Index: jack_mixer.py
===================================================================
--- jack_mixer.py	(wersja 95)
+++ jack_mixer.py	(kopia robocza)
@@ -179,11 +179,15 @@
         self.channel_remove_menu_item.set_sensitive(False)
 
     def add_channel(self, name, stereo):
-        channel = input_channel(self.mixer, self.gui_factory, name, stereo)
-        self.add_channel_precreated(channel)
+        try:
+            channel = input_channel(self.mixer, self.gui_factory, name, stereo)
+            self.add_channel_precreated(channel)
+        except Exception:
+            err = gtk.MessageDialog(None, gtk.DIALOG_MODAL | gtk.DIALOG_DESTROY_WITH_PARENT, gtk.MESSAGE_ERROR, gtk.BUTTONS_OK, "Channel creation failed")
+            err.run()
+            err.destroy()
 
     def add_channel_precreated(self, channel):
-        self.channels.append(channel)
         frame = gtk.Frame()
         frame.add(channel)
         self.hbox_inputs.pack_start(frame, False)
@@ -192,6 +196,7 @@
         self.channel_remove_menu.append(channel_remove_menu_item)
         channel_remove_menu_item.connect("activate", self.on_remove_channel, channel, channel_remove_menu_item)
         self.channel_remove_menu_item.set_sensitive(True)
+        self.channels.append(channel)
 
     def read_meters(self):
         for channel in self.channels:
Index: jack_mixer.c
===================================================================
--- jack_mixer.c	(wersja 95)
+++ jack_mixer.c	(kopia robocza)
@@ -261,6 +261,7 @@
 
 void channel_stereo_meter_read(jack_mixer_channel_t channel, double * left_ptr, double * right_ptr)
 {
+  assert(channel_ptr);
   *left_ptr = value_to_db(channel_ptr->meter_left);
   *right_ptr = value_to_db(channel_ptr->meter_right);
 }
@@ -276,6 +277,7 @@
 {
   bool midi_modified;
 
+  assert(channel_ptr);
   midi_modified = channel_ptr->midi_modified;
   channel_ptr->midi_modified = false;
 
@@ -284,6 +286,7 @@
 
 void channel_volume_write(jack_mixer_channel_t channel, double volume)
 {
+  assert(channel_ptr);
   channel_ptr->volume = db_to_value(volume);
   calc_channel_volumes(channel_ptr);
 }
@@ -292,11 +295,13 @@
 channel_volume_read(
   jack_mixer_channel_t channel)
 {
+  assert(channel_ptr);
   return value_to_db(channel_ptr->volume);
 }
 
 void channel_balance_write(jack_mixer_channel_t channel, double balance)
 {
+  assert(channel_ptr);
   channel_ptr->balance = balance;
   calc_channel_volumes(channel_ptr);
 }
@@ -305,11 +310,13 @@
 channel_balance_read(
   jack_mixer_channel_t channel)
 {
+  assert(channel_ptr);
   return channel_ptr->balance;
 }
 
 double channel_abspeak_read(jack_mixer_channel_t channel)
 {
+  assert(channel_ptr);
   if (channel_ptr->NaN_detected)
   {
     return sqrt(-1);
@@ -835,6 +842,7 @@
   {
     goto exit;
   }
+  memset(channel_ptr, 0, sizeof(struct channel));
 
   channel_ptr->mixer_ptr = mixer_ctx_ptr;
 
@@ -853,13 +861,27 @@
     port_name[channel_name_size+1] = 'L';
     port_name[channel_name_size+2] = 0;
     channel_ptr->port_left = jack_port_register(channel_ptr->mixer_ptr->jack_client, port_name, JACK_DEFAULT_AUDIO_TYPE, JackPortIsInput, 0);
+    if (channel_ptr->port_left == NULL)
+    {
+        free(port_name);
+        goto exit_free_channel;
+    }
     port_name[channel_name_size+1] = 'R';
     channel_ptr->port_right = jack_port_register(channel_ptr->mixer_ptr->jack_client, port_name, JACK_DEFAULT_AUDIO_TYPE, JackPortIsInput, 0);
     free(port_name);
+    if (channel_ptr->port_right == NULL)
+    {
+        jack_port_unregister(channel_ptr->mixer_ptr->jack_client, channel_ptr->port_left);
+        goto exit_free_channel;
+    }
   }
   else
   {
     channel_ptr->port_left = jack_port_register(channel_ptr->mixer_ptr->jack_client, channel_name, JACK_DEFAULT_AUDIO_TYPE, JackPortIsInput, 0);
+    if (channel_ptr->port_left == NULL)
+    {
+        goto exit_free_channel;
+    }
   }
 
   channel_ptr->stereo = stereo;
@@ -917,7 +939,10 @@
   goto exit;
 
 exit_free_channel:
+  if (channel_ptr->name)
+    free(channel_ptr->name);
   free(channel_ptr);
+  channel_ptr = NULL;
 
 exit:
   return channel_ptr;
Index: channel.py
===================================================================
--- channel.py	(wersja 95)
+++ channel.py	(kopia robocza)
@@ -191,8 +191,10 @@
         channel.__init__(self, mixer, gui_factory, name, stereo)
 
     def realize(self):
+        self.channel = jack_mixer_c.add_channel(self.mixer, self.channel_name, self.stereo)
+        if self.channel == None:
+            raise Exception,"Cannot create a channel"
         channel.realize(self)
-        self.channel = jack_mixer_c.add_channel(self.mixer, self.channel_name, self.stereo)
         jack_mixer_c.channel_set_midi_scale(self.channel, self.slider_scale.scale)
 
         self.on_volume_changed(self.slider_adjustment)