An Intentional Library Approach to Lock-Aware Transactional Memory ; CU-CS-1048-08

Transactional memory (TM) has garnered significant interest as an alternative to existing concurrency methods due to its simplified programming model, natural composition characteristics and native support of optimistic concurrency. Yet, mutual exclusion locks are ubiquitous in existing parallel software due to their fast execution, inherent property for irreversible operations and long-standing underlying support in modern instruction set architectures (ISAs). For transactions to become practical, lock-based and TM-based concurrency methods must be unified into a single model. This work presents the first lock-aware transactional memory (LATM) solution with a deliberate library-based approach. Our LATM system supports locks inside of transactions (LiT) and locks outside of transactions (LoT) while preserving the original programmer-intended locking structure. Our solution provides three policies with varying degrees of performance and required programming. The most basic LATM policy enables transactionlock correctness without any programming overhead, while improved performance can be achieved by programmer-specified conflicts between locks and transactions. The differences in LATM policy performance are presented through a number of experimental benchmarks.