From: Eli Zaretskii <eliz@gnu.org>
To: Pip Cet <pipcet@gmail.com>
Cc: 36609@debbugs.gnu.org, politza@hochschule-trier.de
Subject: bug#36609: 27.0.50; Possible race-condition in threading implementation
Date: Fri, 12 Jul 2019 18:02:52 +0300 [thread overview]
Message-ID: <83blxz2t43.fsf@gnu.org> (raw)
In-Reply-To: <CAOqdjBdg4Gkz=Zw+EVwTDNaRjLU0nL8FjQB4nsnOkT7=n4AgHw@mail.gmail.com> (message from Pip Cet on Fri, 12 Jul 2019 14:34:44 +0000)
> From: Pip Cet <pipcet@gmail.com>
> Date: Fri, 12 Jul 2019 14:34:44 +0000
> Cc: politza@hochschule-trier.de, 36609@debbugs.gnu.org
>
> > > When a thread is signalled (by thread-signal, which sets another
> > > thread's error_symbol) while the signalled thread is inside a
> > > select(), thread_select() will return non-locally for that thread, and
> > > we fail to release an internal GLib lock through
> > > g_main_context_release(). That's the first bug.
> >
> > We should either release the global lock before the thread exits, or
> > defer the acting upon the signal until later. We cannot disable the
> > signal handling altogether because it is entirely legitimate to signal
> > another thread, and when we do, that other thread will _always_ be
> > inside thread_select.
>
> Really? What about thread-yield?
What about it?
You are asking whether, when thread-signal is executed, the thread
which we are signaling is necessarily parked inside thread_select? If
so, I don't understand your surprise: only one thread can ever be
running, and that is by definition the thread which calls
thread-signal. All the other threads cannot be running, which means
they are parked either in thread_select or in sys_mutex_lock called
from acquire_global_lock. Right?
As for thread-yield, I'm not sure I understand how is it related to
the issue we are discussing.
> > For the main thread, handling the signal in that situation shouldn't
> > be a problem, because it is not going to exit. Right?
>
> I think the main thread can still fail to release the lock...
Since the main thread doesn't exit, but just longjmp's to top-level,
and then continues to run, why does it need to release the lock? Any
thread should hold the lock for as long as it runs.
> > > When xg_select() fails to acquire the internal GLib lock, it simply
> > > does a select() on the remaining file descriptors:
> >
> > Why does it fail to acquire that lock?
>
> Because another thread holds it, either an Emacs or a non-Emacs
> thread.
OK, and why is it a problem that we continue calling thread_select
regardless of the failure to acquire the Glib lock? is the problem
this one:
> In both cases, I think we might miss events unless we return
> with errno == EINTR.
? Or is there something else? If the problem with missing events,
then which events are those, and what bad things will happen if we
miss them?
next prev parent reply other threads:[~2019-07-12 15:02 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-11 20:51 bug#36609: 27.0.50; Possible race-condition in threading implementation Andreas Politz
2019-07-12 7:47 ` Eli Zaretskii
2019-07-12 8:05 ` Eli Zaretskii
2019-07-12 9:02 ` Pip Cet
2019-07-12 12:42 ` Eli Zaretskii
2019-07-12 12:57 ` Pip Cet
2019-07-12 13:31 ` Eli Zaretskii
2019-07-12 13:51 ` Pip Cet
2019-07-12 15:05 ` Eli Zaretskii
2019-07-12 18:06 ` Pip Cet
2019-07-12 18:27 ` Eli Zaretskii
2019-07-12 18:34 ` Eli Zaretskii
2019-07-12 19:24 ` Pip Cet
2019-07-12 19:57 ` Eli Zaretskii
2019-07-13 14:37 ` Pip Cet
2019-07-13 15:03 ` Eli Zaretskii
2019-07-13 15:13 ` Eli Zaretskii
2019-07-13 15:54 ` Eli Zaretskii
2019-07-13 15:57 ` Pip Cet
2019-07-13 16:02 ` Eli Zaretskii
2019-07-13 18:17 ` Pip Cet
2020-08-21 12:57 ` Lars Ingebrigtsen
2019-07-13 15:04 ` Andreas Politz
2019-07-12 12:44 ` Pip Cet
2019-07-12 12:55 ` Eli Zaretskii
2019-07-12 13:40 ` Pip Cet
2019-07-12 13:51 ` Eli Zaretskii
2019-07-12 14:34 ` Pip Cet
2019-07-12 15:02 ` Eli Zaretskii [this message]
2019-07-12 19:30 ` Pip Cet
2019-07-13 6:50 ` Eli Zaretskii
2021-06-06 15:50 ` dick.r.chiang
[not found] ` <87fsxv8182.fsf@dick>
2021-06-06 16:35 ` Eli Zaretskii
2021-06-06 19:10 ` dick.r.chiang
2021-06-06 19:27 ` Eli Zaretskii
2021-06-09 21:40 ` dick.r.chiang
2021-06-10 6:46 ` Eli Zaretskii
2021-06-10 11:52 ` dick.r.chiang
2021-06-10 14:18 ` Eli Zaretskii
2021-06-10 14:55 ` dick.r.chiang
2021-06-10 15:04 ` Eli Zaretskii
2021-06-10 21:36 ` dick.r.chiang
2021-06-11 6:00 ` Eli Zaretskii
2021-06-19 17:53 ` Eli Zaretskii
2021-06-19 19:14 ` dick.r.chiang
2021-06-19 19:18 ` Eli Zaretskii
2021-06-19 21:12 ` dick.r.chiang
2021-06-20 11:39 ` Eli Zaretskii
2021-06-20 14:01 ` dick.r.chiang
2021-06-20 15:53 ` Eli Zaretskii
2021-06-25 13:54 ` Eli Zaretskii
2021-06-10 15:35 ` Andreas Schwab
2021-06-10 15:39 ` Eli Zaretskii
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