1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one 3 * or more contributor license agreements. See the NOTICE file 4 * distributed with this work for additional information 5 * regarding copyright ownership. The ASF licenses this file 6 * to you under the Apache License, Version 2.0 (the 7 * "License"); you may not use this file except in compliance 8 * with the License. You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, 13 * software distributed under the License is distributed on an 14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 15 * KIND, either express or implied. See the License for the 16 * specific language governing permissions and limitations 17 * under the License. 18 */ 19 package org.eclipse.aether.named.support; 20 21 import java.util.concurrent.Callable; 22 import java.util.concurrent.TimeUnit; 23 import java.util.function.Predicate; 24 25 import org.slf4j.Logger; 26 import org.slf4j.LoggerFactory; 27 28 /** 29 * Retry helper: retries given {@code Callable} as long as it returns {@code null} (interpreted 30 * as "no answer yet") or given time passes. This helper implements similar semantics regarding 31 * caller threads as {@link java.util.concurrent.locks.Lock#tryLock(long, TimeUnit)} method does: 32 * blocks the caller thread until operation return non-{@code null} value within the given waiting 33 * time and the current thread has not been {@linkplain Thread#interrupt interrupted}. 34 * 35 * @since 1.7.3 36 */ 37 public final class Retry { 38 private static final Logger LOGGER = LoggerFactory.getLogger(Retry.class); 39 40 private Retry() { 41 // no instances 42 } 43 44 /** 45 * Retries for given amount of time (time, unit) the passed in operation, sleeping given 46 * {@code sleepMills} between retries. In case operation returns {@code null}, it is assumed 47 * "is not done yet" state, so retry will happen (if time barrier allows). If time barrier 48 * passes, and still {@code null} ("is not done yet") is returned from operation, the 49 * {@code defaultResult} is returned. 50 */ 51 public static <R> R retry( 52 final long time, 53 final TimeUnit unit, 54 final long sleepMillis, 55 final Callable<R> operation, 56 final Predicate<Exception> retryPredicate, 57 final R defaultResult) 58 throws InterruptedException { 59 long now = System.nanoTime(); 60 final long barrier = now + unit.toNanos(time); 61 int attempt = 1; 62 R result = null; 63 while (now < barrier && result == null) { 64 try { 65 result = operation.call(); 66 if (result == null) { 67 LOGGER.trace("Retry attempt {}: no result", attempt); 68 Thread.sleep(sleepMillis); 69 } 70 } catch (InterruptedException e) { 71 throw e; 72 } catch (Exception e) { 73 LOGGER.trace("Retry attempt {}: operation failure", attempt, e); 74 if (retryPredicate != null && !retryPredicate.test(e)) { 75 throw new IllegalStateException(e); 76 } 77 } 78 now = System.nanoTime(); 79 attempt++; 80 } 81 return result == null ? defaultResult : result; 82 } 83 84 /** 85 * Retries attempting max given times the passed in operation, sleeping given 86 * {@code sleepMills} between retries. In case operation returns {@code null}, it is assumed 87 * "is not done yet" state, so retry will happen (if attempt count allows). If all attempts 88 * used, and still {@code null} ("is not done yet") is returned from operation, the 89 * {@code defaultResult} is returned. 90 * <p> 91 * Just to clear things up: 5 attempts is really 4 retries (once do it and retry 4 times). 0 attempts means 92 * "do not even try it", and this method returns without doing anything. 93 */ 94 public static <R> R retry( 95 final int attempts, 96 final long sleepMillis, 97 final Callable<R> operation, 98 final Predicate<Exception> retryPredicate, 99 final R defaultResult) 100 throws InterruptedException { 101 int attempt = 1; 102 R result = null; 103 while (attempt <= attempts && result == null) { 104 try { 105 result = operation.call(); 106 if (result == null) { 107 LOGGER.trace("Retry attempt {}: no result", attempt); 108 Thread.sleep(sleepMillis); 109 } 110 } catch (InterruptedException e) { 111 throw e; 112 } catch (Exception e) { 113 LOGGER.trace("Retry attempt {}: operation failure", attempt, e); 114 if (retryPredicate != null && !retryPredicate.test(e)) { 115 throw new IllegalStateException(e); 116 } 117 } 118 attempt++; 119 } 120 return result == null ? defaultResult : result; 121 } 122 }