On the Correctness of Mixing Lazy and Eager Version Management in Transactions

Transactional memory has been proposed as an optimistic concurrency-control construct to ease parallel programming. Hardware transactional memory (HTM) approaches implement version management and conflict detection in hardware to guarantee the correctness of transaction execution. Based on the style of version management and conflict detection, state-of-the-art HTM systems fall into two main types, namely lazy systems and eager systems. Neither system type is able to always perform better than the other over a wide range of applications due to the broad variations in the execution behaviors in typical parallel workloads. In this paper, we focus on the correctness of mixing lazy and eager version management in a log-based HTM. This hybrid type of version management is demonstrated to satisfy the requirement of atomicity and conflict serializability, which are critical for correctness. Furthermore, it is shown that the new approach does not violate the memory coherence formal model.