modules/core/src/main/java/org/apache/ignite/internal/client/balancer/GridClientRandomBalancer.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.List;
import java.util.Random;
import org.apache.ignite.internal.client.GridClientNode;

/**
 * Simple balancer that relies on random node selection from a given collection. This implementation
 * has no any caches and treats each given collection as a new one.
 * <p>
 * More strictly, for any non-empty collection of size <tt>n</tt> the probability of selection of any
 * node in this collection will be <tt>1/n</tt>.
 */
public class GridClientRandomBalancer extends GridClientBalancerAdapter {
    /** Random for node selection. */
    private Random random = new Random();

    /**
     * Picks up a random node from a collection.
     *
     * @param nodes Nodes to pick from.
     * @return Random node from collection.
     */
    @Override public GridClientNode balancedNode(Collection<? extends GridClientNode> nodes) {
        assert !nodes.isEmpty();

        int size = nodes.size();

        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 < size) {
                nodes = direct;
                size = nodes.size();
            }
        }

        int idx = random.nextInt(size);

        if (nodes instanceof List)
            return ((List<GridClientNode>)nodes).get(idx);
        else {
            Iterator<? extends GridClientNode> it = nodes.iterator();

            while (idx > 0) {
                it.next();

                idx--;
            }

            return it.next();
        }
    }
}