threads.c

/*
 * Add NetID and names of all project partners

Pavan Kumar Kokkiligadda : pkk46
Nicholas Chen : nhc29

 *
 */
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

pthread_t t1, t2, t3, t4;
pthread_mutex_t mutex;
int x = 0;
int loop = 10000;

/* Counter Incrementer function:
 * This is the function that each thread will run which
 * increments the shared counter x by LOOP times.
 *
 * Your job is to implement the incrementing of x
 * such that update to the counter is sychronized across threads.
 *
 */
void *add_counter(void *arg)
{

  int i;

  /* Add thread synchronizaiton logic in this function */

  // Lock the mutex before updating the shared variable
  pthread_mutex_lock(&mutex);
  for (i = 0; i < loop; i++)
  {

    x = x + 1;
  }
  // Unlock the mutex after updating the shared variable
  pthread_mutex_unlock(&mutex);

  return NULL;
}

/* Main function:
 * This is the main function that will run.
 *
 * Your job is to create four threads and have them
 * run the add_counter function().
 */
int main(int argc, char *argv[])
{

  if (argc != 2)
  {
    printf("Bad Usage: Must pass in a integer\n");
    exit(1);
  }

  loop = atoi(argv[1]);

  printf("Going to run four threads to increment x up to %d\n", 4 * loop);

  /* Implement Code Here */

  // Initialize mutex
  pthread_mutex_init(&mutex, NULL);

  /* Create threads */
  pthread_create(&t1, NULL, add_counter, NULL);
  pthread_create(&t2, NULL, add_counter, NULL);
  pthread_create(&t3, NULL, add_counter, NULL);
  pthread_create(&t4, NULL, add_counter, NULL);

  /* Join threads */
  pthread_join(t1, NULL);
  pthread_join(t2, NULL);
  pthread_join(t3, NULL);
  pthread_join(t4, NULL);

  // Destroy mutex
  pthread_mutex_destroy(&mutex);

  /* Make sure to join the threads */

  printf("The final value of x is %d\n", x);

  return 0;
}