Registers the function named by func to be executed when a tick is called. Also, you may pass an array consisting of an object and a method as the func.
// using a function as the callback
// using an object->method
$object = new my_class();
register_tick_function(array(&$object, 'my_method'), true);
register_tick_function() should not be used with threaded webserver modules. Ticks are not working in ZTS mode and may crash your webserver.