Merge pull request #5295 from v12mike/ticket/15726

Ticket/15726 Implement selective purge in APCu cache driver

phpBB/phpbb/cache/driver/apcu.php

@@ -25,7 +25,11 @@ class apcu extends \phpbb\cache\driver\memory
 	*/
 	function purge()
 	{
-		apcu_clear_cache();
+		/*
+		* Use an iterator to selectively delete our cache entries without disturbing
+		* any other cache users (e.g. other phpBB boards hosted on this server)
+		*/
+		apcu_delete(new \APCUIterator('#^' . $this->key_prefix . '#'));
 
 		parent::purge();
 	}