Strange behavior with std::shared_ptr and circular references in C++11
I'm refactoring my project and I'm sure I'm missing something obvious here, but I've been struggling with this for a few days now and could really use some help. I'm encountering an issue with circular references when using `std::shared_ptr` in a class structure, leading to memory not being released as expected. I have two classes, `Node` and `Edge`, where each `Node` can hold a `shared_ptr` to an `Edge`, and each `Edge` holds a `shared_ptr` back to the `Node`. Here’s a simplified version of my code: ```cpp #include <iostream> #include <memory> #include <vector> class Edge; // Forward declaration to avoid circular dependency class Node { public: std::shared_ptr<Edge> edge; void connect(std::shared_ptr<Edge> e) { edge = e; } }; class Edge { public: std::shared_ptr<Node> node; Edge(std::shared_ptr<Node> n) : node(n) {} // Initialize with a Node }; int main() { auto node1 = std::make_shared<Node>(); auto node2 = std::make_shared<Node>(); auto edge = std::make_shared<Edge>(node1); node1->connect(edge); return 0; } ``` When I run this code, I expect that all memory will be released after `main()` ends. However, I notice that the destructors for `Node` and `Edge` are not being called, which suggests that the memory is not being freed up correctly. I’ve read that with `std::shared_ptr`, circular references can cause memory leaks, but I thought that since I'm using `shared_ptr`, it would handle reference counting properly. I've tried using `std::weak_ptr` for one of the pointers to break the circular reference: ```cpp class Edge { public: std::weak_ptr<Node> node; // Change from shared_ptr to weak_ptr Edge(std::shared_ptr<Node> n) : node(n) {} }; ``` This change did allow the destructors to be called correctly, but I’m concerned about whether this is the best practice in this scenario. Is there a more efficient way to manage these relationships without risking memory leaks? Are there any performance concerns I should be aware of when switching from `shared_ptr` to `weak_ptr`? Any insights would be greatly appreciated! I'm working on a service that needs to handle this. Has anyone else encountered this? My development environment is Windows. This is happening in both development and production on Linux. Has anyone dealt with something similar?