从对象原因到此类的调用析构函数的c ++ std :: thread调用方法

我对此代码有一些疑问：

#include <thread>
#include <unistd.h>
#include <iostream>

class A
{
public:
    ~A()
    {
        std::cout << "Destructor A: " << this << std::endl;
    }

    void operator()()
    {
        std::cout << "going to sleep 10 seconds.." << std::endl;
        sleep(10);
        std::cout << "wake" << std::endl;
    }
};

int main()
{
    std::cout << "begin" << std::endl;
    A* a = new A();
    std::thread th(*a);
    th.join();
    std::cout << "end" << std::endl;
    delete a;

    return 0;
}