Java – safely handle concurrent Memcache updates in App Engine

Google Apps engine documentation for secure handling of concurrent Memcache updates:

I am building an application that needs accurate cache values. Here is my code. Please check whether it is correct for me:

...
        IdentifiableValue oldCountIdValue = mc.getIdentifiable( cacheKey );
        Long count = ( Long ) oldCountIdValue.getValue();
        if( count != null )
        {
            this.oldCountValue = oldCountIdValue;
            return count;
        }

        Long result = new Long( q.count() );
        mc.putIfUntouched( cacheKey,oldCountValue,result );
        return result;

My question is: what if putifuntouched () returns false? What should this code return? how?

When adding an entity to the data store, I use the following:

mc.increment( cacheKey,1,initValue );

Is this usage correct?

Thank you.

Solution

I need to know your code:

If yes, the code should be:

IdentifiableValue oldCountIdValue = mc.getIdentifiable( cacheKey );
if (oldCountIdValue != null) {
   return ( Long ) oldCountIdValue.getValue();
}

Long result = new Long( q.count() );
mc.putIfUntouched( cacheKey,result );
return result;

If putifuntouched returns null, the result variable is no longer accurate. You can ignore and return the current result or load the result from the cache