New python event "clear_objfiles".

If one is watching new_objfile events in python, it helps to know
when the list of objfiles is cleared.  This patch adds a new
clear_objfiles event to support this.

This patch is all just cut-n-paste-n-tweak derived from
the new_objfiles event.

gdb/ChangeLog:

	* NEWS: Mention new event gdb.clear_objfiles.
	* python/py-event.h (emit_clear_objfiles_event): Clear
	* python/py-events.h (events_object): New member clear_objfiles.
	* python/py-evts.c (gdbpy_initialize_py_events): Add clear_objfiles
	event.
	* python/py-inferior.c (python_new_objfile): If objfile is NULL,
	emit clear_objfiles event.
	* python/py-newobjfileevent.c (create_clear_objfiles_event_object): New
	function.
	(emit_clear_objfiles_event): New function.
	(clear_objfiles): New event.
	* python/python-internal.h (gdbpy_initialize_clear_objfiles_event):
	Declare.
	* python/python.c (_initialize_python): Call
	gdbpy_initialize_clear_objfiles_event.

gdb/doc/ChangeLog:

	* python.texi (Events In Python): Document clear_objfiles event.

gdb/testsuite/ChangeLog:

	* gdb.python/py-events.exp: Update expected output for clear_objfiles
	event.
	* gdb.python/py-events.py: Add clear_objfiles event.

gdb/python/py-event.h

@@ -112,6 +112,7 @@ extern int evpy_emit_event (PyObject *event,
 extern PyObject *create_event_object (PyTypeObject *py_type);
 extern PyObject *create_thread_event_object (PyTypeObject *py_type);
 extern int emit_new_objfile_event (struct objfile *objfile);
+extern int emit_clear_objfiles_event (void);
 
 extern void evpy_dealloc (PyObject *self);
 extern int evpy_add_attribute (PyObject *event,

gdb/python/py-events.h

@@ -46,6 +46,7 @@ typedef struct
   eventregistry_object *cont;
   eventregistry_object *exited;
   eventregistry_object *new_objfile;
+  eventregistry_object *clear_objfiles;
 
   PyObject *module;
 

gdb/python/py-evts.c

@@ -76,6 +76,9 @@ gdbpy_initialize_py_events (void)
   if (add_new_registry (&gdb_py_events.new_objfile, "new_objfile") < 0)
     return -1;
 
+  if (add_new_registry (&gdb_py_events.clear_objfiles, "clear_objfiles") < 0)
+    return -1;
+
   if (gdb_pymodule_addobject (gdb_module,
 			      "events",
 			      (PyObject *) gdb_py_events.module) < 0)

gdb/python/py-inferior.c

@@ -137,23 +137,32 @@ python_inferior_exit (struct inferior *inf)
 }
 
 /* Callback used to notify Python listeners about new objfiles loaded in the
-   inferior.  */
+   inferior.  OBJFILE may be NULL which means that the objfile list has been
+   cleared (emptied).  */
 
 static void
 python_new_objfile (struct objfile *objfile)
 {
   struct cleanup *cleanup;
 
-  if (objfile == NULL)
-    return;
-
   if (!gdb_python_initialized)
     return;
 
-  cleanup = ensure_python_env (get_objfile_arch (objfile), current_language);
+  cleanup = ensure_python_env (objfile != NULL
+			       ? get_objfile_arch (objfile)
+			       : target_gdbarch (),
+			       current_language);
 
-  if (emit_new_objfile_event (objfile) < 0)
-    gdbpy_print_stack ();
+  if (objfile == NULL)
+    {
+      if (emit_clear_objfiles_event () < 0)
+	gdbpy_print_stack ();
+    }
+  else
+    {
+      if (emit_new_objfile_event (objfile) < 0)
+	gdbpy_print_stack ();
+    }
 
   do_cleanups (cleanup);
 }

gdb/python/py-newobjfileevent.c

@@ -22,6 +22,8 @@
 
 static PyTypeObject new_objfile_event_object_type
     CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF ("event_object");
+static PyTypeObject clear_objfiles_event_object_type
+    CPYCHECKER_TYPE_OBJECT_FOR_TYPEDEF ("event_object");
 
 static PyObject *
 create_new_objfile_event_object (struct objfile *objfile)
@@ -72,3 +74,56 @@ GDBPY_NEW_EVENT_TYPE (new_objfile,
                       "GDB new object file event object",
                       event_object_type,
                       static);
+
+/* Subroutine of emit_clear_objfiles_event to simplify it.  */
+
+static PyObject *
+create_clear_objfiles_event_object (void)
+{
+  PyObject *objfile_event;
+  PyObject *py_progspace;
+
+  objfile_event = create_event_object (&clear_objfiles_event_object_type);
+  if (!objfile_event)
+    goto fail;
+
+  /* Note that pspace_to_pspace_object returns a borrowed reference,
+     so we don't need a decref here.  */
+  py_progspace = pspace_to_pspace_object (current_program_space);
+  if (!py_progspace || evpy_add_attribute (objfile_event,
+					   "progspace",
+					   py_progspace) < 0)
+    goto fail;
+
+  return objfile_event;
+
+ fail:
+  Py_XDECREF (objfile_event);
+  return NULL;
+}
+
+/* Callback function which notifies observers when the "clear objfiles"
+   event occurs.
+   This function will create a new Python clear_objfiles event object.
+   Return -1 if emit fails.  */
+
+int
+emit_clear_objfiles_event (void)
+{
+  PyObject *event;
+
+  if (evregpy_no_listeners_p (gdb_py_events.clear_objfiles))
+    return 0;
+
+  event = create_clear_objfiles_event_object ();
+  if (event)
+    return evpy_emit_event (event, gdb_py_events.clear_objfiles);
+  return -1;
+}
+
+GDBPY_NEW_EVENT_TYPE (clear_objfiles,
+		      "gdb.ClearObjFilesEvent",
+		      "ClearObjFilesEvent",
+		      "GDB clear object files event object",
+		      event_object_type,
+		      static);

gdb/python/python-internal.h

@@ -470,6 +470,8 @@ int gdbpy_initialize_thread_event (void)
   CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
 int gdbpy_initialize_new_objfile_event (void)
   CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
+int gdbpy_initialize_clear_objfiles_event (void)
+  CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
 int gdbpy_initialize_arch (void)
   CPYCHECKER_NEGATIVE_RESULT_SETS_EXCEPTION;
 int gdbpy_initialize_xmethods (void)

gdb/python/python.c

@@ -1756,6 +1756,7 @@ message == an error message without a stack will be printed."),
       || gdbpy_initialize_exited_event () < 0
       || gdbpy_initialize_thread_event () < 0
       || gdbpy_initialize_new_objfile_event ()  < 0
+      || gdbpy_initialize_clear_objfiles_event ()  < 0
       || gdbpy_initialize_arch () < 0
       || gdbpy_initialize_xmethods () < 0)
     goto fail;