Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.lang.c
Subject: Re: exit(main(argc,argv,env));
Message-ID: <494@cresswell.quintus.UUCP>
Date: 24 Dec 87 00:05:59 GMT
References: <1286@laidbak.UUCP> <174@goofy.megatest.UUCP>
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 51
Summary: Sun-3s do have on_exit

In article <174@goofy.megatest.UUCP>, djones@megatest.UUCP (Dave Jones) writes:
> Hum.  "onexit"... Just what's needed.  (See my previous note, where I 
> rambled on about "Lexit()".
> 
> But on my Sun-3, I find no manual-page for onexit, and 
> 
> nm /lib/libc.a | grep onexit
> 
> returns silently.  So it looks as though not ALL unixes have onexit().

	% man exit
	<oh dear, it's raving on about Csh commands>
	% man 2 exit
	<tells me about _exit(), with a cross-reference to exit(3)>
	% man 3 exit
	<tells me about exit(), with a cross-reference to on_exit(3)>
	% man 3 on_exit
	SYNOPSIS
	     int on_exit(procp, arg)
	     void (*procp)();
	     caddr_t arg;
	NOTES
	     This call is specific to Sun Unix and should not be used  if
	     portability is a concern.

Basically, there is a stack of up to 20 termination functions,
and on_exit() pushes the pair procp,arg on the stack.  On exit,
these pairs are popped and procp(arg) called in reverse order.

The problem with this feature (and with the version in dpANS) is that it
is too global.  What I would like to be able to do is

	{
	    FILE *f;
	    EXIT_HANDLER *e;

	    FCHECK(f = fopen(...));
	    e = push_exit_handler(fclose, f);
	    ....
	    pop_run_one_handler(e);
	    ...
	}

so that I can put cleanup actions onto a stack and REMOVE them when they
have been done, but if an exit() happens in between the actions will be
done.  Common Lisp's "unwind-protect" is the kind of thing we're after.

Some other C implementations have a similar thing called "atexit()" or
"at_exit()".  While onexit() or whatever doesn't quite do what I want,
I can at least register my own handler manager with it, so it's ok as a
primitive.