1. A method for use by a transaction program on a computing system for managing memory access to a shared memory location for transaction data of a first thread, the shared memory location being accessible by the first thread and a second thread, the method comprising: using multiple atomic instruction groups (AIGs) of instructions to support execution by multiple systems of a single large transaction that requires operations on multiple threads, and tracking read and write sets of chained AIGs individually, an original AIG supports a chain of AIGs which is established by specialized Application Programming Interface (API) support which generates speculative messaging requests for service which are received by a specialized service provider that makes use of an AIG for speculative execution, and when an original speculative messaging request for a service is received by said speculative service provider the speculative service provider begins an AIG of its own to respond when the requested service is completed and ready to commit, but chained AIGs are not committed until said original AIG is ready to commit.