zookeeper-api/src/main/java/org/apache/helix/zookeeper/zkclient/util/ExponentialBackoffStrategy.java

package org.apache.helix.zookeeper.zkclient.util;

/*
 * 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.
 */

import java.util.Random;


public class ExponentialBackoffStrategy {
  private final long INIT_RETRY_INTERVAL = 500;
  private final long _maxRetryInterval;
  private final boolean _addJitter;
  private final Random _ran;

  public ExponentialBackoffStrategy(long maxRetryInterval, boolean addJitter) {
    _maxRetryInterval = maxRetryInterval;
    _addJitter = addJitter;
    _ran = new Random(System.currentTimeMillis());
  }

  public long getNextWaitInterval(int numberOfTriesFailed) {
    double exponentialMultiplier = Math.pow(2.0, numberOfTriesFailed - 1);
    double result = exponentialMultiplier * INIT_RETRY_INTERVAL;

    if (_maxRetryInterval > 0 && result > _maxRetryInterval) {
      result = _maxRetryInterval;
    }

    if (_addJitter) {
      // Adding jitter so the real result would be 75% to 100% of the original result.
      // Don't directly add jitter here, since it may exceed the max retry interval setup
      result = result * (0.75 + _ran.nextDouble() % 0.25);
    }

    return (long) result;
  }
}