/**
 * increment_personal.c
 * 
 * Generate posix threads to increment a "personal" (i.e. per thread) counter.
 *
 * This is a version has correct output and runs efficiently.
 *
 * gcc -o increment_personal -lpthread increment_personal.c
 */

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
 
#define NUM_THREADS 8
 
/* create thread argument struct for thr_func() */
typedef struct _thread_data_t {
  int tid;
} thread_data_t;
 
/* shared data between threads */
int shared_x[NUM_THREADS];
 
void *thr_func(void *arg) {
  thread_data_t *data = (thread_data_t *)arg;
  int i;
//   printf( "thread %d has i at address %p\n", data->tid, &i );
 
  //printf("hello from thr_func, thread id: %d\n", data->tid);
    for (i = 0; i < 10000000; i++)
        shared_x[data->tid]++;
//   printf("x = %d\n", shared_x);
 
  pthread_exit(NULL);
}

int main(int argc, char **argv) {
  pthread_t thr[NUM_THREADS];
  int i, rc;
  /* create a thread_data_t argument array */
  thread_data_t thr_data[NUM_THREADS];
 
//   printf( "In main, i is at %p, shared_x at %p\n", &i, &shared_x );
 
  /* create threads */
  /* initialize shared data */
  for (i = 0; i < NUM_THREADS; ++i) {
    shared_x[i] = 0;
    thr_data[i].tid = i;
    if ((rc = pthread_create(&thr[i], NULL, thr_func, &thr_data[i]))) {
      fprintf(stderr, "error: pthread_create, rc: %d\n", rc);
      return EXIT_FAILURE;
    }
  }
  /* block until all threads complete */
  for (i = 0; i < NUM_THREADS; ++i) {
    pthread_join(thr[i], NULL);
  }
  
  int total = 0;
  for (i = 0; i < NUM_THREADS; i++) {
    total += shared_x[i];
  }
  printf("x = %d\n", total);
 
  return EXIT_SUCCESS;
}