/**
* Copyright 2009 Google Inc.
*
* Licensed 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;
}
}