In modern software development, multitasking is a crucial aspect of building responsive and efficient applications. Traditionally, multitasking has been achieved through the use of threads or callbacks. However, in recent years, C++ coroutines have emerged as a powerful and intuitive alternative to handle multitasking scenarios.

What are C++ Coroutines?

Coroutines are a language feature introduced in C++20 to simplify asynchronous programming and cooperative multitasking. They allow you to write code that can be suspended and resumed at specific points, without blocking the execution flow.

Unlike threads, which use preemptive multitasking, coroutines rely on cooperative multitasking. This means that each coroutine explicitly yields control to others, enabling efficient context switching without the overhead typically associated with threads.

Getting Started with C++ Coroutines

To use coroutines, you need a C++20-enabled compiler. Some popular C++ compilers, like GCC and Clang, have experimental support for coroutines. Alternatively, you can use libraries like Boost.Coroutine or Microsoft’s cppcoro to add coroutine support to older compilers.

Writing a Coroutine in C++

Here’s an example of a simple coroutine that prints numbers from 1 to 5 with a 500ms delay between each print:

#include <iostream>
#include <coroutine>
#include <chrono>

struct NumberCoroutine {
    struct promise_type {
        NumberCoroutine get_return_object() {
            return NumberCoroutine{std::coroutine_handle<promise_type>::from_promise(*this)};
        }
        std::suspend_never initial_suspend() { return {}; }
        std::suspend_never final_suspend() noexcept { return {}; }
        void return_void() {}
        void unhandled_exception() {}
    };

    std::coroutine_handle<promise_type> handle;

    explicit NumberCoroutine(std::coroutine_handle<promise_type> handle) : handle(handle) {}

    ~NumberCoroutine() {
        if (handle) {
            handle.destroy();
        }
    }

    bool next() {
        if (!handle.done()) {
            handle.resume();
            return true;
        }
        return false;
    }
};

NumberCoroutine countNumbers() {
    for (int i = 1; i <= 5; i++) {
        std::cout << "Number: " << i << std::endl;
        co_await std::suspend_for(std::chrono::milliseconds(500));
    }
}

int main() {
    NumberCoroutine coroutine = countNumbers();
    while (coroutine.next()) {}

    return 0;
}

In this code, we define a coroutine NumberCoroutine that counts from 1 to 5. The promise_type defines the coroutine behavior, including the initial_suspend, final_suspend, return_void, and unhandled_exception methods.

The countNumbers function defines the coroutine logic, printing the numbers and suspending execution for 500 milliseconds using std::suspend_for. The main function initializes the NumberCoroutine and repeatedly calls its next method until the coroutine completes.

Conclusion

C++ coroutines provide a powerful and efficient approach to handle cooperative multitasking in your applications. By explicitly yielding control between coroutines, you can achieve concurrency without the complexity of threads.

With C++20 support in compilers or external libraries, you can start exploring the benefits of coroutines in your projects. Embrace the simplicity and performance of C++ coroutines to build more responsive and scalable software.

#cpp #coroutines