question: private boolean addIfAbsent ( E e , Object [ ] snapshot ) { final ReentrantLock lock = this . lock ; lock . lock ( ) ; try { Object [ ] current = getArray ( ) ; int len = current . length ; if ( snapshot != current ) { int common = Math . min ( snapshot . length , len ) ; for ( int i = 0 ; i < common ; i ++ ) if ( current [ i ] != snapshot [ i ] && eq ( e , current [ i ] ) ) return false ; if ( indexOf ( e , current , common , len ) >= 0 ) return false ; } Object [ ] newElements = Arrays . copyOf ( current , len + 1 ) ; newElements [ len ] = e ; setArray ( newElements ) ; return true ; } finally { lock . unlock ( ) ; } }
target:  A version of addIfAbsent using the strong hint that given recent snapshot does not contain e.