FreeList.hpp

#pragma once
#include <queue>
 
namespace RGL {
 
    template<typename index_t, uint32_t totalCount>
    struct FreeList {
 
        index_t Allocate() {
            index_t allocatedIndex = 0;
            if (freeList.empty()) {
                if (nextFreeIndexNotInQueue == totalCount) {
                    // full -- cannot allocate!
                    throw std::out_of_range("Descriptor heap is full!");
                }
                // place the descriptor at the end
                allocatedIndex = nextFreeIndexNotInQueue;
                nextFreeIndexNotInQueue++;
            }
            else {
                // fill the hole
                allocatedIndex = freeList.front();
                freeList.pop();
            }
 
            return allocatedIndex;
        }
 
        void Deallocate(index_t index) {
            // if the index was the end, then decrement end
            if (index == nextFreeIndexNotInQueue) {
                nextFreeIndexNotInQueue--;
            }
            else {
                // add the index to the free list
                freeList.emplace(index);
            }
        }
 
    private:
        std::queue<index_t> freeList{};
        index_t nextFreeIndexNotInQueue = 0;    // __NOT__ one past the end
    };
 
}