mirrors: Run speed tests as GTask async operations

Quickly opening and closing the mirror selection dialog repeatedly has
a chance of causing a segfault. In addition, the following Gtk critical
error message is printed multiple times for every mirror that has not yet
been tested at the time that the dialog is closed.
Gtk-CRITICAL **: gtk_list_store_get_value: assertion 'iter_is_valid (iter, list_store)' failed.

This occurs because the mirrors model gets cleared without waiting for the
speed test thread to finish thus invalidating the remaining iterators.

The speed tests are now run using Gio Task async operations.
They are launched in new threads and when complete, the callback which
is invoked from the main thread checks if the task has been cancelled
and if so it does not modify the model or access the now invalid iterators.

usr/lib/linuxmint/mintSources/mintSources.py

@@ -56,21 +56,6 @@
 
 os.umask(0o022)
 
-# Used as a decorator to run things in the background
-def run_async(func):
-    def wrapper(*args, **kwargs):
-        thread = threading.Thread(target=func, args=args, kwargs=kwargs)
-        thread.daemon = True
-        thread.start()
-        return thread
-    return wrapper
-
-# Used as a decorator to run things in the main loop, from another thread
-def idle(func):
-    def wrapper(*args):
-        GLib.idle_add(func, *args)
-    return wrapper
-
 def signal_handler(signum, _):
     print("")
     sys.exit(128 + signum)
@@ -502,6 +487,9 @@ def __init__(self, application, ui_builder):
 
         self._mirrors_model.set_sort_column_id(MirrorSelectionDialog.MIRROR_SPEED_COLUMN, Gtk.SortType.DESCENDING)
 
+        # Since GtkListStore sorts the mirrors internally, we need a copy of the iterators in their original order
+        self._mirrors_iters = []
+
         r = Gtk.CellRendererPixbuf()
         col = Gtk.TreeViewColumn(_("Country"), r, pixbuf = MirrorSelectionDialog.MIRROR_COUNTRY_FLAG_COLUMN)
         col.set_cell_data_func(r, self.data_func_surface)
@@ -542,6 +530,8 @@ def get_country(self, country_code):
 
     def _update_list(self):
         self._mirrors_model.clear()
+        self._mirrors_iters.clear()
+
         for mirror in self.visible_mirrors:
             if mirror.country_code == "WD":
                 flag = FLAG_PATH % '_united_nations'
@@ -565,7 +555,10 @@ def _update_list(self):
                 mirror.name
             ))
 
-        self._all_speed_tests()
+        iter = self._mirrors_model.get_iter_first()
+        while iter is not None:
+            self._mirrors_iters.append(iter)
+            iter = self._mirrors_model.iter_next(iter)
 
     def get_url_last_modified(self, url):
         try:
@@ -610,24 +603,6 @@ def check_mint_mirror_up_to_date(self, url):
     def check_base_mirror_up_to_date(self, url):
         return self.check_mirror_up_to_date(url, 14)
 
-    @run_async
-    def _all_speed_tests(self):
-        model_iters = [] # Don't iterate through iters directly.. we're modifying their orders..
-        iter = self._mirrors_model.get_iter_first()
-        while iter is not None:
-            model_iters.append(iter)
-            iter = self._mirrors_model.iter_next(iter)
-
-        for iter in model_iters:
-            try:
-                if iter is not None:
-                    mirror = self._mirrors_model.get_value(iter, MirrorSelectionDialog.MIRROR_COLUMN)
-                    if mirror in self.visible_mirrors:
-                        url = self._mirrors_model.get_value(iter, MirrorSelectionDialog.MIRROR_URL_COLUMN)
-                        self._speed_test (iter, url)
-            except Exception as e:
-                pass # null types will occur here...
-
     def _get_speed_label(self, speed):
         if speed > 0:
             divider = (1024 * 1.0)
@@ -649,10 +624,11 @@ def _get_speed_label(self, speed):
             represented_speed = ("0 %s") % _("kB/s")
         return represented_speed
 
-    def _speed_test(self, iter, url):
+    def _speed_test_thread(self, task, source_object, task_data, cancellable):
         download_speed = 0
         try:
             up_to_date = False
+            url = self.current_speed_test_mirror
 
             if self.is_base:
                 test_url = "%s/dists/%s/main/binary-amd64/Packages.gz" % (url, self.codename)
@@ -679,9 +655,23 @@ def _speed_test(self, iter, url):
             print ("Error '%s' on url %s" % (error, url))
             download_speed = 0
 
+        task.return_value(download_speed)
+
+    def speed_test_finished_cb(self, source, task, iter):
+
+        # Get speed test result
+        if task.get_cancellable().is_cancelled():
+            del self._gtask
+            return
+        download_speed = task.propagate_value().value
+
+        # Add the result to the model
         self.show_speed_test_result(iter, download_speed)
 
-    @idle
+        del self._gtask
+        # Run speed test for the next mirror
+        self._create_speed_test_gtask()
+
     def show_speed_test_result(self, iter, download_speed):
         if (iter is not None): # recheck as it can get null
             if download_speed == -1:
@@ -694,6 +684,17 @@ def show_speed_test_result(self, iter, download_speed):
                 self._mirrors_model.set_value(iter, MirrorSelectionDialog.MIRROR_SPEED_COLUMN, download_speed)
                 self._mirrors_model.set_value(iter, MirrorSelectionDialog.MIRROR_SPEED_LABEL_COLUMN, self._get_speed_label(download_speed))
 
+    def _create_speed_test_gtask(self):
+        if not self._mirrors_iters:
+            return
+
+        iter = self._mirrors_iters.pop(0)
+        self._gtask = Gio.Task.new(self._dialog, Gio.Cancellable(), self.speed_test_finished_cb, iter)
+
+        # This must only be set here and read inside the speed test thread
+        self.current_speed_test_mirror = self._mirrors_model.get_value(iter, MirrorSelectionDialog.MIRROR_URL_COLUMN)
+        self._gtask.run_in_thread(self._speed_test_thread)
+
     def run(self, mirrors, config, is_base):
 
         self.config = config
@@ -795,6 +796,8 @@ def run(self, mirrors, config, is_base):
             self.default_mirror_age = (now - self.default_mirror_date).days
 
         self._update_list()
+        self._create_speed_test_gtask()
+
         self._dialog.show_all()
         retval = self._dialog.run()
         if retval == Gtk.ResponseType.APPLY:
@@ -806,6 +809,8 @@ def run(self, mirrors, config, is_base):
                 res = None
         else:
             res = None
+
+        self._gtask.get_cancellable().cancel()
         self._dialog.hide()
         self._mirrors_model.clear()
         return res