app.c

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

#define NTHREADS     2  //Define Thread Count
#define ARRAYSIZE   10  //Define Array Size
#define ITERATIONS   ARRAYSIZE / NTHREADS

double  sum=0.0;
double a[ARRAYSIZE];
pthread_mutex_t sum_mutex;

void *do_work(void *tid)
{
  int i, start, *mytid, end;
  double mysum=0.0;

  /* Initialize my part of the global array and keep local sum */
  mytid = (int *) tid;
  start = (*mytid * ITERATIONS);
  end = start + ITERATIONS;

  // printf ("\n[Thread %5d] Doing iterations \t%10d to \t %10d",*mytid,start,end-1); 

  for (i=start; i < end ; i++) {
    a[i] = i * 1.0;
    mysum = mysum + a[i];
    sleep(0.1);
    }

  /* Lock the mutex and update the global sum, then exit */
  pthread_mutex_lock (&sum_mutex);
  sum = sum + mysum;
  pthread_mutex_unlock (&sum_mutex);
  pthread_exit(NULL);
}

int main(int argc, char *argv[])
{
  int i, start, tids[NTHREADS];
  pthread_t threads[NTHREADS];
  pthread_attr_t attr;

  /* Pthreads setup: initialize mutex and explicitly create threads in a
     joinable state (for portability).  Pass each thread its loop offset */
  
  pthread_mutex_init(&sum_mutex, NULL);
  pthread_attr_init(&attr);
  pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
  for (i=0; i<NTHREADS; i++) {
    tids[i] = i;
    pthread_create(&threads[i], &attr, do_work, (void *) &tids[i]);
    }

  /* Wait for all threads to complete then print global sum */ 
  for (i=0; i<NTHREADS; i++) {
    pthread_join(threads[i], NULL);
  }

  printf ("\n[MAIN] Done. Sum= %e", sum);
  /* Destroy Threads, Clean up and exit */
  pthread_attr_destroy(&attr);
  pthread_mutex_destroy(&sum_mutex);
  pthread_exit (NULL);
}