Synchronize N-processes in strict order with Semaphores - c

Question

I'm facing simple issue with Semaphore's task.
I am having N-processes (P1, P2, P3, P4...Pn). No matter in what order I create threads, I need them to execute in exact order (P1, P2, P3, P4...Pn). I need to come with solution, where I use minimum semaphores required.
It would be quite simple using Mutex, but the task says "use only semaphores".
I'm using only one semaphore. In while, within the condition, if order number is NOT equals your ID number, just unlock semaphore and cycle in while, till order number is equals to your ID number.
I think that problem might be with "Spurious wakeups".
Here is my code:
sem_t semvar;
int order = 0;
void *sayHello(void *thread_id){
int *my_id = (int *) thread_id;
while(1)
{
// take semaphore and close critical zone to read order variable to recognize who's on turn!
sem_wait(&semvar);
if(*my_id == order)
{
// if I'm on turn, then I shout my number and set order variable to someone behind me
printf("I'm thread no.: %d\n", *my_id);
order++;
break;
}
// release semaphore if I'm not on turn!
sem_post(&semvar);
}
// release semaphore if it was my turn, I shout my number and gonna end (die)!
sem_post(&semvar);
pthread_exit(NULL);
}
int main(int argc, char *argv[]) {
int numbOfThreads = 13;
int *thread_id[numbOfThreads];
int new_thread, i;
pthread_t threads[numbOfThreads];
// generating thread numbers --> NOTE: you need this, if you use random thread generating!!!
for(i = 0; i < numbOfThreads; i++)
{
thread_id[i] = (int *) malloc(sizeof(int));
*thread_id[i] = i;
}
// random thread generating for testing to make sure it works
pthread_create(&threads[10], NULL, sayHello, (void *) thread_id[10]);
pthread_create(&threads[12], NULL, sayHello, (void *) thread_id[12]);
pthread_create(&threads[8], NULL, sayHello, (void *) thread_id[8]);
pthread_create(&threads[3], NULL, sayHello, (void *) thread_id[3]);
pthread_create(&threads[5], NULL, sayHello, (void *) thread_id[5]);
pthread_create(&threads[1], NULL, sayHello, (void *) thread_id[1]);
pthread_create(&threads[0], NULL, sayHello, (void *) thread_id[0]);
pthread_create(&threads[4], NULL, sayHello, (void *) thread_id[4]);
pthread_create(&threads[7], NULL, sayHello, (void *) thread_id[7]);
pthread_create(&threads[6], NULL, sayHello, (void *) thread_id[6]);
pthread_create(&threads[2], NULL, sayHello, (void *) thread_id[2]);
pthread_create(&threads[9], NULL, sayHello, (void *) thread_id[9]);
pthread_create(&threads[11], NULL, sayHello, (void *) thread_id[11]);
/*
// automatic thread generating
for(i = 0; i < numbOfThreads; i++)
{
thread_id[i] = (int *) malloc(sizeof(int));
*thread_id[i] = i;
new_thread = pthread_create(&threads[i], NULL, sayHello, (void *) thread_id[i]);
if(new_thread)
{
printf("Error has occured");
exit(-1);
}
}
*/
// do not end main function before all the threads are done with work!
for(i = 0; i < numbOfThreads; i++)
{
pthread_join( threads[i], NULL);
}
printf("All the threads are gone!");
return 1;
}