std::stop_callback
来自 cppreference.com
| 定义在头文件 <stop_token> 中 |
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| template< class Callback > class stop_callback; |
(自 C++20 起) | |
stop_callback 类模板提供了一个 RAII 对象类型，它为关联的 std::stop_token 对象注册一个回调函数，以便当 std::stop_token 的关联 std::stop_source 被请求停止时，将调用回调函数。
通过 stop_callback 的构造函数注册的回调函数将在成功调用 request_stop() 的同一个线程中调用，该线程是 stop_callback 的关联 std::stop_token 的 std::stop_source；或者，如果在构造函数注册之前已经请求停止，则回调将在构造 stop_callback 的线程中调用。
可以为同一个 std::stop_token 创建多个 stop_callback，它们来自同一线程或不同的线程并发地创建。不保证它们执行的顺序，但它们将被同步调用；除了在为 std::stop_token 请求停止之后构建的 stop_callback，如前所述。
如果回调的调用通过异常退出，则将调用 std::terminate。
std::stop_callback 不是 可复制构造、可复制赋值、可移动构造 或者 可移动赋值.
模板参数 Callback 类型必须同时是 可调用 和 可析构。任何返回值都将被忽略。
内容 |
[编辑] 成员类型
| 类型 | 定义 |
callback_type
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Callback
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[编辑] 成员函数
构造新的 stop_callback 对象(公有成员函数) | |
析构 stop_callback 对象(公有成员函数) | |
| operator= [已删除] |
stop_callback 不可赋值(公有成员函数) |
[编辑] 推断指南
[编辑] 示例
运行此代码
#include <chrono> #include <condition_variable> #include <iostream> #include <mutex> #include <sstream> #include <thread> using namespace std::chrono_literals; // Use a helper class for atomic std::cout streaming. class Writer { std::ostringstream buffer; public: ~Writer() { std::cout << buffer.str(); } Writer& operator<<(auto input) { buffer << input; return *this; } }; int main() { // A worker thread. // It will wait until it is requested to stop. std::jthread worker([] (std::stop_token stoken) { Writer() << "Worker thread's id: " << std::this_thread::get_id() << '\n'; std::mutex mutex; std::unique_lock lock(mutex); std::condition_variable_any().wait(lock, stoken, [&stoken] { return stoken.stop_requested(); }); }); // Register a stop callback on the worker thread. std::stop_callback callback(worker.get_stop_token(), [] { Writer() << "Stop callback executed by thread: " << std::this_thread::get_id() << '\n'; }); // Stop_callback objects can be destroyed prematurely to prevent execution. { std::stop_callback scoped_callback(worker.get_stop_token(), [] { // This will not be executed. Writer() << "Scoped stop callback executed by thread: " << std::this_thread::get_id() << '\n'; }); } // Demonstrate which thread executes the stop_callback and when. // Define a stopper function. auto stopper_func = [&worker] { if (worker.request_stop()) Writer() << "Stop request executed by thread: " << std::this_thread::get_id() << '\n'; else Writer() << "Stop request not executed by thread: " << std::this_thread::get_id() << '\n'; }; // Let multiple threads compete for stopping the worker thread. std::jthread stopper1(stopper_func); std::jthread stopper2(stopper_func); stopper1.join(); stopper2.join(); // After a stop has already been requested, // a new stop_callback executes immediately. Writer() << "Main thread: " << std::this_thread::get_id() << '\n'; std::stop_callback callback_after_stop(worker.get_stop_token(), [] { Writer() << "Stop callback executed by thread: " << std::this_thread::get_id() << '\n'; }); }
可能的输出
Worker thread's id: 140460265039616 Stop callback executed by thread: 140460256646912 Stop request executed by thread: 140460256646912 Stop request not executed by thread: 140460248254208 Main thread: 140460265043776 Stop callback executed by thread: 140460265043776
