From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38768) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fLP3X-0000oM-1j for qemu-devel@nongnu.org; Wed, 23 May 2018 04:23:35 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fLP3T-0000vd-T1 for qemu-devel@nongnu.org; Wed, 23 May 2018 04:23:35 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:39691 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fLP3T-0000vV-Oj for qemu-devel@nongnu.org; Wed, 23 May 2018 04:23:31 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 32B0F40704B8 for ; Wed, 23 May 2018 08:23:31 +0000 (UTC) From: Markus Armbruster References: <20180412061108.10875-1-peterx@redhat.com> Date: Wed, 23 May 2018 10:23:22 +0200 In-Reply-To: <20180412061108.10875-1-peterx@redhat.com> (Peter Xu's message of "Thu, 12 Apr 2018 14:11:08 +0800") Message-ID: <87sh6iixvp.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [PATCH v3] monitor: let cur_mon be per-thread List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Xu Cc: qemu-devel@nongnu.org, "Dr . David Alan Gilbert" , Stefan Hajnoczi , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Paolo Bonzini Peter Xu writes: > In the future the monitor iothread may be accessing the cur_mon as > well (via monitor_qmp_dispatch_one()). Before we introduce a real > Out-Of-Band command, Uh, inhowfar are the commands marked allow-oob: true now not real? These are migrate-recover, migrate-pause, x-oob-test. Aside: having x-oob-test in QEMU proper is awful. Is there really no way around it? > let's convert the cur_mon variable to be a > per-thread variable to make sure there won't be a race between threads. > > Note that thread variables are not initialized to a valid value when new > thread is created. However for our case we don't need to set it up, > since the cur_mon variable is only used in such a pattern: > > old_mon = cur_mon; > cur_mon = xxx; > (do something, read cur_mon if necessary in the stack) > cur_mon = old_mon; > > It plays a role as stack variable, so no need to be initialized at all. > We only need to make sure the variable won't be changed unexpectedly by > other threads. Do we plan to keep switching cur_mon forever? Or do we intend to work towards a 1:1 association between Monitor struct and monitor thread? Even if we want the latter, I'm okay with this patch as an intermediate step. > Signed-off-by: Peter Xu