In recent years, coroutines have gained popularity among developers as a powerful tool for writing efficient and structured asynchronous code. C++ developers, in particular, have been leveraging coroutine libraries to simplify and streamline their codebase.

In this blog post, we will explore two widely used coroutine libraries for C++: Boost.Asio and cppcoro. These libraries provide abstractions and utilities to work with coroutines and make asynchronous programming more intuitive and manageable.

Boost.Asio

Boost.Asio is a popular, mature, and versatile C++ library that provides a wide range of functionality, including coroutine support. It offers a comprehensive set of networking and I/O operations, making it suitable for building high-performance networking applications.

To use coroutines with Boost.Asio, you need to include the “boost/asio.hpp” header and enable coroutine support with C++20 or later. The library provides coroutine-specific versions of functions, such as async_connect and async_read, that can be used with the co_await keyword.

Here’s an example of using Boost.Asio to perform an asynchronous HTTP GET request:

#include <boost/asio.hpp>
#include <iostream>

using boost::asio::ip::tcp;

boost::asio::awaitable<void> asyncHttpGet(const std::string& url)
{
    boost::asio::io_context ioContext;
    tcp::resolver resolver(ioContext);
    tcp::socket socket(ioContext);
    
    co_await resolver.async_resolve(url, "http");
    co_await socket.async_connect(resolver[0].endpoint());
    
    std::string request = "GET / HTTP/1.1\r\nHost: " + url + "\r\n\r\n";
    co_await boost::asio::async_write(socket, boost::asio::buffer(request));
    
    boost::asio::streambuf response;
    co_await boost::asio::async_read_until(socket, response, "\r\n\r\n");
    
    std::cout << &response;
}

int main()
{
    asyncHttpGet("www.example.com").then([](const auto&) {
        std::cout << "GET request completed!" << std::endl;
    }).detach();
    
    boost::asio::io_context ioContext;
    ioContext.run();

    return 0;
}

The asyncHttpGet function is a coroutine that performs an asynchronous HTTP GET request. It uses the async_resolve, async_connect, async_write, and async_read_until functions with the co_await keyword to perform the necessary I/O operations. After the request is completed, a completion handler is executed to print a success message.

cppcoro

Cppcoro is a lightweight coroutine library for C++ that provides a simple and efficient API for writing asynchronous code. It aims to be easy to use and understand without sacrificing performance.

To work with cppcoro, you need to include the “cppcoro/generator.hpp” and “cppcoro/task.hpp” headers. Cppcoro provides generators, which are asynchronous sequences of values, and tasks, which are asynchronous operations.

Here’s an example of using cppcoro to iterate over a directory and process files:

#include <cppcoro/generator.hpp>
#include <cppcoro/task.hpp>
#include <filesystem>
#include <iostream>

cppcoro::generator<std::filesystem::path> asyncListFiles(const std::filesystem::path& path)
{
    for (const auto& entry : std::filesystem::directory_iterator(path))
    {
        if (entry.is_regular_file())
        {
            co_yield entry.path();
        }
    }
}

cppcoro::task<void> asyncProcessFile(const std::filesystem::path& filePath)
{
    // Perform file processing asynchronously...
    co_return;
}

cppcoro::task<> asyncProcessFiles(const std::filesystem::path& path)
{
    for co_await(auto file : asyncListFiles(path))
    {
        co_await asyncProcessFile(file);
    }
}

int main()
{
    asyncProcessFiles(".").then([]() {
        std::cout << "File processing completed!" << std::endl;
    }).resume_on(std::this_thread::get_scheduler());

    std::this_thread::get_scheduler().run();

    return 0;
}

In this example, the asyncListFiles function is a generator that asynchronously yields each file path in a directory. The asyncProcessFile function is a task that performs file processing asynchronously. The asyncProcessFiles function iterates over all the files and asynchronously processes each file.

Finally, the main function asynchronously calls asyncProcessFiles and prints a completion message when the processing is finished.

Conclusion

Coroutine libraries like Boost.Asio and cppcoro provide powerful abstractions for writing efficient and structured asynchronous code in C++. They simplify the codebase and make it easier to handling complex asynchronous operations.

When working with coroutines, it’s important to choose a library that integrates well with your existing codebase and meets your specific requirements. Boost.Asio and cppcoro are excellent options for developers looking to leverage coroutines in their C++ projects, offering different trade-offs of features, performance, and flexibility.

#coroutines #C++