/**
 * increment.c
 *
 * Use posix threads to increment a global counter.
 *
 * This version uses a mutex lock to prevent a race condition.
 *
 * gcc -o increment -lpthread increment.c
 */

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
 
#define NUM_THREADS 10
 
/* create thread argument struct for thr_func() */
typedef struct _thread_data_t {
  int tid;
} thread_data_t;
 
/* shared data between threads */
int shared_x;
pthread_mutex_t count_mutex;
 
void *thr_func(void *arg) {
  thread_data_t *data = (thread_data_t *)arg;
 
  //printf("hello from thr_func, thread id: %d\n", data->tid);
        pthread_mutex_lock(&count_mutex);
    for (int i = 0; i < 100000000; i++) {
        shared_x++;
    }
        pthread_mutex_unlock(&count_mutex);
//   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];
 
  /* initialize shared data */
  shared_x = 0;
  pthread_mutex_init (&count_mutex, NULL);
 
  /* create threads */
  for (i = 0; i < NUM_THREADS; ++i) {
    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);
  }
  
  pthread_mutex_destroy(&count_mutex);
  printf("x = %d\n", shared_x);
 
  return EXIT_SUCCESS;
}