Removing unnecessary synchronization in Java

Java programs perform many synchronization operations on data structures. S ome of these synchronizations are unnecessary; in particular, if an object is reachable only by a single thread, concurrent access is impossible and n o synchronization is needed. We describe an interprocedural, flow- and cont ext-insensitive data-flow analysis that finds such situations. A global opt imizing transformation then eliminates synchronizations on these objects. F or every program in our suite of ten Java benchmarks consisting of SPECjvm9 8 and others, our system optimizes over 90% of the alias sets containing at least one synchronized object. As a result, the dynamic frequency of synch ronizations is reduced by up to 99%. For two benchmarks that perform synchr onizations very frequently, this optimization leads to speedups of 36% and 20%.