Priority selector

DETAILED DESCRIPTION It is an object of the present invention to provide a priority selector which eliminates the above problems of the conventional technique, prevents reductions in processing capacities of processors due to lock request contentions, and has a simple circuit configuration.
According to the present invention, there is provided a priority selector system including a plurality of processors and a shared source commonly used by the plurality of processors, which sets priority for requests supplied from the plurality of processors for using the shared source and supplies permission to use the source, comprising: a plurality of lock request priority setting means, each of which is provided for a corresponding one of the processors and, each of which when a contention occurs between a request from a corresponding processor (referred to as the "own" request hereinafter) and another request from another processor (referred to as the "other" request hereinafter), upgrades non-permitted "own" request as a high priority request when the "other" request is permitted, and downgrades a following "own" request as a low priority request when the "own" request is permitted; and a request selection means for receiving requests from the processors, the priority of which is set by the lock request priority setting means, selecting a high priority request prior to a low priority request, and selecting requests in accordance with a predetermined priority when the requests are of the same priority.