VPTR

#include <cstdio>
#include <mutex>
#include <condition_variable>
#include <thread>

using namespace std;

#define pb push_back
#define mp make_pair

typedef long long int ll;

class A {
public:
    A() : done_(false) {}
    virtual void F() {
        printf("A::F\n");
    }
    void Done() {
        std::unique_lock<std::mutex> lk(m_);
        done_ = true;
        cv_.notify_one();
    }

    virtual ~A() {
        std::unique_lock<std::mutex> lk(m_);
        cv_.wait(lk, [this] {return done_; });
    }
private:
    std::mutex m_;
    std::condition_variable cv_;
    bool done_;
};

class B : public A {
public:
    virtual void F() override {
        printf("F::B\n");
    }
    virtual ~B() override {}

};

int main(int argc, char** argv) {
    A *a = new B();
    thread t1([a] { a->F(); a->Done();});
    thread t2([a] { delete a;});
    t1.join();
    t2.join();
}