/**
* 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.waveprotocol.wave.model.util;
/**
* Simiple fibonacci back off with fuzzing. This is important for reconnection so that
* everyone doesn't retry at the same time.
*
* @author zdwang@google.com (David Wang)
*/
public class FuzzingBackOffGenerator {
public static class BackOffParameters {
public final int targetDelay;
public final int minimumDelay;
private BackOffParameters(int targetDelay, int minimumDelay) {
this.targetDelay = targetDelay;
this.minimumDelay = minimumDelay;
}
}
/** Randomisation factor. Must be between 0 and 1. */
private final double randomisationFactor;
/** The first time we back off. */
private final int initialBackOff;
/** The max back off value, it'll be fuzzed. */
private final int maxBackOff;
/** The next time we've backed off. */
private int nextBackOffTime;
/** The current back off time. */
private int backOffTime;
/**
* @param initialBackOff Initial value to back off. This class does not interpret the meaning of
* this value. must be > 0
* @param maxBackOff Max value to back off
* @param randomisationFactor between 0 and 1 to control the range of randomness.
*/
public FuzzingBackOffGenerator(int initialBackOff, int maxBackOff, double randomisationFactor) {
if (randomisationFactor < 0 || randomisationFactor > 1) {
throw new IllegalArgumentException("randomisationFactor must be between 0 and 1. actual " +
randomisationFactor);
}
if (initialBackOff <= 0) {
throw new IllegalArgumentException("initialBackOff must be between 0 and 1. actual " +
initialBackOff);
}
this.randomisationFactor = randomisationFactor;
this.initialBackOff = initialBackOff;
this.maxBackOff = maxBackOff;
this.nextBackOffTime = initialBackOff;
this.backOffTime = 0;
}
/** Gets the next back off time. Until maxBackOff is reached. */
public BackOffParameters next() {
int ret = Math.min(nextBackOffTime, maxBackOff);
nextBackOffTime += backOffTime;
backOffTime = ret;
int randomizeTime = (int) (backOffTime * (1.0 + (Math.random() * randomisationFactor)));
int minAllowedTime = (int)Math.round(randomizeTime - backOffTime * randomisationFactor);
return new BackOffParameters(randomizeTime, minAllowedTime);
}
/**
* Resets the back off.
*/
public void reset() {
nextBackOffTime = initialBackOff;
backOffTime = 0;
}
}