/* Program to compute sum of the first N positive integers */

/* This version uses two threads of control:    */
/*  - main thread does setup and final output   */
/*  - worker thread computes the sum            */

/* Based on example from page 161 of the textboook. CLW  */

/* Usage: cc -o summer2 summer2.c -pthread               */
/*        ./summer2 value                                */ 

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

int sum;  /* global variable shared by all threads */
void *runner(void *param);  /* the main worker thread */

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

    /* check command line argument */
    if( argc != 2 )
      {
	fprintf(stderr, "Usage: ./summer2 value\n");
	return -1;
      }

    limit = atoi(argv[1]);
    if( limit < 0 )
      {
	fprintf(stderr, "Value must be non-negative!\n");
	return -1;
      }

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

    /* create the thread */
    pthread_create(&tid, &attr, runner, argv[1]);

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

    /* output the final result */
    printf("The sum of the first %d positive integers is: %d\n",
	   limit, sum);
  }

/* The thread will begin control in this function. */
/* It does all the work to compute the required sum. */
void *runner(void *param)
  {
    int i;
    int upper;

    /* initialize */
    upper = atoi(param);
    sum = 0;

    /* main loop */
    for( i = 1; i <= upper; i++ )
      {
	sum += i;
      }

    pthread_exit(0);

  }