Contention Management in Dynamic Software Transactional Memory∗

Obstruction-free concurrent algorithms differ from those with stronger nonblocking conditions in that they separate progress from correctness. While it must always maintain data invariants, an obstructionfree algorithm need only guarantee progress in the absence of contention. The programmer can (and indeed must) address progress as an out-of-band, orthogonal concern. In this work we consider the Java-based obstruction-free Dynamic Software Transaction Memory (DSTM) system of Herlihy et al. When two or more transactions attempt to access the same block of transactional memory concurrently, at least one transaction must be aborted. The decision of which transaction to abort, and under what conditions, is the contention management problem. We introduce several novel policies for contention management, and evaluate their performance on a variety of benchmarks, all running on a 16-processor SunFire 6800. We also evaluate the marginal utility of earlier, but somewhat more expensive detection of conflicts between readers and writers.