Subject: Re: Why garbage collection? From: Erik Naggum <erik@naggum.no> Date: 1996/01/14 Newsgroups: comp.lang.lisp Message-ID: <19960114T050927Z@arcana.naggum.no> [Richard Villanueva] | I understand the classical Lisp method of automatic garbage collection, | and it is very elegant. It reserves only one bit per cons cell (the | mark bit). However, on large systems, the long pause for garbage | collection is bad, so people look for more sophisticated methods. there is no "long pause" in modern systems. numerous brilliant minds have worked on garbage collection for many years. that is nearly a guarantee that you will need to have in-depth knowledge of the prior art in garbage collection techniques to be able to provide useful suggestions. | My question is, why not plain old reference counts? One day a student came to Moon and said, "I understand how to make a better garbage collector. We must keep a reference count of the pointers to each cons." Moon patiently told the student the following story- "One day a student came to Moon and said, "I understand how to make a better garbage collector... (from the AI koans collection, found, among other places, at http://www.cs.rochester.edu/u/miller/ai-koans.html.) | So am I missing something? Or are there other methods that are even | better? I have misplaced the address of the mother of all sites on garbage collection, but there is one that has an excellent survey, and there are many papers available. the literature was sufficiently, um, extensive, that I figured that I had work to do and news to read before I would embark on this long journey. if my plan to become immortal succeeds, I'll certainly study garbage collection. in the meantime, I know only that anything I could come up with on my own is bound to be discarded as too inefficient already, unless I luck out and strike 18 aces in a row. one of the most well-known inefficient and wasteful techniques is reference counting. most C++ programmers invent their own particularly ugly breed of inefficient reference counting. this is why C++ is so popular -- the probability that each and every C++ programmer will actually be able to improve something in that language and feel great about it is exactly 1. btw, your "one byte" stuff won't work. modern computers are no longer byte adressable, but instead waste two or three bits of the precious machine word and address range because some inferior languages think that byte addressability is a win. the smallest efficiently addressable unit on RISC processors is usually 4 bytes, sometimes 8 bytes. even on CISCs, you may pay a hefty penalty for misaligning your data. #<Erik 3030584967> -- the problem with this "information superhighway" is mainly that if you ask people to go play in it, they don't even understand when they get run over.