A Profiling Tool For Exploiting Use Of Packed Objects In Java Programs

Packed objects are an experimental feature in the IBM J9 Virtual Machine. Packed objects can be used to gain greater control over the layout of objects in memory and greater flexibility of memory structures that are not in Java code, to reduce the amount of memory required to store objects, and to increase the efficiency of caching. If the application is accessing a significant amount of native data using JNI method calls, then the use of packed objects will eliminate marshalling/unmarshalling of native data into Java objects and thus eliminate redundant data copying. The purpose of developing this profiling tool is to assist software developers in determining how much memory can be saved if they switch to packed objects from standard Java objects. The correctness and usefulness of the profiling tool is evaluated by running several test programs. Based on the results, the programs were modified to use packed objects instead of standard Java objects and the reduction in memory consumption was measured.