I'm actually using the WriteLock from the ZookeeperNetEx C# code but I've
verified that the same issue exists in the Java recipe. On a busy system, I'm
fairly frequently seeing WriteLock that is never granted to client and gets
stuck.
What I believe is happening is the lock sets a watch on the request before him
via this code:
Stat stat = zookeeper.exists(lastChildId, new
LockWatcher());
if (stat != null) {
return Boolean.FALSE;
} else {
LOG.warn("Could not find the" +
" stats for
less than me: " + lastChildName.getName());
}
The problem (as I see it and I'm still fairly new to Zookeeper) is that if the
node represented by lastChildId has been deleted before the call to exists is
made, stat will return null and the watch will only ever be invoked when the
znode is created. And of course that will never happen.
The message is appearing in my log and my watcher for the lock is never invoked.
[2018-02-13 16:49:17.905 GMT WARNING WriteLock Could not find
the stats for less than me:
/token/SegmentProfileQueueToken/x-72057953399865370-0000000724]
I'm not entirely sure of the proper way of fixing this but I think setting
Id = null;
When stat is null should work.
Can someone verify if my analysis is correct?
--
Kathryn Hogg
Senior Manager Product Development
Phone: 763.201.2000
Fax: 763.201.5333
Open Access Technology International, Inc.
3660 Technology Drive NE, Minneapolis, MN 55418
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