Safe open-nested transactions through ownership (Technical report

Researchers in transactional memory (TM) have proposed open nesting as a methodology for increasing the concurrency of trans-actional programs. The idea is to ignore “low-level ” memory oper-ations of an open-nested transaction when detecting conflicts for its parent transaction, and instead perform abstract concurrency con-trol for the “high-level ” operation that the nested transaction rep-resents. To support this methodology, TM systems use an open-nested commit mechanism that commits all changes performed by an open-nested transaction directly to memory, thereby avoiding low-level conflicts. Unfortunately, because the TM runtime is un-aware of the different levels of memory, unconstrained use of open-nested commits can lead to anomalous program behavior. We describe the framework of ownership-aware transactional memory which incorporates the notion of modules into the T