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Date: Fri, 22 Feb 2019 14:36:58 +0800
From: Peter Xu <peterx@redhat.com>
Message-ID: <20190222063658.GF8904@xz-x1>
References: <20190222031413.20250-1-peterx@redhat.com>
	<20190222031413.20250-2-peterx@redhat.com>
	<CAMxuvayiNpRqudM9Ex_3MDYuTvcs3ya-tHmoAhWvCEu70WzUOA@mail.gmail.com>
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Subject: Re: [Qemu-devel] [PATCH 1/4] iothread: replace init_done_cond with
 a semaphore
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To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau <marcandre.lureau@redhat.com>
Cc: qemu-devel <qemu-devel@nongnu.org>, Paolo Bonzini <pbonzini@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Eric Blake <eblake@redhat.com>

On Fri, Feb 22, 2019 at 07:25:16AM +0100, Marc-Andr=C3=A9 Lureau wrote:
> Hi
>=20
> On Fri, Feb 22, 2019 at 4:14 AM Peter Xu <peterx@redhat.com> wrote:
> >
> > Only sending an init-done message using lock+cond seems an overkill t=
o
> > me.  Replacing it with a simpler semaphore.
> >
> > Meanwhile, init the semaphore unconditionally, then we can destroy it
> > unconditionally too in finalize which seems cleaner.
> >
> > Signed-off-by: Peter Xu <peterx@redhat.com>
>=20
> The lock is also protecting thread_id.

IMHO it's fine because thread_id is only changed at the beginning of
iothread_run where the caller will definitely wait for the thread_id
to be generated.  Here qemu_sem_post() should at least contain one
write memory barrier there to make sure the waker will read the
correct value after sem_wait() and then later on thread_id is never
changed.

Regards,

--=20
Peter Xu