Monitors and exceptions: How to implement Java e#ciently

Ecient implementation of monitors and exceptions is crucial for the performance of Java. One implemen-tation of threads showed a factor of 30 dierence in run time on some benchmark programs. This arti-cle describes an ecient 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 ar-ticle also gives the implementation details of the new exception handling scheme in CACAO. The new ap-proach reduces the size of the generated native code by a half and allows null pointers to be checked by hard-ware. By using these techniques, the CACAO system has become the fastest JavaVM implementation for the Alpha processor.