is nice() used to change the thread priority or the process priority?
void * thread_function1(void *arg)
{

 pid_t tid = syscall(SYS_gettid);

 int ret = setpriority(PRIO_PROCESS, tid, -10);
 printf("tid of high priority thread %d , %dn",tid ,getpriority(PRIO_PROCESS,tid));
 while(1){
  printf("high priority ................n");
    }

}


void * thread_function(void *arg)
{
 pid_t tid = syscall(SYS_gettid);
 int ret = setpriority(PRIO_PROCESS, tid, 10);
 printf("tid of low priority thread %d , %d n",tid ,getpriority(PRIO_PROCESS,tid));
while(1)
{

  printf("lower priorityn");
}
}


int main()
{

pthread_t id1;
pthread_t id2;

pid_t pid = getpid();
pid_t tid = syscall(SYS_gettid);

printf("main thread : pid = %d , tid = %d n" , pid, tid);
pthread_create(&id1, NULL, thread_function1,  NULL);
pthread_create(&id1, NULL,thread_function,   NULL);

pthread_join(id1, NULL);
pthread_join(id2, NULL);


}