Monitors and Exceptions: How to Implement Java Efficiently

EEcient implementation of monitors and exceptions is crucial for the performance of Java. One implementation of threads showed a factor of 30 diierence in run time on some benchmark programs. This article describes an eecient implementation of monitors for Java as used in the CACAO just-in-time compiler. With this implementation the thread overhead is less than 40% for typical application programs and can be completely eliminated for some applications. This article also gives the implementation details of the new exception handling scheme in CACAO. The new approach reduces the size of the generated native code by a half and allows null pointers to be checked by hardware. By using these techniques, the CACAO system has become the fastest JavaVM implementation for the Alpha processor.