CODEWITHSUNDEEP
c++shared-ptrreference-counting
Gbr
Gbr

Reputation: 73

How to use shared_ptr and custom reference counting simultaneously?

I have a legacy class whose lifetime is managed by reference counting (it derives from ACE_Event_Handler, to be precise).

I want to be able to manage it using std::shared_ptr in my code but still keep the old legacy reference counting (objects of the class need to be accessed by a third-party library that doesn't accept shared_ptr - ACE, to be precise).

An object must be deleted when the reference count drops to 0 and all of the shared_ptr instances managing it get destroyed.

I have only one idea: keep an instance of shared_ptr pointing to the object until the reference count drops to 0 and then reset it. Somehow, this feel dirty. Is there a better way?

Upvotes: 1

Views: 1054

Answers (1)

andrgolubev
andrgolubev

Reputation: 885

The normal approach would be to have your own custom ptr implementation with ACE_Event_Handler::add_ref() in the constructor and ACE_Event_Handler::release() in the destructor.

Alternatively, you can use std::unqiue_ptr with custom deleter:

template<typename T>
struct custom_releaser
{
    void operator()(T *p) { if (p) p->release(); }
};

std::unique_ptr<T, custom_releaser<T>> my_ptr;

If you really want std::shared_ptr:

std::shared_ptr<T> ptr = std::shared_ptr(std::move(my_ptr));

I wonder, however, if it will properly call ACE_Event_Handler::add_ref(). I guess, std::shared_ptr will ref count based on it's own member variable - so that you would need to provide a method to do ACE_Event_Handler::add_ref() when creating an instance and adding ref counts.

Upvotes: 1

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