网站推广工作计划,ftp怎么上传网站,江苏省建设考试培训网网站,有趣的h5创意设计在查阅本文之前#xff0c;请先查看本人的另外一篇关于协同程序切换的文献#xff0c;这对于如何正确协同程序编程很有价值。 C/C 如何正确的切换协同程序#xff1f;#xff08;基于协程的并行架构#xff09;-CSDN博客
我本人相当反对#xff0c;在项目之中使用 C 20标…在查阅本文之前请先查看本人的另外一篇关于协同程序切换的文献这对于如何正确协同程序编程很有价值。 C/C 如何正确的切换协同程序基于协程的并行架构-CSDN博客
我本人相当反对在项目之中使用 C 20标准的 stackless 无栈协程在上述博文之中明确提到了大体的原因是什么并且 C/C 越新的标准越存在不可预计的编译风险性问题目前基本可以确保稳定的 C 编译器标准为 C 17。 stackless 协程在 C/C 之中是 “switch 基于步骤的状态机切换” 协同程序展开结构即每一次 MoveNext 切换到下一个工作流片。
这就像在 C# 之中我们使用 C# 语言的迭代器来模拟实现协程一样首先本人提供一个简单的协同程序切换的流程就只使用 co_await 编译器关键字我们就可以实现一个完整的协同程序切换流程。 以下述代码为例将直接展示 C 20 标准提供的 stackless 程序编译器语法支援即三个关键字的用法例子co_await、co_yield、co_return 在只使用 co_await 关键字的情况下实现协同程序正确切换。
例子
#include iostream
#include coroutinestruct MyTask {struct promise_type {public:MyTask get_return_object() {return MyTask{ std::coroutine_handlepromise_type::from_promise(*this) };}public:std::suspend_never initial_suspend() noexcept { return {}; }std::suspend_always final_suspend() noexcept { return {}; }void return_void() noexcept {}void unhandled_exception() noexcept {}};public:explicit MyTask(std::coroutine_handlepromise_type coro) noexcept : coroutine(coro) {}~MyTask() noexcept {if (coroutine) {coroutine.destroy();}}public:bool await_ready() const noexcept { return false; }void await_suspend(std::coroutine_handle) const noexcept {}void await_resume() const noexcept {}public:void resume() noexcept {coroutine.resume();}private:std::coroutine_handlepromise_type coroutine;
};MyTask fork_stackless_coroutine() noexcept {std::cout 协程步一...\n;co_await std::suspend_always{};std::cout 协程步二.\n;co_await std::suspend_always{};std::cout 协程结束.\n;
}int main() {MyTask task fork_stackless_coroutine();std::cout 主线程步一...\n;task.resume();std::cout 主线程步二.\n;task.resume();std::cout 主线程结束.\n;return 0;
}人们可以通过 co_return 关键字以促使 C 20 stackless 协程可以返回数据。
例子协程返回值类型为int
#include iostream
#include coroutinestruct MyTask {struct promise_type {public:MyTask get_return_object() noexcept {return MyTask{ std::coroutine_handlepromise_type::from_promise(*this) };}public:std::suspend_always initial_suspend() noexcept { return {}; }std::suspend_always final_suspend() noexcept { return {}; }public:void return_value(int value) {result value;}void unhandled_exception() noexcept {}public:int result;};public:explicit MyTask(std::coroutine_handlepromise_type coro) noexcept : coroutine(coro) {}~MyTask() {if (coroutine) {coroutine.destroy();}}public:int result() const noexcept {return coroutine.promise().result;}void resume() noexcept {coroutine.resume();}private:std::coroutine_handlepromise_type coroutine;
};MyTask fork_stackless_coroutine() noexcept {std::cout 协程结束返回 std::endl;co_return 42;
}int main() {MyTask task fork_stackless_coroutine();task.resume();std::cout 主线程协程返回: task.result() std::endl;return 0;
}co_yield 迭代关键字在C#、之中的用法与 C 的用户几乎是一摸一样的用法相对来说 C/Cco_yield 关键更好用一点co_await 跟 co_yield 都可以实现协同程序流程分片切换。
但区别是 co_yield 切换的分片可以设置当前的迭代值就像在C#当前我们移动切换迭代器成功时可以通过 Current 属性来获取当前的迭代值co_await 不可以获得值。
#include iostream
#include coroutinestruct MyTask {struct promise_type {public:MyTask get_return_object() noexcept {return MyTask{ std::coroutine_handlepromise_type::from_promise(*this) };}public:std::suspend_always initial_suspend() noexcept { return {}; }std::suspend_always final_suspend() noexcept { return {}; }public:std::suspend_always yield_value(int value) noexcept {current_value value;return {};}void return_void() noexcept {}void unhandled_exception() noexcept {}public:int current_value;};public:explicit MyTask(std::coroutine_handlepromise_type coro) noexcept : coroutine(coro) {}~MyTask() {if (coroutine) {coroutine.destroy();}}public:int current_value() const noexcept {return coroutine.promise().current_value;}bool move_next() noexcept {if (coroutine) {if (coroutine.done()) {return false;}coroutine.resume();return true;}return false;}private:std::coroutine_handlepromise_type coroutine;
};MyTask fork_stackless_coroutine() noexcept {std::cout 协程开始 100 std::endl;co_yield 100;for (int i 1; i 5; i) {std::cout 协程步骤 i std::endl;co_yield i;}
}int main() {MyTask task fork_stackless_coroutine();while (task.move_next()) {std::cout 主线程读值 task.current_value() std::endl;}std::cout 主线程结束 std::endl;return 0;
}如何在 C 20 有栈协程之中在调用其它 stackless 协程c20协程库高级应用即co_await、co_return 共同搭配使用。
#include iostream
#include coroutinestruct MyTask {struct promise_type {public:MyTask get_return_object() {return MyTask{ std::coroutine_handlepromise_type::from_promise(*this) };}public:std::suspend_never initial_suspend() noexcept { return {}; }std::suspend_always final_suspend() noexcept { return {}; }void unhandled_exception() noexcept {}void return_void() noexcept {}};public:explicit MyTask(std::coroutine_handlepromise_type coro) noexcept : coroutine(coro) {}~MyTask() noexcept {if (coroutine) {coroutine.destroy();}}public:bool await_ready() const noexcept { return false; }void await_suspend(std::coroutine_handle co) const noexcept {bool done co.done();if (!done) {co.resume();}}void await_resume() const noexcept {}public:bool move_next() noexcept {if (coroutine) {if (coroutine.done()) {return false;}coroutine.resume();return true;}return false;}private:std::coroutine_handlepromise_type coroutine;
};struct MyTaskInt {struct promise_type {public:MyTaskInt get_return_object() {return MyTaskInt{ std::coroutine_handlepromise_type::from_promise(*this) };}public:std::suspend_never initial_suspend() noexcept {return {};}std::suspend_always final_suspend() noexcept {return {};}void return_value(int value) {result value;}void unhandled_exception() noexcept {}public:int result;};public:explicit MyTaskInt(std::coroutine_handlepromise_type coro) noexcept : coroutine(coro) {}~MyTaskInt() noexcept {if (coroutine) {coroutine.destroy();}}public:bool await_ready() const noexcept { return false; }void await_suspend(std::coroutine_handle co) const noexcept {bool done co.done();if (!done) {co.resume();}}int await_resume() const noexcept {return coroutine.promise().result;}private:std::coroutine_handlepromise_type coroutine;
};MyTaskInt fork_stackless_coroutine_return_100() noexcept {co_return 100;
}MyTaskInt fork_stackless_coroutine_return_200() noexcept {int result co_await fork_stackless_coroutine_return_100();result result 1;co_return result;
}MyTask fork_stackless_coroutine_start() noexcept {int result co_await fork_stackless_coroutine_return_100();std::cout result std::endl;result co_await fork_stackless_coroutine_return_200();std::cout result std::endl;
}int main() {MyTask task fork_stackless_coroutine_start();while (task.move_next());return 0;
}
