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...

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...