From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:41859)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1Uu1vb-0008Qj-6e
	for qemu-devel@nongnu.org; Tue, 02 Jul 2013 10:51:40 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1Uu1rc-0002qw-Tz
	for qemu-devel@nongnu.org; Tue, 02 Jul 2013 10:47:32 -0400
Received: from mail-ye0-f175.google.com ([209.85.213.175]:37800)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1Uu1rc-0002qN-NN
	for qemu-devel@nongnu.org; Tue, 02 Jul 2013 10:47:28 -0400
Received: by mail-ye0-f175.google.com with SMTP id q8so1548294yen.20
	for <qemu-devel@nongnu.org>; Tue, 02 Jul 2013 07:47:28 -0700 (PDT)
From: Anthony Liguori <anthony@codemonkey.ws>
In-Reply-To: <51D29F27.9040706@siemens.com>
References: <51D29F27.9040706@siemens.com>
Date: Tue, 02 Jul 2013 09:47:21 -0500
Message-ID: <87bo6lqarq.fsf@codemonkey.ws>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Subject: Re: [Qemu-devel] [PATCH] qom: Use atomics for object refcounting
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Jan Kiszka <jan.kiszka@siemens.com>, Paolo Bonzini <pbonzini@redhat.com>
Cc: Liu Ping Fan <pingfank@linux.vnet.ibm.com>, qemu-devel <qemu-devel@nongnu.org>

Jan Kiszka <jan.kiszka@siemens.com> writes:

> Objects can soon be referenced/dereference outside the BQL. So we need
> to use atomics in object_ref/unref.
>
> Based on patch by Liu Ping Fan.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>  qom/object.c |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/qom/object.c b/qom/object.c
> index 803b94b..a76a30b 100644
> --- a/qom/object.c
> +++ b/qom/object.c
> @@ -683,16 +683,15 @@ GSList *object_class_get_list(const char *implements_type,
>  
>  void object_ref(Object *obj)
>  {
> -    obj->ref++;
> +     __sync_fetch_and_add(&obj->ref, 1);
>  }
>  
>  void object_unref(Object *obj)
>  {
>      g_assert(obj->ref > 0);
> -    obj->ref--;
>  
>      /* parent always holds a reference to its children */
> -    if (obj->ref == 0) {
> +    if (__sync_sub_and_fetch(&obj->ref, 1) == 0) {
>          object_finalize(obj);
>      }
>  }

Should we introduce something akin to kref now that referencing counting
has gotten fancy?

Regards,

Anthony Liguori

> -- 
> 1.7.3.4