gcc lab9b.c -lpthread -o lab9b

lab9b.c

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

#define NTHREADS 5
#define ITER 10
#define RSRC 100
#define COUNT_R 5

pthread_mutex_t mutex;
pthread_cond_t condition;
int available_resources;
int count_resources;

int decrease_count(int count)
{
  if(available_resources < count)
  {
    return -1;
  }
  else
  {
    available_resources -= count;
    return 0;
  }
}

int increase_count(int count)
{
  available_resources += count;
  return 0;
}

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

  for(int k = 0; k < iter; k++)   //  Thread consuming resources
  {
    pthread_mutex_lock(&mutex);
    while(decrease_count(count_resources) == -1)
    {
      fprintf(stdout, "iter: %d with thread: %d couldnt take the resource\n", k, pthread_self ());
      pthread_cond_wait(&condition, &mutex);
    }

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

    pthread_cond_signal(&condition);
    pthread_mutex_unlock(&mutex);

    pthread_mutex_lock(&mutex);

    increase_count(count_resources);

    pthread_cond_signal(&condition);
    pthread_mutex_unlock(&mutex);    
  }

  return NULL;
}

int main(void)
{
  int nthreads = NTHREADS;

  pthread_t pthread_ids [nthreads];

  available_resources = RSRC;
  count_resources = COUNT_R;

  if(pthread_mutex_init(&mutex, NULL) != 0)
  {
    fprintf(stderr, "%s\n", "pthread_mutex_init");
    return 1;
  }
  
  if(pthread_cond_init(&condition, NULL) != 0)
  {
   fprintf(stderr, "%s\n", "pthread_cond_init");
   return 2;
  }

  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;
}