Hardware Concurrent Garbage Collection for Short-Lived Objects in Mobile Java Devices

摘要

jHISC is an object-oriented processor for embedded system aiming at accelerating Java execution by hardware approach. Garbage collection is one of the critical tasks in a Java Virtual Machine. In this paper, we have conduct a study of dynamic object allocation and garbage collection behavior of Java program based on SPECjvm 98 benchmark suite and MIDP applications for mobile phones. Life, size, and reference count distribution of Java objects are measured. We found most Java objects die very young, small in size and have small number reference counts. Reference counting object cache with hardware write barrier and object allocator is proposed to provide the hardware concurrent garbage collection for small size objects in jHISC. Hardware support on write barrier greatly reduces the overhead to perform the reference count update. The reference counting collector reclaims the memory occupied by object immediately after the object become garbage. The hardware allocator provides a constant time object allocation. From the investigation, over half of Java objects can be garbage collected by the object cache that makes it unnecessary for these objects to copy to the main memory.