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From Andor Molnar <an...@apache.org>
Subject JAVA 11 build is broken on 3.5
Date Fri, 04 Jan 2019 13:23:25 GMT
Hi team / Enrico,

I’d like to get feedback from the community on the following patch (moving the discussion
from GitHub to here):

https://issues.apache.org/jira/browse/ZOOKEEPER-3204 <https://issues.apache.org/jira/browse/ZOOKEEPER-3204>
https://github.com/apache/zookeeper/pull/753 <https://github.com/apache/zookeeper/pull/753>

In a nutshell: looks like that Netty 3.10 is broken under Java 11: it doesn’t properly close
the underlying socket (probably not closing the registered NIO selectors) and reconfig tests
are unable to re-bind the ports. This problem is similar that we already fixed in NIO with
the following patch:
https://github.com/apache/zookeeper/commit/c3babb94275ad667dc71c10dcb08a383a3c154c2 <https://github.com/apache/zookeeper/commit/c3babb94275ad667dc71c10dcb08a383a3c154c2>
The problem doesn’t show up on trunk which has been recently upgraded to Netty 4.

- Start embedded ZK, stop it and try to restart on the same port, or
- Start normal ensemble and reconfig to use different (client) port. Then reconfig back to
the original port which should fail. (that’s the scenario which is covered in ReconfigTest)

I created the above patch (#753) to backport Netty 4 upgrade to 3.5 and it fixes the problem
with Java 11 (it doesn’t cause regression in the pre-commit build either), but Enrico is
having concerns about making such big change before the release.

I tend to agree, but let’s see what are the options.

- Do we have to fix this? - Yes. Java 11 is LTS and I the bug is critical.
- Can we fix Netty 3? - Maybe. Let’s say we find the bug in Netty 3, what can we do?
       a) We cannot workaround from ZooKeeper itself and have to submit a pull request for
Netty. I think it’s quite unlikely that they will accept the change given it’s not a security
bug, but even if they did, only the upgraded version of Netty 3 would work properly with ZooKeeper.
       b) We can workaround it from ZooKeeper: that could be option #1, but I have a strong
feeling about it’s not going to be the case.
- Shall we upgrade to Netty 4? - this is option #2

Please share your thoughts, maybe you know about an option #3.


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