[GitHub] [incubator-livy] jerryshao commented on a change in pull request #267: [LIVY-732][SERVER] A common zookeeper wrapper utility

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jerryshao commented on a change in pull request #267: [LIVY-732][SERVER] A common zookeeper wrapper utility
URL: https://github.com/apache/incubator-livy/pull/267#discussion_r360795968
 
 

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 File path: server/src/main/scala/org/apache/livy/server/recovery/ZooKeeperManager.scala
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 @@ -0,0 +1,137 @@
+/*
+ * 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.livy.server.recovery
+
+import scala.collection.JavaConverters._
+import scala.reflect.ClassTag
+
+import org.apache.curator.framework.api.UnhandledErrorListener
+import org.apache.curator.framework.CuratorFramework
+import org.apache.curator.framework.CuratorFrameworkFactory
+import org.apache.curator.retry.RetryNTimes
+import org.apache.zookeeper.KeeperException.NoNodeException
+
+import org.apache.livy.LivyConf
+import org.apache.livy.LivyConf.Entry
+import org.apache.livy.Logging
+
+object ZooKeeperManager {
+  val ZK_KEY_PREFIX_CONF = Entry("livy.server.recovery.zk-state-store.key-prefix", "livy")
+  val ZK_RETRY_CONF = Entry("livy.server.recovery.zk-state-store.retry-policy", "5,100")
+  val DUPLICATE_CREATE_EXCEPTION = "ZooKeeperManager single instance has already been created"
+
+  @volatile private var zkManager: ZooKeeperManager = _
+
+  def apply(livyConf: LivyConf,
+    mockCuratorClient: Option[CuratorFramework] = None):
+  ZooKeeperManager = synchronized {
+    if (zkManager == null) {
+      zkManager = new ZooKeeperManager(livyConf, mockCuratorClient)
+    } else {
+      throw new IllegalAccessException(DUPLICATE_CREATE_EXCEPTION)
+    }
+
+    zkManager
+  }
+
+  def get(): ZooKeeperManager = zkManager
+
+  // for test
+  private[recovery] def reset(): Unit = {
+    zkManager = null
 
 Review comment:
   I personally don't like singleton here, it is hard for testing, and that's why you need to add this method here. Why don't we change to a normal class object?

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