A scheduler which uses a GPS simulation to determine an order in which to service entities uses a novel dynamic data structure with a sophisticated, but simple, pointer update mechanism. Preferred embodiments of the scheduler perform a fixed amount of work per scheduling event. A scheduling event can be either computing a new virtual finish timestamp upon a new arrival to the scheduler, or determining which entities are to leave the GPS system because their finish timestamp has expired. The scheduler may be used in packet scheduling in a packet handling device, such as a router, scheduling access of software processes to a computer processor or the like. The scheduler may implement weighted fair queuing (WFQ)