[GitHub] [sling-org-apache-sling-distribution-journal] tmaret commented on a change in pull request #8: SLING-8531 - Exponential backoff for retries

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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_r301663064
 
 

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 File path: src/main/java/org/apache/sling/distribution/journal/impl/shared/ExponentialBackOff.java
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 @@ -0,0 +1,75 @@
+/*
+ * 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.io.IOException;
+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 the checkCallback until it does not throw an Exception
+ */
+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(int maxDelay, Runnable checkCallback) {
+        this.currentMaxDelay = 128;
+        this.maxDelay = maxDelay;
+        this.checkCallback = checkCallback;
+        this.executor = Executors.newScheduledThreadPool(1);
+        this.random = new Random();
+        scheduleCheck();
+    }
+
+    @Override
+    public void close() throws IOException {
+        this.executor.shutdown();
+    }
+
+    private void scheduleCheck() {
 
 Review comment:
   This will keep the same schedule for every retry. The initial retry may be really low and thus the checks will issue a constant and heavy load on the checked system.
   
   I think we should support the standard exponential backoff strategy, where the retries are delayed by exponentially increasing delays (up to a limit).

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