From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:33590)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <lersek@redhat.com>) id 1UsW8E-0004Wq-K0
	for qemu-devel@nongnu.org; Fri, 28 Jun 2013 06:42:25 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <lersek@redhat.com>) id 1UsW8C-0006Zh-47
	for qemu-devel@nongnu.org; Fri, 28 Jun 2013 06:42:22 -0400
Received: from mx1.redhat.com ([209.132.183.28]:17147)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <lersek@redhat.com>) id 1UsW8B-0006Zd-Sh
	for qemu-devel@nongnu.org; Fri, 28 Jun 2013 06:42:20 -0400
Message-ID: <51CD6914.5060601@redhat.com>
Date: Fri, 28 Jun 2013 12:44:36 +0200
From: Laszlo Ersek <lersek@redhat.com>
MIME-Version: 1.0
References: <CDF1DFE4.30A0%Tomoki.Sekiyama@hds.com>
In-Reply-To: <CDF1DFE4.30A0%Tomoki.Sekiyama@hds.com>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH v4 06/10] qemu-ga: Add Windows VSS provider
 to quiesce applications on fsfreeze
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: Tomoki Sekiyama <tomoki.sekiyama@hds.com>
Cc: "libaiqing@huawei.com" <libaiqing@huawei.com>, "mdroth@linux.vnet.ibm.com" <mdroth@linux.vnet.ibm.com>, "stefanha@gmail.com" <stefanha@gmail.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "lcapitulino@redhat.com" <lcapitulino@redhat.com>, "vrozenfe@redhat.com" <vrozenfe@redhat.com>, "pbonzini@redhat.com" <pbonzini@redhat.com>, Seiji Aguchi <seiji.aguchi@hds.com>, "areis@redhat.com" <areis@redhat.com>

>>>>> +STDAPI DllCanUnloadNow()
>>>>> +{
>>>>> +    return g_nComObjsInUse == 0 ? S_OK : S_FALSE;
>>>>> +}
>>
>> Don't you need some kind of atomic or locked read here? We could read a
>> stale value here. Granted, most stale values would err on the safe side
>> (ie. read >0 instead of ==0), but in theory the other mistake is
>> possible, no?
> 
> MSDN says "Simple reads and writes to properly-aligned 32bit variables
> are atomic", and I couldn't find a function to atomic read provided.
> (Maybe InterlockedCompareExchange(&g_nComObjsInUse, 0, 0)...?)

Alright then. Thanks!
Laszlo