Date: Sun, 17 Dec 2000 17:03:16 -0600 From: "Jacques A. Vidrine" <n@nectar.com> To: Chris Costello <chris@calldei.com> Cc: hackers@FreeBSD.ORG Subject: Re: Why not another style thread? (was Re: cvs commit: src/lib/libc/gen getgrent.c) Message-ID: <20001217170316.A63227@hamlet.nectar.com> In-Reply-To: <20001217160442.H54486@holly.calldei.com>; from chris@calldei.com on Sun, Dec 17, 2000 at 04:04:42PM -0600 References: <200012172110.eBHLAfU46563@freefall.freebsd.org> <20001217151509.A63051@hamlet.nectar.com> <20001217151735.D54486@holly.calldei.com> <20001217153129.B63080@hamlet.nectar.com> <20001217153656.F54486@holly.calldei.com> <20001217155648.C63080@hamlet.nectar.com> <20001217160442.H54486@holly.calldei.com>
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On Sun, Dec 17, 2000 at 04:04:42PM -0600, Chris Costello wrote:
> On Sunday, December 17, 2000, Jacques A. Vidrine wrote:
> > I may have missed your point ... or maybe you are just agreeing with
> > what I wrote. For this particular implementation of free, you get the
> > following for `free(foo)' when foo == NULL:
> >
> > function call and stack overhead for free()
> > lock something if we are threaded
> > pointer assignment
> > increment
> > compare and branch
> > function call and stack overhead for ifree()
> > compare and branch
> > unwind ifree()
> > More stuff if HAVE_UTRACE
> > decrement
> > unlock something
> > unwind free()
>
> > FreeBSD's free() is not optimized for freeing NULL pointers. Not
> > that I think it should be -- as I said, that would be silly.
>
> The code I pasted _was_ FreeBSD's code,
Yes, I know.
> and it does optimize for freeing NULL pointers.
How so? Many instructions that are unnecessary are executed when you
call free with a NULL pointer (read what I wrote above). To optimize
for this case would be to check whether or not the pointer was NULL
before doing anything else.
This is kinda silly, who the hell started this thread? :-)
> You can still check for the pointer if you wish, before you call
> free().
Of course. And it seems a prudent thing to do if NULL pointers are
not uncommon in the code path.
I hate to give up a line for
if (data)
free(data);
but neither do I care for ``if (data) free(data);''. I guess if I
were writing several statements like that in a single file, I would
consider the macro route (e.g. xfree).
--
Jacques Vidrine / n@nectar.com / jvidrine@verio.net / nectar@FreeBSD.org
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