question: private Map . Entry < K , V > doRemoveFirstEntry ( ) { for ( Node < K , V > b , n ; ; ) { if ( ( n = ( b = head . node ) . next ) == null ) return null ; Node < K , V > f = n . next ; if ( n != b . next ) continue ; Object v = n . value ; if ( v == null ) { n . helpDelete ( b , f ) ; continue ; } if ( ! n . casValue ( v , null ) ) continue ; if ( ! n . appendMarker ( f ) || ! b . casNext ( n , f ) ) findFirst ( ) ; clearIndexToFirst ( ) ; @ SuppressWarnings ( "unchecked" ) V vv = ( V ) v ; return new AbstractMap . SimpleImmutableEntry < K , V > ( n . key , vv ) ; } }
target:  Removes first entry; returns its snapshot.