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Re: [Qemu-devel] [PATCH v7 4/4] monitor: add lock to protect mon_fdsets
From: |
Peter Xu |
Subject: |
Re: [Qemu-devel] [PATCH v7 4/4] monitor: add lock to protect mon_fdsets |
Date: |
Tue, 29 May 2018 13:51:41 +0800 |
User-agent: |
Mutt/1.9.5 (2018-04-13) |
On Mon, May 28, 2018 at 05:19:08PM +0200, Markus Armbruster wrote:
[...]
> >>
> >> > + * Meanwhile it can also be used even at the end of main. Let's keep
> >> > + * it initialized for the whole lifecycle of QEMU.
> >> > + */
> >>
> >> Awkward question, since our main() is such a tangled mess, but here goes
> >> anyway... The existing place to initialize monitor.c's globals is
> >> monitor_init_globals(). But that one runs too late, I guess:
> >> parse_add_fd() runs earlier, and calls monitor_fdset_add_fd(). Unclean
> >> even without this lock; no module should be used before its
> >> initialization function runs. Sure we can't run monitor_init_globals()
> >> sufficiently early?
> >
> > Please see the comment for monitor_init_globals():
> >
> > /*
> > * Note: qtest_enabled() (which is used in monitor_qapi_event_init())
> > * depends on configure_accelerator() above.
> > */
> > monitor_init_globals();
> >
> > So I guess it won't work to directly move it earlier. The init
> > dependency of QEMU is really complicated. I'll be fine now that we
> > mark totally independent init functions (like this one, which is a
> > mutex init only) as constructor, then we can save some time on
> > ordering issue.
>
> Let me rephrase. There's a preexisting issue: main() calls monitor.c
> functions before calling its initialization function
> monitor_init_globals(). This needs to be cleaned up. Would you be
> willing to do it?
>
> Possible solutions:
>
> * Perhaps we can move monitor_init_globals() up and/or the code calling
> into monitor.c early down sufficiently.
>
> * Calculate event_clock_type on each use instead of ahead of time. It's
> qtest_enabled ? QEMU_CLOCK_VIRTUAL : QEMU_CLOCK_REALTIME, and neither
> of its users needs to be fast. Then move monitor_init_globals before
> the code calling into monitor.c.
Indeed. Obviously you thought a step further. :)
>
> I'm not opposed to use of constructors for self-contained initialization
> (no calls to other modules). But I don't like initialization spread
> over multiple functions.
Since this work will actually decide where I should init this new
fdset lock, so I'll try to do that altogether within the series.
Thanks for your suggestions! It makes sense.
--
Peter Xu
- Re: [Qemu-devel] [PATCH v7 3/4] monitor: more comments on lock-free fleids/funcs, (continued)
[Qemu-devel] [PATCH v7 4/4] monitor: add lock to protect mon_fdsets, Peter Xu, 2018/05/24
Re: [Qemu-devel] [PATCH v7 4/4] monitor: add lock to protect mon_fdsets, Stefan Hajnoczi, 2018/05/24
Re: [Qemu-devel] [PATCH v7 0/4] monitor: let Monitor be thread safe, no-reply, 2018/05/24