Ticket #22301: 22301.2.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_stale', $cache, 'widget' );
+                }
         }
 
-        public function widget( $args, $instance ) {
-                global $comments, $comment;
+        /**
+         * Get cached data for a Recent Comments widget.
+         *
+         * Comment queries can be expensive so when the recent comments
+         * cache is flushed, we keep a stale copy and serve it until the
+         * updated data is rebuilt and cached.
+         */
+        public function get_widget_cache( $widget_id ) {
+                if ( $this->is_preview() )
+                        return;
 
-                $cache = array();
-                if ( ! $this->is_preview() ) {
-                        $cache = wp_cache_get('widget_recent_comments', 'widget');
+                $cache = wp_cache_get( 'widget_recent_comments', 'widget' );
+
+                if ( ! empty( $cache[ $widget_id ] ) ) {
+                        // Cache is up to date.
+                        return $cache[ $widget_id ];
+                } else {
+                        // Cache is outdated.
+                        $cache = wp_cache_get( 'widget_recent_comments_stale', 'widget' );
                 }
-                if ( ! is_array( $cache ) ) {
+
+                // No data even in the outdated cache.
+                if ( empty( $cache[ $widget_id ] ) )
+                        return;
+
+                // Attempt to acquire a lock or serve the data from stale cache.
+                if ( false === wp_cache_add( 'widget_recent_comments_lock', true, 'widget' ) )
+                        return $cache[ $widget_id ];
+
+                // Lock acquired, return "empty" cache.
+                return;
+        }
+
+        /**
+         * Updated a Recent Comments widget cache.
+         */
+        public function update_widget_cache( $widget_id, $data ) {
+                if ( $this->is_preview() )
+                        return;
+
+                $cache = wp_cache_get( 'widget_recent_comments', 'widget' );
+                if ( ! is_array( $cache ) )
                         $cache = array();
-                }
 
+                $cache[ $widget_id ] = $data;
+                wp_cache_set( 'widget_recent_comments', $cache, 'widget' );
+                wp_cache_delete( 'widget_recent_comments_lock', 'widget' );
+        }
+
+        public function widget( $args, $instance ) {
+                global $comments, $comment;
+
                 if ( ! isset( $args['widget_id'] ) )
                         $args['widget_id'] = $this->id;
 
-                if ( isset( $cache[ $args['widget_id'] ] ) ) {
-                        echo $cache[ $args['widget_id'] ];
+                // Serve from cache if available.
+                $cache = $this->get_widget_cache( $args['widget_id'] );
+                if ( ! empty( $cache ) ) {
+                        echo $cache;
                         return;
                 }
 
@@ -883 +931 @@
                 $output .= '</ul>';
                 $output .= $args['after_widget'];
 
+                $this->update_widget_cache( $args['widget_id'], $output );
                 echo $output;
-
-                if ( ! $this->is_preview() ) {
-                        $cache[ $args['widget_id'] ] = $output;
-                        wp_cache_set( 'widget_recent_comments', $cache, 'widget' );
-                }
         }
 
         public function update( $new_instance, $old_instance ) {