my thread in zygote process block start up of all other apps on my android phone

I can inject the android system process "zygote", and I can execute my code in it. It is all fine util I do this:

pthread_t id;
int ret = pthread_create(&id, 0, thread_main, 0);

static void* thread_main(void* param){  
int count = 0;
while (count < 10)
{
    count += 1;
    usleep(1000 * 1000);

    printf("wait in loop %d.", count);
}

return 0;
}

Then, startup of any app on my phone is blocked when the loop is running. It is so strange for an c++ developer! It is running in a thread, but it blocks others!