1. A computer program product comprising at least one computer-usable medium having computer-usable program code for making a desirable idempotent atomic modification to a site in a code region forming part of a computer program during execution of the computer program by a plurality of threads, said computer program product comprising computer-usable program code for providing identical modification instructions to each thread for modifying the site in the code region, wherein the modification instructions direct each thread to make the desirable idempotent atomic modification.