"
When gossiper processes its messages in the background some of
the continuations may pop up after the gossiper is shutdown.
This, in turn, may result in unwanted code to be executed when
it doesn't expect.
In particular, storage_service notification hooks may try to
update system keyspace (with "fresh" peer info/state/tokens/etc).
This update doesn't work after drain because drain shuts down
commitlog. The intention was that gossiper did _not_ notify
anyone after drain, because it's shut down during drain too.
But since there are background continuations left, it's not
working as expected.
refs: #9567
tests: unit(dev), dtest.concurrent_schema_changes.snapshot(dev)
"
* 'br-gossiper-background-messages-2' of https://github.com/xemul/scylla:
gossiper: Guard background processing with gate
gossiper: Helper for background messaging processing
(cherry picked from commit 9e2b6176a2)
19da778271