Re: [PATCH][PR guile/17247] Block SIGCHLD while initializing Guile

[Eli Zaretskii <eliz@gnu.org>]

> From: Doug Evans <xdje42@gmail.com>
> Cc: ludo@gnu.org,  guile-devel@gnu.org,  gdb-patches@sourceware.org
> Date: Fri, 05 Sep 2014 01:26:28 -0700
> 
> we can't physically prevent [users] from starting threads.

Of course we can: if Guile gives us a way to disable threads, any user
extension that attempts to start a thread will simply fail.

> We pretty much leave them that way already given the myriad
> of things they can do to mess up gdb without threads.

?? The rest of GDB is compiled C code which users cannot change
without recompiling.  And it's a single-threaded code.  And it's under
our close scrutiny.  So I see no problems here.

> The python side of things is too silent on whether threads are supported
> there.
> https://sourceware.org/gdb/current/onlinedocs/gdb/Basic-Python.html#Basic-Python

I simply don't know enough about Python to discuss this; I do know
about Guile.  If Python extensions can start threads, then the same
considerations apply there.  And if the Python side didn't disallow
that until now, it doesn't sound like a good excuse to add insult to
injury on the Guile side.

> At any rate, the task at hand is getting gdb to work well with Guile,
> regardless of whether the user starts any threads,
> and that's the intent of the patch.

If we disable threads, this patch is unneeded, as are all the future
patches I envision that will have to deal with these issues.  We kill
the problem cleanly and once and for all.  From where I stand, it's a
no-brainer.

> I am happy to make the default value of GC_MARKERS be 1 (regardless
> of libgc version, and if not already set by the user) when initializing Guile,
> that will disable libgc marker threads.

That'd be fine with me, thanks.