java - 如何实现简单的循环负载均衡器

我想实现一个简单的循环负载均衡器，并且希望使用“getServer”方法实现线程安全:

private static int[] servers = new int[]{0,1,2};


private static int SERVER_INDEX = 0;

//not fast enough?
public synchronized static int getServer() {
    SERVER_INDEX++;
    if (SERVER_INDEX >= servers.length - 1) {
        SERVER_INDEX = 0;
    }
    return servers[SERVER_INDEX];
}


private static AtomicInteger SERVER_INDEX_2 = new AtomicInteger(0);

//not thread-safe and will get Exception
public static int getServer2() {
    int index = SERVER_INDEX_2.getAndIncrement();
    if (index >= servers.length - 1) {
        SERVER_INDEX_2.set(0);
    }
    return servers[index]; //ERROR! arrayIndexOutOfRange
}



private static AtomicLong SERVER_INDEX_3 = new AtomicLong(0);

//thread-safe but...
public static int getServer3() {
    long longIndex = SERVER_INDEX_3.getAndIncrement();
    long index = longIndex % servers.length;
    int intIndex = (int)index;
    return servers[intIndex]; //May overflow someday! 'intIndex can be negative'...
}

我认为以上所有内容还不够好。有没有简单而优雅的方法？

最佳答案

在Java 8中，可以按以下方式使用getAndAccumulate:

private static AtomicInteger ind = new AtomicInteger(0);

public static int getServer() {
    return servers[ind.getAndAccumulate(servers.length, (cur, n)->cur >= n-1 ? 0 : cur+1)];
}