bug#65837: 30.0.50; Debugger in non-main threads

[Eli Zaretskii <eliz@gnu.org>]

> From: Helmut Eller <eller.helmut@gmail.com>
> Cc: 65837@debbugs.gnu.org
> Date: Sat, 09 Sep 2023 19:24:31 +0200
> 
> On Sat, Sep 09 2023, Eli Zaretskii wrote:
> 
> > So I think the only reasonably practical way to make this particular
> > use case stable is to disable thread switching for as long as the
> > debugger is active.  WDYT?
> 
> Having to disable thread switching for so long would be quite
> unfortunate.

But not unheard of.  When you debug a program, you almost always want
the other threads stopped (unless the bug you are investigating
happens because of the other threads).

> I think that is safe for the debuggee to call condition-wait or
> accept-process-output on a specific pipe process.  That should be enough
> to implement some form of channel/mailbox to communicate between the
> debuggee and the main thread.  The debuggee would then read commands
> from that channel and the main thread would send messages to that
> channel instead of executing the commands.  Something like the patch in
> the attachment.

I don't see how you could implement that in a portable way.  I also
don't understand how you will support all the different input event
types using this "channel".  And finally, you prevent the main thread
from running "normally", because it is now busy serving the debuggee
thread -- which seems to contradict your desire not to interfere with
other threads.

Preventing thread switch is definitely orders of magnitude simpler,
IMO.