VORRICHTUNG UND VERFAHREN ZUR SYNCHRONISATION VON ARITHMETISCHEN EXCEPTIONEN IN PARALLELEN PIPELINE-AUSFUEHRUNGSEINHEITEN

A data processing system central processing unit (11) is disclosed having a plurality of parallel pipelined execution units (e.g., 25 Fig. 4), and other apparatus (22) for implementing a special, DRAIN instruction, to permit the processor (11) to complete instructions preceding the DRAIN instruction which are currently being processed by the execution units (25), but prevent later processing of instructions until all currently executing instructions are completed and all outstanding exception conditions are resolved. After all the preceding instructions are executed, central processing unit (11) continues to execute the sequential program instructions when no arithmetic exception has been identified, or invokes an exception handling procedure when an arithmetic exception has been identified. The DRAIN instruction permits the response to arithmetic exceptions identified after the execution of the DRAIN instruction to be handled in the same context environment in which the instruction was initiated.