profile-generate won't generate gcda file

Question

I have simplified my source like the following :

void *thread1(void *param)
{
    pthread_detach(pthread_self());
    while(1)
    {
        sleep( 3 ) ;
        printf("hello world in thread1 \n");
    } //while
    return NULL ;
} //thread1


int main()
{
    pthread_t tid ;
    pthread_create(&tid , NULL, thread1, (void*)3);

    while(1)
    {
        sleep( 3 ) ;
        printf("hello world in main \n");
    } //while
} // main

and compile it by :

g++ --std=c++11  -fprofile-generate  xxx.cpp  -pthread  -o xxx.exe

in g++ 4.8.5 , execute xxx.exe can not see xxx.gcda , and then I simplified it to the following ..... only main thread !!

int main()
{
    while(1)
    {
        sleep( 3 ) ;
        printf("hello world in main \n");
    } //while 
} // main

and compiled by :

g++ --std=c++11  -fprofile-generate  yyy.cpp    -o yyy.exe

in the same compiler g++ 4.8.5 and execute , still no yyy.gcda created !!

In a simple case like above , What I missed so no gcda been created ?!