Lightweight Monitor for Java VM

This paper introduces the lightweight monitor in Java VM that is fast on single-threaded programs as well as on multi-threaded programs with little lock contention. A 32-bit lock is embedded into each object for efficient access while the lock queue and the wait set is managed through a hash table. The lock manipulation code is highly optimized and inlined by our Java VM JIT compiler called LaTTe wherever the lock is accessed. In most cases, only 9 SPARC instructions are spent for lock acquisition and 5 instructions for lock release. Our experimental results indicate that the lightweight monitor is faster than the monitor in the latest SUN JDK 1.2 Release Candidate 1 by up to 21 times in the absence of lock contention and by up to 7 times in the presence of lock contention