Dark Reaper isn’t exiting early if there are no quarantined replicas

[dchristidis]

Motivation

This regression was introduced with commit f557841. If there are no quarantined replicas, list_rses() returns an empty list, but the execution continues. This leads to the Dark Reaper crashing with errors such as this:

Exception in thread Worker: 0, Total_Workers: 20:
Traceback (most recent call last):
  File "/usr/lib64/python2.7/threading.py", line 812, in __bootstrap_inner
    self.run()
  File "/usr/lib64/python2.7/threading.py", line 765, in run
    self.__target(*self.__args, **self.__kwargs)
  File "/usr/lib/python2.7/site-packages/rucio/daemons/reaper/dark_reaper.py", line 78, in reaper
    logging.info('Starting Dark Reaper %s-%s: Will work on RSEs: %s', worker_number, total_workers, ', '.join([rse['rse'] for rse in rses]))
TypeError: 'NoneType' object is not iterable

Modification

[patrick-austin]

I've changed the logic so it should exit early when quarantined_replica.list_rses() evaluates to False, but I'm not sure how to make the PR for this, as I made another change that removed the option --all-rses (the Boolean CLI option) as it was being overwritten (with the list of RSEs) before being evaluated (#3943). This was tagged as a feature, so is in the master branch but not 1.23.4, whereas the change here (#3888) was a patch so is in 1.23.4.

So if I create a PR for this fix against master, it'll have conflicts with the more recent #3943 PR which changed the same area of code. How can I make the fix for only 1.23.4? For reference I don't think this should be an issue with #3943 as that should check if there are any RSEs and exit early if needed.

[bziemons]

@patrick-austin if your PR against master fails the merging/testing against the latest release branch, @bari12 will see if he can easily solve the conflicts and otherwise you open a second PR against the release branch. Just wait on the go from Martin for that.

Edit: if it is a fix only for a supported release and not master, you can directly open a PR against the release branch.

[patrick-austin]

Thanks for the advice. It should only be needed for the 1.23.4 release, so I've rebased and will make the PR against 1.23-LTS.

[bari12]

👍 Thanks @patrick-austin and @bziemons 😃