Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!samsung!uunet!auspex!guy
From: guy@auspex.auspex.com (Guy Harris)
Newsgroups: comp.unix.programmer
Subject: Re: shared libraries, when to use them
Keywords: shared libraries .so
Message-ID: <8486@auspex.auspex.com>
Date: 22 Jun 91 00:18:42 GMT
References: <1991Jun11.163544.20234@aio.jsc.nasa.gov> <1991Jun18.050150.17149@thunder.mcrcim.mcgill.edu> <8448@auspex.auspex.com>
Organization: Auspex Systems, Santa Clara
Lines: 32

> >You can't, because SunOS doesn't have shared libraries.  (What it does
> >have is shared object files.  What's the difference?  You can link in
> >part of a library without linking in the rest, among other things.)
>
>Just out of curiosity, who *has* implemented shared libraries?
>("Multics" is, unless I misremember, not the correct answer.)

I apologize for being too subtle.  A number of people have sent me other
incorrect answers; yes, I know, there are a number of OSes that have
what der Mouse would call "shared object files", but I don't know of any
that have what he'd call "shared libraries", the fact that others -
including the vendors of those systems! - might call them shared
libraries nonwithstanding.  Apparently, the fact that I indicated that,
as far as I know, Multics wasn't one of those systems was a bit too
subtle a clue....

So who has implemented what der Mouse would call "shared libraries" -
i.e., that let you "link in part of a library without linking in the
rest", and that let multiple clients of the library share it?

I assume, given that he said "SunOS doesn't have shared libraries", that
the fact that some system might do demand paging and let only those
pages of the shared object file containing code or data that's actually
been used (and not had the page frame containing it be snatched for
smething else) doesn't mean that system necessarily has shared
libraries, as SunOS definitely demand-pages shared libraries.

I.e., you have to be able to *link* in part of the library, not just be
able to *page* in only part of the library even though the entire
library (or its entire text) has been mapped into the address space of a
process using the library.  (No, I don't know what that would mean;
that's one of the reasons why I'm asking the question....)