How do I code to take action when a VBO (bulk action) is finished? I've recently coded a few Drupal\x\Plugin\Action classes that respond nicely to my VBO (now bulk actions?) in Drupal 8.  Now I'd like to implement a hook, or whatever is required, to take action when all the entities in a selected action have been processed...essentially a VBO post-process hook like we had with hook_views_bulk_operations_finish in Drupal 6.  Where and how can I implement that?  

I see no obvious hook in D8 to do this, and unfortunately, I've been unable to get Rules to work in D8 (still really confused by Rules and Actions configuration) so I really don't want to go down that path if I don't have to, yet.
This is how I tackled this scenario in D7.

In my custom VBO code I did a variable_set() and then I use hook_views_pre_render (note that the D8 hook params changed, so don't copy the hook from my code below) and did a variable_get(), if it was not empty, then do your action. 

/**
 * Implements hook_views_pre_render().
 */

function bulk_mail_hauliers_auto_emailing_views_pre_render(&amp;$view) {
// check the view name
if ($view-&gt;name == 'hauliers_auto_emailing') {

    $store_all_in_one_en = variable_get('bulk_mail_hauliers_auto_emailing_all_in_one_en', 0); 

    // check that variable_get is not empty, which means VBO ran.
    if ($store_all_in_one_en != 0) {

      // CUSTOM ACTION GOES HERE

      // delete the variable
      variable_del('bulk_mail_hauliers_auto_emailing_all_in_one_en');

    }

}


So you can basically do this in D8, except use the D8 equivalent of variable_set,get,del.