JDK-1.8-CopyOnWriteSet

CopyOnWriteSet

看了下CopyOnWriteSet源码,底层使用的是CopyOnWriteList,根据底层的实现,每次读取都是N的复杂度.每次写也是N的复杂度.有个代码可以看一下,

来自CopyOnWriteList

 public boolean addIfAbsent(E e) {
        Object[] snapshot = getArray();
        return indexOf(e, snapshot, 0, snapshot.length) >= 0 ? 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 = 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();
        }
    }

代码的逻辑如下,获取数组snapshot,执行indexOf,如果没有,准备把新元素加入进去.

在实际加入方法内,获取锁,获取最新的数组current,如果俩个指针还是同一个指针,那就是没有改变,要不然.

取来个数组长度的最小值.

对current里面获取改变后的元素执行eq方法.对未比较过的元素执行indexof方法.要是还是没有重复的方法,就加入e