A monitor-based synchronization approach for Java packed objects.

Packed object support is an experimental enhancement for Java in the IBM J9 Virtual Machine. In this paper we present a synchronization approach for the packed object data model, which is monitor-based, but in a lockword-free manner. This approach seeks to address the distinctive synchronization issues and situations which are faced by the packed object data model and have never been addressed by traditional Java built-in synchronization mechanisms before. According to the experimental results, our approach performs much better than the Java built-in synchronization for coarse-grained locking. The time overhead is reduced by 18% for the PackedSync approach. For fine-grained locking, although the performance of our approach is overtaken by the Java built-in synchronization as array sizes and the number of threads increase, PackedSync performs reasonably similar while array sizes and thread numbers are small.