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https://issues.apache.org/jira/browse/CURATOR-447?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16361409#comment-16361409
 ] 

ASF GitHub Bot commented on CURATOR-447:
----------------------------------------

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

    https://github.com/apache/curator/pull/250#discussion_r167672355
  
    --- Diff: 
curator-recipes/src/main/java/org/apache/curator/framework/recipes/cache/TreeCache.java
 ---
    @@ -397,14 +396,11 @@ public void processResult(CuratorFramework client, 
CuratorEvent event) throws Ex
                             break;
                         }
     
    -                    ConcurrentMap<String, TreeNode> childMap = children;
    -                    if ( childMap == null )
    +                    ConcurrentMap<String, TreeNode> childMap;
    +                    while ( (childMap = children) == null )
                         {
                             childMap = Maps.newConcurrentMap();
    -                        if ( !childrenUpdater.compareAndSet(this, null, 
childMap) )
    -                        {
    -                            childMap = children;
    -                        }
    +                        if ( childrenUpdater.compareAndSet(this, null, 
childMap) ) break;
    --- End diff --
    
    I see why you turned this into a loop (nice catch), but I think it reads a 
little clearly and more deliberateif you revert back to the original code and 
just change the `if` -> `while`.  Ideally if Curator moves wholesale to Java 
1.8,  funcs, like:
    
    ```
                        ConcurrentMap<String, TreeNode> childMap = 
childrenUpdater.updateAndGet(this, (oldChildren) -> {
                            return oldChildren != null ? oldChildren : 
Maps.newConcurrentMap();
                        });
    ```


> 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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