public boolean addIfAbsent(E e) {

        Object[] snapshot = getArray();

        return indexOf(e, snapshot, , snapshot.length) >=  ? false :

            addIfAbsent(e, snapshot);

    }

 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) {

                // Optimize for lost race to another addXXX operation

                int common = Math.min(snapshot.length, len);

                for (int i = ; i < common; i++)

                    if (current[i] != snapshot[i] && eq(e, current[i]))

                        return false;

                if (indexOf(e, current, common, len) >= )

                        return false;

            }

            Object[] newElements = Arrays.copyOf(current, len + );

            newElements[len] = e;

            setArray(newElements);

            return true;

        } finally {

            lock.unlock();

        }

    }