Semaphore in system I/O space

摘要

A computer system utilizing multiple processes includes a semaphore for controlling exclusive access of a single process to a selected resource. The semaphore is implemented in the system input/output and controlled, at least in part, by an application specific integrated circuit (ASIC). When a process is attempting to acquire an I/O resource, a read is sent to the semaphore. If the resource is available the semaphore will have a first value, and the semaphore will return that first value to the process indicating that the process has acquired the resource. The ASIC will then change the semaphore value to a second value. If the resource is not available the semaphore will have the second value, and the semaphore will return the second value to the process indicating that the resource is not available.