Ticket #15447: 15447.diff

diff --git wp-includes/post-thumbnail-template.php wp-includes/post-thumbnail-template.php
index 3758d1d..3ad64cf 100644
--- wp-includes/post-thumbnail-template.php
+++ wp-includes/post-thumbnail-template.php
@@ -48,6 +48,41 @@ function the_post_thumbnail( $size = 'post-thumbnail', $attr = '' ) {
 }
 
 /**
+ * Update cache for thumbnails in current loop
+ *
+ * @since 3.2
+ */
+function update_thumbnail_cache() {
+       global $wp_query;
+
+       $cache_key = 'thumb_cache:' . md5( implode( ',', wp_list_pluck( $wp_query->posts, 'ID' ) ) );
+       
+       // return if this loop is already cached
+       if ( wp_cache_get( $cache_key, 'thumbnails' ) )
+               return;
+
+       $thumb_ids = array();
+       foreach ( $wp_query->posts as $post ) {
+               if ( $id  = get_post_thumbnail_id( $post->ID ) )
+                       $thumb_ids[] = $id;
+       }
+
+       if ( ! empty( $thumb_ids ) ) {
+               $thumb_ids = array_filter( array_unique( $thumb_ids ) );
+
+               get_posts( array(
+                       'update_post_term_cache' => false,
+                       'include'                => $thumb_ids,
+                       'post_type'              => 'attachment',
+                       'post_status'            => 'inherit',
+                       'nopaging'               => true,
+               ) );
+       }
+       
+       wp_cache_add( $cache_key, 1, 'thumbnails', 86400 ); // 1 day
+}
+
+/**
  * Retrieve Post Thumbnail.
  *
  * @since 2.9.0
@@ -62,6 +97,10 @@ function get_the_post_thumbnail( $post_id = null, $size = 'post-thumbnail', $att
        $size = apply_filters( 'post_thumbnail_size', $size );
        if ( $post_thumbnail_id ) {
                do_action( 'begin_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size ); // for "Just In Time" filtering of all of wp_get_attachment_image()'s filters
+
+               if ( in_the_loop() )
+                       update_thumbnail_cache();
+
                $html = wp_get_attachment_image( $post_thumbnail_id, $size, false, $attr );
                do_action( 'end_fetch_post_thumbnail_html', $post_id, $post_thumbnail_id, $size );
        } else {