code: func (q *Type) Len() int {
  	q.cond.L.Lock()
  	defer q.cond.L.Unlock()
  	return len(q.queue)
  }
docs: // Len returns the current queue length, for informational purposes only. You
  // shouldn't e.g. gate a call to Add() or Get() on Len() being a particular
  // value, that can't be synchronized properly.