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

void * thread_doit(void *unused) {
  int len = (int) ((drand48() * 5) + 1);
  sleep(len);
  return NULL;
}

int main(int argc, char* argv[]) {
  if (argc < 2) {
    printf("Expected usage: %s THREAD_NUM\n", argv[0]);
    return -1;
  }

  int thread_num = atoi(argv[1]);
  pthread_t *pthread_array = malloc(sizeof(pthread_t) * thread_num);
  srand48(42); // arbitrary seed value
  for (int i = 0; i < thread_num; i++) {
    pthread_create(&pthread_array[i], NULL, &thread_doit, NULL);
  }

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

  free(pthread_array);

  return 0;
}