ensure only one subprocess is running at a time

bin/simple-apt-update

@@ -60,9 +60,8 @@ class UpdateWindow(Gtk.ApplicationWindow):
         self.buffer.set_text("")
 
     def scroll_to_bottom(self):
-        adj = self.scrolledwindow.get_vadjustment()
-        adj.set_value(adj.get_upper())
-        self.scrolledwindow.set_vadjustment(adj)
+        self.buffer.get_end_iter()
+        self.text_view.scroll_to_mark(self.text_mark_end, 0, False, 0, 0)
 
     def level_to_color(self, level):
         if level == "INFO":
@@ -113,6 +112,25 @@ class UpdateWindow(Gtk.ApplicationWindow):
     def insert(self, text, iter):
         self.buffer.insert(iter, text + "\n")
 
+    def run_thread(self, args, env):
+        if self.thread is None:
+            do_run = True
+        elif not self.thread.is_alive():
+            do_run = True
+        else:
+            do_run = False
+
+        if do_run:
+            self.thread = threading.Thread(
+                target=self.run,
+                args=(args, env,))
+
+            self.thread.start()
+
+            return False
+        else:
+            return True
+
     def execute(
         self,
         args,
@@ -136,11 +154,7 @@ class UpdateWindow(Gtk.ApplicationWindow):
             "INFO",
             "Running command \"%s\" ..." % " ".join(args))
 
-        thread = threading.Thread(
-            target=self.run,
-            args=(args, env,))
-
-        thread.start()
+        GLib.timeout_add(250, self.run_thread, args, env)
 
     def run(self, args, env={}):
         p = subprocess.Popen(
@@ -192,16 +206,15 @@ class UpdateWindow(Gtk.ApplicationWindow):
             env=env,
             empty_msg="No package upgrades were performed.")
 
-    def on_upgrade(self, *args):
-        self.upgrade()
-
     def update(self, clear=True):
         args = ['/usr/bin/apt-get', '-y', 'update']
         env = {'DEBIAN_FRONTEND': 'noninteractive'}
-        self.execute(args, env=env, clear=clear)
-
-    def on_update(self, *args):
-        self.update()
+        self.execute(
+            args,
+            env=env,
+            clear=clear,
+            output_msg="The package cache was refreshed."
+        )
 
     def list(self, clear=True):
         args = ['/usr/bin/apt', '-qq', 'list', '--upgradable']
@@ -210,7 +223,14 @@ class UpdateWindow(Gtk.ApplicationWindow):
             ignore_stderr=True,
             clear=clear,
             output_msg="Found the following package upgrades:",
-            empty_msg="No package upgrades found.")
+            empty_msg="No package upgrades found."
+        )
+
+    def on_update(self, *args):
+        self.update()
+
+    def on_upgrade(self, *args):
+        self.upgrade()
 
     def on_list(self, *args):
         self.list()
@@ -228,15 +248,17 @@ class UpdateWindow(Gtk.ApplicationWindow):
                 self.append_mesg("STDOUT", text)
             else:
                 exit_code = int(match.group(1))
+                self.thread.join()
 
                 if exit_code != 0:
                     self.append_mesg(
                         "ERROR",
-                        "Command exited with code %d" % exit_code)
+                        "Command exited with code %d" % exit_code
+                    )
                 elif self.stdout == '' and self.empty_msg is not None:
                     self.append_mesg("INFO", self.empty_msg)
                 elif self.stdout != '' and self.output_msg is not None:
-                    self.append_mesg("INFO", self.empty_msg)
+                    self.append_mesg("INFO", self.output_msg)
 
                 self.unlock()
 
@@ -265,6 +287,7 @@ class UpdateWindow(Gtk.ApplicationWindow):
         )
 
         self.application = application
+        self.thread = None
         self.stdout_queue = queue.Queue()
         self.stderr_queue = queue.Queue()
 
@@ -327,12 +350,16 @@ class UpdateWindow(Gtk.ApplicationWindow):
         self.scrolledwindow.set_max_content_height(300)
         self.buffer = Gtk.TextBuffer()
 
-        text_view = Gtk.TextView(buffer=self.buffer)
-        text_view.set_editable(False)
-        text_view.set_monospace(True)
-        text_view.set_cursor_visible(False)
+        self.text_view = Gtk.TextView(buffer=self.buffer)
+        self.text_view.set_editable(False)
+        self.text_view.set_monospace(True)
+        self.text_view.set_cursor_visible(False)
 
-        self.scrolledwindow.add(text_view)
+        text_buffer = self.text_view.get_buffer()
+        iter = text_buffer.get_end_iter()
+        self.text_mark_end = text_buffer.create_mark("", iter, False)
+
+        self.scrolledwindow.add(self.text_view)
         hbox.pack_start(self.scrolledwindow, True, True, 0)
 
 
@@ -350,9 +377,6 @@ class SimpleAptUpdate(Gtk.Application):
 
         signal.signal(signal.SIGINT, signal.SIG_DFL)
 
-    def do_command_line(self, cmdline):
-        pass
-
     def on_activate(self, application):
         self.window = UpdateWindow(application)
 
@@ -381,7 +405,6 @@ class SimpleAptUpdate(Gtk.Application):
 
         self.window.present()
         self.window.show_all()
-        self.window.update()
         self.window.list(clear=False)