Virtual Queue Processing Circuit and Task Processor

A queue control circuit controls the placement and retrieval of a plurality of tasks in a plurality of types of virtual queues. State registers are associated with respective tasks. Each of the state registers stores a task priority order, a queue ID of a virtual queue, and the order of placement in the virtual queue. Upon receipt of a normal placement command ENQ_TL, the queue control circuit establishes, in the state register for the placed task, QID of the virtual queue as the destination of placement and an order value indicating the end of the queue. When a reverse placement command ENQ_TP is received, QID of the destination virtual queue and an order value indicating the start of the queue are established. When a retrieval command DEQ is received, QID is cleared in the destination virtual queue.