  void agent_finish_evict_op() {
    Mutex::Locker l(agent_lock);
    assert(agent_ops > 0);
    --agent_ops;
    agent_cond.Signal();
  }
  void agent_finish_evict_op() {
    Mutex::Locker l(agent_lock);
    assert(agent_ops > 0);
    --agent_ops;
    agent_cond.Signal();
  }