ServiceBus async AutoLockRenewer crashes on disposal if no messages have been registered

[andrea-cassioli-maersk]

• Package Name: azure-servicebus
• Package Version: 7.3.0
• Operating System: Mac OSx
• Python Version: 3.8.7

Describe the bug
I am using the async version of AutoLockRenewer. I have noticed that if I create it but I do not register a message (either directly or via a receiver), then I get an exception when it is disposed.

To Reproduce
Steps to reproduce the behavior: see the following code

import os
import asyncio
from distutils.util import strtobool
from azure.servicebus.aio import ServiceBusClient, AutoLockRenewer

CONNECTION_STR = os.environ['SERVICE_BUS_CONNECTION_STR']
QUEUE_NAME = os.environ["SERVICE_BUS_QUEUE_NAME"]

async def code_failing():

    servicebus_client = ServiceBusClient.from_connection_string(conn_str=CONNECTION_STR)

    async with servicebus_client:

        print('context, register via receiver')
        try:
            async with AutoLockRenewer(max_lock_renewal_duration=20*60) as renewer:

                async with servicebus_client.get_queue_receiver(queue_name=QUEUE_NAME, auto_lock_renewer=renewer) as receiver:
                    _ = await receiver.receive_messages(max_message_count=10, max_wait_time=5)
        except Exception as e:
            print(e)

        print('context, register explicitly')
        try:
            async with AutoLockRenewer(max_lock_renewal_duration=20*60) as renewer:

                async with servicebus_client.get_queue_receiver(queue_name=QUEUE_NAME, ) as receiver:
                    _ = await receiver.receive_messages(max_message_count=10, max_wait_time=5)
        except Exception as e:
            print(e)

        print('no context, register via receiver')
        try:
            renewer = AutoLockRenewer(max_lock_renewal_duration=20*60)

            async with servicebus_client.get_queue_receiver(queue_name=QUEUE_NAME, auto_lock_renewer=renewer) as receiver:
                _ = await receiver.receive_messages(max_message_count=10, max_wait_time=5)

            await renewer.close()
        except Exception as e:
            print(e)


        print('no context, register explicitly')
        try:
            renewer = AutoLockRenewer(max_lock_renewal_duration=20*60)

            async with servicebus_client.get_queue_receiver(queue_name=QUEUE_NAME) as receiver:
                _ = await receiver.receive_messages(max_message_count=10, max_wait_time=5)

            await renewer.close()
        except Exception as e:
            print(e)

if __name__ == '__main__':

    asyncio.run(code_failing())

Expected behavior
The object should be cleanly disposed. Instead I get:

10:57 $ env $(grep -v '^#' env  | xargs -0)  python3 autolock-bug.py 
context, register via receiver
Set of coroutines/Futures is empty.
context, register explicitly
Set of coroutines/Futures is empty.
no context, register via receiver
Set of coroutines/Futures is empty.
no context, register explicitly
Set of coroutines/Futures is empty.

each exception is like:

Traceback (most recent call last):
  File "autolock-bug.py", line 32, in <module>
    asyncio.run(code_failing())
  File "/Users/aca286/.pyenv/versions/3.8.7/lib/python3.8/asyncio/runners.py", line 44, in run
    return loop.run_until_complete(main)
  File "/Users/aca286/.pyenv/versions/3.8.7/lib/python3.8/asyncio/base_events.py", line 616, in run_until_complete
    return future.result()
  File "autolock-bug.py", line 28, in code_failing
    await renewer.close()
  File "/Users/aca286/.local/lib/python3.8/site-packages/azure/servicebus/aio/_async_auto_lock_renewer.py", line 236, in close
    await asyncio.wait(self._futures)
  File "/Users/aca286/.pyenv/versions/3.8.7/lib/python3.8/asyncio/tasks.py", line 413, in wait
    raise ValueError('Set of coroutines/Futures is empty.')
ValueError: Set of coroutines/Futures is empty.

[kristapratico]

Thanks for the feedback, we'll investigate and report back.

[yunhaoling]

hey Andrea Cassioli (@andrea-cassioli-maersk) , thanks for the report!

confirming the issue and the root cause if that when shutting down the async AutoLockRenwer via await asyncio.wait(self._futures), we don't check whether self._futures is empty leading to the error.

sorry about the trouble made to you! have a PR out to fix it: #19722 which should be included in our next release.