Hybrid Transactional Memory with Pessimistic Concurrency Control

Abstract

Transactional Memory (TM) intends to simplify the design and implementation of the shared-memory data structures used in parallel software. Many Software TM systems are based on writer-locks to protect the data being modified. Such implementations can suffer from the "privatization" problem, in which transactional and non-transactional accesses to the same location can lead to inconsistent results.123 376 Int J Parallel Prog (2011) 39:375-396 TM design is proposed to reduce the performance overheads caused by the use of these locks while combining three desirable features: (i) full TM functionality whether or not the architectural support is present; (ii) execution of a single common code path in software or hardware; and, (iii) immunity from the privatization problem. The analysis shows how a Hybrid TM can lose important properties, such as starvation freedom. To overcome this issue, Directory Reservations is presented, a low-cost mechanism improving existent solutions designed for Hardware TM.