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Date: Tue, 02 Jul 2013 13:44:29 +0200
From: Jan Kiszka <jan.kiszka@siemens.com>
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Subject: Re: [Qemu-devel] [PATCH] qom: Use atomics for object refcounting
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Liu Ping Fan <pingfank@linux.vnet.ibm.com>, =?ISO-8859-1?Q?Andreas_F=E4rber?= <afaerber@suse.de>, qemu-devel <qemu-devel@nongnu.org>

On 2013-07-02 13:28, Paolo Bonzini wrote:
> Il 02/07/2013 13:15, Andreas F=E4rber ha scritto:
>>>> @@ -683,16 +683,15 @@ GSList *object_class_get_list(const char *impl=
ements_type,
>>>> =20
>>>>  void object_ref(Object *obj)
>>>>  {
>>>> -    obj->ref++;
>>>> +     __sync_fetch_and_add(&obj->ref, 1);
>> How widespread are these in GCC/clang? Is there any fallback? I rememb=
er
>> seeing some __sync_* warnings on Mac OS X around 4.2...
>=20
> We are using them already in several places (vhost was the first one to
> introduce them, I think, but now they are also in migration ad in some
> tests too).  There is no fallback (asm could be a fallback, but we chos=
e
> to require GCC 4.2 or newer).
>=20
> I'll change this to atomic_inc/dec when applying.  Otherwise

But then atomic_dec_and_test or so. Letting the inc/dec return some
value leaves room for interpretations (value of before or after the
modification?).

Jan

--=20
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