/**
 * 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
        //判斷是否所有服務提供者的權重都相同
 

        for (int i = 1; i < length; i++) {
            int weight = getWeight(invokers.get(i), invocation);
            totalWeight += weight; // Sum
            if (sameWeight && weight != firstWeight) {
                sameWeight = false;
            }
        }
        //所有服務提供者的權重不都相同，且權重之和>0，則隨機生成一個0-totalWeight的隨機數，
 

        // 然後用此隨機數迴圈減去服務提供者的權重直到改值<0,則此服務提供者為目標服務提供者
        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.
        //所有服務提供者的權重都相同，則隨機選取一個服務提供者,則此服務提供者為目標服務提供者
 

        return invokers.get(ThreadLocalRandom.current().nextInt(length));
    }

}