Fixed deadlock in CoreBluetooth backend when device disconnects

This fixes hbldh#535. In the CoreBluetooth backend, when a device disconnects,
none of the peripheral delegate callbacks will be called. So if any
futures are pending, they will be waiting forever. This adds a disconnect
hook that will raise an exception in all pending futures to avoid this
deadlock.

CHANGELOG.rst

@@ -41,6 +41,8 @@ Fixed
 * Fixed waiting for notification start/stop to complete in CoreBluetooth backend.
 * Fixed write without response on BlueZ < 5.51.
 * Fixed error propagation for CoreBluetooth events
+* Fixed deadlock in CoreBluetooth backend when device disconnects while
+  callbacks are pending. Fixes #535.
 
 
 `0.11.0`_ (2021-03-17)

bleak/backends/corebluetooth/CentralManagerDelegate.py

@@ -7,11 +7,12 @@
 """
 
 import asyncio
+import itertools
 import logging
 import platform
 import threading
 from enum import Enum
-from typing import List
+from typing import List, Optional
 
 import objc
 from CoreBluetooth import (
@@ -68,7 +69,7 @@ def init(self):
             return None
 
         self.event_loop = asyncio.get_event_loop()
-        self.connected_peripheral_delegate = None
+        self.connected_peripheral_delegate: Optional[PeripheralDelegate] = None
         self.connected_peripheral = None
         self._connection_state = CMDConnectionState.DISCONNECTED
 
@@ -269,8 +270,8 @@ def did_connect_peripheral(self, central, peripheral):
             )
         )
         if self._connection_state != CMDConnectionState.CONNECTED:
-            peripheralDelegate = PeripheralDelegate.alloc().initWithPeripheral_(
-                peripheral
+            peripheralDelegate: PeripheralDelegate = (
+                PeripheralDelegate.alloc().initWithPeripheral_(peripheral)
             )
             self.connected_peripheral_delegate = peripheralDelegate
             self._connection_state = CMDConnectionState.CONNECTED
@@ -312,6 +313,27 @@ def did_disconnect_peripheral(
         self, central: CBCentralManager, peripheral: CBPeripheral, error: NSError
     ):
         logger.debug("Peripheral Device disconnected!")
+
+        # If there are any pending futures waiting for delegate callbacks, we
+        # need to raise an exception since the callback will no longer be
+        # called because the device is disconnected.
+        delegate = self.connected_peripheral_delegate
+        for future in itertools.chain(
+            (delegate._services_discovered_future,),
+            delegate._service_characteristic_discovered_futures.values(),
+            delegate._characteristic_descriptor_discover_futures.values(),
+            delegate._characteristic_read_futures.values(),
+            delegate._characteristic_write_futures.values(),
+            delegate._characteristic_notify_change_futures.values(),
+            delegate._descriptor_read_futures.values(),
+            delegate._descriptor_write_futures.values(),
+        ):
+            try:
+                future.set_exception(BleakError("disconnected"))
+            except asyncio.InvalidStateError:
+                # the future was already done
+                pass
+
         self.connected_peripheral_delegate = None
         self.connected_peripheral = None
         self._connection_state = CMDConnectionState.DISCONNECTED