【Dubbo源码学习】负载均衡算法（1）-随机算法

/**
 * random load balance.
 *
 */
public class RandomLoadBalance extends AbstractLoadBalance {

    public static final String NAME = "random";

    @Override
    protected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation invocation) {
        int length = invokers.size(); // Number of invokers
        boolean sameWeight = true; // Every invoker has the same weight?
        int firstWeight = getWeight(invokers.get(0), invocation);
        int totalWeight = firstWeight; // The sum of weights
        //判断是否所有服务提供者的权重都相同
        for (int i = 1; i < length; i++) {
            int weight = getWeight(invokers.get(i), invocation);
            totalWeight += weight; // Sum
            if (sameWeight && weight != firstWeight) {
                sameWeight = false;
            }
        }
        //所有服务提供者的权重不都相同，且权重之和>0，则随机生成一个0-totalWeight的随机数，
        // 然后用此随机数循环减去服务提供者的权重直到改值<0,则此服务提供者为目标服务提供者
        if (totalWeight > 0 && !sameWeight) {
            // If (not every invoker has the same weight & at least one invoker's weight>0), select randomly based on totalWeight.
            int offset = ThreadLocalRandom.current().nextInt(totalWeight);
            // Return a invoker based on the random value.
            for (int i = 0; i < length; i++) {
                offset -= getWeight(invokers.get(i), invocation);
                if (offset < 0) {
                    return invokers.get(i);
                }
            }
        }
        // If all invokers have the same weight value or totalWeight=0, return evenly.
        //所有服务提供者的权重都相同，则随机选取一个服务提供者,则此服务提供者为目标服务提供者
        return invokers.get(ThreadLocalRandom.current().nextInt(length));
    }

}