intpthread_barrier_wait(pthread_barrier_t *barrier){  pthread_descr self = thread_self();  pthread_descr temp_wake_queue, th;  int result = 0;
  __pthread_lock(&barrier->__ba_lock, self);
  /* If the required number of threads have achieved rendezvous... */  // pthread_barrier_wait被调用的次数达到阈值，__ba_present + 1 == __ba_required   if (barrier->__ba_present >= barrier->__ba_required - 1)    {      /* ... then this last caller shall be the serial thread */      result = PTHREAD_BARRIER_SERIAL_THREAD;      /* Copy and clear wait queue and reset barrier. */      // 被阻塞的线程队列      temp_wake_queue = barrier->__ba_waiting;      // 重置字段      barrier->__ba_waiting = NULL;      barrier->__ba_present = 0;    }  else    {      result = 0;      // 执行pthread_barrier_wait一次，加一      barrier->__ba_present++;      // 插入等待队列      enqueue(&barrier->__ba_waiting, self);    }
  __pthread_unlock(&barrier->__ba_lock);  // 调用pthread_barrier_wait的次数还不够  if (result == 0)    {      /* Non-serial threads have to suspend */      // 挂起当前线程      suspend(self);      /* We don't bother dealing with cancellation because the POSIX         spec for barriers doesn't mention that pthread_barrier_wait         is a cancellation point. */    }  else    {      /* Serial thread wakes up all others. */      // 唤醒其他的线程      while ((th = dequeue(&temp_wake_queue)) != NULL)  restart(th);    }
  return result;}
intpthread_barrier_init(pthread_barrier_t *barrier,        const pthread_barrierattr_t *attr,        unsigned int count){  if (count == 0)     return EINVAL;
  __pthread_init_lock(&barrier->__ba_lock);  // 需要执行pthread_barrier_wait的次数  barrier->__ba_required = count;  // 已经调用pthread_barrier_wait的次数  barrier->__ba_present = 0;  // 调用pthread_barrier_wait被阻塞的线程队列  barrier->__ba_waiting = NULL;  return 0;}
intpthread_barrier_destroy(pthread_barrier_t *barrier){  // 有线程在等待  if (barrier->__ba_waiting != NULL) return EBUSY;  return 0;}