**Course Title:** Modern C++ Programming: Mastering C++ with Best Practices and Advanced Techniques **Section Title:** Multithreading and Concurrency **Topic:** Futures, promises, and asynchronous programming in C++17/20 Asynchronous programming is an essential feature of modern C++ programming, allowing developers to write efficient and scalable concurrent programs. In this topic, we will delve into the world of futures, promises, and asynchronous programming in C++17/20. **What are Futures?** A future is a special type of object that represents the result of an asynchronous operation. When a task is launched asynchronously, a future object is returned, which can be used to retrieve the result of the task when it completes. In C++17/20, the `std::future` class provides a way to represent the result of an asynchronous operation. A future can be created using the `std::async` function, which launches a task asynchronously and returns a future object that represents the result of the task. **Example: Using `std::async` to Launch a Task Asynchronously** ```cpp #include <future> #include <iostream> int calculate(int x, int y) { // Simulate a time-consuming operation std::this_thread::sleep_for(std::chrono::seconds(2)); return x + y; } int main() { // Launch the task asynchronously std::future<int> result = std::async(std::launch::async, calculate, 2, 3); // Do some other work while the task is running std::cout << "Doing some other work...\n"; // Wait for the task to complete and get the result int sum = result.get(); std::cout << "Result: " << sum << std::endl; return 0; } ``` In this example, we launch a task asynchronously using `std::async` and retrieve the result using the `get` method on the future object. **What are Promises?** A promise is a special type of object that represents the producer side of a asynchronous operation. A promise is used to store the result of an asynchronous operation, which can then be retrieved by a future object. In C++17/20, the `std::promise` class provides a way to represent the producer side of an asynchronous operation. A promise can be used in conjunction with a future object to transfer the result of an asynchronous operation. **Example: Using `std::promise` to Store the Result of an Asynchronous Operation** ```cpp #include <future> #include <iostream> #include <thread> std::promise<int> promise; void calculate(int x, int y) { // Simulate a time-consuming operation std::this_thread::sleep_for(std::chrono::seconds(2)); int result = x + y; promise.set_value(result); } int main() { // Launch the task asynchronously std::thread thread(calculate, 2, 3); // Do some other work while the task is running std::cout << "Doing some other work...\n"; // Wait for the task to complete and get the result int sum = promise.get_future().get(); std::cout << "Result: " << sum << std::endl; thread.join(); return 0; } ``` In this example, we use a `std::promise` object to store the result of an asynchronous operation, and a future object to retrieve the result. **Asynchronous Programming in C++17/20** C++17/20 provides several features that enable asynchronous programming, including: * `std::async`: Launches a task asynchronously and returns a future object that represents the result of the task. * `std::future`: Represents the result of an asynchronous operation. * `std::promise`: Represents the producer side of an asynchronous operation. * `std::thread`: Represents a thread that can be used to launch tasks asynchronously. **Best Practices for Asynchronous Programming in C++17/20** * Use `std::async` to launch tasks asynchronously and retrieve the result using a future object. * Use `std::promise` to store the result of an asynchronous operation and retrieve it using a future object. * Use `std::thread` to launch tasks asynchronously and wait for them to complete using `std::this_thread::join`. * Avoid using `std::this_thread::sleep_for` to wait for tasks to complete; instead, use `std::future::wait_for` or `std::future::wait_until` to wait for the result of an asynchronous operation. **Conclusion** In this topic, we covered the basics of asynchronous programming in C++17/20, including futures, promises, and the use of `std::async`, `std::promise`, and `std::thread` to launch tasks asynchronously and retrieve their results. We also covered some best practices for asynchronous programming in C++17/20. If you have any questions or need help with implementing asynchronous programming in your C++ programs, feel free to ask in the comments below. **What's Next?** In the next topic, we will cover **File I/O and Serialization**. * Learn how to read and write files using `std::ifstream` and `std::ofstream`. * Understand how to serialize data to and from files using `std::deserialize` and `std::serialize`. * Implement a simple file I/O program that reads and writes data to a file. External Resources: * [cppreference.com: `std::async`](https://en.cppreference.com/w/cpp/thread/async) * [cppreference.com: `std::future`](https://en.cppreference.com/w/cpp/thread/future) * [cppreference.com: `std::promise`](https://en.cppreference.com/w/cpp/thread/promise) * [cppreference.com: `std::thread`](https://en.cppreference.com/w/cpp/thread/thread)