/**
 * A pthread program illustrating how to
 * create a simple thread and some of the pthread API
 * This program implements the summation function where
 * the summation operation is run as a separate thread.
 *
 * gcc thrd.c -lpthread
 *
 * Figure 4.6
 *
 * @author Gagne, Galvin, Silberschatz
 * Operating System Concepts  - Seventh Edition
 * Copyright John Wiley & Sons - 2005.
 */

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

int sum; /* this data is shared by the thread(s) */

void *runner(void *param); /* the thread */

int main(int argc, char *argv[])
{
   pthread_t tid; /* the thread identifier */
   pthread_attr_t attr; /* set of attributes for the thread */

   if (argc != 2) {
      fprintf(stderr,"usage: a.out <integer value>\n");
      /*exit(1);*/
      return -1;
   }

   if (atoi(argv[1]) < 0) {
      fprintf(stderr,"Argument %d must be non-negative\n",atoi(argv[1]));
      /*exit(1);*/
      return -1;
   }

   /* get the default attributes */
   pthread_attr_init(&attr);

   /* create the thread with runner() as its code 
      and argv[1] as its argument */
   pthread_create(&tid,&attr,runner,argv[1]);

   /* now wait for the thread to exit */
   pthread_join(tid,NULL);

   printf("sum = %d\n",sum);

   return 0;
}

/**
 * The thread will begin control in this function
 */
void *runner(void *param) 
{
   int i, upper = atoi(param);  /* convert arg to int */
   sum = 0;
   
   if (upper > 0) {   /* check anyway, just in case... */
      for (i = 1; i <= upper; i++)
         sum += i;
   }

   pthread_exit(0);
}