Sometimes, you need to perform actions for a group of UObjects, for instances devices that need to be updated together. The API provides the UObjectHub class for this purpose. To create a hub, simply declare a subclass of UObjectHub, and register it by calling once the macro UStartHub (classname). A single instance of this class will then be created upon server startup. UObject instances can then register to this hub by calling URegister (hubclassname). Timers can be attached to UObjectHub the same way as to UObject (see Timers section above). The kernel will call the update () method of all UObject before calling the update () method of the hub. A hub instance can be retrieved by calling getUObjectHub (string classname). The hub also holds the list of registered UObject in its members attribute.