Allocators in C++ are awkward classes. Allocators are usually zero size to make the containers small, and they have no state because that used to be difficult to do in C++. But nowadays we don’t really care about the size of our containers (we care about the size of the content of the containers) and since C++11 we have support for stateful allocators.
The problem I’m trying to solve is that node based containers have bad cache behavior because they allocate all over the place. So I wrote a small allocator which gives out memory from a contiguous block. It speeds up std::map and std::unordered_map. It’s called plalloc because I think this is a pool allocator.
Code is below: