Memory management is a crucial aspect of any programming language, and C++ is no exception. With the introduction of coroutines in C++20, understanding memory management becomes even more important. In this blog post, we will explore how memory is managed in C++ coroutines and discuss some best practices.

Understanding Coroutines

Before diving into memory management, let’s have a brief overview of coroutines. In C++, coroutines allow you to write asynchronous code in a more sequential manner. Coroutines are essentially special functions that can be suspended and resumed later.

Stack Allocation vs. Heap Allocation

In C++ coroutines, memory can be allocated either on the stack or on the heap. Stack allocation is the default and recommended way of managing memory in coroutines. When you use stack allocation, memory is automatically deallocated when the coroutine is suspended or destroyed.

#include <iostream>
#include <experimental/coroutine>

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

MyCoroutine myCoroutine() {
    std::cout << "Coroutine started" << std::endl;

    co_await std::experimental::suspend_always{};

    std::cout << "Coroutine resumed" << std::endl;

    co_return;
}

int main() {
    MyCoroutine coroutine = myCoroutine();
    coroutine.handle.resume();
    coroutine.handle.destroy();

    return 0;
}

In the example above, we define a simple coroutine myCoroutine. The memory for the coroutine is allocated on the stack, and the handle is used to manage the coroutine execution. When the coroutine is resumed, it prints “Coroutine started” and then suspends itself. When the coroutine handle is destroyed, the memory is automatically deallocated.

If you need to allocate memory on the heap within a coroutine, you need to be careful with memory management. Heap allocation requires manual deallocation using delete or smart pointers. Failing to deallocate memory properly can lead to memory leaks.

Best Practices for Memory Management

To ensure proper memory management in C++ coroutines, here are some best practices to follow:

1. Prefer stack allocation over heap allocation: Stack allocation provides automatic memory deallocation, reducing the risk of memory leaks.
2. Properly manage heap-allocated memory: If you must allocate memory on the heap within a coroutine, make sure to handle deallocation properly to avoid memory leaks.
3. Use smart pointers: If you use heap allocation, consider using smart pointers like std::unique_ptr or std::shared_ptr to manage the memory. These smart pointers automatically handle deallocation for you.

By following these best practices, you can effectively manage memory in C++ coroutines and prevent common memory management issues.

#cpp #coroutines