| /* |
| * 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 static java.util.concurrent.TimeUnit.MILLISECONDS; |
| |
| import java.io.Closeable; |
| import java.time.Duration; |
| import java.util.concurrent.Executors; |
| import java.util.concurrent.ScheduledExecutorService; |
| import java.util.concurrent.ThreadLocalRandom; |
| import java.util.concurrent.atomic.AtomicBoolean; |
| |
| 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 long startDelay; |
| private final long maxDelay; |
| private final boolean randomDelay; |
| private final Runnable checkCallback; |
| |
| private final ScheduledExecutorService executor; |
| private final AtomicBoolean isScheduled; |
| |
| private long currentMaxDelay; |
| private long lastCheck; |
| |
| public ExponentialBackOff(Duration startDelay, Duration maxDelay, boolean randomDelay, Runnable checkCallback) { |
| this.startDelay = startDelay.toMillis(); |
| this.maxDelay = maxDelay.toMillis(); |
| this.randomDelay = randomDelay; |
| this.checkCallback = checkCallback; |
| this.executor = Executors.newScheduledThreadPool(1); |
| this.currentMaxDelay = this.startDelay; |
| this.isScheduled = new AtomicBoolean(); |
| this.lastCheck = 0; |
| } |
| |
| @Override |
| public void close() { |
| this.executor.shutdown(); |
| } |
| |
| public void startChecks() { |
| if (noRecentErrors()) { |
| log.info("No recent errors. Starting with initial delay {}", this.startDelay); |
| this.currentMaxDelay = this.startDelay; |
| } |
| scheduleCheck(); |
| } |
| |
| private boolean noRecentErrors() { |
| long timeSinceLastError = System.currentTimeMillis() - this.lastCheck; |
| return timeSinceLastError > this.currentMaxDelay * 2; |
| } |
| |
| private synchronized void scheduleCheck() { |
| if (isScheduled.compareAndSet(false, true)) { |
| long delay = computeDelay(); |
| log.info("Scheduling next check in {} ms with maximum delay of {} ms.", delay, currentMaxDelay); |
| this.executor.schedule(this::check, delay, MILLISECONDS); |
| this.currentMaxDelay = Math.min(this.currentMaxDelay * 2, maxDelay); |
| } |
| } |
| |
| private long computeDelay() { |
| return this.randomDelay ? ThreadLocalRandom.current().nextLong(currentMaxDelay) + 1 : currentMaxDelay; |
| } |
| |
| private void check() { |
| try { |
| this.lastCheck = System.currentTimeMillis(); |
| this.isScheduled.set(false); |
| this.checkCallback.run(); |
| } catch (RuntimeException e) { |
| scheduleCheck(); |
| } |
| } |
| } |