bluezdbus/client: Make sure the disconnect monitor task is properly c…

…ancelled.

Sometimes the exception on connect is raised so early that the
disconnect monitor task does not get the disconnect event set because the
on_connected_changed callback is already unregistered and the task stays
in pending state causing asyncio to throw an exception:
"Task was destroyed but it is pending!"

CHANGELOG.rst

@@ -15,6 +15,7 @@ Added
 * Added optional hack to use Bluetooth address instead of UUID on macOS.
 * Added ``BleakScanner.find_device_by_name()`` class method.
 * Added optional command line argument to use debug log level to all applicable examples.
+* Make sure the disconnect monitor task is properly cancelled on the BlueZ client.
 
 Changed
 -------

bleak/backends/bluezdbus/client.py

@@ -161,6 +161,8 @@ def on_value_changed(char_path: str, value: bytes) -> None:
         )
         self._remove_device_watcher = lambda: manager.remove_device_watcher(watcher)
 
+        local_disconnect_monitor_event = asyncio.Event()
+
         try:
             try:
                 #
@@ -197,10 +199,10 @@ def on_value_changed(char_path: str, value: bytes) -> None:
                 self._is_connected = True
 
                 # Create a task that runs until the device is disconnected.
-                self._disconnect_monitor_event = asyncio.Event()
+                self._disconnect_monitor_event = local_disconnect_monitor_event
                 asyncio.ensure_future(
                     self._disconnect_monitor(
-                        self._bus, self._device_path, self._disconnect_monitor_event
+                        self._bus, self._device_path, local_disconnect_monitor_event
                     )
                 )
 
@@ -246,6 +248,9 @@ def on_value_changed(char_path: str, value: bytes) -> None:
 
                 raise
         except BaseException:
+            # this effectively cancels the disconnect monitor in case the event
+            # was not triggered by a D-Bus callback
+            local_disconnect_monitor_event.set()
             self._cleanup_all()
             raise