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Date: Thu, 21 Feb 2019 15:59:59 +0800
From: Peter Xu <peterx@redhat.com>
Message-ID: <20190221075959.GB3091@xz-x1>
References: <20190220160628.6555-1-marcandre.lureau@redhat.com>
	<20190220160628.6555-2-marcandre.lureau@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/4] iothread: wait until the glib context
 is acquired
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To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>, Markus Armbruster <armbru@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>

On Wed, Feb 20, 2019 at 05:06:25PM +0100, Marc-Andr=C3=A9 Lureau wrote:
> Another thread may acquire the glib context (temporarily) before
> g_main_context_push_thread_default().
>=20
> This can happen with the following qemu_chr_fe_set_handlers()
> modifications.
>=20
> Unfortunately, g_main_context_wait() is deprecated in glib
> 2.58 (apparently it was a broken interface). Use a polling loop.
>=20
> Signed-off-by: Marc-Andr=C3=A9 Lureau <marcandre.lureau@redhat.com>
> ---
>  iothread.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>=20
> diff --git a/iothread.c b/iothread.c
> index e615b7ae52..93cc3aa875 100644
> --- a/iothread.c
> +++ b/iothread.c
> @@ -70,6 +70,11 @@ static void *iothread_run(void *opaque)
>          if (iothread->running && atomic_read(&iothread->worker_context=
)) {
>              GMainLoop *loop;
> =20
> +            /* we may race with another thread acquiring the context *=
/
> +            while (!g_main_context_acquire(iothread->worker_context)) =
{
> +                g_usleep(10000);
> +            }

Could you help explain why need this explicitly?  Since AFAIU
g_main_loop_run() below will do context acquire too so IIUC you're
taking it twice (while g_main_context_acquire should allow it to
happen, though)?

> +
>              g_main_context_push_thread_default(iothread->worker_contex=
t);
>              iothread->main_loop =3D
>                  g_main_loop_new(iothread->worker_context, TRUE);
> @@ -80,6 +85,8 @@ static void *iothread_run(void *opaque)
>              g_main_loop_unref(loop);
> =20
>              g_main_context_pop_thread_default(iothread->worker_context=
);
> +
> +            g_main_context_release(iothread->worker_context);
>          }
>      }
> =20
> --=20
> 2.21.0.rc1
>=20
>=20

Regards,

--=20
Peter Xu