text: #include <stdio.h>
  #include <pthread.h>
  
  pthread_mutex_t a = PTHREAD_MUTEX_INITIALIZER;
  pthread_mutex_t b = PTHREAD_MUTEX_INITIALIZER;
  pthread_barrier_t bar;
  
  void *ba_lock(void *arg)
  {
  	int ret, i;
  
  	pthread_mutex_lock(&b);
  
  	if (pthread_barrier_wait(&bar) == PTHREAD_BARRIER_SERIAL_THREAD)
  		pthread_barrier_destroy(&bar);
  
  	pthread_mutex_lock(&a);
  
  	pthread_mutex_unlock(&a);
  	pthread_mutex_unlock(&b);
  }
  
  int main(void)
  {
  	pthread_t t;
  
  	pthread_barrier_init(&bar, NULL, 2);
  
  	if (pthread_create(&t, NULL, ba_lock, NULL)) {
  		fprintf(stderr, "pthread_create() failed\n");
  		return 1;
  	}
  	pthread_mutex_lock(&a);
  
  	if (pthread_barrier_wait(&bar) == PTHREAD_BARRIER_SERIAL_THREAD)
  		pthread_barrier_destroy(&bar);
  
  	pthread_mutex_lock(&b);
  
  	pthread_mutex_unlock(&b);
  	pthread_mutex_unlock(&a);
  
  	pthread_join(t, NULL);
  
  	return 0;
  }
  