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From dragonsinth <...@git.apache.org>
Subject [GitHub] curator pull request: CURATOR-151: SharedValue/SharedCount API upd...
Date Thu, 09 Oct 2014 08:50:59 GMT
Github user dragonsinth commented on a diff in the pull request:

    https://github.com/apache/curator/pull/47#discussion_r18633269
  
    --- Diff: curator-recipes/src/main/java/org/apache/curator/framework/recipes/shared/SharedValue.java
---
    @@ -184,6 +178,25 @@ public boolean trySetValue(VersionedValue<byte[]> newValue)
throws Exception
             return false;
         }
     
    +    private void updateValue(int version, byte[] bytes)
    +    {
    +        while (true)
    +        {
    +            VersionedValue<byte[]> current = currentValue.get();
    +            if (current.getVersion() >= version)
    +            {
    +                // A newer version was concurrently set.
    +                return;
    +            }
    +            if ( currentValue.compareAndSet(current, new VersionedValue<byte[]>(version,
bytes)) )
    +            {
    +                // Successfully set.
    +                return;
    +            }
    +            // Lost a race, retry.
    +        }
    +    }
    +
         /**
    --- End diff --
    
    Ah, gotcha.  So this isn't new behavior -- this is just a standard compare-and-set loop
that replaces the synchronized keyword.  It's not round tripping to the server multiple times.
 There's still only one attempt to set the server value, and if it fails the calling methods
return false.  This is just atomically setting currentValue.  We could replace the loop with
a synchronized block, but performance would be worse.


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