Avoid crashes in batch Emacs sub-processes on MS-Windows

* src/w32.c (shutdown_handler): When run in a separate thread,
don't call functions that only the main (a.k.a. "Lisp") thread can
call; instead, arrange for maybe_quit to kill Emacs.
* src/w32fns.c (emacs_abort): Don't show GUI Abort dialogs in
non-interactive sessions.  (Bug#60556)

2 files changed, 47 insertions, 25 deletions

diff --git a/src/w32.c b/src/w32.c
index 47d79abc5b0..213fee15699 100644
--- a/src/w32.c
+++ b/src/w32.c
@@ -10509,10 +10509,13 @@ init_ntproc (int dumping)
   }
 }
 
-/*
-        shutdown_handler ensures that buffers' autosave files are
-	up to date when the user logs off, or the system shuts down.
-*/
+/* shutdown_handler ensures that buffers' autosave files are up to
+   date when the user logs off, or the system shuts down.  It also
+   shuts down Emacs when we get killed by another Emacs process, in
+   which case we get the CTRL_CLOSE_EVENT.  */
+
+extern DWORD dwMainThreadId;
+
 static BOOL WINAPI
 shutdown_handler (DWORD type)
 {
@@ -10521,15 +10524,30 @@ shutdown_handler (DWORD type)
       || type == CTRL_LOGOFF_EVENT    /* User logs off.  */
       || type == CTRL_SHUTDOWN_EVENT) /* User shutsdown.  */
     {
-      /* If we are being shut down in noninteractive mode, we don't
-	 care about the message stack, so clear it to avoid abort in
-	 shut_down_emacs.  This happens when an noninteractive Emacs
-	 is invoked as a subprocess of Emacs, and the parent wants to
-	 kill us, e.g. because it's about to exit.  */
-      if (noninteractive)
-	clear_message_stack ();
-      /* Shut down cleanly, making sure autosave files are up to date.  */
-      shut_down_emacs (0, Qnil);
+      if (GetCurrentThreadId () == dwMainThreadId)
+	{
+	  /* If we are being shut down in noninteractive mode, we don't
+	     care about the message stack, so clear it to avoid abort in
+	     shut_down_emacs.  This happens when an noninteractive Emacs
+	     is invoked as a subprocess of Emacs, and the parent wants to
+	     kill us, e.g. because it's about to exit.  */
+	  if (noninteractive)
+	    clear_message_stack ();
+	  /* Shut down cleanly, making sure autosave files are up to date.  */
+	  shut_down_emacs (0, Qnil);
+	}
+      {
+	/* This handler is run in a thread different from the main
+	   thread.  (This is the normal situation when we are killed
+	   by Emacs, for example, which sends us the WM_CLOSE
+	   message).  We cannot possibly call functions like
+	   shut_down_emacs or clear_message_stack in that case, since
+	   the main (a.k.a. "Lisp") thread could be in the middle of
+	   some Lisp program.  So instead we arrange for maybe_quit to
+	   kill Emacs.  */
+	Vquit_flag = Qkill_emacs;
+	Vinhibit_quit = Qnil;
+      }
     }
 
   /* Allow other handlers to handle this signal.  */
diff --git a/src/w32fns.c b/src/w32fns.c
index b4192a5ffa6..745f561e6b1 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -11112,20 +11112,24 @@ emacs_abort (void)
     abort ();
 
   int button;
-  button = MessageBox (NULL,
-		       "A fatal error has occurred!\n\n"
-		       "Would you like to attach a debugger?\n\n"
-		       "Select:\n"
-		       "YES -- to debug Emacs, or\n"
-		       "NO  -- to abort Emacs and produce a backtrace\n"
-		       "       (emacs_backtrace.txt in current directory)."
+
+  if (noninteractive)
+    button = IDNO;
+  else
+    button = MessageBox (NULL,
+			 "A fatal error has occurred!\n\n"
+			 "Would you like to attach a debugger?\n\n"
+			 "Select:\n"
+			 "YES -- to debug Emacs, or\n"
+			 "NO  -- to abort Emacs and produce a backtrace\n"
+			 "       (emacs_backtrace.txt in current directory)."
 #if __GNUC__
-		       "\n\n(type \"gdb -p <emacs-PID>\" and\n"
-		       "\"continue\" inside GDB before clicking YES.)"
+			 "\n\n(Before clicking YES, type\n"
+			 "\"gdb -p <emacs-PID>\", then \"continue\" inside GDB.)"
 #endif
-		       , "Emacs Abort Dialog",
-		       MB_ICONEXCLAMATION | MB_TASKMODAL
-		       | MB_SETFOREGROUND | MB_YESNO);
+			 , "Emacs Abort Dialog",
+			 MB_ICONEXCLAMATION | MB_TASKMODAL
+			 | MB_SETFOREGROUND | MB_YESNO);
   switch (button)
     {
     case IDYES: