jstorm-core/src/main/java/com/alibaba/jstorm/utils/RandomRange.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 com.alibaba.jstorm.utils;

import java.util.ArrayList;

/**
 * Shuffle the Range, This class is used in shuffle grouping, it is better than random, which can't make sure balance.
 * 
 * @author yannian
 * 
 */
public class RandomRange {
    private ArrayList<Integer> rr;
    private Integer amt;

    public RandomRange(int amt) {
        this.amt = amt;
        this.rr = rotating_random_range(amt);
    }

    public Integer nextInt() {
        return this.acquire_random_range_id();
    }

    private ArrayList<Integer> rotating_random_range(int amt) {

        ArrayList<Integer> range = new ArrayList<Integer>();
        for (int i = 0; i < amt; i++) {
            range.add(i);
        }

        ArrayList<Integer> rtn = new ArrayList<Integer>();
        for (int i = 0; i < amt; i++) {
            int index = (int) (Math.random() * range.size());
            rtn.add(range.remove(index));
        }

        return rtn;
    }

    private synchronized int acquire_random_range_id() {
        int ret = this.rr.remove(0);
        if (this.rr.size() == 0) {
            this.rr.addAll(rotating_random_range(this.amt));
        }
        return ret;
    }

    public static void main(String[] args) {
        RandomRange test = new RandomRange(10);

        for (int i = 0; i < 10; i++) {
            System.out.println(test.acquire_random_range_id());
        }
    }

}