c++ how to manage object cache with ref counting

Question

My program will create and delete a lot of objects (from a REST API). These objects will be referenced from multiple places. I'd like to have a "memory cache" and manage objects lifetime with reference counting so they can be released when they aren't used anymore.

All the objects inherit from a base class Ressource.

The Cache is mostly a std::map<_key_, std::shared_ptr<Ressource> >

Then I'm puzzled, how can the Cacheknow when a Ressource ref count is decremented? ie. A call to the std::shared_ptr destructor or operator=.

1/ I don't want to iterate over the std::map and check each ref.count().

2/ Can I reuse std::shared_ptr and implement a custom hook?

class RessourcePtr : public std::shared_ptr<Ressource>
...

3/ Should I implement my own ref count class? ex. https://stackoverflow.com/a/4910158/1058117

Thanks!

Answer 1

make shared_ptr not use delete shows how you can provide a custom delete function for a shared pointer.

You could also use intrusive pointers if you wanted have customer functions for reference add and delete.