advanced patterns of std::shared_ptr with Custom Deleters in C++14
I'm following best practices but I've been banging my head against this for hours. I'm working with unexpected behavior when trying to use `std::shared_ptr` with a custom deleter in C++14. I have a class `Resource` that opens a file and I want to ensure that the file is properly closed when the `shared_ptr` goes out of scope. However, when I try to use the `shared_ptr` in a multi-threaded context, I sometimes see that the file does not get closed, leading to resource leaks. Here’s a simplified version of my code: ```cpp #include <iostream> #include <memory> #include <thread> #include <vector> class Resource { public: Resource(const std::string& filename) : file_(fopen(filename.c_str(), "w+")) { if (!file_) { throw std::runtime_error("Failed to open file"); } std::cout << "File opened: " << filename << '\n'; } ~Resource() { if (file_) { fclose(file_); std::cout << "File closed.\n"; } } private: FILE* file_; }; void threadFunc(std::shared_ptr<Resource> res) { // Simulated work std::this_thread::sleep_for(std::chrono::milliseconds(100)); } int main() { std::shared_ptr<Resource> res(new Resource("test.txt"), [](Resource* r) { delete r; }); std::vector<std::thread> threads; for (int i = 0; i < 5; ++i) { threads.emplace_back(threadFunc, res); } for (auto& t : threads) { t.join(); } return 0; } ``` The scenario arises when I change the custom deleter to use `delete` instead of closing the file within the `Resource` destructor. Since `Resource` contains a raw pointer to the file, I thought using `delete` would automatically handle the resource cleanup. However, in some cases, I observe that the file remains open even after the program finishes execution. The output does not consistently show "File closed." I'm not sure whether this behavior is due to thread contention or mismanagement in the `shared_ptr`. Can anyone clarify how to properly manage resources in such a scenario, and why my current approach is leading to inconsistent behavior? I'm on Ubuntu 20.04 using the latest version of C++. Has anyone dealt with something similar?