Paul Millar created ZOOKEEPER-2991:
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Summary: Server logs error on shutdown
Key: ZOOKEEPER-2991
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2991
Project: ZooKeeper
Issue Type: Bug
Components: server
Affects Versions: 3.4.11, 3.4.10
Reporter: Paul Millar
Commit d497aac4 introduced the ZooKeeperServer#registerServerShutdownHandler
method and corresponding ZooKeeperServerShutdownHandler class. Both the method
and class are package-protected, resulting in the expectation that non-ZK code
should not use either.
However, if registerServerShutdownHandler is *not* called, then ZK will log an
error:
{quote}ZKShutdownHandler is not registered, so ZooKeeper server won't take any
action on ERROR or SHUTDOWN server state changes
{quote}
There are several problems here. In order of importance (for me, at least!)
First, (most important) this certainly should not be logged as an error.
Depending on usage, there may be no need for a shutdown handler. Always
logging an error (with no opportunity to silence it) is therefore wrong.
Second, the ability to learn of state changes may be of general interest
(monitoring, etc); however, this is not possible if the method is protected.
Third, the method accepts a concrete class that is designed to use a
CountDownLatch. This is not appropriate in all cases. The method should be
updated to accept an interface.
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