CopyOnWriteArraySet源码学习

    /**
     * Creates an empty set.
     */
    public CopyOnWriteArraySet() {
        al = new CopyOnWriteArrayList<E>();
    }

    /**
     * Creates a set containing all of the elements of the specified
     * collection.
     * @param c the collection of elements to initially contain
     * @throws NullPointerException if the specified collection is null
     */
    public CopyOnWriteArraySet(Collection<? extends E> c) {
        if (c.getClass() == CopyOnWriteArraySet.class) {
            @SuppressWarnings("unchecked") CopyOnWriteArraySet<E> cc =
                (CopyOnWriteArraySet<E>)c;
            al = new CopyOnWriteArrayList<E>(cc.al);
        }
        else {
            al = new CopyOnWriteArrayList<E>();
            al.addAllAbsent(c);
        }
    }

    public int addAllAbsent(Collection<? extends E> c) {
        Object[] cs = c.toArray();
        if (cs.length == 0)
            return 0;
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
            Object[] elements = getArray();
            int len = elements.length;
            int added = 0;
            // uniquify and compact elements in cs
            for (int i = 0; i < cs.length; ++i) {
                Object e = cs[i];
                if (indexOf(e, elements, 0, len) < 0 &&
                    indexOf(e, cs, 0, added) < 0)
                    cs[added++] = e;
            }
            if (added > 0) {
                Object[] newElements = Arrays.copyOf(elements, len + added);
                System.arraycopy(cs, 0, newElements, len, added);
                setArray(newElements);
            }
            return added;
        } finally {
            lock.unlock();
        }
    }