/*
 *  Illustrate two threads working the same function
 */
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
int max;                  // number of times to increment the variable per thread
volatile int balance = 0; // shared global variable

void * mythread(void *arg) {
   char *letter = arg;
   int i; // stack (private per thread)
   printf("%s: begin [addr of i: %p]\n", letter, &i);
   for (i = 0; i < max; i++) {
      balance = balance + 1; // shared among threads
   }
   printf("%s: done\n", letter);
   return NULL;
}

int main(int argc, char *argv[]) {
   if (argc != 2) {
      fprintf(stderr, "usage: t1 <loopcount>\n");
      exit(1);
   }
   max = atoi(argv[1]);
   pthread_t p1, p2;
   printf("main: begin [balance = %d] [%p]\n", balance, &balance);
   pthread_create(&p1, NULL, mythread, "A");  // P is capitalized for our textbook only!
   pthread_create(&p2, NULL, mythread, "B");  // p is lower case out in the wild.
   pthread_join(p1, NULL); // join waits for the threads to finish
   pthread_join(p2, NULL);
   printf("main: done\n [balance: %d]\n [should: %d]\n", balance, max*2);
   return 0;
}