std::shared_ptr causing double-free errors when used with custom deleters in C++17
I've searched everywhere and can't find a clear answer. Hey everyone, I'm running into an issue that's driving me crazy... I'm encountering a `double free` error when using `std::shared_ptr` with a custom deleter. I have a scenario where I'm wrapping a dynamically allocated resource, and I'm trying to ensure proper cleanup with a custom deleter. However, when I attempt to use this in a multi-threaded environment, I'm getting segmentation faults that seem to originate from the deleter being called multiple times. Here’s a simplified version of my implementation: ```cpp #include <iostream> #include <memory> #include <thread> #include <vector> struct Resource { int value; Resource(int v) : value(v) { std::cout << "Resource created: " << value << '\n'; } ~Resource() { std::cout << "Resource destroyed: " << value << '\n'; } }; void customDeleter(Resource* res) { std::cout << "Custom deleter called for: " << res->value << '\n'; delete res; } void threadFunction(std::shared_ptr<Resource> res) { // Simulate some work std::this_thread::sleep_for(std::chrono::milliseconds(100)); } int main() { auto res = std::shared_ptr<Resource>(new Resource(42), customDeleter); std::vector<std::thread> threads; for (int i = 0; i < 5; ++i) { threads.emplace_back(threadFunction, res); } for (auto& t : threads) { t.join(); } // Custom deleter is supposed to be called here, but I suspect double free. return 0; } ``` I thought using `std::shared_ptr` should handle reference counting for me, but I'm not sure if sharing the pointer across multiple threads without proper synchronization could be causing the issue. I tried using `std::atomic` for the `std::shared_ptr`, but that doesn't seem to fit my use case as it doesn't allow direct sharing. When I run this code, I sometimes get: ``` *** Error in `./a.out`: double free or corruption (out): 0x0000000000... ``` I would appreciate any guidance on how to manage the ownership and lifetime of the resource properly in this multithreaded scenario. Is there a best practice for using custom deleters with `std::shared_ptr` in this context? I'm working on a service that needs to handle this. Any help would be greatly appreciated! This is for a microservice running on Windows 11. How would you solve this? For context: I'm using Cpp on Ubuntu 20.04.