std::shared_ptr causing double-free scenarios when used with custom deleter in multithreaded environment
I'm getting frustrated with I've looked through the documentation and I'm still confused about I'm working with a double-free behavior when using `std::shared_ptr` with a custom deleter in a multithreaded context. The setup involves two threads accessing a shared resource managed by `std::shared_ptr`. Here’s a simplified version of my code: ```cpp #include <iostream> #include <memory> #include <thread> #include <mutex> struct Resource { int data; Resource(int val) : data(val) { std::cout << "Resource created: " << data << '\n'; } ~Resource() { std::cout << "Resource destroyed: " << data << '\n'; } }; void customDeleter(Resource* res) { std::cout << "Custom deleter called for: " << res->data << '\n'; delete res; } void threadFunc(std::shared_ptr<Resource> resPtr) { // Simulate processing std::this_thread::sleep_for(std::chrono::milliseconds(100)); std::cout << "Thread processing: " << resPtr->data << '\n'; } int main() { std::shared_ptr<Resource> resPtr(new Resource(42), customDeleter); std::thread t1(threadFunc, resPtr); std::thread t2(threadFunc, resPtr); t1.join(); t2.join(); return 0; } ``` When I run this code, I sometimes receive the following behavior messages: ``` *** glibc detected *** ./my_program: double free or corruption (out): 0x0000000000... ``` The scenario seems to stem from the fact that both threads may end up calling the custom deleter if they finish processing simultaneously. I’ve tried using `std::mutex` to guard access to `resPtr`, but that only seems to complicate things further and doesn’t resolve the double-free scenario. I suspect that the management of `std::shared_ptr` in this multithreaded context is where the question lies. How can I safely use `std::shared_ptr` with a custom deleter in this scenario without running into double-free errors? Any insights or best practices would be greatly appreciated! This issue appeared after updating to C++ 3.10.