Nonintrusive Cloning Garbage Collection with Stock Operating System Support

It is well accepted that Garbage Collection simpliies programming, promotes modularity, and reduces development eeort. However it is commonly believed that these advantages do not counteract the price that has to be paid: excesive overheads, possible long pause times, and the need of modifying existing code. Even though there exist publically available garbage collectors that can be used in existing programs, they do not guarantee short pauses, and some modiication of the application using them is still required. In this paper we describe a snapshot-at-beginning concurrent garbage collector algorithm and its implementation. This algorithm is less intrusive than other garbage collecting algorithms, guarantees short pauses, and can be easily implemented in stock unix like operating systems. Our results show that our collector is faster than other implementations that use user-level dirty bits, and is very competitive with explicit deallocation. These advantages are especially true on multiprocessor machines where collector and mutator can run on diierent processors. Our collector has the added advantage of being nonitrusive. Using a dynamic linking technique, we have been able to run our garbage collector with success even in commercial programs where source code is not available. In this paper we describe the algorithm, the implementation, and provide a comparison with other incremental garbage collectors. 1