Unexpected behavior with std::shared_ptr and std::weak_ptr in multithreaded environment
I'm integrating two systems and I'm trying to implement I'm not sure how to approach I'm dealing with I'm experiencing an issue with `std::shared_ptr` and `std::weak_ptr` in a multithreaded application using C++17... I have a class that is supposed to manage a resource and I am using `std::shared_ptr` to handle ownership. However, I'm running into a situation where a `std::weak_ptr` seems to be invalidated unexpectedly. Here's a simplified version of my code: ```cpp #include <iostream> #include <memory> #include <thread> #include <atomic> class Resource { public: void doSomething() { std::cout << "Doing something..." << std::endl; } }; class Manager { private: std::shared_ptr<Resource> resource; public: void setResource(std::shared_ptr<Resource> res) { resource = res; } std::weak_ptr<Resource> getResource() { return resource; } }; void worker(Manager& manager) { auto resWeak = manager.getResource(); if (auto resShared = resWeak.lock()) { resShared->doSomething(); } else { std::cout << "Resource has been released!" << std::endl; } } int main() { Manager manager; { std::shared_ptr<Resource> res = std::make_shared<Resource>(); manager.setResource(res); std::thread t1(worker, std::ref(manager)); std::thread t2(worker, std::ref(manager)); t1.join(); t2.join(); } // Resource goes out of scope here return 0; } ``` In this code, I create a `std::shared_ptr<Resource>` within a block and pass the `Manager` instance to two threads. However, I occasionally see the output "Resource has been released!" even though I'm expecting the resource to remain valid while both threads are executing. I've tried adding atomic flags to synchronize access to the `Manager` but the behavior remains the same. I've also verified that no other parts of the code are manipulating the `shared_ptr` directly. This leads me to believe that the issue might be related to the timing of the resource going out of scope. What could cause this unexpected invalidation of the weak pointer in this multithreaded context? Any insights or suggestions for best practices in managing shared resources in C++ would be greatly appreciated. The stack includes Cpp and several other technologies. I'd really appreciate any guidance on this. I'm working in a Ubuntu 22.04 environment. Cheers for any assistance! Any advice would be much appreciated. Am I approaching this the right way? For reference, this is a production service. Thanks for taking the time to read this!