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Safe Open-Nested Transactions Through Ownership Kunal Agrawal I-Ting Angelina Lee Jim Sukha

Summary: Safe Open-Nested Transactions Through Ownership
Kunal Agrawal I-Ting Angelina Lee Jim Sukha
MIT Computer Science and Artificial Intelligence Laboratory
Cambridge, MA 02139, USA
Researchers in transactional memory (TM) have proposed open nesting as a methodology for increasing the
concurrency of a program. The idea is to ignore certain "low-level" memory operations of an open-nested
transaction when detecting conflicts for its parent transaction, and instead perform abstract concurrency
control for the "high-level" operation that nested transaction represents. 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 unaware of the different levels of memory, an unconstrained use of open-nested commits can lead to
anomalous program behavior.
In this paper, we describe a framework of ownership-aware transactional memory which incorporates the
notion of modules into the TM system and requires that transactions and data be associated with specific
transactional modules or Xmodules. We propose a new ownership-aware commit mechanism, a hybrid
between an open-nested and closed-nested commit which commits a piece of data differently depending
on whether the current Xmodule owns the data or not. Moreover, we give a set of precise constraints on
interactions and sharing of data among the Xmodules based on familiar notions of abstraction. We prove that
ownership-aware TM has has clean memory-level semantics and can guarantee serializability by modules,


Source: Agrawal, Kunal - Department of Computer Science and Engineering, Washington University in St. Louis


Collections: Computer Technologies and Information Sciences