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/*
* Copyright 2011 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 com.google.ipc.invalidation.util;
import java.util.Random;
/**
* An abstraction to "smear" values by a given percent. Useful for randomizing delays a little bit
* so that (say) processes do not get synchronized on time inadvertently, e.g., a heartbeat task
* that sends a message every few minutes is smeared so that all clients do not end up sending a
* message at the same time. In particular, given a {@code delay}, returns a value that is randomly
* distributed between [delay - smearPercent * delay, delay + smearPercent * delay]
*
*/
public class Smearer {
private final Random random;
/** The percentage [0, 1.0] for smearing the delay. */
private double smearFraction;
/**
* Creates a smearer with the given random number generator.
* <p>
* REQUIRES: 0 < smearPercent <= 100
*/
public Smearer(Random random, final int smearPercent) {
Preconditions.checkState((smearPercent >= 0) && (smearPercent <= 100));
this.random = random;
this.smearFraction = smearPercent / 100.0;
}
/**
* Given a {@code delay}, returns a value that is randomly distributed between
* [delay - smearPercent * delay, delay + smearPercent * delay]
*/
public int getSmearedDelay(int delay) {
// Get a random number between -1 and 1 and then multiply that by the smear
// fraction.
double smearFactor = (2 * random.nextDouble() - 1.0) * smearFraction;
return (int) Math.ceil(delay + delay * smearFactor);
}
}
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