/* * 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), ... * *
Example usage: * *
* long initialDelayMillis = 1000; * double multiplier = 1.2; * int backoffs = 10; * ExponentialBackoff backoff = new ExponentialBackoff(initialDelayMillis, multiplier, backoffs); * while (backoff.isInRange()) { * ... * sleep(backoff.getNextBackoff()); * } ** *
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; } }