如何在多线程C++中拆除观察者关系？

#include<iostream>
#include<vector>
#include <mutex>
#include<thread>

class Observer {
public:
    virtual void update() = 0;
};

class Subject {
public:
    void attach(Observer* observer) {
        std::lock_guard<std::mutex> lock(m_mutex);
        m_observers.push_back(observer);
    }

    void detach(Observer* observer) {
        std::lock_guard<std::mutex> lock(m_mutex);
        for (auto it = m_observers.begin(); it != m_observers.end(); ++it) {
            if (*it == observer) {
                m_observers.erase(it);
                break;
            }
        }
    }

    void notify() {
        std::lock_guard<std::mutex> lock(m_mutex);
        for (auto observer : m_observers) {
            observer->update();
        }
    }

private:
    std::vector<Observer*> m_observers;
    std::mutex m_mutex;
};

class MyObserver : public Observer {
public:
    void update() override {
        std::cout << "MyObserver::update() called."<< std::endl;
    }
};

int main() {
    Subject subject;
    MyObserver observer;

    subject.attach(&observer);
    subject.notify();

    subject.detach(&observer);
    subject.notify();

    return 0;
}