Method release

tpool/task.cc:52–58

  }

  void waitable_task::release()
  {
    std::unique_lock<std::mutex> lk(m_mtx);
    m_ref_count--;
    if (!m_ref_count && m_waiter_count)
      m_cv.notify_all();
  }
  void waitable_task::wait(std::unique_lock<std::mutex>& lk)
  {
    m_waiter_count++;