RoundRobinLoadBalance.java

/*
 *  Copyright 2009-2016 Weibo, Inc.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */

package com.weibo.api.motan.cluster.loadbalance;

import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;

import com.weibo.api.motan.core.extension.SpiMeta;
import com.weibo.api.motan.rpc.Referer;
import com.weibo.api.motan.rpc.Request;
import com.weibo.api.motan.util.MathUtil;

/**
 * 
 * Round robin loadbalance.
 * 
 * @author fishermen
 * @version V1.0 created at: 2013-6-13
 */
@SpiMeta(name = "roundrobin")
public class RoundRobinLoadBalance<T> extends AbstractLoadBalance<T> {

    private AtomicInteger idx = new AtomicInteger(0);

    @Override
    protected Referer<T> doSelect(Request request) {
        List<Referer<T>> referers = getReferers();

        int index = getNextPositive();
        for (int i = 0; i < referers.size(); i++) {
            Referer<T> ref = referers.get((i + index) % referers.size());
            if (ref.isAvailable()) {
                return ref;
            }
        }
        return null;
    }

    @Override
    protected void doSelectToHolder(Request request, List<Referer<T>> refersHolder) {
        List<Referer<T>> referers = getReferers();

        int index = getNextPositive();
        for (int i = 0, count = 0; i < referers.size() && count < MAX_REFERER_COUNT; i++) {
            Referer<T> referer = referers.get((i + index) % referers.size());
            if (referer.isAvailable()) {
                refersHolder.add(referer);
                count++;
            }
        }
    }

    // get positive int
    private int getNextPositive() {
        return MathUtil.getPositive(idx.incrementAndGet());
    }
}