Removing unnecessary synchronization in Java

  • Authors:
  • Jeff Bogda;Urs Hölzle

  • Affiliations:
  • Department of Computer Science, University of California, Santa Barbara, CA;Department of Computer Science, University of California, Santa Barbara, CA

  • Venue:
  • Proceedings of the 14th ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications
  • Year:
  • 1999

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Abstract

Java programs perform many synchronization operations on data structures. Some of these synchronization are unnecessary; in particular, if an object is reachable only by a single thread, concurrent access is impossible and no synchronization is needed. We describe an interprocedural, flow- and context-insensitive dataflow analysis that finds such situations. A global optimizing transformation then eliminates synchronizations on these objects. For every program in our suite of ten Java benchmarks consisting of SPECjvm98 and others, our system optimizes over 90% of the alias sets containing at least one synchronized object. As a result, the dynamic frequency of synchronizations is reduced by up to 99%. For two benchmarks that perform synchronizations very frequently, this optimization leads to speedups of 36% and 20%.