Code hangs when BLE client disconnects first

• bleak version: 0.6.5a3 (develop)
• Python version: 3.7.3
• Operating System: Raspbian GNU/Linux 10 (buster), kernel: 4.19.118-v7+
• BlueZ version (bluetoothctl -v) in case of Linux: 5.50

Description

When connecting to a BLE device, if the client disconnects first, bleak seems to hang. This issue was fixed by modifying bluezdbus\client.py.

What I Did

I ran the notifications example “enable_notifications.py”, connecting to a custom-built BLE device. This device was guaranteed to disconnect from the client before the 5 second asyncio.sleep had completed. I only modified it by commenting out the stop_notify line (no longer needed) and by adding a logging line after the BleakClient section, which never ran.

"""
Notifications
-------------
Example showing how to add notifications to a characteristic and handle the responses.
Updated on 2019-07-03 by hbldh <[e-mail]>
""" 
async def run(address, loop, debug=False):
    if debug:
        import sys

        # loop.set_debug(True)
        l = logging.getLogger("asyncio")
        l.setLevel(logging.DEBUG)
        h = logging.StreamHandler(sys.stdout)
        h.setLevel(logging.DEBUG)
        l.addHandler(h)
        logger.addHandler(h)

    async with BleakClient(address, loop=loop) as client:
        x = await client.is_connected()
        logger.info("Connected: {0}".format(x))

        await client.start_notify(CHARACTERISTIC_UUID, notification_handler)
        await asyncio.sleep(5.0, loop=loop)
        #await client.stop_notify(CHARACTERISTIC_UUID)
    logger.info("BleakClient exited successfully")

In order to debug this problem, logger statements were added to bluezdbus\client.py, which made it clear that the code was hanging on BleakClient.disconnect when called by BleakClient.aexit, during the following section:

# Try to disconnect the actual device/peripheral
try:
	await self._bus.callRemote(
		self._device_path,
		"Disconnect",
		interface=defs.DEVICE_INTERFACE,
		destination=defs.BLUEZ_SERVICE,
	).asFuture(self.loop)
except Exception as e:
	logger.error("Attempt to disconnect device failed: {0}".format(e))

This was fixed by making the following changes to bluezdbus\client.py:

...
def __init__(self, address, loop=None, **kwargs):
   ...
        # BillMicro: device disconnection fix
        self._device_disconnected = False
...
async def disconnect(self) -> bool:
	"""Disconnect from the specified GATT server.

	Returns:
		Boolean representing if device is disconnected.

	"""
	# BillMicro: device disconnection fix
	if not self._device_disconnected:
		logger.debug("Disconnecting from BLE device...")

		# Remove all residual notifications.
		await self._cleanup_notifications()
                ...
        else:
            is_disconnected = True
...
def _properties_changed_callback(self, message):
	...
				task = self.loop.create_task(self._cleanup_all())
				# BillMicro: device disconnection fix
				self._device_disconnected = True
				...

However, this is a non-satisfactory solution. It can be be found here: 8794eacd70a4a4f825338e68372c92a75a6a4086

[hbldh]

This is troublesome indeed. An exception is desired, not a complete hanging…

This will be looked at in a later release though. Other issues have precendence right now.

[Ladvien]

Oh nice! Thank you for sharing.

It looks like the Proglove folk are using bleak in testing or production. That’s great. It’s a huge project and would feel bad if Henrik had to maintain it on his own.

I took a look at their additions, they mention a “leaky event loop” on POSIX systems. I’m guessing that’s what we were seeing. Glad there are smarter, more experienced people out there than me. 😃