Using std::unique_ptr with custom deleters in C++20 leads to advanced patterns
I recently switched to Hey everyone, I'm running into an issue that's driving me crazy... After trying multiple solutions online, I still can't figure this out. I've been struggling with this for a few days now and could really use some help. I'm experiencing unexpected behavior when using `std::unique_ptr` with a custom deleter in my C++20 application. I have a class that handles resource management, and I'm trying to ensure that my resources are cleaned up correctly. However, I find that sometimes my resources aren't released as expected, leading to memory leaks. Here’s a simplified version of my code: ```cpp #include <iostream> #include <memory> class Resource { public: Resource() { std::cout << "Resource acquired\n"; } ~Resource() { std::cout << "Resource destroyed\n"; } }; void customDeleter(Resource* res) { std::cout << "Custom deleter called\n"; delete res; } class ResourceManager { public: std::unique_ptr<Resource, decltype(&customDeleter)> resource; ResourceManager() : resource(new Resource(), customDeleter) {} }; int main() { { ResourceManager rm; } // ResourceManager goes out of scope here } ``` In this setup, I expect the custom deleter to be called and the resource to be destroyed when `ResourceManager` goes out of scope. However, I'm observing that the output sometimes skips the "Custom deleter called" message, and I see multiple "Resource acquired" without matching "Resource destroyed". I suspect this might be related to how the `std::unique_ptr` and its custom deleter are being managed, but I'm not sure what I'm missing. I've tried ensuring the `unique_ptr` is initialized properly and checking the ownership semantics, but the scenario continues. Additionally, I recompiling with `-O2` optimization flags seems to exacerbate the question, possibly leading to more aggressive inlining or resource management by the compiler. Could this be a compiler optimization scenario, or am I mismanaging the resource lifecycle somehow? Any insights or suggestions would be greatly appreciated! My development environment is Linux. Any ideas what could be causing this? This is part of a larger application I'm building. I'd really appreciate any guidance on this. For context: I'm using C++ on Windows. What's the best practice here? Any help would be greatly appreciated!