| 1 | /* |
| 2 | * Copyright 2006-2007 the original author or authors. |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | package org.springframework.batch.retry.backoff; |
| 18 | |
| 19 | import org.springframework.batch.retry.RetryContext; |
| 20 | import org.springframework.util.ClassUtils; |
| 21 | |
| 22 | /** |
| 23 | * Implementation of {@link BackOffPolicy} that increases the back off period |
| 24 | * for each retry attempt in a given set using the |
| 25 | * {@link Math#exp(double) exponential} function. <p/> This implementation is |
| 26 | * thread-safe and suitable for concurrent access. Modifications to the |
| 27 | * configuration do not affect any retry sets that are already in progress. <p/> |
| 28 | * The {@link #setInitialInterval(long)} property controls the initial value passed to |
| 29 | * {@link Math#exp(double)} and the {@link #setMultiplier(double)} property controls by |
| 30 | * how much this value is increased for each subsequent attempt. |
| 31 | * |
| 32 | * @author Rob Harrop |
| 33 | * @author Dave Syer |
| 34 | */ |
| 35 | public class ExponentialBackOffPolicy implements BackOffPolicy { |
| 36 | |
| 37 | /** |
| 38 | * The default 'initialInterval' value - 100 millisecs. Coupled with the |
| 39 | * default 'multiplier' value this gives a useful initial spread of pauses |
| 40 | * for 1-5 retries. |
| 41 | */ |
| 42 | public static final long DEFAULT_INITIAL_INTERVAL = 100L; |
| 43 | |
| 44 | /** |
| 45 | * The default maximum backoff time (30 seconds). |
| 46 | */ |
| 47 | public static final long DEFAULT_MAX_INTERVAL = 30000L; |
| 48 | |
| 49 | /** |
| 50 | * The default 'multiplier' value - value 2 (100% increase per backoff). |
| 51 | */ |
| 52 | public static final double DEFAULT_MULTIPLIER = 2; |
| 53 | |
| 54 | /** |
| 55 | * The initial sleep interval. |
| 56 | */ |
| 57 | private volatile long initialInterval = DEFAULT_INITIAL_INTERVAL; |
| 58 | |
| 59 | /** |
| 60 | * The maximum value of the backoff period in milliseconds. |
| 61 | */ |
| 62 | private volatile long maxInterval = DEFAULT_MAX_INTERVAL; |
| 63 | |
| 64 | /** |
| 65 | * The value to increment the exp seed with for each retry attempt. |
| 66 | */ |
| 67 | private volatile double multiplier = DEFAULT_MULTIPLIER; |
| 68 | |
| 69 | private Sleeper sleeper = new ObjectWaitSleeper(); |
| 70 | |
| 71 | /** |
| 72 | * Public setter for the {@link Sleeper} strategy. |
| 73 | * @param sleeper the sleeper to set defaults to {@link ObjectWaitSleeper}. |
| 74 | */ |
| 75 | public void setSleeper(Sleeper sleeper) { |
| 76 | this.sleeper = sleeper; |
| 77 | } |
| 78 | |
| 79 | /** |
| 80 | * Set the initial sleep interval value. Default is <code>1</code> |
| 81 | * millisecond. Cannot be set to a value less than one. |
| 82 | */ |
| 83 | public void setInitialInterval(long initialInterval) { |
| 84 | this.initialInterval = (initialInterval > 1 ? initialInterval : 1); |
| 85 | } |
| 86 | |
| 87 | /** |
| 88 | * Set the multiplier value. Default is '<code>1.0</code>'. |
| 89 | */ |
| 90 | public void setMultiplier(double multiplier) { |
| 91 | this.multiplier = (multiplier > 1.0 ? multiplier : 1.0); |
| 92 | } |
| 93 | |
| 94 | /** |
| 95 | * Setter for maximum back off period. Default is 30000 (30 seconds). the |
| 96 | * value will be reset to 1 if this method is called with a value less than |
| 97 | * 1. |
| 98 | * |
| 99 | * @param maxInterval in milliseconds. |
| 100 | */ |
| 101 | public void setMaxInterval(long maxInterval) { |
| 102 | this.maxInterval = maxInterval > 0 ? maxInterval : 1; |
| 103 | } |
| 104 | |
| 105 | /** |
| 106 | * Returns a new instance of {@link BackOffContext} configured |
| 107 | * with the 'expSeed' and 'increment' values. |
| 108 | */ |
| 109 | public BackOffContext start(RetryContext context) { |
| 110 | return new ExponentialBackOffContext(this.initialInterval, this.multiplier, this.maxInterval); |
| 111 | } |
| 112 | |
| 113 | /** |
| 114 | * Pause for a length of time equal to '<code>exp(backOffContext.expSeed)</code>'. |
| 115 | */ |
| 116 | public void backOff(BackOffContext backOffContext) throws BackOffInterruptedException { |
| 117 | ExponentialBackOffContext context = (ExponentialBackOffContext) backOffContext; |
| 118 | try { |
| 119 | sleeper.sleep(context.getSleepAndIncrement()); |
| 120 | } |
| 121 | catch (InterruptedException e) { |
| 122 | throw new BackOffInterruptedException("Thread interrupted while sleeping", e); |
| 123 | } |
| 124 | } |
| 125 | |
| 126 | private static class ExponentialBackOffContext implements BackOffContext { |
| 127 | |
| 128 | private final double multiplier; |
| 129 | |
| 130 | private long interval; |
| 131 | |
| 132 | private long maxInterval; |
| 133 | |
| 134 | public ExponentialBackOffContext(long expSeed, double multiplier, long maxInterval) { |
| 135 | this.interval = expSeed; |
| 136 | this.multiplier = multiplier; |
| 137 | this.maxInterval = maxInterval; |
| 138 | } |
| 139 | |
| 140 | public synchronized long getSleepAndIncrement() { |
| 141 | long sleep = this.interval; |
| 142 | if (sleep > maxInterval) { |
| 143 | sleep = (long) maxInterval; |
| 144 | } |
| 145 | else { |
| 146 | this.interval *= this.multiplier; |
| 147 | } |
| 148 | return sleep; |
| 149 | } |
| 150 | } |
| 151 | |
| 152 | public String toString() { |
| 153 | return ClassUtils.getShortName(getClass()) + "[initialInterval=" + initialInterval + ", multiplier=" |
| 154 | + multiplier + ", maxInterval=" + maxInterval + "]"; |
| 155 | } |
| 156 | |
| 157 | } |