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<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 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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 "><a href="../advance-practice/async.html"><strong aria-hidden="true">6.8.</strong> 深入 async</a></li><li class="chapter-item expanded "><a href="../advance-practice/select.html" class="active"><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>
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<h1 id="select"><a class="header" href="#select">select!</a></h1>
<p>在实际使用时，一个重要的场景就是同时等待多个异步操作的结果，并且对其结果进行进一步处理，在本章节，我们来看看，强大的 <code>select!</code> 是如何帮助咱们更好的控制多个异步操作并发执行的。</p>
<h2 id="tokioselect"><a class="header" href="#tokioselect">tokio::select!</a></h2>
<p><code>select!</code> 允许同时等待多个计算操作，然后当其中一个操作完成时就退出等待:</p>
<pre><pre class="playground"><code class="language-rust edition2021">use tokio::sync::oneshot;
#[tokio::main]
async fn main() {
let (tx1, rx1) = oneshot::channel();
let (tx2, rx2) = oneshot::channel();
tokio::spawn(async {
let _ = tx1.send(&quot;one&quot;);
});
tokio::spawn(async {
let _ = tx2.send(&quot;two&quot;);
});
tokio::select! {
val = rx1 =&gt; {
println!(&quot;rx1 completed first with {:?}&quot;, val);
}
val = rx2 =&gt; {
println!(&quot;rx2 completed first with {:?}&quot;, val);
}
}
// 任何一个 select 分支结束后，都会继续执行接下来的代码
}</code></pre></pre>
<p>这里用到了两个 <code>oneshot</code> 消息通道，虽然两个操作的创建在代码上有先后顺序，但在实际执行时却不这样。因此， <code>select</code> 在从两个通道<strong>阻塞等待</strong>接收消息时，<code>rx1</code> 和 <code>rx2</code> 都有可能被先打印出来。</p>
<p>需要注意，任何一个 <code>select</code> 分支完成后，都会继续执行后面的代码，没被执行的分支会被丢弃( <code>dropped</code> )。</p>
<h4 id="取消"><a class="header" href="#取消">取消</a></h4>
<p>对于 <code>Async Rust</code> 来说，释放( drop )掉一个 <code>Future</code> 就意味着取消任务。从上一章节可以得知， <code>async</code> 操作会返回一个 <code>Future</code>，而后者是惰性的，直到被 <code>poll</code> 调用时，才会被执行。一旦 <code>Future</code> 被释放，那操作将无法继续，因为所有相关的状态都被释放。</p>
<p>对于 Tokio 的 <code>oneshot</code> 的接收端来说，它在被释放时会发送一个关闭通知到发送端，因此发送端可以通过释放任务的方式来终止正在执行的任务。</p>
<pre><pre class="playground"><code class="language-rust edition2021">use tokio::sync::oneshot;
async fn some_operation() -&gt; String {
// 在这里执行一些操作...
}
#[tokio::main]
async fn main() {
let (mut tx1, rx1) = oneshot::channel();
let (tx2, rx2) = oneshot::channel();
tokio::spawn(async {
// 等待 `some_operation` 的完成
// 或者处理 `oneshot` 的关闭通知
tokio::select! {
val = some_operation() =&gt; {
let _ = tx1.send(val);
}
_ = tx1.closed() =&gt; {
// 收到了发送端发来的关闭信号
// `select` 即将结束，此时，正在进行的 `some_operation()` 任务会被取消，任务自动完成，
// tx1 被释放
}
}
});
tokio::spawn(async {
let _ = tx2.send(&quot;two&quot;);
});
tokio::select! {
val = rx1 =&gt; {
println!(&quot;rx1 completed first with {:?}&quot;, val);
}
val = rx2 =&gt; {
println!(&quot;rx2 completed first with {:?}&quot;, val);
}
}
}</code></pre></pre>
<p>上面代码的重点就在于 <code>tx1.closed</code> 所在的分支，一旦发送端被关闭，那该分支就会被执行，然后 <code>select</code> 会退出，并清理掉还没执行的第一个分支 <code>val = some_operation()</code> ，这其中 <code>some_operation</code> 返回的 <code>Future</code> 也会被清理，根据之前的内容，<code>Future</code> 被清理那相应的任务会立即取消，因此 <code>some_operation</code> 会被取消，不再执行。</p>
<h4 id="future-的实现"><a class="header" href="#future-的实现">Future 的实现</a></h4>
<p>为了更好的理解 <code>select</code> 的工作原理，我们来看看如果使用 <code>Future</code> 该如何实现。当然，这里是一个简化版本，在实际中，<code>select!</code> 会包含一些额外的功能，例如一开始会随机选择一个分支进行 <code>poll</code>。</p>
<pre><pre class="playground"><code class="language-rust edition2021">use tokio::sync::oneshot;
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
struct MySelect {
rx1: oneshot::Receiver&lt;&amp;'static str&gt;,
rx2: oneshot::Receiver&lt;&amp;'static str&gt;,
}
impl Future for MySelect {
type Output = ();
fn poll(mut self: Pin&lt;&amp;mut Self&gt;, cx: &amp;mut Context&lt;'_&gt;) -&gt; Poll&lt;()&gt; {
if let Poll::Ready(val) = Pin::new(&amp;mut self.rx1).poll(cx) {
println!(&quot;rx1 completed first with {:?}&quot;, val);
return Poll::Ready(());
}
if let Poll::Ready(val) = Pin::new(&amp;mut self.rx2).poll(cx) {
println!(&quot;rx2 completed first with {:?}&quot;, val);
return Poll::Ready(());
}
Poll::Pending
}
}
#[tokio::main]
async fn main() {
let (tx1, rx1) = oneshot::channel();
let (tx2, rx2) = oneshot::channel();
// 使用 tx1 和 tx2
MySelect {
rx1,
rx2,
}.await;
}</code></pre></pre>
<p><code>MySelect</code> 包含了两个分支中的 <code>Future</code>，当它被 <code>poll</code> 时，第一个分支会先执行。如果执行完成，那取出的值会被使用，然后 <code>MySelect</code> 也随之结束。而另一个分支对应的 <code>Future</code> 会被释放掉，对应的操作也会被取消。</p>
<p>还记得上一章节中很重要的一段话吗？</p>
<blockquote>
<p>当一个 <code>Future</code> 返回 <code>Poll::Pending</code> 时，它必须确保会在某一个时刻通过 <code>Waker</code> 来唤醒，不然该 <code>Future</code> 将永远地被挂起</p>
</blockquote>
<p>但是仔细观察我们之前的代码，里面并没有任何的 <code>wake</code> 调用！事实上，这是因为参数 <code>cx</code> 被传入了内层的 <code>poll</code> 调用。 只要内部的 <code>Future</code> 实现了唤醒并且返回了 <code>Poll::Pending</code>，那 <code>MySelect</code> 也等于实现了唤醒！</p>
<h2 id="语法"><a class="header" href="#语法">语法</a></h2>
<p>目前来说，<code>select!</code> 最多可以支持 64 个分支，每个分支形式如下：</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>&lt;模式&gt; = &lt;async 表达式&gt; =&gt; &lt;结果处理&gt;,
<span class="boring">}</span></code></pre></pre>
<p>当 <code>select</code> 宏开始执行后，所有的分支会开始并发的执行。当任何一个<strong>表达式</strong>完成时，会将结果跟<strong>模式</strong>进行匹配。若匹配成功，则剩下的表达式会被释放。</p>
<p>最常用的<strong>模式</strong>就是用变量名去匹配表达式返回的值，然后该变量就可以在<strong>结果处理</strong>环节使用。</p>
<p>如果当前的模式不能匹配，剩余的 <code>async</code> 表达式将继续并发的执行，直到下一个完成。</p>
<p>由于 <code>select!</code> 使用的是一个 <code>async</code> 表达式，因此我们可以定义一些更复杂的计算。</p>
<p>例如从在分支中进行 TCP 连接：</p>
<pre><pre class="playground"><code class="language-rust edition2021">use tokio::net::TcpStream;
use tokio::sync::oneshot;
#[tokio::main]
async fn main() {
let (tx, rx) = oneshot::channel();
// 生成一个任务，用于向 oneshot 发送一条消息
tokio::spawn(async move {
tx.send(&quot;done&quot;).unwrap();
});
tokio::select! {
socket = TcpStream::connect(&quot;localhost:3465&quot;) =&gt; {
println!(&quot;Socket connected {:?}&quot;, socket);
}
msg = rx =&gt; {
println!(&quot;received message first {:?}&quot;, msg);
}
}
}</code></pre></pre>
<p>再比如，在分支中进行 TCP 监听:</p>
<pre><pre class="playground"><code class="language-rust edition2021">use tokio::net::TcpListener;
use tokio::sync::oneshot;
use std::io;
#[tokio::main]
async fn main() -&gt; io::Result&lt;()&gt; {
let (tx, rx) = oneshot::channel();
tokio::spawn(async move {
tx.send(()).unwrap();
});
let mut listener = TcpListener::bind(&quot;localhost:3465&quot;).await?;
tokio::select! {
_ = async {
loop {
let (socket, _) = listener.accept().await?;
tokio::spawn(async move { process(socket) });
}
// 给予 Rust 类型暗示
Ok::&lt;_, io::Error&gt;(())
} =&gt; {}
_ = rx =&gt; {
println!(&quot;terminating accept loop&quot;);
}
}
Ok(())
}</code></pre></pre>
<p>分支中接收连接的循环会一直运行，直到遇到错误才停止，或者当 <code>rx</code> 中有值时，也会停止。 <code>_</code> 表示我们并不关心这个值，这样使用唯一的目的就是为了结束第一分支中的循环。</p>
<h2 id="返回值"><a class="header" href="#返回值">返回值</a></h2>
<p><code>select!</code> 还能返回一个值:</p>
<pre><pre class="playground"><code class="language-rust edition2021">async fn computation1() -&gt; String {
// .. 计算
}
async fn computation2() -&gt; String {
// .. 计算
}
#[tokio::main]
async fn main() {
let out = tokio::select! {
res1 = computation1() =&gt; res1,
res2 = computation2() =&gt; res2,
};
println!(&quot;Got = {}&quot;, out);
}</code></pre></pre>
<p>需要注意的是，此时 <code>select!</code> 的所有分支必须返回一样的类型，否则编译器会报错！</p>
<h2 id="错误传播"><a class="header" href="#错误传播">错误传播</a></h2>
<p>在 Rust 中使用 <code>?</code> 可以对错误进行传播，但是在 <code>select!</code> 中，<code>?</code> 如何工作取决于它是在分支中的 <code>async</code> 表达式使用还是在结果处理的代码中使用:</p>
<ul>
<li>在分支中 <code>async</code> 表达式使用会将该表达式的结果变成一个 <code>Result</code></li>
<li>在结果处理中使用，会将错误直接传播到 <code>select!</code> 之外</li>
</ul>
<pre><pre class="playground"><code class="language-rust edition2021">use tokio::net::TcpListener;
use tokio::sync::oneshot;
use std::io;
#[tokio::main]
async fn main() -&gt; io::Result&lt;()&gt; {
// [设置 `rx` oneshot 消息通道]
let listener = TcpListener::bind(&quot;localhost:3465&quot;).await?;
tokio::select! {
res = async {
loop {
let (socket, _) = listener.accept().await?;
tokio::spawn(async move { process(socket) });
}
Ok::&lt;_, io::Error&gt;(())
} =&gt; {
res?;
}
_ = rx =&gt; {
println!(&quot;terminating accept loop&quot;);
}
}
Ok(())
}</code></pre></pre>
<p><code>listener.accept().await?</code> 是分支表达式中的 <code>?</code>，因此它会将表达式的返回值变成 <code>Result</code> 类型，然后赋予给 <code>res</code> 变量。</p>
<p>与之不同的是，结果处理中的 <code>res?;</code> 会让 <code>main</code> 函数直接结束并返回一个 <code>Result</code>，可以看出，这里 <code>?</code> 的用法跟我们平时的用法并无区别。</p>
<h2 id="模式匹配"><a class="header" href="#模式匹配">模式匹配</a></h2>
<p>既然是模式匹配，我们需要再来回忆下 <code>select!</code> 的分支语法形式:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>&lt;模式&gt; = &lt;async 表达式&gt; =&gt; &lt;结果处理&gt;,
<span class="boring">}</span></code></pre></pre>
<p>迄今为止，我们只用了变量绑定的模式，事实上，<a href="https://course.rs/basic/match-pattern/all-patterns.html">任何 Rust 模式</a>都可以在此处使用。</p>
<pre><pre class="playground"><code class="language-rust edition2021">use tokio::sync::mpsc;
#[tokio::main]
async fn main() {
let (mut tx1, mut rx1) = mpsc::channel(128);
let (mut tx2, mut rx2) = mpsc::channel(128);
tokio::spawn(async move {
// 用 tx1 和 tx2 干一些不为人知的事
});
tokio::select! {
Some(v) = rx1.recv() =&gt; {
println!(&quot;Got {:?} from rx1&quot;, v);
}
Some(v) = rx2.recv() =&gt; {
println!(&quot;Got {:?} from rx2&quot;, v);
}
else =&gt; {
println!(&quot;Both channels closed&quot;);
}
}
}</code></pre></pre>
<p>上面代码中，<code>rx</code> 通道关闭后，<code>recv()</code> 方法会返回一个 <code>None</code>，可以看到没有任何模式能够匹配这个 <code>None</code>，那为何不会报错？秘密就在于 <code>else</code> 上：当使用模式去匹配分支时，若之前的所有分支都无法被匹配，那 <code>else</code> 分支将被执行。</p>
<h2 id="借用"><a class="header" href="#借用">借用</a></h2>
<p>当在 Tokio 中生成( spawn )任务时，其 async 语句块必须拥有其中数据的所有权。而 <code>select!</code> 并没有这个限制，它的每个分支表达式可以直接借用数据，然后进行并发操作。只要遵循 Rust 的借用规则，多个分支表达式可以不可变的借用同一个数据，或者在一个表达式可变的借用某个数据。</p>
<p>来看个例子，在这里我们同时向两个 TCP 目标发送同样的数据:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use tokio::io::AsyncWriteExt;
use tokio::net::TcpStream;
use std::io;
use std::net::SocketAddr;
async fn race(
data: &amp;[u8],
addr1: SocketAddr,
addr2: SocketAddr
) -&gt; io::Result&lt;()&gt; {
tokio::select! {
Ok(_) = async {
let mut socket = TcpStream::connect(addr1).await?;
socket.write_all(data).await?;
Ok::&lt;_, io::Error&gt;(())
} =&gt; {}
Ok(_) = async {
let mut socket = TcpStream::connect(addr2).await?;
socket.write_all(data).await?;
Ok::&lt;_, io::Error&gt;(())
} =&gt; {}
else =&gt; {}
};
Ok(())
}
<span class="boring">}</span></code></pre></pre>
<p>这里其实有一个很有趣的题外话，由于 TCP 连接过程是在模式中发生的，因此当某一个连接过程失败后，它通过 <code>?</code> 返回的 <code>Err</code> 类型并无法匹配 <code>Ok</code>，因此另一个分支会继续被执行，继续连接。</p>
<p>如果你把连接过程放在了结果处理中，那连接失败会直接从 <code>race</code> 函数中返回，而不是继续执行另一个分支中的连接！</p>
<p>还有一个非常重要的点，<strong>借用规则在分支表达式和结果处理中存在很大的不同</strong>。例如上面代码中，我们在两个分支表达式中分别对 <code>data</code> 做了不可变借用，这当然 ok，但是若是两次可变借用，那编译器会立即进行报错。但是转折来了：当在结果处理中进行两次可变借用时，却不会报错，大家可以思考下为什么，提示下：思考下分支在执行完成后会发生什么？</p>
<pre><pre class="playground"><code class="language-rust edition2021">use tokio::sync::oneshot;
#[tokio::main]
async fn main() {
let (tx1, rx1) = oneshot::channel();
let (tx2, rx2) = oneshot::channel();
let mut out = String::new();
tokio::spawn(async move {
});
tokio::select! {
_ = rx1 =&gt; {
out.push_str(&quot;rx1 completed&quot;);
}
_ = rx2 =&gt; {
out.push_str(&quot;rx2 completed&quot;);
}
}
println!(&quot;{}&quot;, out);
}</code></pre></pre>
<p>例如以上代码，就在两个分支的结果处理中分别进行了可变借用，并不会报错。原因就在于：<code>select!</code>会保证只有一个分支的结果处理会被运行，然后在运行结束后，另一个分支会被直接丢弃。</p>
<h2 id="循环"><a class="header" href="#循环">循环</a></h2>
<p>来看看该如何在循环中使用 <code>select!</code>，顺便说一句，跟循环一起使用是最常见的使用方式。</p>
<pre><pre class="playground"><code class="language-rust edition2021">use tokio::sync::mpsc;
#[tokio::main]
async fn main() {
let (tx1, mut rx1) = mpsc::channel(128);
let (tx2, mut rx2) = mpsc::channel(128);
let (tx3, mut rx3) = mpsc::channel(128);
loop {
let msg = tokio::select! {
Some(msg) = rx1.recv() =&gt; msg,
Some(msg) = rx2.recv() =&gt; msg,
Some(msg) = rx3.recv() =&gt; msg,
else =&gt; { break }
};
println!(&quot;Got {}&quot;, msg);
}
println!(&quot;All channels have been closed.&quot;);
}</code></pre></pre>
<p>在循环中使用 <code>select!</code> 最大的不同就是，当某一个分支执行完成后，<code>select!</code> 会继续循环等待并执行下一个分支，直到所有分支最终都完成，最终匹配到 <code>else</code> 分支，然后通过 <code>break</code> 跳出循环。</p>
<p>老生常谈的一句话：<code>select!</code> 中哪个分支先被执行是无法确定的，因此不要依赖于分支执行的顺序！想象一下，在异步编程场景，若 <code>select!</code> 按照分支的顺序来执行会如何：若 <code>rx1</code> 中总是有数据，那每次循环都只会去处理第一个分支，后面两个分支永远不会被执行。</p>
<h4 id="恢复之前的异步操作"><a class="header" href="#恢复之前的异步操作">恢复之前的异步操作</a></h4>
<pre><pre class="playground"><code class="language-rust edition2021">async fn action() {
// 一些异步逻辑
}
#[tokio::main]
async fn main() {
let (mut tx, mut rx) = tokio::sync::mpsc::channel(128);
let operation = action();
tokio::pin!(operation);
loop {
tokio::select! {
_ = &amp;mut operation =&gt; break,
Some(v) = rx.recv() =&gt; {
if v % 2 == 0 {
break;
}
}
}
}
}</code></pre></pre>
<p>在上面代码中，我们没有直接在 <code>select!</code> 分支中调用 <code>action()</code> ，而是在 <code>loop</code> 循环外面先将 <code>action()</code> 赋值给 <code>operation</code>，因此 <code>operation</code> 是一个 <code>Future</code>。</p>
<p><strong>重点来了</strong>，在 <code>select!</code> 循环中，我们使用了一个奇怪的语法 <code>&amp;mut operation</code>，大家想象一下，如果不加 <code>&amp;mut</code> 会如何？答案是，每一次循环调用的都是一次全新的 <code>action()</code>调用，但是当加了 <code>&amp;mut operatoion</code> 后，每一次循环调用就变成了对同一次 <code>action()</code> 的调用。也就是我们实现了在每次循环中恢复了之前的异步操作！</p>
<p><code>select!</code> 的另一个分支从消息通道收取消息，一旦收到值是偶数，就跳出循环，否则就继续循环。</p>
<p>还有一个就是我们使用了 <code>tokio::pin!</code>，具体的细节这里先不介绍，值得注意的点是：如果要在一个引用上使用 <code>.await</code>，那么引用的值就必须是不能移动的或者实现了 <code>Unpin</code>，关于 <code>Pin</code> 和 <code>Unpin</code> 可以参见<a href="https://course.rs/async/pin-unpin.html">这里</a>。</p>
<p>一旦移除 <code>tokio::pin!</code> 所在行的代码，然后试图编译，就会获得以下错误:</p>
<pre><code class="language-console">error[E0599]: no method named `poll` found for struct
`std::pin::Pin&lt;&amp;mut &amp;mut impl std::future::Future&gt;`
in the current scope
--&gt; src/main.rs:16:9
|
16 | / tokio::select! {
17 | | _ = &amp;mut operation =&gt; break,
18 | | Some(v) = rx.recv() =&gt; {
19 | | if v % 2 == 0 {
... |
22 | | }
23 | | }
| |_________^ method not found in
| `std::pin::Pin&lt;&amp;mut &amp;mut impl std::future::Future&gt;`
|
= note: the method `poll` exists but the following trait bounds
were not satisfied:
`impl std::future::Future: std::marker::Unpin`
which is required by
`&amp;mut impl std::future::Future: std::future::Future`
</code></pre>
<p>虽然我们已经学了很多关于 <code>Future</code> 的知识，但是这个错误依然不太好理解。但是它不难解决：当你试图在<strong>一个引用上调用 <code>.await</code> 然后遇到了 <code>Future 未实现</code> 这种错误时</strong>，往往只需要将对应的 <code>Future</code> 进行固定即可: <code> tokio::pin!(operation);</code>。</p>
<h4 id="修改一个分支"><a class="header" href="#修改一个分支">修改一个分支</a></h4>
<p>下面一起来看一个稍微复杂一些的 <code>loop</code> 循环，首先，我们拥有：</p>
<ul>
<li>一个消息通道可以传递 <code>i32</code> 类型的值</li>
<li>定义在 <code>i32</code> 值上的一个异步操作</li>
</ul>
<p>想要实现的逻辑是：</p>
<ul>
<li>在消息通道中等待一个偶数出现</li>
<li>使用该偶数作为输入来启动一个异步操作</li>
<li>等待异步操作完成，与此同时监听消息通道以获取更多的偶数</li>
<li>若在异步操作完成前一个新的偶数到来了，终止当前的异步操作，然后接着使用新的偶数开始异步操作</li>
</ul>
<pre><pre class="playground"><code class="language-rust edition2021">async fn action(input: Option&lt;i32&gt;) -&gt; Option&lt;String&gt; {
// 若 input（输入）是None，则返回 None
// 事实上也可以这么写: `let i = input?;`
let i = match input {
Some(input) =&gt; input,
None =&gt; return None,
};
// 这里定义一些逻辑
}
#[tokio::main]
async fn main() {
let (mut tx, mut rx) = tokio::sync::mpsc::channel(128);
let mut done = false;
let operation = action(None);
tokio::pin!(operation);
tokio::spawn(async move {
let _ = tx.send(1).await;
let _ = tx.send(3).await;
let _ = tx.send(2).await;
});
loop {
tokio::select! {
res = &amp;mut operation, if !done =&gt; {
done = true;
if let Some(v) = res {
println!(&quot;GOT = {}&quot;, v);
return;
}
}
Some(v) = rx.recv() =&gt; {
if v % 2 == 0 {
// `.set` 是 `Pin` 上定义的方法
operation.set(action(Some(v)));
done = false;
}
}
}
}
}</code></pre></pre>
<p>当第一次循环开始时， 第一个分支会立即完成，因为 <code>operation</code> 的参数是 <code>None</code>。当第一个分支执行完成时，<code>done</code> 会变成 <code>true</code>，此时第一个分支的条件将无法被满足，开始执行第二个分支。</p>
<p>当第二个分支收到一个偶数时，<code>done</code> 会被修改为 <code>false</code>，且 <code>operation</code> 被设置了值。 此后再一次循环时，第一个分支会被执行，且 <code>operation</code> 返回一个 <code>Some(2)</code>，因此会触发 <code>return</code> ，最终结束循环并返回。</p>
<p>这段代码引入了一个新的语法: <code>if !done</code>，在解释之前，先看看去掉后会如何：</p>
<pre><code class="language-console">thread 'main' panicked at '`async fn` resumed after completion', src/main.rs:1:55
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
</code></pre>
<p><code>'`async fn` resumed after completion'</code> 错误的含义是：<code>async fn</code> 异步函数在完成后，依然被恢复了(继续使用)。</p>
<p>回到例子中来，这个错误是由于 <code>operation</code> 在它已经调用完成后依然被使用。通常来说，当使用 <code>.await</code> 后，调用 <code>.await</code> 的值会被消耗掉，因此并不存在这个问题。但是在这例子中，我们在引用上调用 <code>.await</code>，因此之后该引用依然可以被使用。</p>
<p>为了避免这个问题，需要在第一个分支的 <code>operation</code> 完成后禁止再使用该分支。这里的 <code>done</code> 的引入就很好的解决了问题。对于 <code>select!</code> 来说 <code>if !done</code> 的语法被称为预条件( <strong>precondition</strong> )，该条件会在分支被 <code>.await</code> 执行前进行检查。</p>
<p>那大家肯定有疑问了，既然 <code>operation</code> 不能再被调用了，我们该如何在有偶数值时，再回到第一个分支对其进行调用呢？答案就是 <code>operation.set(action(Some(v)));</code>，该操作会重新使用新的参数设置 <code>operation</code>。</p>
<h2 id="spawn-和-select-的一些不同"><a class="header" href="#spawn-和-select-的一些不同">spawn 和 select! 的一些不同</a></h2>
<p>学到现在，相信大家对于 <code>tokio::spawn</code> 和 <code>select!</code> 已经非常熟悉，它们的共同点就是都可以并发的运行异步操作。
然而它们使用的策略大相径庭。</p>
<p><code>tokio::spawn</code> 函数会启动新的任务来运行一个异步操作，每个任务都是一个独立的对象可以单独被 Tokio 调度运行，因此两个不同的任务的调度都是独立进行的，甚至于它们可能会运行在两个不同的操作系统线程上。鉴于此，生成的任务和生成的线程有一个相同的限制：不允许对外部环境中的值进行借用。</p>
<p>而 <code>select!</code> 宏就不一样了，它在同一个任务中并发运行所有的分支。正是因为这样，在同一个任务中，这些分支无法被同时运行。 <code>select!</code> 宏在单个任务中实现了多路复用的功能。</p>
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