bug#69561: 30.0.50; Freeze from M-x gnus on macOS

["Gerd Möllmann" <gerd.moellmann@gmail.com>]

Alan Third <alan@idiocy.org> writes:

> On Thu, Mar 07, 2024 at 06:01:02PM +0100, Gerd Möllmann wrote:
>> Alan Third <alan@idiocy.org> writes:
>> 
>> > On Thu, Mar 07, 2024 at 05:30:28PM +0100, Gerd Möllmann wrote:
>> >> Alan Third <alan@idiocy.org> writes:
>> >> 
>> >> > But keyboard input (ns_read_socket) is handled immediately after that
>> >> > "if (nfds < 0)" block and well before the "if (no_avail...".
>> >> 
>> >> Could you please tell the line number?
>> >
>> > detect_input_pending_run_timers at process.c:5839 calls
>> > get_input_pending which calls gobble_input which calls
>> > t->read_socket_hook.
>> >
>> > There seem to be a lot of ways for it to bail out, though.
>> 
>> Thanks. That's in if (read_kbd), and the first backtrace I sent had
>> 
>>     frame #6: 0x00000001001d94d2
>> emacs`wait_reading_process_output(time_limit=<unavailable>,
>> nsecs=<unavailable>, read_kbd=0, do_display=false,
>> wait_for_cell=(struct Lisp_Symbol *) $123 = 0x00000001007d24b0,
>> wait_proc=0x00007fccffdcc9d8, just_wait_proc=0) at process.c:5484:9
>> [opt]
>> 
>> i.e. read_kbd should be 0.
>> 
>> Maybe that's also an explanation why it doesn't freeze most of time?
>> If it sometimes does detect_input_pending...
>
> So this
>
>    READ_KBD is:
>      0 to ignore keyboard input, or
>      1 to return when input is available, or
>     -1 meaning caller will actually read the input, so don't throw to
>        the quit handler
>
> implies that if read_kbd is zero then we should be able to quit?

I'm afraid I can't answer that. Maybe Eli can, or knows someone who can?

> If that's the case then we need some special handling in nsterm.m for
> C-g, I suppose.
>
> Having dug around in other terms I assume this means setting
> Vquit_flag? So in the keyDown method we should identify C-g and set
> Vquit_flag...?

As far as I understand the code, Vquit_flag will also be set by storing
the event in question with kbd_buffer_store_event_hold. I think that
would be the easiest way. And it's what ns_read_socket already does.

In addition, returning -1 from ns_select if events are in the hold
queue, and not doing anything else, looks super suspicious to me. If
no-one else does an [NSApp run], like in my freeze, I think it's natural
that the system says Emacs is not responding. And what dowensides would
it have to [NSApp run]?

And finally, I would at least question the raise (SIGIO). I don't
understand the reason for that if, for example, keyboard input is the
hold queue. And, of course there is no comment...

But that just my 2 cents as a newcomer :-).