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Summary: Memory Models for Open-Nested Transactions
Kunal Agrawal Charles E. Leiserson Jim Sukha
MIT Computer Science and Artificial Intelligence Laboratory
Cambridge, MA 02139, USA
ABSTRACT
Open nesting provides a loophole in the strict model of atomic
transactions. Moss and Hosking suggested adapting open nesting
for transactional memory, and Moss and a group at Stanford have
proposed hardware schemes to support open nesting. Since these
researchers have described their schemes using only operational
definitions, however, the semantics of these systems have not been
specified in an implementation-independent way. This paper offers
a framework for defining and exploring the memory semantics of
open nesting in a transactional-memory setting.
Our framework allows us to define the traditional model of
serializability and two new transactional-memory models, race
freedom and prefix race freedom. The weakest of these memory
models, prefix race freedom, closely resembles the Stanford open-
nesting model. We prove that these three memory models are equiv-
alent for transactional-memory systems that support only closed
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