question: @ Override public Long call ( ) throws Exception { final boolean TRACE = log . isTraceEnabled ( ) ; if ( pushDownApply ( ) ) { program . apply ( gasState , u , null ) ; } if ( ! program . isChanged ( gasState , u ) ) { return 0L ; } long nedges = 0L ; final IGASScheduler sch = scheduler ( ) ; final Iterator < Statement > eitr = graphAccessor . getEdges ( GASContext . this , u , getEdgesEnum ( ) ) ; try { while ( eitr . hasNext ( ) ) { final Statement e = eitr . next ( ) ; nedges ++ ; if ( TRACE ) log . trace ( "e=" + gasState . toString ( e ) ) ; program . scatter ( gasState , sch , u , e ) ; } } finally { } return nedges ; }
target:  Execute the scatter for the vertex.