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From: gillies@p.cs.uiuc.edu
Newsgroups: comp.sys.mac.programmer
Subject: Re: what the heck is "reentrant"?
Message-ID: <104700046@p.cs.uiuc.edu>
Date: 3 Aug 88 23:44:00 GMT
References: <730049@hpcilzb.HP.COM>
Lines: 17
Nf-ID: #R:hpcilzb.HP.COM:730049:p.cs.uiuc.edu:104700046:000:808
Nf-From: p.cs.uiuc.edu!gillies    Aug  3 18:44:00 1988


Here are a few common ways to make something NON-reentrant:

(1) Have a subroutine generate and execute its own assembly-language
instructions.  Two separate threads of execution might try to write
different instructions to the same place.

(2) Old Fortran linkage.  One of the first proposed ways of
implementing a subroutines was to "deposit & jump", e.g. deposit the
return location in a global (right before the subroutine
instructions), and then jump to the beginning of the subroutine.  if
two different threads of execution call the same subroutine at the same
time, then one will probably return to the wrong location.

Don Gillies, Dept. of Computer Science, University of Illinois
1304 W. Springfield, Urbana, Ill 61801      
ARPA: gillies@cs.uiuc.edu   UUCP: {uunet,ihnp4,harvard}!uiucdcs!gillies