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From bdumon <...@git.apache.org>
Subject [GitHub] curator pull request: CURATOR-157 Avoid stack traces on close
Date Thu, 30 Oct 2014 17:36:57 GMT
Github user bdumon commented on a diff in the pull request:

    https://github.com/apache/curator/pull/51#discussion_r19621734
  
    --- Diff: curator-recipes/src/main/java/org/apache/curator/framework/recipes/cache/PathChildrenCache.java
---
    @@ -382,6 +383,11 @@ public void close() throws IOException
                 connectionStateListener = null;
                 childrenWatcher = null;
                 dataWatcher = null;
    +
    +            synchronized (backgroundTaskMonitor) {
    --- End diff --
    
    No problem, there might a problem in my reasoning, which is as follows: a refresh might
be going on when PathChildrenCache.close() is called. The refresh runs on a background thread,
the ZK event thread if I'm not mistaken. Since the processResult will be running within a
synchronized block, the PathChildrenCache.close() method will not be able to return until
the processResult is finished, since it tries to acquire the same lock.
    
    The second synchronized block in refresh(), around the statements "if-closed-return, getChildren()..."
is for similar reasons: the if-closed in that block might be called before the closed state
is set, while the getChildren might be launched afterwards, but by then zookeeper might already
be closed as well. By putting it in a synchronized block, we are sure no ZooKeeper operation
is going on after returning from the close() method, and CuratorFramework/ZooKeeper can be
closed without causing errors to be logged.


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