A stop-and-copy garbage collector updates one-bit reference counting with essentially no extra space and minimal memory cycles beyond the conventional collection algorithm. Any object that is uniquely referenced during a collection becomes a candidate for cheap recovery before the next one, or faster recopying then if it remains uniquely referenced. Since most objects stay uniquely referenced, subsequent collections run faster even if none are recycled between garbage collections. This algorithm extends to generation scavenging, it admits uncounted references from roots, and it corrects conservatively stuck counters, that result from earlier uncertainty whether references were unique. CR categories and Subject Descriptors: D.4.2 [Storage Management]: Allocation/Deallocation strategies; E.2 [Data Storage Representations]: Linked representations. General Term: Algorithms. Additional Key Words and Phrases: multiple reference bit, MRB. Research reported herein was sponsored, in part...

this paper.

Stoye's one-bit reference tagging scheme can be extended to local counts of two or more via two strategies. The first, suited to pure register transactions, is a cache of referents to two shared references. The analog of Deutsch's and Bobrow's multiple-reference table, this cache is sufficient to manage small counts across successive assignment statements. Thus, accurate reference counts above one can be tracked for short intervals, like those bridging one function 's environment to its successor's. The second, motivated by runtime stacks that duplicate references, avoids counting any references from the stack. It requires a local pointer-inversion protocol in the mutator, but one still local to the referent and the stack frame. Thus, an accurate reference count of one can be maintained regardless of references from the recursion stack. CCS categories and Subject Descriptors: D.4.2 [Storage Management]: Allocation/Deallocation strategies; E.2 [Data Storage Representations]: Linked re...

The Japanese Fifth Generation Computer Systems (FGCS) extending from 1982--1992 has been enshrouded in hype since its inception. The national project made bold promises in the fields of artifical intelligence and computer engineering, and these goals were amplified by the media and overseas researchers. Now that the dust is settling, it is time to take a good long look at the project, its accomplishments, and failures. This essay is a personal account of my experiences working within, and around, the FGCS project at the Institute for New Generation Computer Technology (ICOT) and elsewhere. I focus on the development of hard and soft technologies, as well as human infrastructure. This article will appear in the Communications of the ACM, March 1993. "It is not very often that Westerners get to see the Japanese just as they are. The difficulty we have when we look at Japan --- the layers-of-the-onion problem --- can be so frustrating that we tend to raise our own screen of assumptions an...

This paper describes an efficient mechanism of inter-processor message transfer on loosely-coupled/message-base parallel processing systems. This mechanism eliminates transit processors, which merely relay messages transferred between other processors, using one-way communication with three additional physical messages. 1 Introduction For large scale parallel processing, it is desirable that programming languages have capability to represent parallelism in problems naturally. In various programming languages proposed for parallel processing, parallel logic programming languages, such as GHC [Ueda 85], and parallel object-oriented programming languages, such as ABCL[Yonezawa 86], will be hopeful candidates because concurrent processes communicating messages each other are easily and naturally described in them. It is also natural to map these processes onto loosely-coupled/ message-base parallel processing systems [Nakajima 89, Takada 89]. From the viewpoint of efficiency, however, t...