#include <bits/stdc++.h>
#include <semaphore.h>
#include <pthread.h>
#include <unistd.h>
#define N 3
using namespace std;

pthread_t m_counter[N];
pthread_t m_monitor;
pthread_t m_collector;
//sem_t read_sem; //forces mutual exclusion on read
sem_t write_sem; //forces mutual exclusion on writes
int messages_cnt = 0;

void* counter_update_count(void* counter_index)
{
  sleep(rand()%100);
  int* x = (int*) counter_index;
  cout << "Counter thread [" << *x <<"] received a message" << endl;
  sem_wait(&write_sem);
  cout << "Counter thread[" << *x <<"] : waiting to write" << endl;
  messages_cnt++;
  cout << "Counter thread[" << *x <<"] : now adding to counter, counter value = " << messages_cnt << endl;
  sem_post(&write_sem);
  return 0;
}
void* mointor_update_count(void*)
{
  cout << "Monitor thread waiting to read counter";
  sleep(rand()%100);
  sem_wait(&write_sem);
  cout << "Monitor thread reading a count of " << messages_cnt << endl;
  messages_cnt = 0;
  //cout << "Monitor thread waiting to write" << endl;
  sem_post(&write_sem);
  return 0;
}

int main()
{
    sem_init(&write_sem, 0, 1);
    for(int i = 0; i < N; ++i)
    {
     pthread_create(&m_counter[i],NULL,counter_update_count,(void*)(&i));
    }
     pthread_create(&m_monitor, NULL,mointor_update_count, NULL);
    for(int i = 0; i < N; ++i)
    {
      pthread_join(m_counter[i],NULL);
    }
    pthread_join(m_monitor, NULL);
    return 0;
}