tmaret commented on a change in pull request #8: SLING-8531 - Exponential backoff for retries URL: https://github.com/apache/sling-org-apache-sling-distribution-journal/pull/8#discussion_r301979137
########## File path: src/main/java/org/apache/sling/distribution/journal/impl/shared/ExponentialBackOff.java ########## @@ -0,0 +1,81 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you 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 org.apache.sling.distribution.journal.impl.shared; + +import java.io.Closeable; +import java.time.Duration; +import java.util.Random; +import java.util.concurrent.Executors; +import java.util.concurrent.ScheduledExecutorService; +import java.util.concurrent.TimeUnit; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * Retry with exponential backoff. + * + * Calls checkCallback until it does not throw an Exception. + * Retries are first done with startDelay, then doubled until maxDelay is reached. + */ +public class ExponentialBackOff implements Closeable { + private final Logger log = LoggerFactory.getLogger(this.getClass()); + + private final ScheduledExecutorService executor; + private final Runnable checkCallback; + + private Random random; + private int maxDelay; + + private int currentMaxDelay; + + public ExponentialBackOff(Duration startDelay, Duration maxDelay, Runnable checkCallback) { + this.currentMaxDelay = asMS(startDelay); + this.maxDelay = asMS(maxDelay); + this.checkCallback = checkCallback; + this.executor = Executors.newScheduledThreadPool(1); + this.random = new Random(); + scheduleCheck(); + } + + private int asMS(Duration startDelay) { + return new Long(startDelay.toMillis()).intValue(); + } + + @Override + public synchronized void close() { + this.executor.shutdown(); + } + + private void scheduleCheck() { + this.currentMaxDelay = Math.min(this.currentMaxDelay *2, maxDelay); + int delay = this.random.nextInt(currentMaxDelay) + 1; + log.info("Scheduling next check in {} ms with maximum {} ms.", delay, currentMaxDelay); + this.executor.schedule(this::check, delay, TimeUnit.MILLISECONDS); + } + + private void check() { + try { + this.checkCallback.run(); + this.close(); Review comment: I think we should avoid invoking `close` here, because close may throw a RuntimeException which would re-schedule checks ;-). It should be possible to manage closing the ExponentialBackOff from the outside. I think it's already the case. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services
