question: final protected void startOp ( final IStartOpMessage msg ) { if ( ! controller ) throw new UnsupportedOperationException ( ERR_NOT_CONTROLLER ) ; if ( msg == null ) throw new IllegalArgumentException ( ) ; if ( ! queryId . equals ( msg . getQueryId ( ) ) ) throw new IllegalArgumentException ( ) ; lock . lock ( ) ; try { if ( log . isTraceEnabled ( ) ) log . trace ( msg . toString ( ) ) ; if ( future . isDone ( ) ) throw new RuntimeException ( "Query is done" ) ; runState . startOp ( msg ) ; } catch ( TimeoutException ex ) { halt ( ex ) ; } finally { lock . unlock ( ) ; } }
target:  Message provides notice that the operator has started execution and will consume some specific number of binding set chunks.