[英]how to implement a simple round-robin load balancer
我想實現一個簡單的循環負載均衡器,我希望'getServer'方法是線程安全的:
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'...
}
我認為以上都不夠好。 有一種簡單而優雅的方法嗎?
在Java 8中,您可以使用getAndAccumulate ,如下所示:
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)];
}
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