97 lines
3.1 KiB
Java
97 lines
3.1 KiB
Java
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/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.android.dialer.common.backoff;
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import com.android.dialer.common.Assert;
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/**
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* Given an initial backoff delay, D, a base multiplier, B, and a total number of backoffs, N, this
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* class returns values in the exponential sequence, D, D*B, D*B^2, ... D*B^(N-1), ...
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*
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* <p>Example usage:
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*
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* <pre>
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* long initialDelayMillis = 1000;
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* double multiplier = 1.2;
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* int backoffs = 10;
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* ExponentialBackoff backoff = new ExponentialBackoff(initialDelayMillis, multiplier, backoffs);
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* while (backoff.isInRange()) {
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* ...
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* sleep(backoff.getNextBackoff());
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* }
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* </pre>
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*
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* <p>Note: the base multiplier can be calculated using {@code ExponentialBaseCalculator}
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*/
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public final class ExponentialBackoff {
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public final long initialDelayMillis;
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public final double baseMultiplier;
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public final int maximumBackoffs;
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private double nextBackoff;
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private int backoffCount;
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/**
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* Setup an exponential backoff with an initial delay, a base multiplier and a maximum number of
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* backoff steps.
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*
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* @throws IllegalArgumentException for negative argument values
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*/
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public ExponentialBackoff(long initialDelayMillis, double baseMultiplier, int maximumBackoffs) {
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Assert.checkArgument(initialDelayMillis > 0);
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Assert.checkArgument(baseMultiplier > 0);
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Assert.checkArgument(maximumBackoffs > 0);
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this.initialDelayMillis = initialDelayMillis;
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this.baseMultiplier = baseMultiplier;
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this.maximumBackoffs = maximumBackoffs;
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reset();
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}
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/**
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* @return the next backoff time in the exponential sequence. Specifically, if D is the initial
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* delay, B is the base multiplier and N is the total number of backoffs, then the return
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* values will be: D, D*B, D*B^2, ... D*B^(N-1), ...
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*/
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public long getNextBackoff() {
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long backoff = Math.round(nextBackoff);
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backoffCount++;
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nextBackoff *= baseMultiplier;
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return backoff;
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}
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/** @return the number of times getNextBackoff() has been called */
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public int getBackoffCount() {
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return backoffCount;
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}
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/**
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* @return {@code true} if getNextBackoff() has been called less than the maximumBackoffs value
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* specified in the constructor.
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*/
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public boolean isInRange() {
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return backoffCount < maximumBackoffs;
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}
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/**
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* Reset the sequence of backoff values so the next call to getNextBackoff() will return the
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* initial delay and getBackoffCount() will return 0
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*/
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public void reset() {
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nextBackoff = initialDelayMillis;
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backoffCount = 0;
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}
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}
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