// Just counting again, but with protected access to the counter.
// N is smaller than for "badcounter", because it gets too slow
// with the N == 2000000 (and there is nothing interesting to see - it works)
//
//
// Compile: gcc goodcounter.c -o goodcounter -lpthread
// Run: ./goodcounter


#include <stdlib.h>
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <semaphore.h>
#define P 4
#define N 200000

// make sure that the compiler doesn't
// optimise this into a register
volatile int target;

sem_t lock;

void *adderthread (void *arg)
{
  int i;

  for (i=0; i<N; i++) {
    sem_wait(&lock);
    target = target+1;
    sem_post(&lock);
  }
}

int main (int argc, char *argv[]) { 
  int i;
  pthread_t thread[P];

  target = 0;
  printf("Used %d threads, each making %d increments to a counter \n", P, N);

  sem_init(&lock, 0, 1); 

  for (i=0; i<P; i++) {
    pthread_create(&thread[i], NULL, adderthread, NULL);
  }

  for (i=0; i<P; i++) {
    pthread_join(thread[i], NULL);
  }


  printf("Final counter value was %d (should be %d)\n", target, P*N);

  exit(0);
}