Problems and Challenges when Building a Manager for Unused Objects

Large object-oriented applications may occupy hundreds of megabytes or even gigabytes of memory. During program execution, a large graph of objects is created and constantly changed. Most object runtimes support some kind of automatic memory management based on garbage collectors (GC) whose idea is the automatic destruction of unreferenced objects. However, there are referenced objects which are not used for a long period of time or that are used just once. These are not garbage-collected because they are still reachable and might be used in the future. Due to these unused objects, applications use much more resources than they actually need. In this paper we present the challenges and possible approaches towards an unused object manager for Pharo. The goal is to use less memory by swapping out the unused objects to secondary memory and only leaving in primary memory only those objects which are needed and used. When one of the unused objects is needed, it is brought back into primary memory.