Use connection manager for keepalives

[DavidStirling]

Fixes #18

If you don't close sessions aggressively the omero-py keepalive system currerntly doesn't shut down properly and hangs Python on exit (we're trying to use an atexit handler to manage sessions). To fix this I've added our own keepalive ping system which makes use of the connection tracker we already have, which should do until the underlying issues in omero-py are resolved.

Basic test script:

import omero2pandas
import time

print("Starting test")
connector = omero2pandas.connect_to_omero(allow_token=False, server=<server>, username=<user>, password=<pwd>)
client = connector.get_client()
print("Connected:", connector.connected)
time.sleep(5)
print("Complete, shutting down!")

Should fail to exit without PR, but exit properly with.

[chris-allan]

I'm not sure about this. It effectively recapitulates and effectively works against what the omero-py client object and service factory already do. We should talk this through more to understand what's going on.

[chris-allan]

Relevant upstream PR is ome/omero-py#424.

[chris-allan]

Going to approve this for now so it can go in temporarily for as long as it's required.

We will need to work to get ome/omero-py#424 in as soon as possible and then follow up here refactoring as required and depending explicitly on the omero-py version that includes that change.

This PR will be for @erindiel, @sbesson and @emilroz to get integrated and shipping as required for other work next week.

[sbesson]

I can reproduce the exit issue using the existing omero2pandas and latest omero-py code. With the proposed changes, I confirm the test script exits as expected rather than hanging.

There is a lot of logic injected in connect.py and I have not assessed all the conditions of error but it is my understanding this is meant as a temporary workaround so also proposing to get this into the next omero2pandas release and focus on getting the omero-py changes reviewed under all scenarios and merged so that we can revert to using the upstream keep alive logic.

[sbesson]

omero-py 5.19.5 has just been released with the corresponding upstream fix