Write barrier elision for concurrent garbage collectors

Abstract

Concurrent garbage collectors require write barriers to preserve consistency, but these barriers impose significant direct and indirect costs. While there has been a lot of work on optimizing write barriers, we present the first study of their elision in a concurrent collector. We show conditions under which write barriers are redundant, and describe how these conditions can be applied to both incremental update or snapshot-at-the-beginning barriers. We then evaluate the potential for write barrier elimination with a trace-based limit study, which shows that a significant percentage of write barriers are redundant. On average, 54% of incremental barriers and 83% of snapshot barriers are unnecessary. Copyright 2004 ACM.