.html"><strong aria-hidden="true">4.5.2.</strong> 结构体中的自引用</a></li></ol></li><li class="chapter-item "><a href="../advance/concurrency-with-threads/intro.html"><strong aria-hidden="true">4.6.</strong> 多线程并发编程</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance/concurrency-with-threads/concurrency-parallelism.html"><strong aria-hidden="true">4.6.1.</strong> 并发和并行</a></li><li class="chapter-item "><a href="../advance/concurrency-with-threads/thread.html"><strong aria-hidden="true">4.6.2.</strong> 使用多线程</a></li><li class="chapter-item "><a href="../advance/concurrency-with-threads/message-passing.html"><strong aria-hidden="true">4.6.3.</strong> 线程同步：消息传递</a></li><li class="chapter-item "><a href="../advance/concurrency-with-threads/sync1.html"><strong aria-hidden="true">4.6.4.</strong> 线程同步：锁、Condvar 和信号量</a></li><li class="chapter-item "><a href="../advance/concurrency-with-threads/sync2.html"><strong aria-hidden="true">4.6.5.</strong> 线程同步：Atomic 原子操作与内存顺序</a></li><li class="chapter-item "><a href="../advance/concurrency-with-threads/send-sync.html"><strong aria-hidden="true">4.6.6.</strong> 基于 Send 和 Sync 的线程安全</a></li></ol></li><li class="chapter-item "><a href="../advance/global-variable.html"><strong aria-hidden="true">4.7.</strong> 全局变量</a></li><li class="chapter-item "><a href="../advance/errors.html"><strong aria-hidden="true">4.8.</strong> 错误处理</a></li><li class="chapter-item "><a href="../advance/unsafe/intro.html"><strong aria-hidden="true">4.9.</strong> Unsafe Rust</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance/unsafe/superpowers.html"><strong aria-hidden="true">4.9.1.</strong> 五种兵器</a></li><li class="chapter-item "><a href="../advance/unsafe/inline-asm.html"><strong aria-hidden="true">4.9.2.</strong> 内联汇编</a></li></ol></li><li class="chapter-item "><a href="../advance/macro.html"><strong aria-hidden="true">4.10.</strong> Macro 宏编程</a></li><li class="chapter-item "><a href="../advance/async/intro.html"><strong aria-hidden="true">4.11.</strong> async/await 异步编程</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance/async/getting-started.html"><strong aria-hidden="true">4.11.1.</strong> async 编程入门</a></li><li class="chapter-item "><a href="../advance/async/future-excuting.html"><strong aria-hidden="true">4.11.2.</strong> 底层探秘: Future 执行与任务调度</a></li><li class="chapter-item "><a href="../advance/async/pin-unpin.html"><strong aria-hidden="true">4.11.3.</strong> 定海神针 Pin 和 Unpin</a></li><li class="chapter-item "><a href="../advance/async/async-await.html"><strong aria-hidden="true">4.11.4.</strong> async/await 和 Stream 流处理</a></li><li class="chapter-item "><a href="../advance/async/multi-futures-simultaneous.html"><strong aria-hidden="true">4.11.5.</strong> 同时运行多个 Future</a></li><li class="chapter-item "><a href="../advance/async/pain-points-and-workarounds.html"><strong aria-hidden="true">4.11.6.</strong> 一些疑难问题的解决办法</a></li><li class="chapter-item "><a href="../advance/async/web-server.html"><strong aria-hidden="true">4.11.7.</strong> 实践应用：Async Web 服务器</a></li></ol></li></ol></li><li class="chapter-item "><a href="../advance-practice1/intro.html"><strong aria-hidden="true">5.</strong> 进阶实战1: 实现一个 web 服务器</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance-practice1/web-server.html"><strong aria-hidden="true">5.1.</strong> 单线程版本</a></li><li class="chapter-item "><a href="../advance-practice1/multi-threads.html"><strong aria-hidden="true">5.2.</strong> 多线程版本</a></li><li class="chapter-item "><a href="../advance-practice1/graceful-shutdown.html"><strong aria-hidden="true">5.3.</strong> 优雅关闭和资源清理</a></li></ol></li><li class="chapter-item expanded "><a href="../advance-practice/intro.html"><strong aria-hidden="true">6.</strong> 进阶实战2: 实现一个简单 Redis</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../advance-practice/overview.html"><strong aria-hidden="true">6.1.</strong> tokio 概览</a></li><li class="chapter-item "><a href="../advance-practice/getting-startted.html"><strong aria-hidden="true">6.2.</strong> 使用初印象</a></li><li class="chapter-item "><a href="../advance-practice/spawning.html"><strong aria-hidden="true">6.3.</strong> 创建异步任务</a></li><li class="chapter-item "><a href="../advance-practice/shared-state.html"><strong aria-hidden="true">6.4.</strong> 共享状态</a></li><li class="chapter-item "><a href="../advance-practice/channels.html"><strong aria-hidden="true">6.5.</strong> 消息传递</a></li><li class="chapter-item "><a href="../advance-practice/io.html"><strong aria-hidden="true">6.6.</strong> I/O</a></li><li class="chapter-item "><a href="../advance-practice/frame.html"><strong aria-hidden="true">6.7.</strong> 解析数据帧</a></li><li class="chapter-item expanded "><a href="../advance-practice/async.html" class="active"><strong aria-hidden="true">6.8.</strong> 深入 async</a></li><li class="chapter-item "><a href="../advance-practice/select.html"><strong aria-hidden="true">6.9.</strong> select</a></li><li class="chapter-item "><a href="../advance-practice/stream.html"><strong aria-hidden="true">6.10.</strong> 类似迭代器的 Stream</a></li><li class="chapter-item "><a href="../advance-practice/graceful-shutdown.html"><strong aria-hidden="true">6.11.</strong> 优雅的关闭</a></li><li class="chapter-item "><a href="../advance-practice/bridging-with-sync.html"><strong aria-hidden="true">6.12.</strong> 异步跟同步共存</a></li></ol></li><li class="chapter-item "><a href="../difficulties/intro.html"><strong aria-hidden="true">7.</strong> Rust 难点攻关</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../difficulties/slice.html"><strong aria-hidden="true">7.1.</strong> 切片和切片引用</a></li><li class="chapter-item "><a href="../difficulties/eq.html"><strong aria-hidden="true">7.2.</strong> Eq 和 PartialEq</a></li><li class="chapter-item "><a href="../difficulties/string.html"><strong aria-hidden="true">7.3.</strong> String、&str 和 str TODO</a></li><li class="chapter-item "><a href="../difficulties/lifetime.html"><strong aria-hidden="true">7.4.</strong> 作用域、生命周期和 NLL TODO</a></li><li class="chapter-item "><a href="../difficulties/move-copy.html"><strong aria-hidden="true">7.5.</strong> move、Copy 和 Clone TODO</a></li><li class="chapter-item "><a href="../advance/difficulties/pointer.html"><strong aria-hidden="true">7.6.</strong> 裸指针、引用和智能指针 TODO</a></li></ol></li><li class="chapter-item "><li class="part-title">常用工具链</li><li class="spacer"></li><li class="chapter-item "><a href="../test/intro.html"><strong aria-hidden="true">8.</strong> 自动化测试</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../test/write-tests.html"><strong aria-hidden="true">8.1.</strong> 编写测试及控制执行</a></li><li class="chapter-item "><a href="../test/unit-integration-test.html"><strong aria-hidden="true">8.2.</strong> 单元测试和集成测试</a></li><li class="chapter-item "><a href="../test/assertion.html"><strong aria-hidden="true">8.3.</strong> 断言 assertion</a></li><li class="chapter-item "><a href="../test/ci.html"><strong aria-hidden="true">8.4.</strong> 用 GitHub Actions 进行持续集成</a></li><li class="chapter-item "><a href="../test/benchmark.html"><strong aria-hidden="true">8.5.</strong> 基准测试 benchmark</a></li></ol></li><li class="chapter-item "><a href="../cargo/intro.html"><strong aria-hidden="true">9.</strong> Cargo 使用指南</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../cargo/getting-started.html"><strong aria-hidden="true">9.1.</strong> 上手使用</a></li><li class="chapter-item "><a href="../cargo/guide/intro.html"><strong aria-hidden="true">9.2.</strong> 基础指南</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../cargo/guide/why-exist.html"><strong aria-hidden="true">9.2.1.</strong> 为何会有 Cargo</a></li><li class="chapter-item "><a href="../cargo/guide/download-package.html"><strong aria-hidden="true">9.2.2.</strong> 下载并构建 Package</a></li><li class="chapter-item "><a href="../cargo/guide/dependencies.html"><strong aria-hidden="true">9.2.3.</strong> 添加依赖</a></li><li class="chapter-item "><a href="../cargo/guide/package-layout.html"><strong aria-hidden="true">9.2.4.</strong> Package 目录结构</a></li><li class="chapter-item "><a href="../cargo/guide/cargo-toml-lock.html"><strong aria-hidden="true">9.2.5.</strong> Cargo.toml vs Cargo.lock</a></li><li class="chapter-item "><a href="../cargo/guide/tests-ci.html"><strong aria-hidden="true">9.2.6.</strong> 测试和 CI</a></li><li class="chapter-item "><a href="../cargo/guide/cargo-cache.html"><strong aria-hidden="true">9.2.7.</strong> Cargo 缓存</a></li><li class="chapter-item "><a href="../cargo/guide/build-cache.html"><strong aria-hidden="true">9.2.8.</strong> Build 缓存</a></li></ol></li><li class="chapter-item "><a href="../cargo/reference/intro.html"><strong aria-hidden="true">9.3.</strong> 进阶指南</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../cargo/reference/specify-deps.html"><strong aria-hidden="true">9.3.1.</strong> 指定依赖项</a></li><li class="chapter-item "><a href="../cargo/reference/deps-overriding.html"><strong aria-hidden="true">9.3.2.</strong> 依赖覆盖</a></li><li class="chapter-item "><a href="../cargo/reference/manifest.html"><strong aria-hidden="true">9.3.3.</strong> Cargo.toml 清单详解</a></li><li class="chapter-item "><a href="../cargo/reference/cargo-target.html"><strong aria-hidden="true">9.3.4.</strong> Cargo Target</a></li><li class="chapter-item "><a href="../cargo/reference/workspaces.html"><strong aria-hidden="true">9.3.5.</strong> 工作空间 Workspace</a></li><li class="chapter-item "><a href="../cargo/reference/features/intro.html"><strong aria-hidden="true">9.3.6.</strong> 条件编译 Features</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../cargo/reference/features/examples.html"><strong aria-hidden="true">9.3.6.1.</strong> Features 示例</a></li></ol></li><li class="chapter-item "><a href="../cargo/reference/profiles.html"><strong aria-hidden="true">9.3.7.</strong> 发布配置 Profile</a></li><li class="chapter-item "><a href="../cargo/reference/configuration.html"><strong aria-hidden="true">9.3.8.</strong> 通过 config.toml 对 Cargo 进行配置</a></li><li class="chapter-item "><a href="../cargo/reference/publishing-on-crates.io.html"><strong aria-hidden="true">9.3.9.</strong> 发布到 crates.io</a></li><li class="chapter-item "><a href="../cargo/reference/build-script/intro.html"><strong aria-hidden="true">9.3.10.</strong> 构建脚本 build.rs</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../cargo/reference/build-script/examples.html"><strong aria-hidden="true">9.3.10.1.</strong> 构建脚本示例</a></li></ol></li></ol></li></ol></li><li class="chapter-item "><li class="part-title">开发实践</li><li class="spacer"></li><li class="chapter-item "><a href="../usecases/intro.html"><strong aria-hidden="true">10.</strong> 企业落地实践</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../usecases/aws-rust.html"><strong aria-hidden="true">10.1.</strong> AWS 为何这么喜欢 Rust?</a></li></ol></li><li class="chapter-item "><a href="../logs/intro.html"><strong aria-hidden="true">11.</strong> 日志和监控</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../logs/about-log.html"><strong aria-hidden="true">11.1.</strong> 日志详解</a></li><li class="chapter-item "><a href="../logs/log.html"><strong aria-hidden="true">11.2.</strong> 日志门面 log</a></li><li class="chapter-item "><a href="../logs/tracing.html"><strong aria-hidden="true">11.3.</strong> 使用 tracing 记录日志</a></li><li class="chapter-item "><a href="../logs/tracing-logger.html"><strong aria-hidden="true">11.4.</strong> 自定义 tracing 的输出格式</a></li><li class="chapter-item "><a href="../logs/observe/intro.html"><strong aria-hidden="true">11.5.</strong> 监控</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../logs/observe/about-observe.html"><strong aria-hidden="true">11.5.1.</strong> 可观测性</a></li><li class="chapter-item "><a href="../logs/observe/trace.html"><strong aria-hidden="true">11.5.2.</strong> 分布式追踪</a></li></ol></li></ol></li><li class="chapter-item "><a href="../practice/intro.html"><strong aria-hidden="true">12.</strong> Rust 最佳实践</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../practice/third-party-libs.html"><strong aria-hidden="true">12.1.</strong> 日常开发三方库精选</a></li><li class="chapter-item "><a href="../practice/naming.html"><strong aria-hidden="true">12.2.</strong> 命名规范</a></li><li class="chapter-item "><a href="../practice/interview.html"><strong aria-hidden="true">12.3.</strong> 面试经验</a></li><li class="chapter-item "><a href="../practice/best-pratice.html"><strong aria-hidden="true">12.4.</strong> 代码开发实践 todo</a></li></ol></li><li class="chapter-item "><a href="../too-many-lists/intro.html"><strong aria-hidden="true">13.</strong> 手把手带你实现链表</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../too-many-lists/do-we-need-it.html"><strong aria-hidden="true">13.1.</strong> 我们到底需不需要链表</a></li><li class="chapter-item "><a href="../too-many-lists/bad-stack/intro.html"><strong aria-hidden="true">13.2.</strong> 不太优秀的单向链表：栈</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../too-many-lists/bad-stack/layout.html"><strong aria-hidden="true">13.2.1.</strong> 数据布局</a></li><li class="chapter-item "><a href="../too-many-lists/bad-stack/basic-operations.html"><strong aria-hidden="true">13.2.2.</strong> 基本操作</a></li><li class="chapter-item "><a href="../too-many-lists/bad-stack/final-code.html"><strong aria-hidden="true">13.2.3.</strong> 最后实现</a></li></ol></li><li class="chapter-item "><a href="../too-many-lists/ok-stack/intro.html"><strong aria-hidden="true">13.3.</strong> 还可以的单向链表</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../too-many-lists/ok-stack/type-optimizing.html"><strong aria-hidden="true">13.3.1.</strong> 优化类型定义</a></li><li class="chapter-item "><a href="../too-many-lists/ok-stack/peek.html"><strong aria-hidden="true">13.3.2.</strong> 定义 Peek 函数</a></li><li class="chapter-item "><a href="../too-many-lists/ok-stack/iter.html"><strong aria-hidden="true">13.3.3.</strong> IntoIter 和 Iter</a></li><li class="chapter-item "><a href="../too-many-lists/ok-stack/itermut.html"><strong aria-hidden="true">13.3.4.</strong> IterMut 以及完整代码</a></li></ol></li><li class="chapter-item "><a href="../too-many-lists/persistent-stack/intro.html"><strong aria-hidden="true">13.4.</strong> 持久化单向链表</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../too-many-lists/persistent-stack/layout.html"><strong aria-hidden="true">13.4.1.</strong> 数据布局和基本操作</a></li><li class="chapter-item "><a href="../too-many-lists/persistent-stack/drop-arc.html"><strong aria-hidden="true">13.4.2.</strong> Drop、Arc 及完整代码</a></li></ol></li><li class="chapter-item "><a href="../too-many-lists/deque/intro.html"><strong aria-hidden="true">13.5.</strong> 不咋样的双端队列</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../too-many-lists/deque/layout.html"><strong aria-hidden="true">13.5.1.</strong> 数据布局和基本操作</a></li><li class="chapter-item "><a href="../too-many-lists/deque/peek.html"><strong aria-hidden="true">13.5.2.</strong> Peek</a></li><li class="chapter-item "><a href="../too-many-lists/deque/symmetric.html"><strong aria-hidden="true">13.5.3.</strong> 基本操作的对称镜像</a></li><li class="chapter-item "><a href="../too-many-lists/deque/iterator.html"><strong aria-hidden="true">13.5.4.</strong> 迭代器</a></li><li class="chapter-item "><a href="../too-many-lists/deque/final-code.html"><strong aria-hidden="true">13.5.5.</strong> 最终代码</a></li></ol></li><li class="chapter-item "><a href="../too-many-lists/unsafe-queue/intro.html"><strong aria-hidden="true">13.6.</strong> 不错的 unsafe 队列</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../too-many-lists/unsafe-queue/layout.html"><strong aria-hidden="true">13.6.1.</strong> 数据布局</a></li><li class="chapter-item "><a href="../too-many-lists/unsafe-queue/basics.html"><strong aria-hidden="true">13.6.2.</strong> 基本操作</a></li><li class="chapter-item "><a href="../too-many-lists/unsafe-queue/miri.html"><strong aria-hidden="true">13.6.3.</strong> Miri</a></li><li class="chapter-item "><a href="../too-many-lists/unsafe-queue/stacked-borrow.html"><strong aria-hidden="true">13.6.4.</strong> 栈借用</a></li><li class="chapter-item "><a href="../too-many-lists/unsafe-queue/testing-stacked-borrow.html"><strong aria-hidden="true">13.6.5.</strong> 测试栈借用</a></li><li class="chapter-item "><a href="../too-many-lists/unsafe-queue/layout2.html"><strong aria-hidden="true">13.6.6.</strong> 数据布局 2</a></li><li class="chapter-item "><a href="../too-many-lists/unsafe-queue/extra-junk.html"><strong aria-hidden="true">13.6.7.</strong> 额外的操作</a></li><li class="chapter-item "><a href="../too-many-lists/unsafe-queue/final-code.html"><strong aria-hidden="true">13.6.8.</strong> 最终代码</a></li></ol></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/intro.html"><strong aria-hidden="true">13.7.</strong> 生产级的双向 unsafe 队列</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/layout.html"><strong aria-hidden="true">13.7.1.</strong> 数据布局</a></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/variance-and-phantomData.html"><strong aria-hidden="true">13.7.2.</strong> 型变与子类型</a></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/basics.html"><strong aria-hidden="true">13.7.3.</strong> 基础结构</a></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/drop-and-panic-safety.html"><strong aria-hidden="true">13.7.4.</strong> 恐慌与安全</a></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/boring-combinatorics.html"><strong aria-hidden="true">13.7.5.</strong> 无聊的组合</a></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/filling-in-random-bits.html"><strong aria-hidden="true">13.7.6.</strong> 其它特征</a></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/testing.html"><strong aria-hidden="true">13.7.7.</strong> 测试</a></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/send-sync-and-compile-tests.html"><strong aria-hidden="true">13.7.8.</strong> Send,Sync和编译测试</a></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/implementing-cursors.html"><strong aria-hidden="true">13.7.9.</strong> 实现游标</a></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/testing-cursors.html"><strong aria-hidden="true">13.7.10.</strong> 测试游标</a></li><li class="chapter-item "><a href="../too-many-lists/production-unsafe-deque/final-code.html"><strong aria-hidden="true">13.7.11.</strong> 最终代码</a></li></ol></li><li class="chapter-item "><a href="../too-many-lists/advanced-lists/intro.html"><strong aria-hidden="true">13.8.</strong> 使用高级技巧实现链表</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../too-many-lists/advanced-lists/double-singly.html"><strong aria-hidden="true">13.8.1.</strong> 双单向链表</a></li><li class="chapter-item "><a href="../too-many-lists/advanced-lists/stack-allocated.html"><strong aria-hidden="true">13.8.2.</strong> 栈上的链表</a></li></ol></li></ol></li><li class="chapter-item "><li class="part-title">攻克编译错误</li><li class="spacer"></li><li class="chapter-item "><a href="../compiler/intro.html"><strong aria-hidden="true">14.</strong> 征服编译错误</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../compiler/fight-with-compiler/intro.html"><strong aria-hidden="true">14.1.</strong> 对抗编译检查</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../compiler/fight-with-compiler/lifetime/intro.html"><strong aria-hidden="true">14.1.1.</strong> 生命周期</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../compiler/fight-with-compiler/lifetime/too-long1.html"><strong aria-hidden="true">14.1.1.1.</strong> 生命周期过大-01</a></li><li class="chapter-item "><a href="../compiler/fight-with-compiler/lifetime/too-long2.html"><strong aria-hidden="true">14.1.1.2.</strong> 生命周期过大-02</a></li><li class="chapter-item "><a href="../compiler/fight-with-compiler/lifetime/loop.html"><strong aria-hidden="true">14.1.1.3.</strong> 循环中的生命周期</a></li><li class="chapter-item "><a href="../compiler/fight-with-compiler/lifetime/closure-with-static.html"><strong aria-hidden="true">14.1.1.4.</strong> 闭包碰到特征对象-01</a></li></ol></li><li class="chapter-item "><a href="../compiler/fight-with-compiler/borrowing/intro.html"><strong aria-hidden="true">14.1.2.</strong> 重复借用</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../compiler/fight-with-compiler/borrowing/ref-exist-in-out-fn.html"><strong aria-hidden="true">14.1.2.1.</strong> 同时在函数内外使用引用</a></li><li class="chapter-item "><a href="../compiler/fight-with-compiler/borrowing/borrow-distinct-fields-of-struct.html"><strong aria-hidden="true">14.1.2.2.</strong> 智能指针引起的重复借用错误</a></li></ol></li><li class="chapter-item "><a href="../compiler/fight-with-compiler/unconstrained.html"><strong aria-hidden="true">14.1.3.</strong> 类型未限制(todo)</a></li><li class="chapter-item "><a href="../compiler/fight-with-compiler/phantom-data.html"><strong aria-hidden="true">14.1.4.</strong> 幽灵数据(todo)</a></li></ol></li><li class="chapter-item "><a href="../compiler/pitfalls/index.html"><strong aria-hidden="true">14.2.</strong> Rust 常见陷阱</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../compiler/pitfalls/use-vec-in-for.html"><strong aria-hidden="true">14.2.1.</strong> for 循环中使用外部数组</a></li><li class="chapter-item "><a href="../compiler/pitfalls/stack-overflow.html"><strong aria-hidden="true">14.2.2.</strong> 线程类型导致的栈溢出</a></li><li class="chapter-item "><a href="../compiler/pitfalls/arithmetic-overflow.html"><strong aria-hidden="true">14.2.3.</strong> 算术溢出导致的 panic</a></li><li class="chapter-item "><a href="../compiler/pitfalls/closure-with-lifetime.html"><strong aria-hidden="true">14.2.4.</strong> 闭包中奇怪的生命周期</a></li><li class="chapter-item "><a href="../compiler/pitfalls/the-disabled-mutability.html"><strong aria-hidden="true">14.2.5.</strong> 可变变量不可变？</a></li><li class="chapter-item "><a href="../compiler/pitfalls/multiple-mutable-references.html"><strong aria-hidden="true">14.2.6.</strong> 可变借用失败引发的深入思考</a></li><li class="chapter-item "><a href="../compiler/pitfalls/lazy-iterators.html"><strong aria-hidden="true">14.2.7.</strong> 不太勤快的迭代器</a></li><li class="chapter-item "><a href="../compiler/pitfalls/weird-ranges.html"><strong aria-hidden="true">14.2.8.</strong> 奇怪的序列 x..y</a></li><li class="chapter-item "><a href="../compiler/pitfalls/iterator-everywhere.html"><strong aria-hidden="true">14.2.9.</strong> 无处不在的迭代器</a></li><li class="chapter-item "><a href="../compiler/pitfalls/main-with-channel-blocked.html"><strong aria-hidden="true">14.2.10.</strong> 线程间传递消息导致主线程无法结束</a></li><li class="chapter-item "><a href="../compiler/pitfalls/utf8-performance.html"><strong aria-hidden="true">14.2.11.</strong> 警惕 UTF-8 引发的性能隐患</a></li></ol></li></ol></li><li class="chapter-item "><li class="part-title">性能优化</li><li class="spacer"></li><li class="chapter-item "><a href="../profiling/intro.html"><strong aria-hidden="true">15.</strong> Rust 性能优化 todo</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../profiling/memory/intro.html"><strong aria-hidden="true">15.1.</strong> 深入内存 todo</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../profiling/memory/pointer-ref.html"><strong aria-hidden="true">15.1.1.</strong> 指针和引用 todo</a></li><li class="chapter-item "><a href="../profiling/memory/uninit.html"><strong aria-hidden="true">15.1.2.</strong> 未初始化内存 todo</a></li><li class="chapter-item "><a href="../profiling/memory/allocation.html"><strong aria-hidden="true">15.1.3.</strong> 内存分配 todo</a></li><li class="chapter-item "><a href="../profiling/memory/layout.html"><strong aria-hidden="true">15.1.4.</strong> 内存布局 todo</a></li><li class="chapter-item "><a href="../profiling/memory/virtual.html"><strong aria-hidden="true">15.1.5.</strong> 虚拟内存 todo</a></li></ol></li><li class="chapter-item "><a href="../profiling/performance/intro.html"><strong aria-hidden="true">15.2.</strong> 性能调优 doing</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../profiling/performance/string.html"><strong aria-hidden="true">15.2.1.</strong> 字符串操作性能</a></li><li class="chapter-item "><a href="../profiling/performance/deep-into-move.html"><strong aria-hidden="true">15.2.2.</strong> 深入理解 move</a></li><li class="chapter-item "><a href="../profiling/performance/early-optimise.html"><strong aria-hidden="true">15.2.3.</strong> 糟糕的提前优化 todo</a></li><li class="chapter-item "><a href="../profiling/performance/clone-copy.html"><strong aria-hidden="true">15.2.4.</strong> Clone 和 Copy todo</a></li><li class="chapter-item "><a href="../profiling/performance/runtime-check.html"><strong aria-hidden="true">15.2.5.</strong> 减少 Runtime check(todo)</a></li><li class="chapter-item "><a href="../profiling/performance/cpu-cache.html"><strong aria-hidden="true">15.2.6.</strong> CPU 缓存性能优化 todo</a></li><li class="chapter-item "><a href="../profiling/performance/calculate.html"><strong aria-hidden="true">15.2.7.</strong> 计算性能优化 todo</a></li><li class="chapter-item "><a href="../profiling/performance/heap-stack.html"><strong aria-hidden="true">15.2.8.</strong> 堆和栈 todo</a></li><li class="chapter-item "><a href="../profiling/performance/allocator.html"><strong aria-hidden="true">15.2.9.</strong> 内存 allocator todo</a></li><li class="chapter-item "><a href="../profiling/performance/tools.html"><strong aria-hidden="true">15.2.10.</strong> 常用性能测试工具 todo</a></li><li class="chapter-item "><a href="../profiling/performance/enum.html"><strong aria-hidden="true">15.2.11.</strong> Enum 内存优化 todo</a></li></ol></li><li class="chapter-item "><a href="../profiling/compiler/intro.html"><strong aria-hidden="true">15.3.</strong> 编译优化 todo</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../profiling/compiler/llvm.html"><strong aria-hidden="true">15.3.1.</strong> LLVM todo</a></li><li class="chapter-item "><a href="../profiling/compiler/attributes.html"><strong aria-hidden="true">15.3.2.</strong> 常见属性标记 todo</a></li><li class="chapter-item "><a href="../profiling/compiler/speed-up.html"><strong aria-hidden="true">15.3.3.</strong> 提升编译速度 todo</a></li><li class="chapter-item "><a href="../profiling/compiler/optimization/intro.html"><strong aria-hidden="true">15.3.4.</strong> 编译器优化 todo</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../profiling/compiler/optimization/option.html"><strong aria-hidden="true">15.3.4.1.</strong> Option 枚举 todo</a></li></ol></li></ol></li></ol></li><li class="chapter-item "><li class="part-title">附录</li><li class="spacer"></li><li class="chapter-item "><div><strong aria-hidden="true">16.</strong> Appendix</div><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../appendix/keywords.html"><strong aria-hidden="true">16.1.</strong> 关键字</a></li><li class="chapter-item "><a href="../appendix/operators.html"><strong aria-hidden="true">16.2.</strong> 运算符与符号</a></li><li class="chapter-item "><a href="../appendix/expressions.html"><strong aria-hidden="true">16.3.</strong> 表达式</a></li><li class="chapter-item "><a href="../appendix/derive.html"><strong aria-hidden="true">16.4.</strong> 派生特征 trait</a></li><li class="chapter-item "><a href="../appendix/prelude.html"><strong aria-hidden="true">16.5.</strong> prelude 模块 todo</a></li><li class="chapter-item "><a href="../appendix/rust-version.html"><strong aria-hidden="true">16.6.</strong> Rust 版本说明</a></li><li class="chapter-item "><a href="../appendix/rust-versions/intro.html"><strong aria-hidden="true">16.7.</strong> Rust 历次版本更新解读</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../appendix/rust-versions/1.58.html"><strong aria-hidden="true">16.7.1.</strong> 1.58</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.59.html"><strong aria-hidden="true">16.7.2.</strong> 1.59</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.60.html"><strong aria-hidden="true">16.7.3.</strong> 1.60</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.61.html"><strong aria-hidden="true">16.7.4.</strong> 1.61</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.62.html"><strong aria-hidden="true">16.7.5.</strong> 1.62</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.63.html"><strong aria-hidden="true">16.7.6.</strong> 1.63</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.64.html"><strong aria-hidden="true">16.7.7.</strong> 1.64</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.65.html"><strong aria-hidden="true">16.7.8.</strong> 1.65</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.66.html"><strong aria-hidden="true">16.7.9.</strong> 1.66</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.67.html"><strong aria-hidden="true">16.7.10.</strong> 1.67</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.68.html"><strong aria-hidden="true">16.7.11.</strong> 1.68</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.69.html"><strong aria-hidden="true">16.7.12.</strong> 1.69</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.70.html"><strong aria-hidden="true">16.7.13.</strong> 1.70</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.71.html"><strong aria-hidden="true">16.7.14.</strong> 1.71</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.72.html"><strong aria-hidden="true">16.7.15.</strong> 1.72</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.73.html"><strong aria-hidden="true">16.7.16.</strong> 1.73</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.74.html"><strong aria-hidden="true">16.7.17.</strong> 1.74</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.75.html"><strong aria-hidden="true">16.7.18.</strong> 1.75</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.76.html"><strong aria-hidden="true">16.7.19.</strong> 1.76</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.77.html"><strong aria-hidden="true">16.7.20.</strong> 1.77</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.78.html"><strong aria-hidden="true">16.7.21.</strong> 1.78</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.79.html"><strong aria-hidden="true">16.7.22.</strong> 1.79</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.80.html"><strong aria-hidden="true">16.7.23.</strong> 1.80</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.81.html"><strong aria-hidden="true">16.7.24.</strong> 1.81</a></li><li class="chapter-item "><a href="../appendix/rust-versions/1.82.html"><strong aria-hidden="true">16.7.25.</strong> 1.82</a></li></ol></li></ol></li></ol>
</div>
<div id="sidebar-resize-handle" class="sidebar-resize-handle">
<div class="sidebar-resize-indicator"></div>
</div>
</nav>
<!-- Track and set sidebar scroll position -->
<script>
var sidebarScrollbox = document.querySelector('#sidebar .sidebar-scrollbox');
sidebarScrollbox.addEventListener('click', function(e) {
if (e.target.tagName === 'A') {
sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop);
}
}, { passive: true });
var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll');
sessionStorage.removeItem('sidebar-scroll');
if (sidebarScrollTop) {
// preserve sidebar scroll position when navigating via links within sidebar
sidebarScrollbox.scrollTop = sidebarScrollTop;
} else {
// scroll sidebar to current active section when navigating via "next/previous chapter" buttons
var activeSection = document.querySelector('#sidebar .active');
if (activeSection) {
activeSection.scrollIntoView({ block: 'center' });
}
}
</script>
<div id="page-wrapper" class="page-wrapper">
<div class="page">
<div id="menu-bar-hover-placeholder"></div>
<div id="menu-bar" class="menu-bar sticky">
<div class="left-buttons">
<label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
<i class="fa fa-bars"></i>
</label>
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
<i class="fa fa-paint-brush"></i>
</button>
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
<li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
</ul>
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
<i class="fa fa-search"></i>
</button>
</div>
<h1 class="menu-title">Rust语言圣经(Rust Course)</h1>
<div class="right-buttons">
<a href="../print.html" title="Print this book" aria-label="Print this book">
<i id="print-button" class="fa fa-print"></i>
</a>
<a href="https://github.com/sunface/rust-course" title="Git repository" aria-label="Git repository">
<i id="git-repository-button" class="fa fa-github"></i>
</a>
<a href="https://github.com/sunface/rust-course/edit/main/src/advance-practice/async.md" title="Suggest an edit" aria-label="Suggest an edit">
<i id="git-edit-button" class="fa fa-edit"></i>
</a>
</div>
</div>
<div id="search-wrapper" class="hidden">
<form id="searchbar-outer" class="searchbar-outer">
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
</form>
<div id="searchresults-outer" class="searchresults-outer hidden">
<div id="searchresults-header" class="searchresults-header"></div>
<ul id="searchresults">
</ul>
</div>
</div>
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
<script>
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
</script>
<div id="content" class="content">
<!-- Page table of contents -->
<div class="sidetoc"><nav class="pagetoc"></nav></div>
<main>
<h1 id="深入-tokio-背后的异步原理"><a class="header" href="#深入-tokio-背后的异步原理">深入 Tokio 背后的异步原理</a></h1>
<p>在经过多个章节的深入学习后，Tokio 对我们来说不再是一座隐于云雾中的高山，它其实蛮简单好用的，甚至还有一丝丝的可爱!?</p>
<p>但从现在开始，如果想要进一步的深入 Tokio ，首先需要深入理解 <code>async</code> 的原理，其实我们在<a href="https://course.rs/async/intro.html">之前的章节</a>已经深入学习过，这里结合 Tokio 再来回顾下。</p>
<h2 id="future"><a class="header" href="#future">Future</a></h2>
<p>先来回顾一下 <code>async fn</code> 异步函数 :</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use tokio::net::TcpStream;
async fn my_async_fn() {
println!(&quot;hello from async&quot;);
// 通过 .await 创建 socket 连接
let _socket = TcpStream::connect(&quot;127.0.0.1:3000&quot;).await.unwrap();
println!(&quot;async TCP operation complete&quot;);
// 关闭socket
}
<span class="boring">}</span></code></pre></pre>
<p>接着对它进行调用获取一个返回值，再在返回值上调用 <code>.await</code>：</p>
<pre><pre class="playground"><code class="language-rust edition2021">#[tokio::main]
async fn main() {
let what_is_this = my_async_fn();
// 上面的调用不会产生任何效果
// ... 执行一些其它代码
what_is_this.await;
// 直到 .await 后，文本才被打印，socket 连接也被创建和关闭
}</code></pre></pre>
<p>在上面代码中 <code>my_async_fn</code> 函数为何可以惰性执行( 直到 .await 调用时才执行)？秘密就在于 <code>async fn</code> 声明的函数返回一个 <code>Future</code>。</p>
<p><code>Future</code> 是一个实现了 <a href="https://doc.rust-lang.org/std/future/trait.Future.html"><code>std::future::Future</code></a> 特征的值，该值包含了一系列异步计算过程，而这个过程直到 <code>.await</code> 调用时才会被执行。</p>
<p><code>std::future::Future</code> 的定义如下所示:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::pin::Pin;
use std::task::{Context, Poll};
pub trait Future {
type Output;
fn poll(self: Pin&lt;&amp;mut Self&gt;, cx: &amp;mut Context)
-&gt; Poll&lt;Self::Output&gt;;
}
<span class="boring">}</span></code></pre></pre>
<p>代码中有几个关键点：</p>
<ul>
<li><a href="https://course.rs/basic/trait/advance-trait.html#%E5%85%B3%E8%81%94%E7%B1%BB%E5%9E%8B">关联类型</a> <code>Output</code> 是 <code>Future</code> 执行完成后返回的值的类型</li>
<li><code>Pin</code> 类型是在异步函数中进行借用的关键，在<a href="https://course.rs/advance/async/pin-unpin.html">这里</a>有非常详细的介绍</li>
</ul>
<p>和其它语言不同，Rust 中的 <code>Future</code> 不代表一个发生在后台的计算，而是 <code>Future</code> 就代表了计算本身，因此
<code>Future</code> 的所有者有责任去推进该计算过程的执行，例如通过 <code>Future::poll</code> 函数。听上去好像还挺复杂？但是大家不必担心，因为这些都在 Tokio 中帮你自动完成了 :)</p>
<h4 id="实现-future"><a class="header" href="#实现-future">实现 Future</a></h4>
<p>下面来一起实现个五脏俱全的 <code>Future</code>，它将：1. 等待某个特定时间点的到来 2. 在标准输出打印文本 3. 生成一个字符串</p>
<pre><pre class="playground"><code class="language-rust edition2021">use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::time::{Duration, Instant};
struct Delay {
when: Instant,
}
// 为我们的 Delay 类型实现 Future 特征
impl Future for Delay {
type Output = &amp;'static str;
fn poll(self: Pin&lt;&amp;mut Self&gt;, cx: &amp;mut Context&lt;'_&gt;)
-&gt; Poll&lt;&amp;'static str&gt;
{
if Instant::now() &gt;= self.when {
// 时间到了，Future 可以结束
println!(&quot;Hello world&quot;);
// Future 执行结束并返回 &quot;done&quot; 字符串
Poll::Ready(&quot;done&quot;)
} else {
// 目前先忽略下面这行代码
cx.waker().wake_by_ref();
Poll::Pending
}
}
}
#[tokio::main]
async fn main() {
let when = Instant::now() + Duration::from_millis(10);
let future = Delay { when };
// 运行并等待 Future 的完成
let out = future.await;
// 判断 Future 返回的字符串是否是 &quot;done&quot;
assert_eq!(out, &quot;done&quot;);
}</code></pre></pre>
<p>以上代码很清晰的解释了如何自定义一个 <code>Future</code>，并指定它如何通过 <code>poll</code> 一步一步执行，直到最终完成返回 <code>&quot;done&quot;</code> 字符串。</p>
<h4 id="async-fn-作为-future"><a class="header" href="#async-fn-作为-future">async fn 作为 Future</a></h4>
<p>大家有没有注意到，上面代码我们在 <code>main</code> 函数中初始化一个 <code>Future</code> 并使用 <code>.await</code> 对其进行调用执行，如果你是在 <code>fn main</code> 中这么做，是会报错的。</p>
<p>原因是 <code>.await</code> 只能用于 <code>async fn</code> 函数中，因此我们将 <code>main</code> 函数声明成 <code>async fn main</code> 同时使用 <code>#[tokio::main]</code> 进行了标注，此时 <code>async fn main</code> 生成的代码类似下面：</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::time::{Duration, Instant};
enum MainFuture {
// 初始化，但永远不会被 poll
State0,
// 等待 `Delay` 运行，例如 `future.await` 代码行
State1(Delay),
// Future 执行完成
Terminated,
}
impl Future for MainFuture {
type Output = ();
fn poll(mut self: Pin&lt;&amp;mut Self&gt;, cx: &amp;mut Context&lt;'_&gt;)
-&gt; Poll&lt;()&gt;
{
use MainFuture::*;
loop {
match *self {
State0 =&gt; {
let when = Instant::now() +
Duration::from_millis(10);
let future = Delay { when };
*self = State1(future);
}
State1(ref mut my_future) =&gt; {
match Pin::new(my_future).poll(cx) {
Poll::Ready(out) =&gt; {
assert_eq!(out, &quot;done&quot;);
*self = Terminated;
return Poll::Ready(());
}
Poll::Pending =&gt; {
return Poll::Pending;
}
}
}
Terminated =&gt; {
panic!(&quot;future polled after completion&quot;)
}
}
}
}
}
<span class="boring">}</span></code></pre></pre>
<p>可以看出，编译器会将 <code>Future</code> 变成状态机， 其中 <code>MainFuture</code> 包含了 <code>Future</code> 可能处于的状态：从 <code>State0</code> 状态开始，当 <code>poll</code> 被调用时， <code>Future</code> 会尝试去尽可能的推进内部的状态，若它可以被完成时，就会返回 <code>Poll::Ready</code>，其中还会包含最终的输出结果。</p>
<p>若 <code>Future</code> 无法被完成，例如它所等待的资源还没有准备好，此时就会返回 <code>Poll::Pending</code>，该返回值会通知调用者： <code>Future</code> 会在稍后才能完成。</p>
<p>同时可以看到：当一个 <code>Future</code> 由其它 <code>Future</code> 组成时，调用外层 <code>Future</code> 的 <code>poll</code> 函数会同时调用一次内部 <code>Future</code> 的 <code>poll</code> 函数。</p>
<h2 id="执行器-excecutor-"><a class="header" href="#执行器-excecutor-">执行器( Excecutor )</a></h2>
<p><code>async fn</code> 返回 <code>Future</code> ，而后者需要通过被不断的 <code>poll</code> 才能往前推进状态，同时该 <code>Future</code> 还能包含其它 <code>Future</code> ，那么问题来了谁来负责调用最外层 <code>Future</code> 的 <code>poll</code> 函数？</p>
<p>回一下之前的内容，为了运行一个异步函数，我们必须使用 <code>tokio::spawn</code> 或 通过 <code>#[tokio::main]</code> 标注的 <code>async fn main</code> 函数。它们有一个非常重要的作用：将最外层 <code>Future</code> 提交给 Tokio 的执行器。该执行器负责调用 <code>poll</code> 函数，然后推动 <code>Future</code> 的执行，最终直至完成。</p>
<h4 id="mini-tokio"><a class="header" href="#mini-tokio">mini tokio</a></h4>
<p>为了更好理解相关的内容，我们一起来实现一个迷你版本的 Tokio，完整的代码见<a href="https://github.com/tokio-rs/website/blob/master/tutorial-code/mini-tokio/src/main.rs">这里</a>。</p>
<p>先来看一段基础代码:</p>
<pre><pre class="playground"><code class="language-rust edition2021">use std::collections::VecDeque;
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::time::{Duration, Instant};
use futures::task;
fn main() {
let mut mini_tokio = MiniTokio::new();
mini_tokio.spawn(async {
let when = Instant::now() + Duration::from_millis(10);
let future = Delay { when };
let out = future.await;
assert_eq!(out, &quot;done&quot;);
});
mini_tokio.run();
}
struct MiniTokio {
tasks: VecDeque&lt;Task&gt;,
}
type Task = Pin&lt;Box&lt;dyn Future&lt;Output = ()&gt; + Send&gt;&gt;;
impl MiniTokio {
fn new() -&gt; MiniTokio {
MiniTokio {
tasks: VecDeque::new(),
}
}
/// 生成一个 Future并放入 mini-tokio 实例的任务队列中
fn spawn&lt;F&gt;(&amp;mut self, future: F)
where
F: Future&lt;Output = ()&gt; + Send + 'static,
{
self.tasks.push_back(Box::pin(future));
}
fn run(&amp;mut self) {
let waker = task::noop_waker();
let mut cx = Context::from_waker(&amp;waker);
while let Some(mut task) = self.tasks.pop_front() {
if task.as_mut().poll(&amp;mut cx).is_pending() {
self.tasks.push_back(task);
}
}
}
}</code></pre></pre>
<p>以上代码运行了一个 <code>async</code> 语句块 <code>mini_tokio.spawn(async {...})</code>， 还创建了一个 <code>Delay</code> 实例用于等待所需的时间。看上去相当不错，但这个实现有一个 <strong>重大缺陷</strong>：我们的执行器永远也不会休眠。执行器会持续的循环遍历所有的 <code>Future</code> ，然后不停的 <code>poll</code> 它们，但是事实上，大多数 <code>poll</code> 都是没有用的，因为此时 <code>Future</code> 并没有准备好，因此会继续返回 <code>Poll::Pending</code> ，最终这个循环遍历会让你的 CPU 疲于奔命，真打工人！</p>
<p>鉴于此，我们的 mini-tokio 只应该在 <code>Future</code> 准备好可以进一步运行后，才去 <code>poll</code> 它，例如该 <code>Future</code> 之前阻塞等待的<strong>资源</strong>已经准备好并可以被使用了，就可以对其进行 <code>poll</code>。再比如，如果一个 <code>Future</code> 任务在阻塞等待从 TCP socket 中读取数据，那我们只想在 <code>socket</code> 中有数据可以读取后才去 <code>poll</code> 它，而不是没事就 <code>poll</code> 着玩。</p>
<p>回到上面的代码中，mini-tokio 只应该当任务的延迟时间到了后，才去 <code>poll</code> 它。 为了实现这个功能，我们需要 <code>通知 -&gt; 运行</code> 机制：当任务可以进一步被推进运行时，它会主动通知执行器，然后执行器再来 <code>poll</code>。</p>
<h2 id="waker"><a class="header" href="#waker">Waker</a></h2>
<p>一切的答案都在 <code>Waker</code> 中，资源可以用它来通知正在等待的任务：该资源已经准备好，可以继续运行了。</p>
<p>再来看下 <code>Future::poll</code> 的定义：</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>fn poll(self: Pin&lt;&amp;mut Self&gt;, cx: &amp;mut Context)
-&gt; Poll&lt;Self::Output&gt;;
<span class="boring">}</span></code></pre></pre>
<p><code>Context</code> 参数中包含有 <code>waker()</code>方法。该方法返回一个绑定到当前任务上的 <code>Waker</code>，然后 <code>Waker</code> 上定义了一个 <code>wake()</code> 方法，用于通知执行器相关的任务可以继续执行。</p>
<p>准确来说，当 <code>Future</code> 阻塞等待的资源已经准备好时(例如 socket 中有了可读取的数据)，该资源可以调用 <code>wake()</code> 方法，来通知执行器可以继续调用该 <code>Future</code> 的 <code>poll</code> 函数来推进任务的执行。</p>
<h4 id="发送-wake-通知"><a class="header" href="#发送-wake-通知">发送 wake 通知</a></h4>
<p>现在，为 <code>Delay</code> 添加下 <code>Waker</code> 支持：</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::time::{Duration, Instant};
use std::thread;
struct Delay {
when: Instant,
}
impl Future for Delay {
type Output = &amp;'static str;
fn poll(self: Pin&lt;&amp;mut Self&gt;, cx: &amp;mut Context&lt;'_&gt;)
-&gt; Poll&lt;&amp;'static str&gt;
{
if Instant::now() &gt;= self.when {
println!(&quot;Hello world&quot;);
Poll::Ready(&quot;done&quot;)
} else {
// 为当前任务克隆一个 waker 的句柄
let waker = cx.waker().clone();
let when = self.when;
// 生成一个计时器线程
thread::spawn(move || {
let now = Instant::now();
if now &lt; when {
thread::sleep(when - now);
}
waker.wake();
});
Poll::Pending
}
}
}
<span class="boring">}</span></code></pre></pre>
<p>此时，计时器用来模拟一个阻塞等待的资源，一旦计时结束(该资源已经准备好)，资源会通过 <code>waker.wake()</code> 调用通知执行器我们的任务再次被调度执行了。</p>
<p>当然，现在的实现还较为粗糙，等会我们会来进一步优化，在此之前，先来看看如何监听这个 <code>wake</code> 通知。</p>
<blockquote>
<p>当 Future 会返回 <code>Poll::Pending</code> 时，一定要确保 <code>wake</code> 能被正常调用，否则会导致任务永远被挂起，再也不会被执行器 <code>poll</code>。</p>
<p><strong>忘记在返回 <code>Poll::Pending</code> 时调用 <code>wake</code> 是很多难以发现 bug 的潜在源头！</strong></p>
</blockquote>
<p>再回忆下最早实现的 <code>Delay</code> 代码：</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>impl Future for Delay {
type Output = &amp;'static str;
fn poll(self: Pin&lt;&amp;mut Self&gt;, cx: &amp;mut Context&lt;'_&gt;)
-&gt; Poll&lt;&amp;'static str&gt;
{
if Instant::now() &gt;= self.when {
// 时间到了，Future 可以结束
println!(&quot;Hello world&quot;);
// Future 执行结束并返回 &quot;done&quot; 字符串
Poll::Ready(&quot;done&quot;)
} else {
// 目前先忽略下面这行代码
cx.waker().wake_by_ref();
Poll::Pending
}
}
}
<span class="boring">}</span></code></pre></pre>
<p>在返回 <code>Poll::Pending</code> 之前，先调用了 <code>cx.waker().wake_by_ref()</code> ，由于此时我们还没有模拟计时资源，因此这里直接调用了 <code>wake</code> 进行通知，这样做会导致当前的 <code>Future</code> 被立即再次调度执行。</p>
<p>由此可见，这种通知的控制权是在你手里的，甚至可以像上面代码这样，还没准备好资源，就直接进行 <code>wake</code> 通知，但是总归意义不大，而且浪费了 CPU，因为这种 <code>执行 -&gt; 立即通知再调度 -&gt; 执行</code> 的方式会造成一个非常繁忙的循环。</p>
<h4 id="处理-wake-通知"><a class="header" href="#处理-wake-通知">处理 wake 通知</a></h4>
<p>下面，让我们更新 mini-tokio 服务，让它能接收 wake 通知：当 <code>waker.wake()</code> 被调用后，相关联的任务会被放入执行器的队列中，然后等待执行器的调用执行。</p>
<p>为了实现这一点，我们将使用消息通道来排队存储这些被唤醒并等待调度的任务。有一点需要注意，从消息通道接收消息的线程(执行器所在的线程)和发送消息的线程（唤醒任务时所在的线程）可能是不同的，因此消息( <code>Waker</code> )必须要实现 <code>Send</code>和 <code>Sync</code>，才能跨线程使用。</p>
<blockquote>
<p>关于 <code>Send</code> 和 <code>Sync</code> 的具体讲解见<a href="https://course.rs/advance/concurrency-with-threads/send-sync.html">这里</a></p>
</blockquote>
<p>基于以上理由，我们选择使用来自于 <code>crossbeam</code> 的消息通道，因为标准库中的消息通道不是 <code>Sync</code> 的。在 <code>Cargo.toml</code> 中添加以下依赖：</p>
<pre><code class="language-toml">crossbeam = &quot;0.8&quot;
</code></pre>
<p>再来更新下 <code>MiniTokio</code> 结构体：</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use crossbeam::channel;
use std::sync::Arc;
struct MiniTokio {
scheduled: channel::Receiver&lt;Arc&lt;Task&gt;&gt;,
sender: channel::Sender&lt;Arc&lt;Task&gt;&gt;,
}
struct Task {
// 先空着，后面会填充代码
}
<span class="boring">}</span></code></pre></pre>
<p><code>Waker</code> 实现了 <code>Sync</code> 特征，同时还可以被克隆，当 <code>wake</code> 被调用时，任务就会被调度执行。</p>
<p>为了实现上述的目的，我们引入了消息通道，当 <code>waker.wake()</code> 函数被调用时，任务会被发送到该消息通道中:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::sync::{Arc, Mutex};
struct Task {
// `Mutex` 是为了让 `Task` 实现 `Sync` 特征，它能保证同一时间只有一个线程可以访问 `Future`。
// 事实上 `Mutex` 并没有在 Tokio 中被使用，这里我们只是为了简化： Tokio 的真实代码实在太长了 :D
future: Mutex&lt;Pin&lt;Box&lt;dyn Future&lt;Output = ()&gt; + Send&gt;&gt;&gt;,
executor: channel::Sender&lt;Arc&lt;Task&gt;&gt;,
}
impl Task {
fn schedule(self: &amp;Arc&lt;Self&gt;) {
self.executor.send(self.clone());
}
}
<span class="boring">}</span></code></pre></pre>
<p>接下来，我们需要让 <code>std::task::Waker</code> 能准确的找到所需的调度函数 关联起来，对此标准库中提供了一个底层的 API <a href="https://doc.rust-lang.org/std/task/struct.RawWakerVTable.html"><code>std::task::RawWakerVTable</code></a> 可以用于手动的访问 <code>vtable</code>，这种实现提供了最大的灵活性，但是需要大量 <code>unsafe</code> 的代码。</p>
<p>因此我们选择更加高级的实现：由 <code>futures</code> 包提供的 <a href="https://docs.rs/futures/0.3.19/futures/task/trait.ArcWake.html"><code>ArcWake</code></a> 特征，只要简单实现该特征，就可以将我们的 <code>Task</code> 转变成一个 <code>waker</code>。在 <code>Cargo.toml</code> 中添加以下包：</p>
<pre><code class="language-toml">futures = &quot;0.3&quot;
</code></pre>
<p>然后为我们的任务 <code>Task</code> 实现 <code>ArcWake</code>:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use futures::task::{self, ArcWake};
use std::sync::Arc;
impl ArcWake for Task {
fn wake_by_ref(arc_self: &amp;Arc&lt;Self&gt;) {
arc_self.schedule();
}
}
<span class="boring">}</span></code></pre></pre>
<p>当之前的计时器线程调用 <code>waker.wake()</code> 时，所在的任务会被推入到消息通道中。因此接下来，我们需要实现接收端的功能，然后 <code>MiniTokio::run()</code> 函数中执行该任务:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>impl MiniTokio {
// 从消息通道中接收任务，然后通过 poll 来执行
fn run(&amp;self) {
while let Ok(task) = self.scheduled.recv() {
task.poll();
}
}
/// 初始化一个新的 mini-tokio 实例
fn new() -&gt; MiniTokio {
let (sender, scheduled) = channel::unbounded();
MiniTokio { scheduled, sender }
}
/// 在下面函数中，通过参数传入的 future 被 `Task` 包裹起来，然后会被推入到调度队列中，当 `run` 被调用时，该 future 将被执行
fn spawn&lt;F&gt;(&amp;self, future: F)
where
F: Future&lt;Output = ()&gt; + Send + 'static,
{
Task::spawn(future, &amp;self.sender);
}
}
impl Task {
fn poll(self: Arc&lt;Self&gt;) {
// 基于 Task 实例创建一个 waker, 它使用了之前的 `ArcWake`
let waker = task::waker(self.clone());
let mut cx = Context::from_waker(&amp;waker);
// 没有其他线程在竞争锁时，我们将获取到目标 future
let mut future = self.future.try_lock().unwrap();
// 对 future 进行 poll
let _ = future.as_mut().poll(&amp;mut cx);
}
// 使用给定的 future 来生成新的任务
//
// 新的任务会被推到 `sender` 中，接着该消息通道的接收端就可以获取该任务，然后执行
fn spawn&lt;F&gt;(future: F, sender: &amp;channel::Sender&lt;Arc&lt;Task&gt;&gt;)
where
F: Future&lt;Output = ()&gt; + Send + 'static,
{
let task = Arc::new(Task {
future: Mutex::new(Box::pin(future)),
executor: sender.clone(),
});
let _ = sender.send(task);
}
}
<span class="boring">}</span></code></pre></pre>
<p>首先，我们实现了 <code>MiniTokio::run()</code> 函数，它会持续从消息通道中接收被唤醒的任务，然后通过 <code>poll</code> 来推动其继续执行。</p>
<p>其次，<code>MiniTokio::new()</code> 和 <code>MiniTokio::spawn()</code> 使用了消息通道而不是一个 <code>VecDeque</code> 。当新任务生成后，这些任务中会携带上消息通道的发送端，当任务中的资源准备就绪时，会使用该发送端将该任务放入消息通道的队列中，等待执行器 <code>poll</code>。</p>
<p><code>Task::poll()</code> 函数使用 <code>futures</code> 包提供的 <code>ArcWake</code> 创建了一个 <code>waker</code>，后者可以用来创建 <code>task::Context</code>，最终该 <code>Context</code> 会被传给执行器调用的 <code>poll</code> 函数。</p>
<blockquote>
<p>注意，Task::poll 和执行器调用的 poll 是完全不同的，大家别搞混了</p>
</blockquote>
<h2 id="一些遗留问题"><a class="header" href="#一些遗留问题">一些遗留问题</a></h2>
<p>至此，我们的程序已经差不多完成，还剩几个遗留问题需要解决下。</p>
<h4 id="在异步函数中生成异步任务"><a class="header" href="#在异步函数中生成异步任务">在异步函数中生成异步任务</a></h4>
<p>之前实现 <code>Delay Future</code> 时，我们提到有几个问题需要解决。Rust 的异步模型允许一个 Future 在执行过程中可以跨任务迁移:</p>
<pre><pre class="playground"><code class="language-rust edition2021">use futures::future::poll_fn;
use std::future::Future;
use std::pin::Pin;
#[tokio::main]
async fn main() {
let when = Instant::now() + Duration::from_millis(10);
let mut delay = Some(Delay { when });
poll_fn(move |cx| {
let mut delay = delay.take().unwrap();
let res = Pin::new(&amp;mut delay).poll(cx);
assert!(res.is_pending());
tokio::spawn(async move {
delay.await;
});
Poll::Ready(())
}).await;
}</code></pre></pre>
<p>首先，<code>poll_fn</code> 函数使用闭包创建了一个 <code>Future</code>，其次，上面代码还创建一个 <code>Delay</code> 实例，然后在闭包中，对其进行了一次 <code>poll</code> ，接着再将该 <code>Delay</code> 实例发送到一个新的任务，在此任务中使用 <code>.await</code> 进行了执行。</p>
<p>在例子中，<code>Delay:poll</code> 被调用了不止一次，且使用了不同的 <code>Waker</code> 实例，在这种场景下，你必须确保调用最近一次 <code>poll</code> 函数中的 <code>Waker</code> 参数中的<code>wake</code>方法。也就是调用最内层 <code>poll</code> 函数参数( <code>Waker</code> )上的 <code>wake</code> 方法。</p>
<p>当实现一个 <code>Future</code> 时，很关键的一点就是要假设每次 <code>poll</code> 调用都会应用到一个不同的 <code>Waker</code> 实例上。因此 <code>poll</code> 函数必须要使用一个新的 <code>waker</code> 去更新替代之前的 <code>waker</code>。</p>
<p>我们之前的 <code>Delay</code> 实现中，会在每一次 <code>poll</code> 调用时都生成一个新的线程。这么做问题不大，但是当 <code>poll</code> 调用较多时会出现明显的性能问题！一个解决方法就是记录你是否已经生成了一个线程，然后只有在没有生成时才去创建一个新的线程。但是一旦这么做，就必须确保线程的 <code>Waker</code> 在后续 <code>poll</code> 调用中被正确更新，否则你无法唤醒最近的 <code>Waker</code> ！</p>
<p>这一段大家可能会看得云里雾里的，没办法，原文就绕来绕去，好在终于可以看代码了。。我们可以通过代码来解决疑惑：</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::future::Future;
use std::pin::Pin;
use std::sync::{Arc, Mutex};
use std::task::{Context, Poll, Waker};
use std::thread;
use std::time::{Duration, Instant};
struct Delay {
when: Instant,
// 用于说明是否已经生成一个线程
// Some 代表已经生成， None 代表还没有
waker: Option&lt;Arc&lt;Mutex&lt;Waker&gt;&gt;&gt;,
}
impl Future for Delay {
type Output = ();
fn poll(mut self: Pin&lt;&amp;mut Self&gt;, cx: &amp;mut Context&lt;'_&gt;) -&gt; Poll&lt;()&gt; {
// 若这是 Future 第一次被调用，那么需要先生成一个计时器线程。
// 若不是第一次调用(该线程已在运行)，那要确保已存储的 `Waker` 跟当前任务的 `waker` 匹配
if let Some(waker) = &amp;self.waker {
let mut waker = waker.lock().unwrap();
// 检查之前存储的 `waker` 是否跟当前任务的 `waker` 相匹配.
// 这是必要的，原因是 `Delay Future` 的实例可能会在两次 `poll` 之间被转移到另一个任务中，然后
// 存储的 waker 被该任务进行了更新。
// 这种情况一旦发生，`Context` 包含的 `waker` 将不同于存储的 `waker`。
// 因此我们必须对存储的 `waker` 进行更新
if !waker.will_wake(cx.waker()) {
*waker = cx.waker().clone();
}
} else {
let when = self.when;
let waker = Arc::new(Mutex::new(cx.waker().clone()));
self.waker = Some(waker.clone());
// 第一次调用 `poll`，生成计时器线程
thread::spawn(move || {
let now = Instant::now();
if now &lt; when {
thread::sleep(when - now);
}
// 计时结束，通过调用 `waker` 来通知执行器
let waker = waker.lock().unwrap();
waker.wake_by_ref();
});
}
// 一旦 waker 被存储且计时器线程已经开始，我们就需要检查 `delay` 是否已经完成
// 若计时已完成，则当前 Future 就可以完成并返回 `Poll::Ready`
if Instant::now() &gt;= self.when {
Poll::Ready(())
} else {
// 计时尚未结束，Future 还未完成，因此返回 `Poll::Pending`.
//
// `Future` 特征要求当 `Pending` 被返回时，那我们要确保当资源准备好时，必须调用 `waker` 以通
// 知执行器。 在我们的例子中，会通过生成的计时线程来保证
//
// 如果忘记调用 waker， 那等待我们的将是深渊：该任务将被永远的挂起，无法再执行
Poll::Pending
}
}
}
<span class="boring">}</span></code></pre></pre>
<p>这着实有些复杂(原文。。)，但是简单来看就是：在每次 <code>poll</code> 调用时，都会检查 <code>Context</code> 中提供的 <code>waker</code> 和我们之前记录的 <code>waker</code> 是否匹配。若匹配，就什么都不用做，若不匹配，那之前存储的就必须进行更新。</p>
<h4 id="notify"><a class="header" href="#notify">Notify</a></h4>
<p>我们之前证明了如何用手动编写的 <code>waker</code> 来实现 <code>Delay Future</code>。 <code>Waker</code> 是 Rust 异步编程的基石，因此绝大多数时候，我们并不需要直接去使用它。例如，在 <code>Delay</code> 的例子中， 可以使用 <a href="https://docs.rs/tokio/1.16.0/tokio/sync/struct.Notify.html"><code>tokio::sync::Notify</code></a> 去实现。</p>
<p>该 <code>Notify</code> 提供了一个基础的任务通知机制，它会处理这些 <code>waker</code> 的细节，包括确保两次 <code>waker</code> 的匹配:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use tokio::sync::Notify;
use std::sync::Arc;
use std::time::{Duration, Instant};
use std::thread;
async fn delay(dur: Duration) {
let when = Instant::now() + dur;
let notify = Arc::new(Notify::new());
let notify2 = notify.clone();
thread::spawn(move || {
let now = Instant::now();
if now &lt; when {
thread::sleep(when - now);
}
notify2.notify_one();
});
notify.notified().await;
}
<span class="boring">}</span></code></pre></pre>
<p>当使用 <code>Notify</code> 后，我们就可以轻松的实现如上的 <code>delay</code> 函数。</p>
<h2 id="总结"><a class="header" href="#总结">总结</a></h2>
<p>在看完这么长的文章后，我们来总结下，否则大家可能还会遗忘:</p>
<ul>
<li>在 Rust 中，<code>async</code> 是惰性的，直到执行器 <code>poll</code> 它们时，才会开始执行</li>
<li><code>Waker</code> 是 <code>Future</code> 被执行的关键，它可以链接起 <code>Future</code> 任务和执行器</li>
<li>当资源没有准备时，会返回一个 <code>Poll::Pending</code></li>
<li>当资源准备好时，会通过 <code>waker.wake</code> 发出通知</li>
<li>执行器会收到通知，然后调度该任务继续执行，此时由于资源已经准备好，因此任务可以顺利往前推进了</li>
</ul>
<div id="giscus-container"></div>
</main>
<nav class="nav-wrapper" aria-label="Page navigation">
<!-- Mobile navigation buttons -->
<a rel="prev" href="../advance-practice/frame.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next prefetch" href="../advance-practice/select.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
<div style="clear: both"></div>
</nav>
</div>
</div>
<nav class="nav-wide-wrapper" aria-label="Page navigation">
<a rel="prev" href="../advance-practice/frame.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next prefetch" href="../advance-practice/select.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
</nav>
</div>
<script>
window.playground_copyable = true;
</script>
<script src="../ace.js"></script>
<script src="../editor.js"></script>
<script src="../mode-rust.js"></script>
<script src="../theme-dawn.js"></script>
<script src="../theme-tomorrow_night.js"></script>
<script src="../elasticlunr.min.js"></script>
<script src="../mark.min.js"></script>
<script src="../searcher.js"></script>
<script src="../clipboard.min.js"></script>
<script src="../highlight.js"></script>
<script src="../book.js"></script>
<script type="text/javascript" charset="utf-8">
var pagePath = "advance-practice/async.md"
</script>
<!-- Custom JS scripts -->
<script src="../assets/custom.js"></script>
<script src="../assets/bigPicture.js"></script>
</div>
</body>
</html>
Reference in new issue View Git Blame Copy Permalink