A
hybrid Single-Compare-Single-Store (SCSS) operation may
exploit best-effort hardware
transactional memory (HTM) for good performance in the case that it succeeds, and may transparently resort to
software-mediated transactions if the hardware transactional mechanisms fail. The SCSS operation may compare a value in a control location to a specified expected value, and if they match, may store a new value in a separate
data location. The control value may include a global lock, a transaction status indicator, and / or a portion of an ownership
record, in different embodiments. If another transaction in progress owns the
data location, the SCSS operation may abort the other transaction or may help it complete by
copying the other transactions' write set into its own right set before acquiring ownership. A
hybrid SCSS operation, which is usually nonblocking, may be applied to building
software transactional memories (STMs) and / or
hybrid transactional memories (HyTMs), in some embodiments.