using namespace std;
const static int kThreadSize = 48;
map<string, string> gMap;
string gStr = "";
void * func(void * data)
{
    while(true)
    {
        printf("%sn", gStr.c_str());
        pthread_mutex_t m;
        pthread_mutex_init(&m, NULL);
        pthread_mutex_lock(&m);

        gStr = gStr + "a";//core in this line
        printf("%xn", &gStr);//print the address

        pthread_mutex_unlock(&m);
        pthread_mutex_destroy(&m);

        printf("%sn", gStr.c_str());
    }
}

int main()
{
    pthread_t threads[kThreadSize];
    for(int i = 0; i < kThreadSize; i ++)
    {
        pthread_create(&threads[i], NULL, &func, &gMap);
    }
    for(int i = 0; i < kThreadSize; i ++)
    {
        pthread_join(threads[i], NULL);
    }
    return 0;
}