Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!natinst!sequoia!rpp386!jfh
From: jfh@rpp386.cactus.org (John F Haugh II)
Newsgroups: comp.unix.internals
Subject: Re: Shared Lib Question (ISC)
Message-ID: <19261@rpp386.cactus.org>
Date: 12 May 91 18:14:47 GMT
References: <19252@rpp386.cactus.org> <kre.673798776@mundamutti.cs.mu.OZ.AU> <19255@rpp386.cactus.org> <1991May10.192648.3147@Think.COM>
Reply-To: jfh@rpp386.cactus.org (John F Haugh II)
Organization: Lone Star Cat Emporium and BBQ Grill
Lines: 35
X-Clever-Slogan: Help Prevent Robbery.  Tax the IRS.

In article <1991May10.192648.3147@Think.COM> barmar@think.com writes:
>In article <19255@rpp386.cactus.org> jfh@rpp386.cactus.org (John F Haugh II) writes:
>>  Name a single library function
>>which cannot be implemented well without global variables.
>
>Malloc() needs a global variable that points to the arena.
>
>Stdio uses the global variables stdin, stdout, and stderr.
>
>Errno is a global variable, and some library routines set it.

The key word was "well", not "at all".  malloc() can be
implemented as a function which is bound static and has
a single pointer to all the private data that it requires.
It then calls the real routine which takes a pointer to
the arena glarp and size of the desired object.

Likewise for the stdio library.  Functions which have
implied (FILE *) objects can be re-implemented as wrappers
for the versions which require the explicit argument.  The
FILE _iob[] 

Given that the functions were =designed= with the notion
of shared global data, I don't see any reason not to cheat
and leave certain parts =out= of the shared library.

I'll leave errno as an exercise for the reader.

[ Hint: How does the system get errno out of the kernel and
  into the user space, if it is a user space global variable? ]
-- 
John F. Haugh II        | Distribution to  | UUCP: ...!cs.utexas.edu!rpp386!jfh
Ma Bell: (512) 255-8251 | GEnie PROHIBITED :-) |  Domain: jfh@rpp386.cactus.org
"If liberals interpreted the 2nd Amendment the same way they interpret the
 rest of the Constitution, gun ownership would be mandatory."