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Date: Wed, 10 Jun 2015 15:15:00 -0000
From: Eli Zaretskii <eliz@gnu.org>
Subject: Re: Inadvertently run inferior threads
In-reply-to: <55045AB9.2000408@redhat.com>
To: Pedro Alves <palves@redhat.com>
Cc: gdb@sourceware.org
Reply-to: Eli Zaretskii <eliz@gnu.org>
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References: <83h9tq3zu3.fsf@gnu.org> <55043A63.6020103@redhat.com> <8361a339xd.fsf@gnu.org> <5504555C.804@redhat.com> <550458E0.10206@redhat.com> <55045AB9.2000408@redhat.com>
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> Date: Sat, 14 Mar 2015 15:58:49 +0000
> From: Pedro Alves <palves@redhat.com>
> CC: gdb@sourceware.org
> 
> On 03/14/2015 03:50 PM, Pedro Alves wrote:
> 
> >> Calling a function that ends up starting new threads should
> >> work OK, but indeed that seems to be broken...
> >>
> >> On GNU/Linux, and a trivial program with:
> >>
> >> ~~~
> >> void
> >> start_thread (void)
> >> {
> >>   pthread_t thread;
> >>
> >>   pthread_create (&thread, NULL, thread_function, NULL);
> >> }
> >> ~~~
> >>
> >> results in:
> >>
> >> (gdb) p start_thread ()
> >> [New Thread 0x7ffff7fc1700 (LWP 9903)]
> >> $1 = void
> >> (gdb) info threads
> >>   Id   Target Id         Frame
> >>   2    Thread 0x7ffff7fc1700 (LWP 9903) "start-thread-in" (running)
> >> * 1    Thread 0x7ffff7fc2740 (LWP 9899) "start-thread-in" main () at start-thread-infcall.c:35
> >>
> > 
> > I see what's going on here:
> > 
> >  #1 - we suppress the *stopped -> *running transitions/notification when
> >    doing an inferior function call (the in_infcall checks in infrun.c).
> > 
> >  #2 - new threads are spawned and given *running state, because well,
> >    they're running.
> > 
> >  #3 - we suppress the running -> *stopped transition when doing
> >    an infcall, like in #1.  (The in_infcall check in normal_stop).
> > 
> >  #4 - result: _new_ threads end up in "running" state, even though they
> >     are stopped.
> > 
> > I don't know off hand what the best fix is.
> 
> This is now: https://sourceware.org/bugzilla/show_bug.cgi?id=18127

I think I'm starting to understand why this happens.  I will describe
my findings in the bug report.