Abstract: A system and method for performing an operation within limits upon a shared value stored in an actual value location. The method provides a plurality of memory locations, two of the memory locations being first and second reservation memory locations, and two of the memory locations being limit memory locations containing limit values. An operand is obtained and the operation is performed upon an affected reservation register using the operand. A resulting value is compared to the limit values in the limit memory locations and if the resulting value is not within the values in the limit memory locations, an inverse operation is performed to restore the affected reservation register and a failure is reported. Else the operation is performed to update the actual value location, the operation is performed to update an unaffected reservation register, and a success is reported.

Abstract: A method for enhancing concurrency in a multiprocessor computer system is described. Various tasks in a computer system communicate using commonly accessible mailboxes to access valid data from a location in the mailbox. A task holding the valid data places that data in a mailbox, and other tasks read the valid data from the mailbox. The task that inputs the valid data into the mailbox is caused to notify other tasks addressing the mailbox that the valid data is contained therein. Thus, no central coordination of mailbox access is required. Further, busy waits for valid data are minimized and the ressources of tasks and processors are used more efficiently. By coordinating several lists associated with each mailbox, conflicts in accessing data and delays in obtaining data are also minimized.