With the introduction of C++17, a new feature called “polymorphic memory resources” was added to provide more flexibility and customization for memory management. This feature allows developers to decouple memory allocations from memory management, enabling them to easily switch between different memory resources without modifying the existing code.

What are Polymorphic Memory Resources?

In traditional C++ programming, memory allocation is directly performed using global operator new and deallocation using operator delete. With polymorphic memory resources, instead of directly utilizing these global allocation functions, C++ standard library provides a set of polymorphic memory resource classes that can be used to allocate and deallocate memory in a customizable way.

The key classes involved in polymorphic memory resources are std::pmr::memory_resource and std::pmr::polymorphic_allocator.

std::pmr::memory_resource is an abstract base class that serves as the interface for all memory resources. It defines virtual member functions for allocating, deallocating, and querying memory resources.

std::pmr::polymorphic_allocator is a template class that takes a std::pmr::memory_resource as a template argument. It provides an interface similar to a regular allocator but uses the specified memory resource for all allocation and deallocation operations.

Customizing Memory Allocation with Polymorphic Memory Resources

To customize memory allocation using polymorphic memory resources, developers can create their own memory resource classes by subclassing std::pmr::memory_resource and implementing the virtual member functions for allocation and deallocation.

Example: Custom Memory Resource

#include <memory_resource>

class CustomMemoryResource : public std::pmr::memory_resource {
public:
    // Implement virtual member functions for allocation and deallocation
    void* do_allocate(size_t bytes, size_t alignment) override {
        // Custom memory allocation logic
    }

    void do_deallocate(void* p, size_t bytes, size_t alignment) override {
        // Custom memory deallocation logic
    }

    bool do_is_equal(const std::pmr::memory_resource& other) const noexcept override {
        // Custom comparison logic
    }
};

Using Polymorphic Memory Resources with Polymorphic Allocators

Once custom memory resources are defined, developers can use them with polymorphic allocators to allocate and deallocate memory for STL containers and other memory-managed objects.

Example: Using Polymorphic Allocator with Custom Memory Resource

#include <vector>

int main() {
    CustomMemoryResource customResource;
    std::pmr::polymorphic_allocator<int> allocator(&customResource);

    // Create a vector using polymorphic allocator
    std::vector<int, std::pmr::polymorphic_allocator<int>> vec(allocator);
    vec.push_back(10);
    // ...
}

Benefits of Polymorphic Memory Resources

• Flexibility: Allows developers to easily switch between different memory resources without modifying the existing code.
• Customization: Provides the ability to customize memory allocation logic for specific use cases.
• Efficiency: Can improve performance by using specialized memory resources tailored to specific requirements.

Polymorphic memory resources in C++ provide a powerful and flexible mechanism for customizing memory allocation and management in a way that was not easily achievable before C++17. By leveraging this feature, developers can tailor memory management to their specific application needs while maintaining compatibility with standard library containers and algorithms.

References:

• C++17 - Polymorphic Memory Resources

의역된 내용이포함된 위 C++ 키워드는 C++ 프로그래밍 언어의 데이터 형식과 기능을 기술하는 데 사용됩니다. C++17에서 제공되는 다형 메모리 리소스는 메모리 할당 및 해제 방법을 유연하게 커스터마이징할 수 있는 기능을 제공합니다. 다형 메모리 리소스를 활용하여 메모리를 할당하고 해제하는 방식을 유연하게 조정할 수 있으며, 해당 기능을 활용하면 코드 수정 없이 다양한 메모리 리소스 간에 손쉽게 전환할 수 있습니다.