Fix deadlock introduced in #2109 #2196
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In the before times (Feb 2020), we submitted this issue asking for feedback prior to submitting a PR:
#1608
In January of this year, some aspects of the fix were merged through #2109. We noticed, however, that a fix for a deadlock issue we found after about a year of running #1608 in heavy production did not make its way into #2109.
This was quite a while ago, so I do not recall the details of how exactly we recreated the issue but I definitely recall identifying hanging workers that printed "consumer/broker/%d accumulated %d new subscriptions" but not the expected subsequent logs. I also imagine that at the time I implemented this fix I tracked down the precise scenario where bc.wait would block and cause a deadlock... but I don't have this explanation at hand. Do with this PR what you will :)