boost::thread not updating global variable

I am using a wrapper function in an external software to start a new thread, which updates a global variable, but yet this seems invisible to the main thread. I cant call join(), not to block the main thread and crash the software. boost::async, boost::thread and boost::packaged_task all behave the same way.

uint32 *Dval;

bool hosttask1()
{

        while(*Dval<10)
        {
            ++*Dval;
            PlugIn::gResultOut << " within thread global value: " << *Dval << std::endl;    
            Sleep(500);
        }


return false;
}



void SU_HostThread1(uint32 *value)
{

Dval = value; 
*Dval = 2;
PlugIn::gResultOut << " before thread: " << *value <<  " before thread global: " << *Dval << std::endl;

    auto myFuture = boost::async(boost::launch::async,&hosttask1);

    //boost::thread thread21 = boost::thread(&hosttask1);
    //boost::packaged_task<bool> pt(&hosttask1);
    //boost::thread thread21 = boost::thread(boost::move(pt)); 
}

When I call the function:

number a=0 
su_hostthread1(a)
sleep(2) //seconds
result(" function returned "+a+"  \n")

OUTPUT:

before thread value: 2 before thread global value: 2
 within thread global value: 3
 within thread global value: 4
 within thread global value: 5
 within thread global value: 6
 function returned 2  
 within thread global value: 7
 within thread global value: 8
 within thread global value: 9
 within thread global value: 10

Any ideas? Thanks in advance!