code: func (r *ready) check() bool {
  	rwMutex := r.c.L.(*sync.RWMutex)
  	rwMutex.RLock()
  	defer rwMutex.RUnlock()
  	return r.ok
  }
docs: // TODO: Make check() function more sophisticated, in particular
  // allow it to behave as "waitWithTimeout".