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
{
			return ( result instanceof Date ) || ( result instanceof String );
		}
		/**
		 * To check whether the expressions are comparable. If so, they will be
		 * formatted to the comparable.For operands, only ExprTextAndValue is
		 * acceptable.
		 * 
		 * @param obj
		 * @param operator
		 * @param op1
		 * @param op2
		 * @return
		 * @throws DataException
		 */
		private static Object[] isComparable( Object obj, int operator,
				ExprTextAndValue op1, ExprTextAndValue op2 )
				throws DataException
		{
			if ( isFormatNeeded( obj, operator, op1, op2 ) )
				return formatToComparable( obj, op1, op2 );
			return null;
		}
		/**
		 * 
		 * @param obj
		 * @param operator
		 * @param op1
		 * @param op2
		 * @return