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.