Integration of TOS: Add RetryableUtils.

hadoop-cloud-storage-project/hadoop-tos/src/main/java/org/apache/hadoop/fs/tosfs/util/RetryableUtils.java

@@ -0,0 +1,55 @@
+/*
+ * 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.hadoop.fs.tosfs.util;
+
+import java.util.concurrent.ThreadLocalRandom;
+
+public class RetryableUtils {
+  private static final ThreadLocalRandom RANDOM = ThreadLocalRandom.current();
+
+  private RetryableUtils() {
+  }
+
+  /**
+   * Copy from {@link com.volcengine.tos.internal.util.TosUtils#backoff(int)}
+   *
+   * @param attempt the attempt count
+   * @return backoff milliseconds
+   */
+  public static long backoff(int attempt) {
+    if (attempt == 0) {
+      return 1000L;
+    } else {
+      double backoff = 1.0;
+
+      double max;
+      for (max = 10.0; backoff < max && attempt > 0; --attempt) {
+        backoff *= 1.6;
+      }
+
+      if (backoff > max) {
+        backoff = max;
+      }
+
+      backoff *= 1.0 + 0.2 * (RANDOM.nextDouble(1.0) * 2.0 - 1.0);
+      return backoff < 0.0 ? 0L : (long) (backoff * 1000.0);
+    }
+  }
+}
+