Optimizing Memory Allocation with Custom Allocators

Efficient Memory Management with Custom Allocators

The Need for Custom Allocators

When it comes to memory management, efficiency is key. Traditional memory allocation methods like malloc and new can be slow and wasteful, especially for small objects. This is where custom allocators come in – they provide a way to manage memory that is tailored to specific use cases.

Introducing the Arena Allocator

One such custom allocator is the Arena allocator. This allocator uses a pre-allocated buffer to store objects, which eliminates the need for dynamic memory allocation. The Arena allocator is particularly useful for allocating small objects, as it reduces fragmentation and improves performance.

How the Arena Allocator Works

The Arena allocator consists of a pre-allocated buffer, a pointer to the current allocation position, and two functions: allocate and deallocate. The allocate function returns a pointer to a correctly aligned memory block of the specified size. If the buffer is full, it falls back to using operator new. The deallocate function checks whether the pointer to be deallocated is from the buffer and, if so, reclaims the memory by moving the current pointer.

Implementing the Arena Allocator

To implement the Arena allocator, we need to define the allocate and deallocate functions. The allocate function uses a helper function align_up to round up the requested size to the alignment requirement. It then checks if there is enough space in the buffer and, if so, returns a pointer to the allocated memory. If not, it falls back to using operator new.

The deallocate function first checks whether the pointer to be deallocated is from the buffer. If so, it checks whether the memory to be deallocated is the last memory allocated from the buffer and, if so, reclaims it by moving the current pointer.

Using the Arena Allocator

To use the Arena allocator, we need to create an instance of the Arena class and override the new and delete operators for the objects we want to allocate. For example, we can create an Arena instance for allocating User objects:

“`cpp
auto user_arena = Arena<1024>{};

class User {
public:
auto operator new(sizet size) -> void* {
return userarena.allocate(size);
}
auto operator delete(void* p) -> void {
userarena.deallocate(staticcast(p), sizeof(User));
}
};
“`

With this implementation, we can efficiently allocate and deallocate User objects using the Arena allocator.