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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">Datav: 可编程的数据可视化平台和可观测性平台</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 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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 expanded "><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 expanded "><a href="../advance-practice1/multi-threads.html" class="active"><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 "><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 "><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></ol></li></ol></li></ol>
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<h1 id="构建多线程-web-服务器"><a class="header" href="#构建多线程-web-服务器">构建多线程 Web 服务器</a></h1>
<p>目前的单线程版本只能依次处理用户的请求：一时间只能处理一个请求连接。随着用户的请求数增多，可以预料的是排在后面的用户可能要等待数十秒甚至超时！</p>
<p>本章我们将解决这个问题，但是首先来模拟一个慢请求场景，看看单线程是否真的如此糟糕。</p>
<h2 id="基于单线程模拟慢请求"><a class="header" href="#基于单线程模拟慢请求">基于单线程模拟慢请求</a></h2>
<p>下面的代码中，使用 sleep 的方式让每次请求持续 5 秒，模拟真实的慢请求:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// in main.rs
use std::{
fs,
io::{prelude::*, BufReader},
net::{TcpListener, TcpStream},
thread,
time::Duration,
};
// --snip--
fn handle_connection(mut stream: TcpStream) {
// --snip--
let (status_line, filename) = match &amp;request_line[..] {
&quot;GET / HTTP/1.1&quot; =&gt; (&quot;HTTP/1.1 200 OK&quot;, &quot;hello.html&quot;),
&quot;GET /sleep HTTP/1.1&quot; =&gt; {
thread::sleep(Duration::from_secs(5));
(&quot;HTTP/1.1 200 OK&quot;, &quot;hello.html&quot;)
}
_ =&gt; (&quot;HTTP/1.1 404 NOT FOUND&quot;, &quot;404.html&quot;),
};
// --snip--
}
<span class="boring">}</span></code></pre></pre>
<p>由于增加了新的请求路径 <code>/sleep</code>，之前的 <code>if else</code> 被修改为 <code>match</code>，需要注意的是，由于 <code>match</code> 不会像方法那样自动做引用或者解引用，因此我们需要显式调用: <code>match &amp;request_line[..]</code> ，来获取所需的 <code>&amp;str</code> 类型。</p>
<p>可以看出，当用户访问 <code>/sleep</code> 时，请求会持续 5 秒后才返回，下面来试试，启动服务器后，打开你的浏览器，这次要分别打开两个页面(tab页): <code>http://127.0.0.1:7878/</code> 和 <code>http://127.0.0.1:7878/sleep</code>。</p>
<p>此时，如果我们连续访问 <code>/</code> 路径，那效果跟之前一样：立刻看到请求的页面。但假如先访问 <code>/sleep</code> ，接着在另一个页面访问 <code>/</code>，就会看到 <code>/</code> 的页面直到 5 秒后才会刷出来，验证了请求排队这个糟糕的事实。</p>
<p>至于如何解决，其实办法不少，本章我们来看看一个经典解决方案：线程池。</p>
<h2 id="使用线程池改善吞吐"><a class="header" href="#使用线程池改善吞吐">使用线程池改善吞吐</a></h2>
<p>线程池包含一组已生成的线程，它们时刻等待着接收并处理新的任务。当程序接收到新任务时，它会将线程池中的一个线程指派给该任务，在该线程忙着处理时，新来的任务会交给池中剩余的线程进行处理。最终，当执行任务的线程处理完后，它会被重新放入到线程池中，准备处理新任务。</p>
<p>假设线程池中包含 N 个线程，那么可以推断出，服务器将拥有并发处理 N 个请求连接的能力，从而增加服务器的吞吐量。</p>
<p>同时，我们将限制线程池中的线程数量，以保护服务器免受拒绝服务攻击（DoS）的影响：如果针对每个请求创建一个新线程，那么一个人向我们的服务器发出1000万个请求，会直接耗尽资源，导致后续用户的请求无法被处理，这也是拒绝服务名称的来源。</p>
<p>因此，还需对线程池进行一定的架构设计，首先是设定最大线程数的上限，其次维护一个请求队列。池中的线程去队列中依次弹出请求并处理。这样就可以同时并发处理 N 个请求，其中 N 是线程数。</p>
<p>但聪明的读者可能会想到，假如每个请求依然耗时很长，那请求队列依然会堆积，后续的用户请求还是需要等待较长的时间，毕竟你也就 N 个线程，但总归比单线程要强 N 倍吧 :D</p>
<p>当然，线程池依然是较为传统的提升吞吐方法，比较新的有：单线程异步 IO，例如 redis；多线程异步 IO，例如 Rust 的主流 web 框架。事实上，大家在下一个实战项目中，会看到相关技术的应用。</p>
<h3 id="为每个请求生成一个线程"><a class="header" href="#为每个请求生成一个线程">为每个请求生成一个线程</a></h3>
<p>这显然不是我们的最终方案，原因在于它会生成无上限的线程数，最终导致资源耗尽。但它确实是一个好的起点:</p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let listener = TcpListener::bind(&quot;127.0.0.1:7878&quot;).unwrap();
for stream in listener.incoming() {
let stream = stream.unwrap();
thread::spawn(|| {
handle_connection(stream);
});
}
}</code></pre></pre>
<p>这种实现下，依次访问 <code>/sleep</code> 和 <code>/</code> 就无需再等待，不错的开始。</p>
<h3 id="限制创建线程的数量"><a class="header" href="#限制创建线程的数量">限制创建线程的数量</a></h3>
<p>原则上，我们希望在上面代码的基础上，尽量少的去修改，下面是一个假想的线程池 API 实现:</p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let listener = TcpListener::bind(&quot;127.0.0.1:7878&quot;).unwrap();
let pool = ThreadPool::new(4);
for stream in listener.incoming() {
let stream = stream.unwrap();
pool.execute(|| {
handle_connection(stream);
});
}
}</code></pre></pre>
<p>代码跟之前的类似，也非常简洁明了， <code>ThreadPool::new(4)</code> 创建一个包含 4 个线程的线程池，接着通过 <code>pool.execute</code> 去分发执行请求。</p>
<p>显然，上面的代码无法编译，下面来逐步实现。</p>
<h3 id="使用编译器驱动的方式开发-threadpool"><a class="header" href="#使用编译器驱动的方式开发-threadpool">使用编译器驱动的方式开发 ThreadPool</a></h3>
<p>你可能听说过测试驱动开发，但听过编译器驱动开发吗？来见识下 Rust 中的绝招吧。</p>
<p>检查之前的代码，看看报什么错:</p>
<pre><code class="language-shell">$ cargo check
Checking hello v0.1.0 (file:///projects/hello)
error[E0433]: failed to resolve: use of undeclared type `ThreadPool`
--&gt; src/main.rs:11:16
|
11 | let pool = ThreadPool::new(4);
| ^^^^^^^^^^ use of undeclared type `ThreadPool`
For more information about this error, try `rustc --explain E0433`.
error: could not compile `hello` due to previous error
</code></pre>
<p>俗话说，不怕敌人很强，就怕他们不犯错，很好，编译器漏出了破绽。看起来我们需要实现 <code>ThreadPool</code> 类型。看起来，还需要添加一个库包，未来线程池的代码都将在这个独立的包中完成，甚至于未来你要实现其它的服务，也可以复用这个多线程库包。</p>
<p>创建 <code>src/lib.rs</code> 文件并写入如下代码:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub struct ThreadPool;
<span class="boring">}</span></code></pre></pre>
<p>接着在 <code>main.rs</code> 中引入:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// main.rs
use hello::ThreadPool;
<span class="boring">}</span></code></pre></pre>
<p>编译后依然报错:</p>
<pre><code class="language-shell">$ cargo check
Checking hello v0.1.0 (file:///projects/hello)
error[E0599]: no function or associated item named `new` found for struct `ThreadPool` in the current scope
--&gt; src/main.rs:12:28
|
12 | let pool = ThreadPool::new(4);
| ^^^ function or associated item not found in `ThreadPool`
For more information about this error, try `rustc --explain E0599`.
error: could not compile `hello` due to previous error
</code></pre>
<p>好，继续实现 <code>new</code> 函数 :</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub struct ThreadPool;
impl ThreadPool {
pub fn new(size: usize) -&gt; ThreadPool {
ThreadPool
}
}
<span class="boring">}</span></code></pre></pre>
<p>继续检查：</p>
<pre><code class="language-shell">$ cargo check
Checking hello v0.1.0 (file:///projects/hello)
error[E0599]: no method named `execute` found for struct `ThreadPool` in the current scope
--&gt; src/main.rs:17:14
|
17 | pool.execute(|| {
| ^^^^^^^ method not found in `ThreadPool`
For more information about this error, try `rustc --explain E0599`.
error: could not compile `hello` due to previous error
</code></pre>
<p>这个方法类似于 <code>thread::spawn</code>，用于将闭包中的任务交给某个空闲的线程去执行。</p>
<p>其实这里有一个小难点：<code>execute</code> 的参数是一个闭包，回忆下之前学过的内容，闭包作为参数时可以由三个特征进行约束: <code>Fn</code>、<code>FnMut</code> 和 <code>FnOnce</code>，选哪个就成为一个问题。由于 <code>execute</code> 在实现上类似 <code>thread::spawn</code>，我们可以参考下后者的签名如何声明。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub fn spawn&lt;F, T&gt;(f: F) -&gt; JoinHandle&lt;T&gt;
where
F: FnOnce() -&gt; T,
F: Send + 'static,
T: Send + 'static,
<span class="boring">}</span></code></pre></pre>
<p>可以看出，<code>spawn</code> 选择 <code>FnOnce</code> 作为 <code>F</code> 闭包的特征约束，原因是闭包作为任务只需被线程执行一次即可。</p>
<p><code>F</code> 还有一个特征约束 <code>Send</code> ，也可以照抄过来，毕竟闭包需要从一个线程传递到另一个线程，至于生命周期约束 <code>'static</code>，是因为我们并不知道线程需要多久时间来执行该任务。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>impl ThreadPool {
// --snip--
pub fn execute&lt;F&gt;(&amp;self, f: F)
where
F: FnOnce() + Send + 'static,
{
}
}
<span class="boring">}</span></code></pre></pre>
<p>在理解 <code>spawn</code> 后，就可以轻松写出如上的 <code>execute</code> 实现，注意这里的 <code>FnOnce()</code> 跟 <code>spawn</code> 有所不同，原因是要 <code>execute</code> 传入的闭包没有参数也没有返回值。</p>
<pre><code class="language-shell">$ cargo check
Checking hello v0.1.0 (file:///projects/hello)
Finished dev [unoptimized + debuginfo] target(s) in 0.24s
</code></pre>
<p>成功编译，但在浏览器访问依然会报之前类似的错误，下面来实现 <code>execute</code>。</p>
<h3 id="new-还是-build"><a class="header" href="#new-还是-build"><code>new</code> 还是 <code>build</code></a></h3>
<p>关于 <code>ThreadPool</code> 的构造函数，存在两个选择 <code>new</code> 和 <code>build</code>。</p>
<p><code>new</code> 往往用于简单初始化一个实例，而 <code>build</code> 往往会完成更加复杂的构建工作，例如入门实战中的 <code>Config::build</code>。</p>
<p>在这个项目中，我们并不需要在初始化线程池的同时创建相应的线程，因此 <code>new</code> 是更适合的选择:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>impl ThreadPool {
/// Create a new ThreadPool.
///
/// The size is the number of threads in the pool.
///
/// # Panics
///
/// The `new` function will panic if the size is zero.
pub fn new(size: usize) -&gt; ThreadPool {
assert!(size &gt; 0);
ThreadPool
}
// --snip--
}
<span class="boring">}</span></code></pre></pre>
<p>这里有两点值得注意:</p>
<ul>
<li><code>usize</code> 类型包含 <code>0</code>，但是创建没有任何线程的线程池显然是无意义的，因此做一下 <code>assert!</code> 验证</li>
<li><code>ThreadPool</code> 拥有不错的<a href="https://course.rs/basic/comment.html#%E6%96%87%E6%A1%A3%E6%B3%A8%E9%87%8A">文档注释</a>，甚至包含了可能 <code>panic</code> 的情况，通过 <code>cargo doc --open</code> 可以访问文档注释</li>
</ul>
<h3 id="存储线程"><a class="header" href="#存储线程">存储线程</a></h3>
<p>创建 <code>ThreadPool</code> 后，下一步就是存储具体的线程，既然要存放线程，一个绕不过去的问题就是：用什么类型来存放，例如假如使用 <code>Vec&lt;T&gt;</code> 来存储，那这个 <code>T</code> 应该是什么？</p>
<p>估计还得探索下 <code>thread::spawn</code> 的签名，毕竟它生成并返回一个线程:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>pub fn spawn&lt;F, T&gt;(f: F) -&gt; JoinHandle&lt;T&gt;
where
F: FnOnce() -&gt; T,
F: Send + 'static,
T: Send + 'static,
<span class="boring">}</span></code></pre></pre>
<p>看起来 <code>JoinHandle&lt;T&gt;</code> 是我们需要的，这里的 <code>T</code> 是传入的闭包任务所返回的，我们的任务无需任何返回，因此 <code>T</code> 直接使用 <code>()</code> 即可。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::thread;
pub struct ThreadPool {
threads: Vec&lt;thread::JoinHandle&lt;()&gt;&gt;,
}
impl ThreadPool {
// --snip--
pub fn new(size: usize) -&gt; ThreadPool {
assert!(size &gt; 0);
let mut threads = Vec::with_capacity(size);
for _ in 0..size {
// create some threads and store them in the vector
}
ThreadPool { threads }
}
// --snip--
}
<span class="boring">}</span></code></pre></pre>
<p>如上所示，最终我们使用 <code>Vec&lt;thread::JoinHandle&lt;()&gt;&gt;</code> 来存储线程，同时设定了容量上限 <code>with_capacity(size)</code>，该方法还可以提前分配好内存空间，比 <code>Vec::new</code> 的性能要更好一点。</p>
<h3 id="将代码从-threadpool-发送到线程中"><a class="header" href="#将代码从-threadpool-发送到线程中">将代码从 ThreadPool 发送到线程中</a></h3>
<p>上面的代码留下一个未实现的 <code>for</code> 循环，用于创建和存储线程。</p>
<p>学过多线程一章后，大家应该知道 <code>thread::spawn</code> 虽然是生成线程最好的方式，但是它会立即执行传入的任务，然而，在我们的使用场景中，创建线程和执行任务明显是要分离的，因此标准库看起来不再适合。</p>
<p>可以考虑创建一个 <code>Worker</code> 结构体，作为 <code>ThreadPool</code> 和任务线程联系的桥梁，它的任务是获得将要执行的代码，然后在具体的线程中去执行。想象一个场景：一个餐馆，<code>Worker</code> 等待顾客的点餐，然后将具体的点餐信息传递给厨房，感觉类似服务员？</p>
<p>引入 <code>Worker</code> 后，就无需再存储 <code>JoinHandle&lt;()&gt;</code> 实例，直接存储 <code>Worker</code> 实例：该实例内部会存储 <code>JoinHandle&lt;()&gt;</code>。下面是新的线程池创建流程:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>use std::thread;
pub struct ThreadPool {
workers: Vec&lt;Worker&gt;,
}
impl ThreadPool {
// --snip--
pub fn new(size: usize) -&gt; ThreadPool {
assert!(size &gt; 0);
let mut workers = Vec::with_capacity(size);
for id in 0..size {
workers.push(Worker::new(id));
}
ThreadPool { workers }
}
// --snip--
}
struct Worker {
id: usize,
thread: thread::JoinHandle&lt;()&gt;,
}
impl Worker {
fn new(id: usize) -&gt; Worker {
// 尚未实现..
let thread = thread::spawn(|| {});
// 每个 `Worker` 都拥有自己的唯一 id
Worker { id, thread }
}
}
<span class="boring">}</span></code></pre></pre>
<p>由于外部调用者无需知道 <code>Worker</code> 的存在，因此这里使用了私有的声明。</p>
<p>大家可以编译下代码，如果出错了，请仔细检查下，是否遗漏了什么，截止目前，代码是完全可以通过编译的，但是任务该怎么执行依然还没有实现。</p>
<h3 id="将请求发送给线程"><a class="header" href="#将请求发送给线程">将请求发送给线程</a></h3>
<p>在上面的代码中， <code>thread::spawn(|| {})</code> 还没有给予实质性的内容，现在一起来完善下。</p>
<p>首先 <code>Worker</code> 结构体需要从线程池 <code>TreadPool</code> 的队列中获取待执行的代码，对于这类场景，消息传递非常适合：我们将使用消息通道( channel )作为任务队列。</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::mpsc, thread};
pub struct ThreadPool {
workers: Vec&lt;Worker&gt;,
sender: mpsc::Sender&lt;Job&gt;,
}
struct Job;
impl ThreadPool {
// --snip--
pub fn new(size: usize) -&gt; ThreadPool {
assert!(size &gt; 0);
let (sender, receiver) = mpsc::channel();
let mut workers = Vec::with_capacity(size);
for id in 0..size {
workers.push(Worker::new(id));
}
ThreadPool { workers, sender }
}
// --snip--
}
<span class="boring">}</span></code></pre></pre>
<p>阅读过之前内容的同学应该知道，消息通道有发送端和接收端，其中线程池 <code>ThreadPool</code> 持有发送端，通过 <code>execute</code> 方法来发送任务。那么问题来了，谁持有接收端呢？答案是 <code>Worker</code>，它的内部线程将接收任务，然后进行处理。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>impl ThreadPool {
// --snip--
pub fn new(size: usize) -&gt; ThreadPool {
assert!(size &gt; 0);
let (sender, receiver) = mpsc::channel();
let mut workers = Vec::with_capacity(size);
for id in 0..size {
workers.push(Worker::new(id, receiver));
}
ThreadPool { workers, sender }
}
// --snip--
}
// --snip--
impl Worker {
fn new(id: usize, receiver: mpsc::Receiver&lt;Job&gt;) -&gt; Worker {
let thread = thread::spawn(|| {
receiver;
});
Worker { id, thread }
}
}
<span class="boring">}</span></code></pre></pre>
<p>看起来很美好，但是很不幸，它会报错: </p>
<pre><code class="language-shell">$ cargo check
Checking hello v0.1.0 (file:///projects/hello)
error[E0382]: use of moved value: `receiver`
--&gt; src/lib.rs:26:42
|
21 | let (sender, receiver) = mpsc::channel();
| -------- move occurs because `receiver` has type `std::sync::mpsc::Receiver&lt;Job&gt;`, which does not implement the `Copy` trait
...
26 | workers.push(Worker::new(id, receiver));
| ^^^^^^^^ value moved here, in previous iteration of loop
For more information about this error, try `rustc --explain E0382`.
error: could not compile `hello` due to previous error
</code></pre>
<p>原因也很简单，<code>receiver</code> 并没有实现 <code>Copy</code>，因此它的所有权在第一次循环中，就被传入到第一个 <code>Worker</code> 实例中，后续自然无法再使用。</p>
<p>报错就解决呗，但 Rust 中的 channel 实现是 mpsc，即多生产者单消费者，因此我们无法通过克隆消费者的方式来修复这个错误。当然，发送多条消息给多个接收者也不在考虑范畴，该怎么办？似乎陷入了绝境。</p>
<p>雪上加霜的是，就算 <code>receiver</code> 可以克隆，但是你得保证同一个时间只有一个<code>receiver</code> 能接收消息，否则一个任务可能同时被多个 <code>Worker</code> 执行，因此多个线程需要安全的共享和使用 <code>receiver</code>，等等，安全的共享？听上去 <code>Arc</code> 这个多所有权结构非常适合，互斥使用？貌似 <code>Mutex</code> 很适合，结合一下，<code>Arc&lt;Mutex&lt;T&gt;&gt;</code>，这不就是我们之前见过多次的线程安全类型吗？</p>
<p>总之，<code>Arc</code> 允许多个 <code>Worker</code> 同时持有 <code>receiver</code>，而 <code>Mutex</code> 可以确保一次只有一个 <code>Worker</code> 能从 <code>receiver</code> 接收消息。</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::{mpsc, Arc, Mutex},
thread,
};
// --snip--
impl ThreadPool {
// --snip--
pub fn new(size: usize) -&gt; ThreadPool {
assert!(size &gt; 0);
let (sender, receiver) = mpsc::channel();
let receiver = Arc::new(Mutex::new(receiver));
let mut workers = Vec::with_capacity(size);
for id in 0..size {
workers.push(Worker::new(id, Arc::clone(&amp;receiver)));
}
ThreadPool { workers, sender }
}
// --snip--
}
// --snip--
impl Worker {
fn new(id: usize, receiver: Arc&lt;Mutex&lt;mpsc::Receiver&lt;Job&gt;&gt;&gt;) -&gt; Worker {
// --snip--
}
}
<span class="boring">}</span></code></pre></pre>
<p>修改后，每一个 Worker 都可以安全的持有 <code>receiver</code>，同时不必担心一个任务会被重复执行多次，完美！</p>
<h3 id="实现-execute-方法"><a class="header" href="#实现-execute-方法">实现 execute 方法</a></h3>
<p>首先，需要为一个很长的类型创建一个别名, 有多长呢？ </p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// --snip--
type Job = Box&lt;dyn FnOnce() + Send + 'static&gt;;
impl ThreadPool {
// --snip--
pub fn execute&lt;F&gt;(&amp;self, f: F)
where
F: FnOnce() + Send + 'static,
{
let job = Box::new(f);
self.sender.send(job).unwrap();
}
}
// --snip--
<span class="boring">}</span></code></pre></pre>
<p>创建别名的威力暂时还看不到，敬请期待。总之，这里的工作很简单，将传入的任务包装成 <code>Job</code> 类型后，发送出去。</p>
<p>但是还没完，接收的代码也要完善下:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// --snip--
impl Worker {
fn new(id: usize, receiver: Arc&lt;Mutex&lt;mpsc::Receiver&lt;Job&gt;&gt;&gt;) -&gt; Worker {
let thread = thread::spawn(move || loop {
let job = receiver.lock().unwrap().recv().unwrap();
println!(&quot;Worker {id} got a job; executing.&quot;);
job();
});
Worker { id, thread }
}
}
<span class="boring">}</span></code></pre></pre>
<p>修改后，就可以不停地循环去接收任务，最后进行执行。还可以看到因为之前 <code>Job</code> 别名的引入， <code>new</code> 函数的签名才没有过度复杂，否则你将看到的是 <code>fn new(id: usize, receiver: Arc&lt;Mutex&lt;mpsc::Receiver&lt;Box&lt;dyn FnOnce() + Send + 'static&gt;&gt;&gt;&gt;) -&gt; Worker</code> ，感受下类型别名的威力吧 :D</p>
<p><code>lock()</code> 方法可以获得一个 <code>Mutex</code> 锁，至于为何使用 <code>unwrap</code>，难道获取锁还能失败？没错，假如当前持有锁的线程 <code>panic</code> 了，那么这些等待锁的线程就会获取一个错误，因此 通过 <code>unwrap</code> 来让当前等待的线程 <code>panic</code> 是一个不错的解决方案，当然你还可以换成 <code>expect</code>。</p>
<p>一旦获取到锁里的内容 <code>mpsc::Receiver&lt;Job&gt;&gt;</code> 后，就可以调用其上的 <code>recv</code> 方法来接收消息，依然是一个 <code>unwrap</code>，原因在于持有发送端的线程可能会被关闭，这种情况下直接 <code>panic</code> 也是不错的。</p>
<p><code>recv</code> 的调用过程是阻塞的，意味着若没有任何任务，那当前的调用线程将一直等待，直到接收到新的任务。<code>Mutex&lt;T&gt;</code> 可以同一个任务只会被一个 Worker 获取，不会被重复执行。</p>
<pre><code class="language-shell">$ cargo run
Compiling hello v0.1.0 (file:///projects/hello)
warning: field is never read: `workers`
--&gt; src/lib.rs:7:5
|
7 | workers: Vec&lt;Worker&gt;,
| ^^^^^^^^^^^^^^^^^^^^
|
= note: `#[warn(dead_code)]` on by default
warning: field is never read: `id`
--&gt; src/lib.rs:48:5
|
48 | id: usize,
| ^^^^^^^^^
warning: field is never read: `thread`
--&gt; src/lib.rs:49:5
|
49 | thread: thread::JoinHandle&lt;()&gt;,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
warning: `hello` (lib) generated 3 warnings
Finished dev [unoptimized + debuginfo] target(s) in 1.40s
Running `target/debug/hello`
Worker 0 got a job; executing.
Worker 2 got a job; executing.
Worker 1 got a job; executing.
Worker 3 got a job; executing.
Worker 0 got a job; executing.
Worker 2 got a job; executing.
Worker 1 got a job; executing.
Worker 3 got a job; executing.
Worker 0 got a job; executing.
Worker 2 got a job; executing.
</code></pre>
<p>终于，程序如愿运行起来，我们的线程池可以并发处理任务了！从打印的数字可以看到，只有 4 个线程去执行任务，符合我们对线程池的要求，这样再也不用担心系统的线程资源会被消耗殆尽了！</p>
<blockquote>
<p>注意： 处于缓存的考虑，有些浏览器会对多次同样的请求进行顺序的执行，因此你可能还是会遇到访问 <code>/sleep</code> 后，就无法访问另一个 <code>/sleep</code> 的问题 :(</p>
</blockquote>
<h2 id="while-let-的巨大陷阱"><a class="header" href="#while-let-的巨大陷阱">while let 的巨大陷阱</a></h2>
<p>还有一个问题，为啥之前我们不用 <code>while let</code> 来循环？例如：</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>// --snip--
impl Worker {
fn new(id: usize, receiver: Arc&lt;Mutex&lt;mpsc::Receiver&lt;Job&gt;&gt;&gt;) -&gt; Worker {
let thread = thread::spawn(move || {
while let Ok(job) = receiver.lock().unwrap().recv() {
println!(&quot;Worker {id} got a job; executing.&quot;);
job();
}
});
Worker { id, thread }
}
}
<span class="boring">}</span></code></pre></pre>
<p>这段代码编译起来没问题，但是并不会产生我们预期的结果：后续请求依然需要等待慢请求的处理完成后，才能被处理。奇怪吧，仅仅是从 <code>let</code> 改成 <code>while let</code> 就会变成这样？大家可以思考下为什么会这样，具体答案会在下一章节末尾给出，这里先出给一个小提示：<code>Mutex</code> 获取的锁在作用域结束后才会被释放。</p>
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