Abstract: Using this invention, more than one variable that is shared in a multiprocessing environment can be updated atomically. Each computer processor operating in the multiprocessing environment contains more than one reservation register which, along with this novel method, are used to place reservations on each of more than one shared variable. During the execution of a program, a plurality of shared variables can be reserved, each by its respective reservation register. A reservation is placed on a shared variable by means of a special instruction. The reservation register keeps track of: the address of the shared variable that it is reserving, the value of the modified results that are to be updated in the shared variable address, whether the variable has been updated, whether the reservation is valid, and whether the processor containing the reservation register has a privilege to update the shared variable.