#include <pthread.h>

typedef struct {
  pthread_mutex_t *lock;
  pthread_cond_t *cv;
  int *ndone;
  int id;
} TStruct;

#define NTHREADS 5

void *barrier(void *arg)
{
  TStruct *ts;
  int i;

  ts = (TStruct *) arg;

  printf("Thread %d -- waiting for barrier\n", ts->id);

  pthread_mutex_lock(ts->lock);
  *ts->ndone = *ts->ndone + 1;
  if (*ts->ndone < NTHREADS) {
    pthread_cond_wait(ts->cv, ts->lock);
  } else {
    for (i = 1; i < NTHREADS; i++) pthread_cond_signal(ts->cv);
  }
  pthread_mutex_unlock(ts->lock);

  printf("Thread %d -- after barrier\n", ts->id);
}

main()
{
  TStruct ts[NTHREADS];
  pthread_t tids[NTHREADS];
  int i, ndone;
  pthread_mutex_t lock;
  pthread_cond_t cv;
  void *retval;

  pthread_mutex_init(&lock, NULL);
  pthread_cond_init(&cv, NULL);
  ndone = 0;

  for (i = 0; i < NTHREADS; i++) {
    ts[i].lock = &lock;
    ts[i].cv = &cv;
    ts[i].ndone = &ndone;
    ts[i].id = i;
  }

  for (i = 0; i < NTHREADS; i++) {
    pthread_create(tids+i, NULL, barrier, ts+i);
  }

  for (i = 0; i < NTHREADS; i++) {
    pthread_join(tids[i], &retval);
  }
  printf("done\n");
}