Eliminating Unnecessary Synchronization

Monitors are appealing constructs for synchronization, because they promote reusable code and present a simple model to the programmer. For these reasons, several programming languages, such as Java and Modula-3, directly support them. However, monitors can incur significant run-time overhead: reusable code modules such as classes in the Java standard library often contain monitor-based synchronization for the most general case of concurrent access, even though particular programs them in a context that is already protected from concurrency. For instance, a synchronized data structure may be accessed by only one thread at run time, or access to a synchronized data structure may be protected by another monitor in the program. In both cases, unnecessary synchronization increases execution overhead. Even single-threaded Java programs typically spend 10-60% of their execution time on synchronization operations. Synchronization overhead can be reduced by manually restructuring programs but any performance improvement gained typically comes at the cost of simplicity, maintainability, reusability, and even program correctness.

The goal of our group is first to characterize the synchronization behavior of Java benchmarks, and then to develop compiler analyses for automatically detecting and eliminating sources of unnecessary synchronization operations. To date, we have developed a comprehensive suite of analyses for eliminating thread-local, enclosed and reentrant locks. These analyses eliminate 35-100% of all synchronization in typical single and multithreaded benchmarks without any programmer annotations. They are described in more detail in our papers.

->  Benchmarks
A comprehensive list of Java benchmarks that others in the research community have used, along with benchmarks that we decided to use for our project.
->  Paper Trail
Our papers and talks on synchronization elimination.
->  Related Work Links to work on eliminating synchronization operations.
->  Project Members Who we are.

Java Synchronization / email
Department of Computer Science and Engineering
© 1997, University of Washington