com.bfd.harpc.loadbalance.RoundRobinStrategy.java Source code

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Here is the source code for com.bfd.harpc.loadbalance.RoundRobinStrategy.java

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/**
 * Copyright (C) 2015 Baifendian Corporation
 *
 * 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.bfd.harpc.loadbalance;

import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import com.bfd.harpc.loadbalance.common.ResourceExhaustedException;
import com.google.common.collect.Iterators;
import com.google.common.collect.Lists;

/**
 * A load balancer that distributes load by randomizing the list of available
 * backends, and then rotating through them evenly.
 */
public class RoundRobinStrategy<S> extends StaticLoadBalancingStrategy<S> {

    private volatile Iterator<S> iterator = Iterators.emptyIterator();

    @Override
    protected Collection<S> onBackendsOffered(Set<S> targets) {
        List<S> newTargets = Lists.newArrayList(targets);
        Collections.shuffle(newTargets);
        iterator = Iterators.cycle(newTargets);
        return newTargets;
    }

    @Override
    public S nextBackend() throws ResourceExhaustedException {
        if (!iterator.hasNext())
            throw new ResourceExhaustedException("No backends available!");
        return iterator.next();
    }

}