ASF GitHub Bot commented on CURATOR-447:

Github user dragonsinth commented on a diff in the pull request:

    --- Diff: 
    @@ -702,19 +687,18 @@ private TreeNode find(String findPath)
                 ImmutableMap.Builder<String, ChildData> builder = 
                 for ( Map.Entry<String, TreeNode> entry : map.entrySet() )
    -                TreeNode childNode = entry.getValue();
    -                ChildData childData = childNode.childData;
    -                // Double-check liveness after retreiving data.
    -                if ( childData != null && childNode.nodeState == 
NodeState.LIVE )
    +                ChildData childData = entry.getValue().childData;
    +                // Double-check liveness after retrieving data.
    +                if ( isLive(childData) )
    --- End diff --
    It's subtle, but the point I'm trying to make is that you have to read 
`.childData` exactly once, then check the liveness, then use only that value 
going forward.  It would be an error to remove the local variable here and 
reference `entry.getValue().childData` twice.
    It's a "double" check because _generally_ there shouldn't be any non-LIVE 
children in the parent `children` map that we're iterating.  But due to 
volatility we have to "double check" that child nodes read from the map are 
still alive after pulling `.childData`

> TreeCache: Improve memory usage and concurrent update logic
> -----------------------------------------------------------
>                 Key: CURATOR-447
>                 URL: https://issues.apache.org/jira/browse/CURATOR-447
>             Project: Apache Curator
>          Issue Type: Improvement
>          Components: Recipes
>    Affects Versions: 3.3.0, 2.12.0
>            Reporter: Nick Hill
>            Priority: Minor
>              Labels: performance
> Jira https://issues.apache.org/jira/browse/CURATOR-374 reduced per-node 
> memory usage in {{TreeCache}}. It can be improved further via removal of the 
> {{nodeState}} field - its {{LIVE}} state corresponds exactly to the adjacent 
> {{childData}} field being non-null, and a sentinel {{ChildData}} value can be 
> used for the {{DEAD}} state. This simplification also reduces the room for 
> bugs and state inconsistencies.
> Other improvements included:
> * A further simplification to have {{TreeNode}} extend {{AtomicReference}}, 
> which obviates the need for an explicit {{childData}} field
> * More robust cache update logic (in get-children and get-data event 
> callbacks)
> * Avoid overhead of incrementing/decrementing the {{outstandingOps}} atomic 
> integer post-initialization

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