Method _clear

src/common/WorkQueue.h:335–338

      m_pool->add_work_queue(this);
    }
    void _clear() override {
      ceph_assert(ceph_mutex_is_locked(m_pool->_lock));
      m_items.clear();
    }
    bool _empty() override {
      ceph_assert(ceph_mutex_is_locked(m_pool->_lock));
      return m_items.empty();