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


struct barrier {
  int barrier_size;
  int count;
  int round;
  pthread_mutex_t mutex;
};


void barrier_init(struct barrier* barrier, int barrier_size) {
  barrier->barrier_size = barrier_size;
  barrier->count = 0;
  barrier->round = 0;
  pthread_mutex_init(&barrier->mutex, NULL);
}

void barrier_wait(struct barrier* barrier) {
  pthread_mutex_lock(&barrier->mutex);

  int cur_round = barrier->round;
  barrier->count ++;

  if(barrier->count == barrier->barrier_size) {
    pthread_mutex_unlock(&barrier->mutex);
    barrier->round++;
    barrier->count = 0;
  } else {
    pthread_mutex_unlock(&barrier->mutex);
    while(barrier->round == cur_round) {
      sched_yield();
    }
  }
}



void* worker(void* arg) {
  struct barrier *b = (struct barrier*) arg;
  static _Atomic int next_id = 0;
  int my_id = next_id++;

  for(int i=0; i<10; i++) {
    printf("Hello from thread %d\n", my_id);
    barrier_wait(b);
    printf("Goodbye from thread %d\n", my_id);
    barrier_wait(b);
  }
  return NULL;
}

int main(int argc, char**argv) {
  pthread_t tid[4];
  struct barrier barrier;
  barrier_init(&barrier, 4);

  for(int i = 0; i<4; i++) {
    pthread_create(&tid[i], NULL, worker, &barrier);
  }

  for(int i = 0; i<4; i++) {
    pthread_join(tid[i], NULL);
  }

  return EXIT_SUCCESS;
}