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From: cedman@lynx.ps.uci.edu (Carl Edman)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Does Everybody leave dos.library open?
Message-ID: <CEDMAN.90Oct14141233@lynx.ps.uci.edu>
Date: 14 Oct 90 21:12:29 GMT
References: <14721@netcom.UUCP> <CEDMAN.90Oct13225759@lynx.ps.uci.edu>
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In-reply-to: mcmahan@netcom.UUCP's message of 14 Oct 90 19:38:38 GMT

In article <14766@netcom.UUCP> mcmahan@netcom.UUCP (Dave Mc Mahan) writes:
    In a previous article, cedman@lynx.ps.uci.edu (Carl Edman) writes:
   >In article <14721@netcom.UUCP> mcmahan@netcom.UUCP (Dave Mc Mahan) writes:
   >   I was just cruising through some software today, and noticed that many,many,
   >   programs leave the dos.library open after exiting.  In fact, it seems to be
   >   a majority in the (limited) sample of stuff I tested, mostly PD.
   >
   >Yes, I have noticed that many programms do this. It is not very nice and
   >very clean, but in the case of "dos.library" it doesn't really matter.
   >There is only one copy of "dos.library" around anyway and that copy
   >is not in RAM but in WOM (yes, for you people out there who use these
   >new-fangled (:-) 500s and 2000s that is ROM). Even if you could
   >expunge it , it wouldn't be very likely that you would ever with a
   >running system get in the situation where no task anylonger needs
   >the dos.library. So never mind about that. It is only a matter of
   >tidyness (or neuroticism if you prefer).

   I realize that it is generally no big deal, since one would never want to
   expunge the dos.library, but it seems to indicate a possible problem.  For
   those that want to leave the amiga on for weeks or months at a time and
   run lots of programs (we are talking about thousands if not billions of
   program executions) that leave dos.library open, wouldn't the variable
   eventually overflow and possibly cause problems.  I'm messy in the rest
   of my life, but I try to make my programs thoughtful and tidy.  Leaving
   a library open is not tidy.  Who knows, it might cause bad effects in
   AmigaDos 5.3 or higher.   It's just a good idea.

I just checked the source to exec.library. Two points: a) The open_cnt
really only is a UWORD i.e. its maximal value is 65535, a value which
could possibly be reached in month long execution. b) OpenLibrary()
doesn't itself do anything about open_cnt but expects the library
open routine to take care of that. So it is possible that a badly
written library, in conjunction with badly written program, in conjunction
with veyr long running could lead to problems like this:

	1. Programm BadProgram gets loaded and opens BadLibrary , but
	as it is a BadProgram it doesn't close it again. open_cnt
	stays 1 to large.

	2. GoodUser leaves the computer running for months during which
	time BadProgramm gets loaded 65536 times.

	3. As BadLibrary doesn't check for overflow it increases the
	open_cnt to 0 from 65535 when it is called by BadProgram again.

	4. While BadProgramm still runs there is a memory crunch.
	All libraries are checked for expunging and BadLibrary has
	an open_cnt of 0 and is expunged

	5. BadProgram accesses BadLibrary which is gone and ** CRASH ** !

All of this could be prevented if Exec OpenLibrary() took care of
of open_cnt and other such details and checked for overflow. Why
doesn't it ?

Last irrelevant question: Does dos.library check for overflow ? (Not
that it matters. It can't be expunged).

	Carl Edman


Theorectial Physicist,N.:A physicist whose   | Send mail
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