Bug 123840 Incorrect use of static fields in NEvaluator and FilterPassController
Data Engine classes org.eclipse.birt.data.engine.script.NEvaluator and FilterPassController (used for top-n and bottom-n filter process) use static class fields to store proessing data. This is not multi-thread safe. If there are concurrent requests running in the same JVM (even if they use different instances of DataEngine), data corruption will occur since multiple requests may get/set the static fields at the same time. These classes should keep all per-request data in instance fields. Each report query need to have its own instance.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/script/ScriptEvalUtil.java
}
	
	/**
	 * 
	 * @param resultObject
	 * @param resultOp1
	 * @return true if resultObject is Bottom N, false otherwise 
	 * @throws DataException
	 */
	private static boolean isBottomN( Object resultObject, Object resultOp1 )
			throws DataException
	{
		return NEvaluator.getInstance( NEvaluator.BOTTOM_INSTANCE )
				.evaluate( resultObject, resultOp1, false );
	}
	
	/**
	 * 
	 * @param resultObject
	 * @param resultOp1
	 * @return true if resultObject is Top Percent, false otherwise
	 * @throws DataException
	 */
	private static boolean isTopPercent( Object resultObject, Object resultOp1 )
			throws DataException
	{
		return NEvaluator.getInstance( NEvaluator.TOP_INSTANCE )
				.evaluate( resultObject, resultOp1, true );
	}
	/**