Add extension_language_ops::shutdown

Right now, Python is shut down via a final cleanup.  However, it seems
to me that it is better for extension languages to be shut down
explicitly, after all the ordinary final cleanups are run.  The main
reason for this is that a subsequent patch adds another case like
finalize_values; and rather than add a series of workarounds for
Python shutdown, it seemed better to let these be done via final
cleanups, and then have Python shutdown itself be the special case.

gdb/extension-priv.h

@@ -119,6 +119,10 @@ struct extension_language_ops
      This method is required.  */
   int (*initialized) (const struct extension_language_defn *);
 
+  /* Called just before GDB exits.  This shuts down the extension
+     language.  This can be NULL.  */
+  void (*shutdown) (const struct extension_language_defn *);
+
   /* Process a sequence of commands embedded in GDB's own scripting language.
      E.g.,
      python

gdb/extension.c

@@ -341,6 +341,18 @@ ext_lang_initialization (void)
     }
 }
 
+/* See extension.h.  */
+
+void
+ext_lang_shutdown ()
+{
+  for (const struct extension_language_defn *extlang : extension_languages)
+    {
+      if (extlang->ops != nullptr && extlang->ops->shutdown != nullptr)
+	extlang->ops->shutdown (extlang);
+    }
+}
+
 /* Invoke the appropriate extension_language_ops.eval_from_control_command
    method to perform CMD, which is a list of commands in an extension language.
 

gdb/extension.h

@@ -282,6 +282,9 @@ extern bool ext_lang_auto_load_enabled (const struct extension_language_defn *);
 
 extern void ext_lang_initialization (void);
 
+/* Shut down all extension languages.  */
+extern void ext_lang_shutdown ();
+
 extern void eval_ext_lang_from_control_command (struct command_line *cmd);
 
 extern void auto_load_ext_lang_scripts_for_objfile (struct objfile *);

gdb/guile/guile.c

@@ -115,6 +115,7 @@ static const struct extension_language_ops guile_extension_ops =
 {
   gdbscm_initialize,
   gdbscm_initialized,
+  nullptr,
 
   gdbscm_eval_from_control_command,
 

gdb/python/python.c

@@ -110,6 +110,7 @@ static objfile_script_sourcer_func gdbpy_source_objfile_script;
 static objfile_script_executor_func gdbpy_execute_objfile_script;
 static void gdbpy_initialize (const struct extension_language_defn *);
 static int gdbpy_initialized (const struct extension_language_defn *);
+static void finalize_python (const struct extension_language_defn *);
 static void gdbpy_eval_from_control_command
   (const struct extension_language_defn *, struct command_line *cmd);
 static void gdbpy_start_type_printers (const struct extension_language_defn *,
@@ -147,6 +148,7 @@ static const struct extension_language_ops python_extension_ops =
 {
   gdbpy_initialize,
   gdbpy_initialized,
+  finalize_python,
 
   gdbpy_eval_from_control_command,
 
@@ -2057,7 +2059,7 @@ static struct cmd_list_element *user_show_python_list;
    interpreter.  This lets Python's 'atexit' work.  */
 
 static void
-finalize_python ()
+finalize_python (const struct extension_language_defn *ignore)
 {
   struct active_ext_lang_state *previous_active;
 
@@ -2297,8 +2299,6 @@ init_done:
   /* Release the GIL while gdb runs.  */
   PyEval_SaveThread ();
 
-  add_final_cleanup (finalize_python);
-
   /* Only set this when initialization has succeeded.  */
   gdb_python_initialized = 1;
   return true;

gdb/top.c

@@ -1819,6 +1819,8 @@ quit_force (int *exit_arg, int from_tty)
       exception_print (gdb_stderr, ex);
     }
 
+  ext_lang_shutdown ();
+
   exit (exit_code);
 }