👀 Views: 42 💬 Answers: 1 📅 Created: 2025-06-15

c++ multithreading smart-pointers shared_ptr cpp

I'm experiencing unexpected behavior when using `std::shared_ptr` with a custom deleter in a multi-threaded C++17 application. Specifically, it seems that the custom deleter is being called multiple times, which is leading to double-delete errors and subsequent crashes. Here's a simplified version of what I'm doing: ```cpp #include <iostream> #include <memory> #include <thread> #include <vector> struct MyType { int value; MyType(int val) : value(val) { std::cout << "MyType created: " << value << '\n'; } ~MyType() { std::cout << "MyType destroyed: " << value << '\n'; } }; void customDeleter(MyType* ptr) { std::cout << "Custom deleter called for: " << ptr->value << '\n'; delete ptr; } void threadFunction(std::shared_ptr<MyType> ptr) { // Simulate some processing std::this_thread::sleep_for(std::chrono::milliseconds(100)); } int main() { std::vector<std::shared_ptr<MyType>> pointers; for (int i = 0; i < 5; ++i) { std::shared_ptr<MyType> ptr(new MyType(i), customDeleter); pointers.push_back(ptr); std::thread(threadFunction, ptr).detach(); } // Wait for threads to finish std::this_thread::sleep_for(std::chrono::seconds(1)); return 0; } ``` In this code, I create a `shared_ptr` for `MyType` with a custom deleter and then spawn a thread that takes a copy of that shared pointer. However, when I run this code, I sometimes see the custom deleter being called twice for the same object, which results in a crash. I thought that `std::shared_ptr` should manage the reference count correctly, especially since I'm only using the `shared_ptr` within the thread without any modification. I've tried a few approaches to mitigate this scenario, including ensuring that I don't share the pointer across threads in a not thread-safe manner. However, the scenario continues. Has anyone encountered similar issues with `std::shared_ptr` and custom deleters? What am I missing here? Any insights would be appreciated!