Garbage Collection Is Useful

Is it possible that by knowing less about garbage collection in Java this person might have arrived at the same solution earlier? After all his initial construction of a tracing garbage collector was wasted effort.

Had similar epiphanies some many years ago (ugh, I'm old) when I was playing around writing a garbage collected persistent (in the 'stored on [spinny spinny] disk' sense not the FP sense of the word) programming language / runtime. This was back when it was roughly infeasible to be holding large "worlds" of objects purely in-memory on machines of the style of the time, so intelligently paging objects in and out was imperative. (Aside, I think with the recent doubling... tripling of RAM prices this area of thinking is now again more imperative)...

In any case, if one is doing GC in such a language, a full tracing collector (whether copying or mark & sweep) is madness, as to find live references means walking nearly the entire heap including the portions living in secondary storage, and now you're in a world of pain.

In this case, an intelligent cycle collecting garbage collector in the Bacon style was the answer. You keep in in-memory table of reference counts, and you only trace when you hit cycles. [and hopefully design your language semantics to discourage cycles]

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