Andrzej Bialecki created SOLR-11535:
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Summary: Weird behavior of CollectionStateWatcher
Key: SOLR-11535
URL: https://issues.apache.org/jira/browse/SOLR-11535
Project: Solr
Issue Type: Bug
Security Level: Public (Default Security Level. Issues are Public)
Affects Versions: 7.2, master (8.0)
Reporter: Andrzej Bialecki
While working on SOLR-11320 I noticed a strange behavior in
{{ActiveReplicaWatcher}}, which is a subclass of {{CollectionStateWatcher}} -
it appears that its {{onStateChanged}} method can be called from multiple
threads with exactly the same {{DocCollection}} state, ie. unchanged between
the calls.
This seems to run contrary to the javadoc, which implies that this method is
called only when the state actually changes, and it also doesn't mention
anything about the need for thread-safety in the method implementation.
I attached the log, which has a lot of additional debugging - but the most
pertinent part being where a Watcher-s hashCode is printed together with the
{{DocCollection}} - notice that these overlapping calls both submit an instance
of {{DocCollection}} with the same zkVersion.
[~dragonsinth], [~romseygeek] - could you please take a look at this? If this
behavior is expected then the javadoc should be updated to state clearly that
multiple calls can be made concurrently, with exactly the same state (which is
kind of a weak guarantee for a method called {{onStateChanged}} ;) ).
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