From owner-freebsd-hackers  Sun Dec 17 13:56:56 2000
From owner-freebsd-hackers@FreeBSD.ORG  Sun Dec 17 13:56:52 2000
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from gw.nectar.com (gw.nectar.com [208.42.49.153])
	by hub.freebsd.org (Postfix) with ESMTP id 76DDE37B400
	for <hackers@FreeBSD.ORG>; Sun, 17 Dec 2000 13:56:52 -0800 (PST)
Received: from hamlet.nectar.com (hamlet.nectar.com [10.0.1.102])
	by gw.nectar.com (Postfix) with ESMTP
	id 64A49193E1; Sun, 17 Dec 2000 15:56:48 -0600 (CST)
Received: (from nectar@localhost)
	by hamlet.nectar.com (8.11.1/8.9.3) id eBHLumm63172;
	Sun, 17 Dec 2000 15:56:48 -0600 (CST)
	(envelope-from nectar@spawn.nectar.com)
Date: Sun, 17 Dec 2000 15:56:48 -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: <20001217155648.C63080@hamlet.nectar.com>
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>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.2.5i
In-Reply-To: <20001217153656.F54486@holly.calldei.com>; from chris@calldei.com on Sun, Dec 17, 2000 at 03:36:56PM -0600
X-Url: http://www.nectar.com/
Sender: nectar@nectar.com
Sender: owner-freebsd-hackers@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.ORG

On Sun, Dec 17, 2000 at 03:36:56PM -0600, Chris Costello wrote:
> On Sunday, December 17, 2000, Jacques A. Vidrine wrote:
> > It would be silly to optimize for freeing NULL pointers.
> 
>    You mean as seen in:
[snip ifree(), which checks for a NULL pointer, first thing]
>    called by free():
> 
>      void
>      free(void *ptr)
>      {
>          THREAD_LOCK();
>          malloc_func = " in free():";
>          if (malloc_active++) {
>              wrtwarning("recursive call.\n");
>              malloc_active--;
>              return;
>          } else {
>              ifree(ptr);
>          .
>          .
>          .
> 
>    That's how it's worked since before FreeBSD came into being.
> It wasn't implemented the same, but it behaved the same.

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()

Compare to `if (foo) free(foo);'

   compare and branch


i.e. FreeBSD's free() is not optimized for freeing NULL pointers.  Not
that I think it should be -- as I said, that would be silly.

-- 
Jacques Vidrine / n@nectar.com / jvidrine@verio.net / nectar@FreeBSD.org


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message