Re-entering the event loop

Re-entering the event loop

[Alan Third]

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The NS port has an event loop that contains this code:

    if (++apploopnr != 1)
      {
        emacs_abort ();
      }

So if the loop is entered again it crashes Emacs instantly and gives
a stack trace. This shows up in a couple of bugs.

Bug#11049, for example, is where it receives a SIGHUP and should quit
cleanly and write out backups of open buffers, etc. but actually just
crashes because it re-enters the event loop.

What happens here is that the SIGHUP is received as an event, which
then calls a function that unblocks *all* input. Then Emacs tries to
clean up before quitting but that results with it handling input
events again, therefore re-entering the event loop and aborting.

I've sent a patch to this bug that simply re-blocks input, but the
alternative is to remove this check and let Emacs re-enter the event
loop. As far as I can tell this works fine for this particular case
(SIGHUP), but I don't know if it will break something else.

Is there any way, other than sending signal to kill it, that would
result in Emacs re-entering the event loop?

Thanks!
-- 
Alan Third

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diff --git a/src/nsterm.m b/src/nsterm.m
index f2b0d90..10e22fd 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -288,7 +288,6 @@ - (NSColor *)colorUsingDefaultColorSpace
 static struct timespec select_timeout = { 0, 0 };
 static int selfds[2] = { -1, -1 };
 static pthread_mutex_t select_mutex;
-static int apploopnr = 0;
 static NSAutoreleasePool *outerpool;
 static struct input_event *emacs_event = NULL;
 static struct input_event *q_event_ptr = NULL;
@@ -4054,15 +4053,6 @@ in certain situations (rapid incoming events).
 }
 #endif /* NS_IMPL_COCOA */
 
-static void
-unwind_apploopnr (Lisp_Object not_used)
-{
-  --apploopnr;
-  n_emacs_events_pending = 0;
-  ns_finish_events ();
-  q_event_ptr = NULL;
-}
-
 static int
 ns_read_socket (struct terminal *terminal, struct input_event *hold_quit)
 /* --------------------------------------------------------------------------
@@ -4126,13 +4116,8 @@ in certain situations (rapid incoming events).
       send_appdefined = YES;
       ns_send_appdefined (-1);
 
-      if (++apploopnr != 1)
-        {
-          emacs_abort ();
-        }
-      record_unwind_protect (unwind_apploopnr, Qt);
       [NSApp run];
-      unbind_to (specpdl_count, Qnil);  /* calls unwind_apploopnr */
+      unbind_to (specpdl_count, Qnil);
     }
 
   nevents = n_emacs_events_pending;
@@ -4235,16 +4220,10 @@ in certain situations (rapid incoming events).
 
   block_input ();
   ns_init_events (&event);
-  if (++apploopnr != 1)
-    {
-      emacs_abort ();
-    }
-
   {
     ptrdiff_t specpdl_count = SPECPDL_INDEX ();
-    record_unwind_protect (unwind_apploopnr, Qt);
     [NSApp run];
-    unbind_to (specpdl_count, Qnil);  /* calls unwind_apploopnr */
+    unbind_to (specpdl_count, Qnil);
   }
 
   ns_finish_events ();