gcc lab9a.c -lpthread -o lab9a

lab9a.c

#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>

#define NTHREADS 5
#define ITER 10

sem_t semaphore;

void* thread_func(void* arg)
{
  int iter = ITER;
  int value;

  for(int k = 0; k < iter; k++)   //  Thread consuming resources
  {
    sem_getvalue(&semaphore, &value);

    if(value == 0)
    {
      fprintf(stdout, "iter: %d with thread: %d couldnt take the resource\n", k, pthread_self ());
    }

    sem_wait(&semaphore);
    fprintf(stdout, "iter: %d with thread: %d has taken the resource\n", k, pthread_self ());
    sleep(1);
    sem_post(&semaphore);
    fprintf(stdout, "iter: %d with thread: %d has returned the resource\n", k, pthread_self ());
  }

  return NULL;
}

int main(void)
{
  int nthreads = NTHREADS;

  pthread_t pthread_ids [nthreads];

  sem_init(&semaphore, 0, 1);

  for(int i = 0; i < nthreads; i++)   //  Create all threads
  {
    
    if(pthread_create(&pthread_ids[i], NULL, thread_func, NULL))
    {
      fprintf(stderr, "iter: %d couldnt create a thread\n", i);
    }
    else
    {
      fprintf(stdout, "created thread: %d\n", pthread_ids[i]); 
    } 
  }

  for(int j = 0; j < nthreads; j++)   //  Wait for all treads
  {
    if(pthread_join(pthread_ids[j], NULL))
    {
      fprintf(stderr, "iter: %d couldnt join a thread\n", j);
    }
    else{
      fprintf(stdout, "joined thread: %d\n", pthread_ids[j]); 
    }
  }

  return 0;
}