Implementing an on-the-fly garbage collector for Java

Java uses garbage collection (GC) for the automatic reclamation of computer memory no longer required by a running application. GC implementations for Java Virtual Machines (JVM) are typically designed for single processor ma chines, and do not necessarily perform well for a server program with many threads running on a multiprocessor. We designed and implemented an on-the- fly CC, based on the algorithm of Doligez, Leroy and Gonthier [13, 12] (DLG ), for Java in this environment. An on-the-fly collector, a collector that does not stop the program threads, allows all processors to be utilized dur ing collection and provides uniform response times. We extended and adapted DLG for Java (e.g., adding support for weak references) and for modern mul tiprocessors without sequential consistency, and added performance improvem ents (e.g., to keep track of the objects remaining to be traced). We compar ed the performance of our implementation with stop-the-world mark-sweep GC, Our measurements show that the performance advantage for our collector inc reases as the number of threads increase and that it provides uniformly low response times.