Re: [RFC] [PATCH] C exceptions in kernel

[Larry McVoy <lm@bitmover.com>]

On Sat, Feb 23, 2002 at 06:05:48PM +0200, Dan Aloni wrote:
> But, it CAN be used in *local* driver call branches. Writing a new
> driver? have a lot of local nested calls? Hate goto's? You can use
> exceptions.

Is this really anything other than syntactic sugar?  Maybe it's different 
in drivers, but I find myself doing the following in user space all the time

	#define	unless(x)	if (!(x))	/* perl/BCPL corrupted me */

	function(...)
	{
		char	*foo = 0, *bar = 0;
		int	locked = 0;
		int	rc = -1;

		if (bad args or something) {
	out:		if (foo) free(foo);
			if (bar) free(bar);
			if (locked) unlock();
			return (rc);
		}

		unless (locked = get_the_lock()) goto out;
		unless (foo = allocate_foo()) goto out;
		unless (bar = allocate_bar()) goto out;

		more code....

		rc = 0;
		goto out;
	}

It seems ugly at first but it has some nice attributes:

    a) all the cleanup is in one place, for both the error path and the 
       non-error path.  I could put it at the bottom, I like it at the
       top because that's where I tend to have the list of things needed
       to be cleaned.

    b) all the error cases are branches, the normal path is straightline.

    c) it's as dense as I can make it.

So how would you do the same thing with exceptions?
-- 
---
Larry McVoy            	 lm at bitmover.com           http://www.bitmover.com/lm