Introduce wp_suspend_cache_addition() to allow reduced memory usage when cache additions aren't useful. Fixes #5389.

git-svn-id: https://develop.svn.wordpress.org/trunk@18681 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/cache.php

@@ -294,6 +294,9 @@ class WP_Object_Cache {
 	 * @return bool False if cache key and group already exist, true on success
 	 */
 	function add( $key, $data, $group = 'default', $expire = '' ) {
+		if ( wp_suspend_cache_addition() )
+			return false;
+
 		if ( empty ($group) )
 			$group = 'default';
 

wp-includes/functions.php

@@ -3709,6 +3709,30 @@ function wp_guess_url() {
 	return rtrim($url, '/');
 }
 
+/**
+ * Temporarily suspend cache additions.
+ *
+ * Stops more data being added to the cache, but still allows cache retrieval.
+ * This is useful for actions, such as imports, when a lot of data would otherwise
+ * be almost uselessly added to the cache.
+ *
+ * Suspension lasts for a single page load at most. Remember to call this
+ * function again if you wish to re-enable cache adds earlier.
+ *
+ * @since 3.3.0
+ *
+ * @param bool $suspend Optional. Suspends additions if true, re-enables them if false.
+ * @return bool The current suspend setting
+ */
+function wp_suspend_cache_addition( $suspend = null ) {
+	static $_suspend = false;
+
+	if ( is_bool( $suspend ) )
+		$_suspend = $suspend;
+
+	return $_suspend;
+}
+
 /**
  * Suspend cache invalidation.
  *