Harnessing the Power of Async in C++20: What’s New and What’s Next
Ah, async programming! It’s like asking your computer to cook a full-course meal while simultaneously managing the lights, playing music, and keeping track of which doors are open — and you want all of this done without any of them interfering with each other. Imagine the chaos if every action was like grandma hogging the kitchen for three hours to make her special soup.
But we’re not talking about a grandma’s kitchen. We’re talking about C++20, where asynchronous programming has reached a new level of refinement and control, a significant leap from its predecessors. Let’s dive into what’s new in C++20’s async world — and where it is heading next. But first, let’s break down some key concepts.
A Quick Refresher: What is Asynchronous Programming?
In simple terms, asynchronous programming is the art of starting a task, allowing it to run in the background, and moving on to other tasks without waiting for it to finish. When the task is done, it taps you on the shoulder and says, “Hey, I’m ready. Want the results now?”
Think of it as sending an intern to pick up coffee while you continue working on other things. When the intern returns, you take the coffee (hopefully, the right order) and continue with your day.
In older versions of C++, async behaviour existed, but it felt a little like asking that intern to bring coffee while they’re handcuffed to your desk. You still had to check up on them constantly, and they would trip over your work if you weren’t careful.
C++20’s Supercharged Async Capabilities
With C++20, the intern is finally getting smarter. The introduction of coroutines has revolutionized how asynchronous code is written and executed, making it more natural and efficient. Let’s look at the key features that make async in C++20 stand out:
1. Coroutines: The Star of the Show
Coroutines in C++20 are like a personal assistant that keeps track of your work and remembers exactly where they left off. They allow you to suspend and resume functions without the overhead of threads or the messiness of callbacks. Before C++20, async programming often felt like juggling chainsaws — difficult to manage and prone to disaster. Now, coroutines allow you to manage tasks in a clean and safe way.
Here’s an example of a simple coroutine:
#include <iostream>
#include <coroutine>
struct MyCoroutine {
struct promise_type {
MyCoroutine get_return_object() { return {}; }
std::suspend_never initial_suspend() { return {}; }
std::suspend_never final_suspend() noexcept { return {}; }
void return_void() {}
void unhandled_exception() { std::terminate(); }
};
};
MyCoroutine asyncTask() {
std::cout << "Task started..." << std::endl;
co_await std::suspend_always{};
std::cout << "Task resumed..." << std::endl;
}
int main() {
auto task = asyncTask();
std::cout << "Doing other stuff..." << std::endl;
}This coroutine suspends itself with co_await std::suspend_always{} and resumes later, allowing you to manage asynchronous operations without blocking the main thread. It’s like telling the intern, “Go get coffee, but don’t bother me until you’re back,” and trusting them to check back in at just the right time.
2. No More Callback Hell
Previously, asynchronous code in C++ often led to callbacks within callbacks, leaving you untangling spaghetti code just to track what is happening. C++20 introduces a more straightforward, declarative style of writing async code with coroutines, avoiding descending into callback hell.
Instead of piling up function pointers and lambda functions to keep track of various states, you can now simply co_await operations in a human-readable way. It’s like getting rid of sticky notes all over your office and consolidating everything into a neat to-do list.
3. Async vs. Threads: A Clearer Choice
In the land of C++ before C++20, async tasks were sometimes hard to distinguish from multithreading. Developers frequently found themselves creating threads for everything, but threads are heavyweight, resource-hungry beasts. It’s like hiring a full-time staff member to water the plants once a week.
C++20’s coroutines are a much more lightweight alternative. They don’t create operating system threads unless you explicitly need them. The runtime cost is minimal compared to traditional threads, making them perfect for I/O-bound tasks like networking or file handling. Coroutines are the intern you send for coffee, whereas threads are like hiring a professional barista to brew it in your office.
4. Efficient Resource Management: You Don’t Pay for What You Don’t Use
C++ has always prided itself on the principle of “you don’t pay for what you don’t use,” and this continues with C++20 async. Coroutines provide lazy evaluation — meaning the task doesn’t actually run until you need the result. This is great for tasks that might get cancelled or delayed. Imagine asking your intern to get coffee, but they only actually head out once you confirm you really need that caffeine boost.
What’s Next for Async in C++?
Now that C++20 has given us a solid foundation with coroutines, what’s next on the horizon for async programming?
1. Easier Composability
One of the current challenges with async programming is orchestrating multiple asynchronous tasks and handling error propagation. While C++20 made big strides with coroutines, the future promises more improvements around making multiple async tasks easier to manage.
This might look like building more advanced libraries or language-level constructs that allow you to manage many async operations more elegantly. Imagine a system where you could send out multiple interns for coffee, doughnuts, and sandwiches, and they all come back at just the right time with minimal management effort.
2. Enhanced Integration with Executors
Executors are the upcoming big deal for asynchronous programming in C++. They are an abstraction over how tasks are scheduled and executed. Think of them as the manager of all your interns, deciding who should run where and when. The current scheduling model of coroutines still leaves some flexibility to the user, but executors will bring more structured control over task execution.
Executors will allow you to better manage the underlying resources, ensuring your async tasks run efficiently across threads, cores, or even distributed systems. It’s like having an intern manager who ensures no one is overworked while still making sure every coffee is delivered piping hot.
3. Parallel Algorithms with Coroutines
C++20 already introduced several parallel algorithms like std::for_each and std::reduce. Combining these with coroutines could unlock even more powerful constructs. Imagine running your async task on multiple cores seamlessly, leveraging both parallelism and asynchrony. It’s like having a whole team of interns doing your errands across town, but they’re all working in harmony to bring back exactly what you need, when you need it.
Wrapping Up: The Future is Async
C++20 has made asynchronous programming far less painful and far more efficient, thanks to the introduction of coroutines. Async tasks are now more manageable, more performant, and much easier to understand than in previous versions of the language. And with exciting features on the horizon, C++ async programming is only going to get better.
So, next time you’re diving into async code in C++, remember: you’re not just sending an intern for coffee — you’re mastering a whole fleet of them with precision and ease. And when C++23 and beyond roll around, who knows? You might just have a full team of robot baristas handling all your tasks in parallel, with not a single coffee spill in sight.
