In order to demonstrate priority scheduling with Pthreads, I have written the following short c- program. I think its Output isn't very demonstrative because there is no descending order in the threads priorities.

>>> Program-Output
6'er Gruppe an der Barriere synchronisiert
Thread (1077267376) running at FIFO with priority 2
Thread (1087773616) running at FIFO with priority 4
Thread (1081469872) running at FIFO with priority 4
Thread (1085672368) running at FIFO with priority 3
Thread (1079368624) running at FIFO with priority 3
Thread (1083571120) running at FIFO with priority 2
6'er Gruppe an der Barriere synchronisiert
Thread (1083571120) running at FIFO with priority 2
Thread (1087773616) running at FIFO with priority 4
Thread (1081469872) running at FIFO with priority 4
Thread (1085672368) running at FIFO with priority 3
Thread (1079368624) running at FIFO with priority 3
Thread (1077267376) running at FIFO with priority 2
...
>>>

Instead the order 2 4 4 3 3 2, I would expect an priority order of 4 4 3 3 2 2. Does anyone know what is the problem here?

#define PRIO_GROUP 2

pthread_t hpt[PRIO_GROUP];
pthread_t mpt[PRIO_GROUP];
pthread_t npt[PRIO_GROUP];

barrier_t mybarrier;

void *highprior_thread(void *arg){
pthread_t thread_id = pthread_self();

while(1){
barrier_wait(&mybarrier);
print_scheduling_info(thread_id);
}

return NULL;
}

void *middleprior_thread(void *arg){
pthread_t thread_id = pthread_self();

while(1){
barrier_wait(&mybarrier);
print_scheduling_info(thread_id);
}

return NULL;
}

void *lowprior_thread(void *arg){
pthread_t thread_id = pthread_self();
int count = 0;

while(1){
barrier_wait(&mybarrier);
print_scheduling_info(thread_id);
}

return NULL;
}

int main(int argc, char *argv[]){
struct sched_param my_param;
pthread_attr_t hp_attr;
pthread_attr_t mp_attr;
pthread_attr_t lp_attr;
int i;

/* MAIN-THREAD WITH LOW PRIORITY */
my_param.sched_priority = sched_get_priority_min(SCHED_FIFO);
pthread_setschedparam(pthread_self(), SCHED_RR, &my_param);
print_scheduling_info(pthread_self());


/* SCHEDULING POLICY AND PRIORITY FOR OTHER THREADS */
pthread_attr_init(&lp_attr);
pthread_attr_init(&mp_attr);
pthread_attr_init(&hp_attr);

pthread_attr_setinheritsched(&lp_attr, PTHREAD_EXPLICIT_SCHED);
pthread_attr_setinheritsched(&mp_attr, PTHREAD_EXPLICIT_SCHED);
pthread_attr_setinheritsched(&hp_attr, PTHREAD_EXPLICIT_SCHED);

pthread_attr_setschedpolicy(&lp_attr, SCHED_FIFO);
pthread_attr_setschedpolicy(&mp_attr, SCHED_FIFO);
pthread_attr_setschedpolicy(&hp_attr, SCHED_FIFO);

my_param.sched_priority = min_priority + 1;
pthread_attr_setschedparam(&np_attr, &my_param);
my_param.sched_priority = min_priority + 2;
pthread_attr_setschedparam(&mp_attr, &my_param);
my_param.sched_priority = min_priority + 3;
pthread_attr_setschedparam(&hp_attr, &my_param);

barrier_init(&mybarrier, PRIO_GROUP*3);

for(i=0; i<PRIO_GROUP; i++){
pthread_create(&lpt[i], &np_attr, lowprior_thread, NULL);
pthread_create(&mpt[i], &mp_attr, middleprior_thread, NULL);
pthread_create(&hpt[i], &hp_attr, highprior_thread, NULL);
}

for(i=0; i<PRIO_GROUP; i++){
pthread_join(hpt[i], NULL);
pthread_join(mpt[i], NULL);
pthread_join(lpt[i], NULL);
}

printf("main exiting\n");

return 0;
}