WalletSynchronizer had a race condition caused by calling the callback before the Qt event loop (or other initialisation) finished. Ergo we split initialisation and the running of the thread, then use Qt SIGNALs to yield back into the Qt event loop. This ensures that the callback for the servers_list_changed is not called until the main Qt event loop is actually running.

electrum

@@ -173,7 +173,8 @@ if __name__ == '__main__':
             sys.exit("Error: Unknown GUI: " + options.gui)
 
         gui = gui.ElectrumGui(wallet)
-        WalletSynchronizer(wallet,True).start()
+        interface = WalletSynchronizer(wallet, True, gui.server_list_changed)
+        interface.start()
 
         try:
             found = wallet.file_exists

lib/gui_lite.py

@@ -42,14 +42,18 @@ def resize_line_edit_width(line_edit, text_input):
     text_input += "A"
     line_edit.setMinimumWidth(metrics.width(text_input))
 
-class ElectrumGui:
+class ElectrumGui(QObject):
 
     def __init__(self, wallet):
+        super(QObject, self).__init__()
+
         self.wallet = wallet
         self.app = QApplication(sys.argv)
 
     def main(self, url):
         actuator = MiniActuator(self.wallet)
+        self.connect(self, SIGNAL("updateservers()"),
+                     actuator.update_servers_list)
         # Should probably not modify the current path but instead
         # change the behaviour of rsrc(...)
         old_path = QDir.currentPath()
@@ -74,6 +78,9 @@ class ElectrumGui:
 
         self.app.exec_()
 
+    def server_list_changed(self):
+        self.emit(SIGNAL("updateservers()"))
+
     def expand(self):
         """Hide the lite mode window and show pro-mode."""
         self.mini.hide()
@@ -495,16 +502,13 @@ class ReceivePopup(QDialog):
         QCursor.setPos(center_mouse_pos)
         self.show()
 
-class MiniActuator(QObject):
+class MiniActuator:
     """Initialize the definitions relating to themes and 
-    sending/recieving bitcoins.
+    sending/recieving bitcoins."""
-    """
     
     
     def __init__(self, wallet):
         """Retrieve the gui theme used in previous session."""
-        super(QObject, self).__init__()
-
         self.wallet = wallet
         self.theme_name = self.wallet.theme
         self.themes = util.load_theme_paths()
@@ -549,11 +553,9 @@ class MiniActuator(QObject):
     def set_servers_gui_stuff(self, servers_menu, servers_group):
         self.servers_menu = servers_menu
         self.servers_group = servers_group
-        self.connect(self, SIGNAL("updateservers()"), self.update_servers_list)
 
     def populate_servers_menu(self):
         interface = self.wallet.interface
-        interface.servers_loaded_callback = self.server_list_changed
         if not interface.servers:
             print "No servers loaded yet."
             self.servers_list = []
@@ -583,9 +585,6 @@ class MiniActuator(QObject):
             server_action.toggled.connect(delegate)
             self.servers_group.addAction(server_action)
 
-    def server_list_changed(self):
-        self.emit(SIGNAL("updateservers()"))
-
     def update_servers_list(self):
         # Clear servers_group
         for action in self.servers_group.actions():

lib/gui_qt.py

@@ -1430,6 +1430,9 @@ class ElectrumGui:
         if app is None:
             self.app = QApplication(sys.argv)
 
+    def server_list_changed(self):
+        pass
+
     def waiting_dialog(self):
 
         s = Timer()

lib/interface.py

@@ -306,14 +306,15 @@ class TcpStratumInterface(Interface):
 
 class WalletSynchronizer(threading.Thread):
 
-    def __init__(self, wallet, loop=False):
+    def __init__(self, wallet, loop=False, servers_loaded_callback=None):
         threading.Thread.__init__(self)
         self.daemon = True
         self.wallet = wallet
         self.loop = loop
         self.init_interface()
+        self.servers_loaded_callback = servers_loaded_callback
 
-    def init_interface(self, servers_loaded_callback=None):
+    def init_interface(self):
         try:
             host, port, protocol = self.wallet.server.split(':')
             port = int(port)
@@ -332,10 +333,8 @@ class WalletSynchronizer(threading.Thread):
             InterfaceClass = TcpStratumInterface
 
         self.interface = InterfaceClass(host, port, self.wallet.debug_server)
-        self.interface.servers_loaded_callback = servers_loaded_callback
         self.wallet.interface = self.interface
 
-
     def handle_response(self, r):
         if r is None:
             return
@@ -364,8 +363,13 @@ class WalletSynchronizer(threading.Thread):
                 if ports and version:
                     servers.append((host, ports))
             self.interface.servers = servers
-            assert self.interface.servers_loaded_callback is not None
+            # TODO: This assert fails with commands so it should be removed
-            self.interface.servers_loaded_callback()
+            # after we've ascertained it never fails when running the GUI.
+            assert self.servers_loaded_callback is not None
+            # servers_loaded_callback is None for commands, but should
+            # NEVER be None when using the GUI.
+            if self.servers_loaded_callback is not None:
+                self.servers_loaded_callback()
 
         elif method == 'blockchain.address.subscribe':
             addr = params[0]
@@ -429,7 +433,7 @@ class WalletSynchronizer(threading.Thread):
             if self.loop:
                 time.sleep(5)
                 # Server has been changed. Copy callback for new interface.
-                self.init_interface(self.interface.servers_loaded_callback)
+                self.init_interface()
                 self.start_interface()
                 continue
             else: