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From:     GSB@MIT-ML
Date: Fri, 16 Feb 80 00:08:18 GMT
Original-Date: 02/15/80 20:08:18 EDT
Subject: Re: wjl's "reader bug"
    If the garbage collector is called by a conser, and it runs
    the gc-daemon, and the gc-daemon uses EXACTLY the number of
    cells of that type that were freed, things lose big because
    when AGC returns the conser assumes that its freelist is non-0.
    In this example, AGC was called from ACONS, and when it returned
    FFS was 0, so the EXCH A,@FFS clobbers NIL, etc.
VERY good analysis, here!  I've just put in some code into GCBIB
(the midas source file for lisp with the GC in it) to run the
"panic" error if, after GC-DAEMONing, some space has a null freelist.
This will be testible in LISP 1941 (and > versions), which should
be XLISP today.