Ticket #22301: 22301.diff

src/wp-includes/default-widgets.php

@@ -811 +811 @@
         }
 
         public function flush_widget_cache() {
-                wp_cache_delete('widget_recent_comments', 'widget');
+                $cache = wp_cache_get( 'widget_recent_comments', 'widget' );
+                if ( ! empty( $cache ) ) {
+                        // If the cache is flushed multiple times, we don't want to save an empty copy
+                        wp_cache_delete( 'widget_recent_comments', 'widget' );
+                        wp_cache_set( 'widget_recent_comments_old', $cache, 'widget' );
+                }
         }
 
         public function widget( $args, $instance ) {
                 global $comments, $comment;
 
                 $cache = array();
+                $cache_lock = false;
                 if ( ! $this->is_preview() ) {
-                        $cache = wp_cache_get('widget_recent_comments', 'widget');
+                        $cache = wp_cache_get( 'widget_recent_comments', 'widget' );
+                        if ( empty( $cache ) ) {
+                                // The cache has been deleted. Grab the old copy (if it exists),
+                                // and try to get the update lock
+                                $cache = wp_cache_get( 'widget_recent_comments_old', 'widget' );
+                                $cache_lock = wp_cache_add( 'widget_recent_comments_lock', 1, 'widget' );
+                        }
                 }
                 if ( ! is_array( $cache ) ) {
                         $cache = array();
@@ -885 +897 @@
 
                 echo $output;
 
-                if ( ! $this->is_preview() ) {
+                if ( ! $this->is_preview() && $cache_lock ) {
                         $cache[ $args['widget_id'] ] = $output;
                         wp_cache_set( 'widget_recent_comments', $cache, 'widget' );
+                        wp_cache_delete( 'widget_recent_comments_lock', 'widget' );
                 }
         }