// To compile:  gcc -g3 -pthread THIS_FILE

// QUESTION:  How would you implement this using semaphores
//            and mutexes instead of barriers?

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

int PRINT;

pthread_barrier_t barrier;

void * thread_doit(void *t)
{
  int *tid = (int*)t;
  if (PRINT) {
    printf("Thread %d: Waiting at barrier\n", *tid);
  }
  pthread_barrier_wait(&barrier);
  if (PRINT) {
    printf("Thread %d: Crossed barrier\n", *tid);
  }
  return NULL;
}

int main(int argc, char* argv[])
{
  if (argc < 3) {
    printf("Expected usage: %s THREAD_NUM PRINT_FLAG\n", argv[0]);
    printf("PRINT_FLAG: 0 - Don't display debug information, 1 - Display debug information\n");
    return -1;
  }

  int THREAD_NUM = atoi(argv[1]);
  PRINT = atoi(argv[2]);

  pthread_t *threads = malloc(sizeof(pthread_t) * THREAD_NUM);

  pthread_barrier_init(&barrier, NULL, THREAD_NUM);

  int *tids = malloc(sizeof(int) * THREAD_NUM);
  for (int i = 0; i < THREAD_NUM; i++) {
    tids[i] = i;
    pthread_create(&threads[i], NULL, &thread_doit, &tids[i]);
  }

  for (int i = 0; i < THREAD_NUM; i++) {
    pthread_join(threads[i], NULL);
  }

  free(threads);
  free(tids);
  pthread_barrier_destroy(&barrier);

  return 0;
}