怎样在C++中实现线程安全的观察者模式 使用weak_ptr解决监听器生命周期问题

std::weak_ptr

std::shared_ptr

std::weak_ptr

lock()

shared_ptr

class Observer {
public:
    virtual void onEvent() = 0;
    virtual ~Observer() = default;
};

class Subject {
public:
    using WeakObserverPtr = std::weak_ptr<Observer>;

    void addObserver(const std::shared_ptr<Observer>& observer) {
        std::lock_guard<std::mutex> lock(mtx_);
        observers_.push_back(observer);
    }

    void removeObserver(const std::shared_ptr<Observer>& observer) {
        std::lock_guard<std::mutex> lock(mtx_);
        observers_.remove_if([&](const auto& wp) {
            auto sp = wp.lock();
            return !sp || sp.get() == observer.get();
        });
    }

    void notifyObservers() {
        std::lock_guard<std::mutex> lock(mtx_);
        for (auto it = observers_.begin(); it != observers_.end();) {
            if (auto observer = it->lock()) {
                observer->onEvent();
                ++it;
            } else {
                it = observers_.erase(it); // 自动清理失效项
            }
        }
    }

private:
    std::list<WeakObserverPtr> observers_;
    std::mutex mtx_;
};

struct MyObserver : public Observer, public std::enable_shared_from_this<MyObserver> {
    void onEvent() override {
        // 可以安全访问 this
    }
};

shared_from_this()

weak_ptr

weak_ptr