Method joinable

include/dmlc/thread_group.h:224–231

! * \brief Check whether the thread is joinable * \return true if the thread is joinable */

     * \return true if the thread is joinable
     */
    bool joinable() const {
      if (thread_.load()) {
        CHECK_EQ(auto_remove_, false);
        // be checked by searching the group or exit event.
        return thread_.load()->joinable();
      }
      return false;
    }

    /*!
     * \brief Thread join