threads.c

#include <stdio.h>
#include <pthread.h>
#define ARRAYSIZE 1000
#define THREADS 2
void *slave(void *myid);


/* shared data */
int data[ARRAYSIZE]; /* Array of numbers to sum */
int sum = 0;
pthread_mutex_t mutex; /* mutually exclusive lock variable */
int wsize;
/* size of work for each thread */
/* end of shared data */

void *slave(void *myid)
{
	  int i,low,high,myresult=0;

	  low = (int) myid * wsize;
	  high = low + wsize;

		for (i=low;i<high;i++)
		   myresult += data[i];
	
	pthread_mutex_lock(&mutex);
	sum += myresult; /* add partial sum to local sum */
	pthread_mutex_unlock(&mutex);

	return;
}

main() {
	int i;
	pthread_t tid[THREADS];
	pthread_mutex_init(&mutex,NULL); /* initialize mutex */

	wsize = ARRAYSIZE/THREADS; /* wsize must be an integer */

	for (i=0;i<ARRAYSIZE;i++)
	  data[i] = i+1; /* initialize data[] */

	for (i=0;i<THREADS;i++) /* create threads */
	  if (pthread_create(&tid[i],NULL,slave,(void *)i) != 0)
		perror("Pthread_create fails");

	for (i=0;i<THREADS;i++) /* join threads */
	  if (pthread_join(tid[i],NULL) != 0)
		perror("Pthread_join fails");

	printf("The sum from 1 to %i is %d\n",ARRAYSIZE,sum);
}