[GitHub] [sling-org-apache-sling-jcr-repoinit] bdelacretaz commented on a change in pull request #18: SLING-10418 implement a retry for the application of the statements

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bdelacretaz commented on a change in pull request #18:
URL: https://github.com/apache/sling-org-apache-sling-jcr-repoinit/pull/18#discussion_r646639224



##########
File path: src/main/java/org/apache/sling/jcr/repoinit/impl/RetryableOperation.java
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@@ -0,0 +1,120 @@
+/*
+ * 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.jcr.repoinit.impl;
+
+import java.util.concurrent.TimeUnit;
+import java.util.function.Supplier;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * A simple implementation of retryable operations.
+ * Use the builder class to create an instance of it.
+ *
+ */
+public class RetryableOperation {
+
+    private static final Logger LOG = LoggerFactory.getLogger(RetryableOperation.class);
+
+    int backoffBase;
+    int maxRetries;
+    int jitter;
+
+    int retryCount = 0;
+
+    RetryableOperation(int backoff, int maxRetries, int jitter) {
+        this.backoffBase = backoff;
+        this.maxRetries = maxRetries;
+        this.jitter = jitter;
+    }
+    /**
+     * Execute the operation with the defined retry until it returns true or
+     * the retry aborts; in case the operation is retried, a log message is logged on INFO with the
+     * provided logMessage and the current number of retries
+     * @param operation
+     * @param logMessage the log message
+     * @return true if the supplier was eventually successful, false if it failed despite all retries
+     */
+    public boolean apply(Supplier<Boolean> operation, String logMessage) {
+
+        boolean successful = false;
+        successful = operation.get();
+        while (! successful && retryCount < maxRetries) {
+            retryCount++;
+            LOG.info("%s (retry %d/%d)", logMessage, retryCount, maxRetries);
+            delay(retryCount);
+            successful = operation.get();
+        }
+        return successful;
+    }
+
+    private void delay(int retryCount) {
+
+        int j = (int) (Math.random() * (jitter));
+        int delayInMilis = (backoffBase * retryCount) + j;
+        try {
+            TimeUnit.MILLISECONDS.sleep(delayInMilis);
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+        }
+    }
+
+
+
+    public static class Builder {
+
+        int exponentialBackoff = 1000; // default
+        int maxRetries = 3; // default
+        int jitter = 200;
+
+        /**
+         * The backoff time
+         * @param msec backoff time in miliseconds
+         * @return the builder
+         */
+        Builder withBackoffBase(int msec) {

Review comment:
       Unless a method takes a Duration I like to express units in its name to avoid any ambiguities, so I would call this method `withBackoffBaseMsec`




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