Nonintrusive Cloning Garbage Collection with Stock Operating System Support

Abstract

It is well accepted that automatic garbage collection simplifies programming, promotes modularity, and reduces development effort. However it is commonly believed that these advantages do not counteract the perceived price: excessive overheads, possible long pause times while garbage collections occur, and the need to modify existing code. Even though there are publically available garbage collector implementations that can be used in existing programs, they do not guarantee short pauses, and some modification 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 guarantees short pauses, and can be easily implemented on stock UNIX-like operating systems. Our results show that our collector performs comparable to other garbage collection implementations on uniprocessor machines and outperforms similar collectors on multiprocessor machines. We also show our collector to be competitive in performance with explicit deallocation. Our collector has the added advantage of being non-intrusive. Using a dynamic linking technique and effective root set inferencing, we have been able to successfully run our collector even in commercial programs where only the binary executable and no source code is available. In this paper we describe our algorithm, its implementation, and provide both an algorithmic and a performance comparison between our collector and other similar garbage collectors. ©1997 by John Wiley & Sons, Ltd.