Path: utzoo!attcan!uunet!munnari.oz.au!bruce!alanf
From: alanf@bruce.cs.monash.OZ.AU (Alan Grant Finlay)
Newsgroups: comp.lang.c
Subject: re-entrant libraries - is C deficient?
Message-ID: <3154@bruce.cs.monash.OZ.AU>
Date: 2 Oct 90 15:21:42 GMT
Organization: Monash Uni. Computer Science, Australia
Lines: 26

I am writing a library of C procedures which need access to a global 
data structure.  I wish to write them in a portable manner (i.e. even
outside UNIX) and to be re-entrant.

Currently I am doing this by having a compulsary first parameter to all
the procedures which is a pointer to the global data structure (apart from
one procedure which allocates this data structure and returns the pointer).
This is fine but the inefficiency annoys me.  A lot of these procedures call
each other so the pointer is popped off and onto the stack all the time.  I 
know popping it off doesn't cost anything but pushing on again does.  What 
I would like to do (and could do in assembly) is to push it on the stack
once (i.e. implicitly or explicitly dedicate a register to the task of 
locating this pointer).

I'm sure there are other languages that provide a solution to this problem.
For example in Pascal I can have nested procedures (I know this is not quite
a solution since the application must be compiled in the scope of the nested
procedures - but it is part way to a solution).

My question is: have I overlooked something or do I need to descend into
assembly language to solve this problem in C (assuming a C compiler has a 
"base" register, can do without a register or provides some means to know
where the stack base is)?  I know there are solutions for each particular
operating system but I want a techique that can be ported without having to
worry about such matters (i.e if all else fails I'll stick with the wasted
parameter).