Design of a New OFTM Algorithm towards Abort-Free Execution

Abstract

The Software Transactional Memory (STM) is a promising alternative to lock based concurrency control. Three well studied progress conditions for implementing STM are, wait-freedom, lock-freedom and obstruction-freedom. The wait-freedom is the strongest progress property. It rules out the occurrence of deadlock and starvation but impose too much implementation overhead. The obstruction freedom property is weaker than wait-freedom and lock-freedom. Obstruction Free Transactional Memory (OFTM) is simpler to implement, rules out the occurrence of deadlock and has faster performance in absence of contention. A transaction T _k that opens an object, say X, for updating may be in the active state even after completion of update operation on X. Hence, object X cannot be accessed by any other transaction as the current transaction T _k is still active. At this point, if another transaction T _m wants to acquire object X at this point (for read/write), either T _k needs to be aborted or T _m must wait till T _k finishes. Both of these approaches are detrimental for the performance of the system. Besides, OFTM does not allow T _m to wait for the completion of T _k. In this paper, a new OFTM implementation methodology has been proposed to allow the second transaction T _m to proceed immediately without affecting the execution of the first transaction T _k. The proposed approach yields higher throughput as compared to existing OFTM approaches that calls for aborting transactions.