How to use coroutines to implement concurrent programming in C++?

How to use coroutines to implement concurrent programming in C++

Coroutines are lightweight concurrency primitives that allow programs to Workers can perform parallel tasks without creating separate threads. This is useful for highly I/O-intensive applications because coroutines consume much less overhead than threads when switching tasks.

Coroutines in C++

Coroutines were introduced in C++ 20 as the std::coroutine framework. A coroutine is a generator function that suspends execution and returns a value via a co_yield expression. Unlike regular generators, coroutines can suspend and resume execution multiple times.

// 一个协程示例
std::coroutine<int> my_coroutine() {
  int value = 0;
  while (true) {
    value++;
    co_yield value;  // 挂起执行并返回 value
  }
}

Practical cases of coroutines

Coroutines are very useful in the following scenarios:

• Non-blocking I/O Operations: Coroutines can be used to implement non-blocking I/O operations, such as network requests or file reads.
• Pipelines and filters: Coroutines can be used to create pipelines and filters for processing and transforming data streams.
• Coordinate concurrent tasks: Coroutines can be used to coordinate multiple concurrent tasks, such as parallel data processing or distributed computing.

Example: Using coroutines for non-blocking I/O

The following example demonstrates how to use coroutines for non-blocking network requests:

#include <iostream>
#include <future>

// 一个协程来发送 HTTP 请求
std::coroutine<std::string> get_url(const std::string& url) {
  // 创建一个 HTTP 客户端
  auto client = std::make_unique<cpprestsdk::http_client>(url);
  
  // 向服务器发送 GET 请求
  auto response = co_await client->request(cpprestsdk::methods::GET);
  
  // 返回响应体
  co_return response.extract_string().get();
}

int main() {
  // 并发发送两个 HTTP 请求
  auto f1 = std::async(std::launch::async, get_url("https://example.com/1"));
  auto f2 = std::async(std::launch::async, get_url("https://example.com/2"));
  
  // 获取请求结果
  std::cout << f1.get() << std::endl;
  std::cout << f2.get() << std::endl;
}

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