Issues with lambda capturing shared_ptr causing unexpected behavior in C++17
I can't seem to get I'm stuck on something that should probably be simple. I've searched everywhere and can't find a clear answer. I'm encountering a puzzling issue when using a lambda function that captures a `std::shared_ptr` in C++17. I have a class that stores a `std::shared_ptr` to an object, and I want to use a lambda to modify this object in a thread-safe manner. However, the behavior is not what I expected. Here’s a simplified version of what I’m doing: ```cpp #include <iostream> #include <memory> #include <thread> #include <vector> class Data { public: void update(int value) { this->value = value; } int getValue() const { return value; } private: int value = 0; }; class Manager { public: Manager() : data(std::make_shared<Data>()) {} void run() { std::vector<std::thread> threads; for (int i = 0; i < 5; ++i) { threads.emplace_back([this, i]() { data->update(i); }); } for (auto &t : threads) { t.join(); } } void printValue() const { std::cout << "Final Value: " << data->getValue() << '\n'; } private: std::shared_ptr<Data> data; }; int main() { Manager manager; manager.run(); manager.printValue(); return 0; } ``` After running this code, I expected the final value to be `4`, since the threads should all update the shared data object. However, I see inconsistent values being printed, and sometimes even a value that seems to be less than `0`. I’ve tried using `std::atomic` for the `value` in the `Data` class, but that leads to a different set of synchronization issues. Also, I've ensured that there are no other threads modifying the data at the same time. I suspect it might be a timing issue with the access to the shared pointer or how the lambda captures the context. Is there anything I am missing in the way I’m managing the `std::shared_ptr`, or do I need to introduce additional synchronization mechanisms? I'm working on a API that needs to handle this. I'd really appreciate any guidance on this. For context: I'm using C++ on Linux. Is there a better approach? I'm coming from a different tech stack and learning C++. What am I doing wrong? I'm using C++ 3.11 in this project. I'd really appreciate any guidance on this.