Delegate of C++

#include <iostream>
#include <boost/thread.hpp>
#include <boost/signals2.hpp>
#include <boost/bind.hpp>

boost::mutex theMutex;

struct Obj
{
    void fn1()
    {
        boost::lock_guard<boost::mutex> lock(theMutex);
        std::cout << (void *)this << "::fn1" << std::endl;
    }
    void fn2()
    {
        boost::lock_guard<boost::mutex> lock(theMutex);
        std::cout << (void *)this << "::fn2" << std::endl;
    }
    void fn3()
    {
        boost::lock_guard<boost::mutex> lock(theMutex);
        std::cout << (void *)this << "::fn3" << std::endl;
    }
};

struct Obj2
{
    void operator()()
    {
        boost::lock_guard<boost::mutex> lock(theMutex);
        std::cout << (void *)this << ":Hello world" << std::endl;
    }
};

int main()
{
    Obj o1, o2;
    Obj2 HW;
    boost::signals2::signal<void(void)> sig1, sig2;
    sig1.connect(HW);
    sig1.connect(boost::bind(&Obj::fn1, &o1));
    sig1.connect(boost::bind(&Obj::fn2, &o1));
    sig1.connect(boost::bind(&Obj::fn3, &o2));
    sig2.connect(boost::bind(&Obj::fn1, &o2));
    sig2.connect(boost::bind(&Obj::fn2, &o2));
    sig2.connect(boost::bind(&Obj::fn3, &o1));
    sig2.connect(HW);
    boost::thread t1(boost::ref(sig1)), t2(boost::ref(sig2));
    t1.join();
    t2.join();
}