modules/core/src/main/java/org/apache/ignite/internal/client/balancer/GridClientRoundRobinBalancer.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.ignite.internal.client.balancer;

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import org.apache.ignite.internal.client.GridClientException;
import org.apache.ignite.internal.client.GridClientNode;
import org.apache.ignite.internal.client.GridClientTopologyListener;
import org.apache.ignite.internal.util.typedef.internal.U;

/**
 * Simple balancer that implements round-robin balancing.
 */
public class GridClientRoundRobinBalancer extends GridClientBalancerAdapter implements GridClientTopologyListener {
    /** Lock. */
    private Lock lock = new ReentrantLock();

    /** Nodes to share load. */
    private LinkedList<UUID> nodeQueue = new LinkedList<>();

    /** {@inheritDoc} */
    @Override public GridClientNode balancedNode(Collection<? extends GridClientNode> nodes)
        throws GridClientException {
        assert !nodes.isEmpty();

        if (isPreferDirectNodes()) {
            Collection<GridClientNode> direct = selectDirectNodes(nodes);

            int directSize = direct.size();

            // If set of direct nodes is not empty and differ from original one
            // replace original set of nodes with directly available.
            if (directSize > 0 && directSize < nodes.size())
                nodes = direct;
        }

        Map<UUID, GridClientNode> lookup = U.newHashMap(nodes.size());

        for (GridClientNode node : nodes)
            lookup.put(node.nodeId(), node);

        lock.lock();

        try {
            GridClientNode balanced = null;

            for (Iterator<UUID> iter = nodeQueue.iterator(); iter.hasNext();) {
                UUID nodeId = iter.next();

                balanced = lookup.get(nodeId);

                if (balanced != null) {
                    iter.remove();

                    break;
                }
            }

            if (balanced != null) {
                nodeQueue.addLast(balanced.nodeId());

                return balanced;
            }

            throw new GridClientException("Passed nodes doesn't present in topology " +
                "[nodes=" + nodes + ", top=" + nodeQueue);
        }
        finally {
            lock.unlock();
        }
    }

    /** {@inheritDoc} */
    @Override public void onNodeAdded(GridClientNode node) {
        lock.lock();

        try {
            nodeQueue.addFirst(node.nodeId());
        }
        finally {
            lock.unlock();
        }
    }

    /** {@inheritDoc} */
    @Override public void onNodeRemoved(GridClientNode node) {
        lock.lock();

        try {
            nodeQueue.remove(node.nodeId());
        }
        finally {
            lock.unlock();
        }
    }
}