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/*
* Copyright (C) 2017 The Android Open Source Project
*
* 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.android.dialer.common.backoff;
import com.android.dialer.common.Assert;
/**
* Given an initial backoff delay, D, a base multiplier, B, and a total number of backoffs, N, this
* class returns values in the exponential sequence, D, D*B, D*B^2, ... D*B^(N-1), ...
*
* <p>Example usage:
*
* <pre>
* long initialDelayMillis = 1000;
* double multiplier = 1.2;
* int backoffs = 10;
* ExponentialBackoff backoff = new ExponentialBackoff(initialDelayMillis, multiplier, backoffs);
* while (backoff.isInRange()) {
* ...
* sleep(backoff.getNextBackoff());
* }
* </pre>
*
* <p>Note: the base multiplier can be calculated using {@code ExponentialBaseCalculator}
*/
public final class ExponentialBackoff {
public final long initialDelayMillis;
public final double baseMultiplier;
public final int maximumBackoffs;
private double nextBackoff;
private int backoffCount;
/**
* Setup an exponential backoff with an initial delay, a base multiplier and a maximum number of
* backoff steps.
*
* @throws IllegalArgumentException for negative argument values
*/
public ExponentialBackoff(long initialDelayMillis, double baseMultiplier, int maximumBackoffs) {
Assert.checkArgument(initialDelayMillis > 0);
Assert.checkArgument(baseMultiplier > 0);
Assert.checkArgument(maximumBackoffs > 0);
this.initialDelayMillis = initialDelayMillis;
this.baseMultiplier = baseMultiplier;
this.maximumBackoffs = maximumBackoffs;
reset();
}
/**
* @return the next backoff time in the exponential sequence. Specifically, if D is the initial
* delay, B is the base multiplier and N is the total number of backoffs, then the return
* values will be: D, D*B, D*B^2, ... D*B^(N-1), ...
*/
public long getNextBackoff() {
long backoff = Math.round(nextBackoff);
backoffCount++;
nextBackoff *= baseMultiplier;
return backoff;
}
/** @return the number of times getNextBackoff() has been called */
public int getBackoffCount() {
return backoffCount;
}
/**
* @return {@code true} if getNextBackoff() has been called less than the maximumBackoffs value
* specified in the constructor.
*/
public boolean isInRange() {
return backoffCount < maximumBackoffs;
}
/**
* Reset the sequence of backoff values so the next call to getNextBackoff() will return the
* initial delay and getBackoffCount() will return 0
*/
public void reset() {
nextBackoff = initialDelayMillis;
backoffCount = 0;
}
}
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