Abstract: In multiprocessor data processing systems that utilize individual processors having interlaced cycles of operation controlled by complementarily phased clocks, contention for fixed resources such as memory, I/O, or data storage for example, may result unless an interlock method allocating the use of the fixed resource to one or another of the interlaced cycle processors is included. The usual test and set instruction approach for allocating fixed resources will not effectively interlock the use of fixed resources in a multiprocessor system having interlaced cycles without potential contention arising. The present invention resolves this difficulty by providing means for identifying which processor currently has been allocated control of a given fixed resource.