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https://issues.apache.org/jira/browse/CURATOR-157?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14327675#comment-14327675
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ASF GitHub Bot commented on CURATOR-157:
----------------------------------------
Github user madrob commented on the pull request:
https://github.com/apache/curator/pull/51#issuecomment-75078668
Ok, I think I got myself confused between the two close operations.
Can you add a test (probably with an artificial delay to ensure ordering)
that would fail before your patch and pass after to make sure that we properly
handle this? Sorry to push back on this, but I'm not sure anymore of my own
ability to understand the code 100%.
> Avoid stack traces closing PathChildrenCache followed by closing
> CuratorFramework
> ---------------------------------------------------------------------------------
>
> Key: CURATOR-157
> URL: https://issues.apache.org/jira/browse/CURATOR-157
> Project: Apache Curator
> Issue Type: Improvement
> Reporter: Bruno Dumon
> Assignee: Jordan Zimmerman
> Attachments: LogProblemIllustration.java
>
>
> When closing PathChildrenCache, and immediately afterwards closing
> CuratorFramework, some ERROR-level stack traces are logged.
> This was previously reported on the mailing list:
> http://curator.markmail.org/thread/bmfr62ekx5p2vv7f
> The cause is that the BackgroundCallback defined in
> PathChildrenCache.refresh() will, when triggered, perform some more ZooKeeper
> operations.
> Thus one can get in sequences such as:
> * operation with BackgroundCallback is submitted
> * processResult of the BackgroundCallback is called
> * PathChildrenCache is closed
> * CuratorFramework is closed
> * processResult, which is running on another thread, comes to the point it
> does operations on ZooKeeper, which fail because ZooKeeper is closed.
> There is no real impact on the application, it is just for log-esthetical
> reasons that I'd like to avoid it.
> In the more common case, the processResult will receive an
> IllegalStateException, which could be easily catched and ignored in
> PathChildrenCache if the PathChildrenCache is closed:
> {noformat}
> 14/10/30 11:24:51 ERROR
> org.apache.curator.framework.imps.CuratorFrameworkImpl: Background exception
> was not retry-able or retry gave up
> java.lang.IllegalStateException: instance must be started before calling this
> method
> at
> com.google.common.base.Preconditions.checkState(Preconditions.java:149)
> at
> org.apache.curator.framework.imps.CuratorFrameworkImpl.getData(CuratorFrameworkImpl.java:360)
> at
> org.apache.curator.framework.recipes.cache.PathChildrenCache.getDataAndStat(PathChildrenCache.java:545)
> at
> org.apache.curator.framework.recipes.cache.PathChildrenCache.processChildren(PathChildrenCache.java:668)
> at
> org.apache.curator.framework.recipes.cache.PathChildrenCache.access$200(PathChildrenCache.java:68)
> at
> org.apache.curator.framework.recipes.cache.PathChildrenCache$4.processResult(PathChildrenCache.java:490)
> at
> org.apache.curator.framework.imps.CuratorFrameworkImpl.sendToBackgroundCallback(CuratorFrameworkImpl.java:715)
> at
> org.apache.curator.framework.imps.CuratorFrameworkImpl.processBackgroundOperation(CuratorFrameworkImpl.java:502)
> at
> org.apache.curator.framework.imps.GetChildrenBuilderImpl$2.processResult(GetChildrenBuilderImpl.java:166)
> at
> org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:590)
> at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:498)
> {noformat}
> But sometimes it also fails with other async operations deeper down:
> {noformat}
> 14/10/30 11:24:51 ERROR
> org.apache.curator.framework.imps.CuratorFrameworkImpl: Background exception
> was not retry-able or retry gave up
> java.lang.IllegalStateException: Client is not started
> at
> com.google.common.base.Preconditions.checkState(Preconditions.java:149)
> at
> org.apache.curator.CuratorZookeeperClient.getZooKeeper(CuratorZookeeperClient.java:113)
> at
> org.apache.curator.framework.imps.CuratorFrameworkImpl.getZooKeeper(CuratorFrameworkImpl.java:474)
> at
> org.apache.curator.framework.imps.GetDataBuilderImpl.performBackgroundOperation(GetDataBuilderImpl.java:263)
> at
> org.apache.curator.framework.imps.OperationAndData.callPerformBackgroundOperation(OperationAndData.java:65)
> at
> org.apache.curator.framework.imps.CuratorFrameworkImpl.performBackgroundOperation(CuratorFrameworkImpl.java:789)
> at
> org.apache.curator.framework.imps.CuratorFrameworkImpl.processBackgroundOperation(CuratorFrameworkImpl.java:487)
> at
> org.apache.curator.framework.imps.GetDataBuilderImpl.forPath(GetDataBuilderImpl.java:275)
> at
> org.apache.curator.framework.imps.GetDataBuilderImpl.forPath(GetDataBuilderImpl.java:41)
> at
> org.apache.curator.framework.recipes.cache.PathChildrenCache.getDataAndStat(PathChildrenCache.java:545)
> at
> org.apache.curator.framework.recipes.cache.PathChildrenCache.processChildren(PathChildrenCache.java:668)
> at
> org.apache.curator.framework.recipes.cache.PathChildrenCache.access$200(PathChildrenCache.java:68)
> at
> org.apache.curator.framework.recipes.cache.PathChildrenCache$4.processResult(PathChildrenCache.java:490)
> at
> org.apache.curator.framework.imps.CuratorFrameworkImpl.sendToBackgroundCallback(CuratorFrameworkImpl.java:715)
> at
> org.apache.curator.framework.imps.CuratorFrameworkImpl.processBackgroundOperation(CuratorFrameworkImpl.java:502)
> at
> org.apache.curator.framework.imps.GetChildrenBuilderImpl$2.processResult(GetChildrenBuilderImpl.java:166)
> at
> org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:590)
> at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:498)
> {noformat}
> Therefore I have created a patch where PathChildrenCache.close() will wait
> until the possibly running BackgroundCallback is finished.
> I will also attach a small class that illustrates the problem.
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