C++ 多线程示例 =============== 功能说明 -------- 演示 C++ 标准库中的多线程编程特性，包括线程创建、异常处理、``std::future``/``std::promise`` 异步编程以及互斥锁和条件变量的使用。本示例展示了如何在多线程环境下安全地共享数据和进行线程同步。 硬件连接 -------- 无需外部连接，多线程为软件功能，不依赖硬件资源。 示例内容 -------- 1. 演示 C++ 异常处理机制（``try-catch``） 2. 演示基本线程创建和同步（``std::thread``） 3. 演示 ``std::future`` 和 ``std::promise`` 异步编程 4. 演示 ``std::packaged_task`` 和 ``std::async`` 的使用 5. 演示互斥锁（``std::mutex``）保护共享数据 6. 演示条件变量（``std::condition_variable``）实现生产者-消费者模式 编译 -------- .. include:: /sample_build.rst 烧录固件 -------- .. include:: /sample_flash.rst 预期输出 -------- .. code-block:: text Caught a runtime error: Error occurred Thread 1: 1 Thread 2: 1 Thread 1: 2 Thread 2: 2 Thread 1: 3 Thread 2: 3 Thread 1: 4 Thread 2: 4 Thread 1: 5 Thread 2: 5 Both threads completed. ======= Starting Future/Promise Tests ======= === Basic Future/Promise Example === Promise thread: calculating value... Main thread: waiting for value... Promise thread: value set Main thread: received value 42 === Another Future/Promise Example === Another promise thread: calculating value... Main thread: waiting for another value... Another promise thread: value set Main thread: received another value 100 === Packaged Task Example === Packaged task: calculating result for 5... Main thread: waiting for packaged task result... Main thread: packaged task result is 25 === Async Example === Starting async task with launch::async... Main thread: doing other work while waiting... Async task: working in separate thread... Main thread: getting async result... Main thread: async result is 100 Starting async task with launch::deferred... Main thread: calling get() on deferred task... Deferred task: executing in caller's thread when get() is called... Main thread: deferred result is 200 ======= Future/Promise Tests Completed ======= ======= Starting Mutex/Condition Variable Tests ======= === Mutex and Condition Variable Tests === === Basic Mutex Example === Starting two threads that increment a counter with mutex protection... Final counter value: 20000 Expected value: 20000 === Basic Condition Variable Example === Starting consumer thread... Starting producer thread... Produced: 1 Consumed: 1 Produced: 2 Consumed: 2 ... ======= Mutex/Condition Variable Tests Completed ======= 核心 API -------- .. list-table:: :header-rows: 1 * - API - 说明 * - ``std::thread`` - C++11 线程类，用于创建和管理线程 * - ``std::future`` - 异步操作结果的占位符 * - ``std::promise`` - 用于在线程间传递值或异常 * - ``std::mutex`` - 互斥锁，保护共享资源 * - ``std::condition_variable`` - 条件变量，用于线程间同步 * - ``std::async`` - 异步执行函数并返回 future * - ``std::packaged_task`` - 封装可调用对象，用于异步执行 关键代码 -------- .. code-block:: cpp // 异常处理 try { throw std::runtime_error("Error occurred"); } catch (const std::runtime_error &e) { std::cout << "Caught a runtime error: " << e.what() << std::endl; } // 创建和同步线程 std::thread t1(printNumbers, 1); std::thread t2(printNumbers, 2); t1.join(); t2.join(); // 使用 promise 和 future std::promise<int> intPromise; std::future<int> intFuture = intPromise.get_future(); std::thread t(promiseFunction, std::move(intPromise)); int value = intFuture.get(); // 等待并获取值 // 使用互斥锁保护共享数据（推荐使用 lock_guard） std::mutex mtx; { std::lock_guard<std::mutex> lock(mtx); // 访问共享数据（自动加锁和解锁） counter++; } 注意事项 -------- 1. **线程同步**: 多个线程访问共享数据时必须使用互斥锁或其他同步机制保护 2. **线程生命周期**: 必须调用 ``join()`` 或 ``detach()`` 来管理线程生命周期，否则程序会异常终止 3. **异常安全**: 在多线程环境中，异常处理需要特别注意，确保资源正确释放 4. **死锁避免**: 使用多个互斥锁时要注意避免死锁，建议按固定顺序获取锁 5. **条件变量**: 使用条件变量时必须配合互斥锁，等待条件时必须使用 ``std::unique_lock`` 6. **Future/Promise**: ``std::promise`` 只能设置一次值，多次设置会导致异常