qt hww show_settings_dialog: don't scan devices in GUI thread

Just makes sense in general.
Also, previously, the GUI would freeze if right after startup the user
clicked the hww status bar icon (especially with multiple hww connected).

electrum/plugins/hw_wallet/plugin.py

@@ -36,6 +36,7 @@ from electrum.storage import get_derivation_used_for_hw_device_encryption
 from electrum.keystore import Xpub, Hardware_KeyStore
 
 if TYPE_CHECKING:
+    import threading
     from electrum.wallet import Abstract_Wallet
     from electrum.base_wizard import BaseWizard
 
@@ -210,6 +211,11 @@ class HardwareHandlerBase:
             if hasattr(self.win, 'wallet'):
                 return self.win.wallet
 
+    def get_gui_thread(self) -> Optional['threading.Thread']:
+        if self.win is not None:
+            if hasattr(self.win, 'gui_thread'):
+                return self.win.gui_thread
+
     def update_status(self, paired: bool) -> None:
         pass
 

electrum/plugins/hw_wallet/qt.py

@@ -67,6 +67,7 @@ class QtHandlerBase(HardwareHandlerBase, QObject, Logger):
     def __init__(self, win: Union[ElectrumWindow, InstallWizard], device: str):
         QObject.__init__(self)
         Logger.__init__(self)
+        assert win.gui_thread == threading.current_thread(), 'must be called from GUI thread'
         self.clear_signal.connect(self.clear_dialog)
         self.error_signal.connect(self.error_dialog)
         self.message_signal.connect(self.message_dialog)
@@ -254,6 +255,7 @@ class QtPluginBase(object):
                       keystore: 'Hardware_KeyStore') -> Optional[str]:
         '''This dialog box should be usable even if the user has
         forgotten their PIN or it is in bootloader mode.'''
+        assert window.gui_thread != threading.current_thread(), 'must not be called from GUI thread'
         device_id = self.device_manager().xpub_id(keystore.xpub)
         if not device_id:
             try:
@@ -264,7 +266,10 @@ class QtPluginBase(object):
         return device_id
 
     def show_settings_dialog(self, window: ElectrumWindow, keystore: 'Hardware_KeyStore') -> None:
-        device_id = self.choose_device(window, keystore)
+        # default implementation (if no dialog): just try to connect to device
+        def connect():
+            device_id = self.choose_device(window, keystore)
+        keystore.thread.add(connect)
 
     def add_show_address_on_hw_device_button_for_receive_addr(self, wallet: 'Abstract_Wallet',
                                                               keystore: 'Hardware_KeyStore',

electrum/plugins/keepkey/qt.py

@@ -208,9 +208,13 @@ class QtPlugin(QtPluginBase):
                 menu.addAction(_("Show on {}").format(device_name), show_address)
 
     def show_settings_dialog(self, window, keystore):
-        device_id = self.choose_device(window, keystore)
-        if device_id:
-            SettingsDialog(window, self, keystore, device_id).exec_()
+        def connect():
+            device_id = self.choose_device(window, keystore)
+            return device_id
+        def show_dialog(device_id):
+            if device_id:
+                SettingsDialog(window, self, keystore, device_id).exec_()
+        keystore.thread.add(connect, on_success=show_dialog)
 
     def request_trezor_init_settings(self, wizard, method, device):
         vbox = QVBoxLayout()

electrum/plugins/safe_t/qt.py

@@ -84,9 +84,13 @@ class QtPlugin(QtPluginBase):
                 menu.addAction(_("Show on {}").format(device_name), show_address)
 
     def show_settings_dialog(self, window, keystore):
-        device_id = self.choose_device(window, keystore)
-        if device_id:
-            SettingsDialog(window, self, keystore, device_id).exec_()
+        def connect():
+            device_id = self.choose_device(window, keystore)
+            return device_id
+        def show_dialog(device_id):
+            if device_id:
+                SettingsDialog(window, self, keystore, device_id).exec_()
+        keystore.thread.add(connect, on_success=show_dialog)
 
     def request_safe_t_init_settings(self, wizard, method, device):
         vbox = QVBoxLayout()

electrum/plugins/trezor/qt.py

@@ -182,9 +182,13 @@ class QtPlugin(QtPluginBase):
                 menu.addAction(_("Show on {}").format(device_name), show_address)
 
     def show_settings_dialog(self, window, keystore):
-        device_id = self.choose_device(window, keystore)
-        if device_id:
-            SettingsDialog(window, self, keystore, device_id).exec_()
+        def connect():
+            device_id = self.choose_device(window, keystore)
+            return device_id
+        def show_dialog(device_id):
+            if device_id:
+                SettingsDialog(window, self, keystore, device_id).exec_()
+        keystore.thread.add(connect, on_success=show_dialog)
 
     def request_trezor_init_settings(self, wizard, method, device_id):
         vbox = QVBoxLayout()