Fixes #2617: Perform cache rebuild during updb in same process (#2621)

This is a backport of bc8bb69

commands/core/drupal/update.inc

@@ -102,6 +102,25 @@ function drush_update_do_one($module, $number, $dependency_map,  &$context) {
   $context['message'] = 'Performing ' . $function;
 }
 
+/**
+ * Clears caches and rebuilds the container.
+ *
+ * This is called in between regular updates and post updates. Do not use
+ * drush_drupal_cache_clear_all() as the cache clearing and container rebuild
+ * must happen in the same process that the updates are run in.
+ *
+ * Drupal core's update.php uses drupal_flush_all_caches() directly without
+ * explicitly rebuilding the container as the container is rebuilt on the next
+ * HTTP request of the batch.
+ *
+ * @see drush_drupal_cache_clear_all()
+ * @see \Drupal\system\Controller\DbUpdateController::triggerBatch()
+ */
+function drush_update_cache_rebuild() {
+  drupal_flush_all_caches();
+  \Drupal::service('kernel')->rebuildContainer();
+}
+
 function update_main() {
   // In D8, we expect to be in full bootstrap.
   drush_bootstrap_to_phase(DRUSH_BOOTSTRAP_DRUPAL_FULL);
@@ -212,7 +231,7 @@ function drush_update_batch() {
   // Apply post update hooks.
   $post_updates = \Drupal::service('update.post_update_registry')->getPendingUpdateFunctions();
   if ($post_updates) {
-    $operations[] = ['drush_drupal_cache_clear_all', []];
+    $operations[] = ['drush_update_cache_rebuild', []];
     foreach ($post_updates as $function) {
       $operations[] = ['update_invoke_post_update', [$function]];
     }