Github user uce commented on a diff in the pull request:
https://github.com/apache/flink/pull/1153#discussion_r41115679
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/checkpoint/ZooKeeperCheckpointIDCounter.java
---
@@ -0,0 +1,130 @@
+/*
+ * 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.flink.runtime.checkpoint;
+
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.framework.recipes.shared.SharedCount;
+import org.apache.curator.framework.recipes.shared.VersionedValue;
+import org.apache.curator.framework.state.ConnectionState;
+import org.apache.curator.framework.state.ConnectionStateListener;
+import org.apache.flink.runtime.jobmanager.RecoveryMode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * {@link CheckpointIDCounter} instances for JobManagers running in {@link
RecoveryMode#ZOOKEEPER}.
+ *
+ * <p>Each counter creates a ZNode:
+ * <pre>
+ * +----O /flink/checkpoint-counter/<job-id> 1 [persistent]
+ * .
+ * .
+ * .
+ * +----O /flink/checkpoint-counter/<job-id> N [persistent]
+ * </pre>
+ *
+ * <p>The checkpoints IDs are required to be ascending (per job). In order
to guarantee this in case
+ * of job manager failures we use ZooKeeper to have a shared counter
across job manager instances.
+ */
+public class ZooKeeperCheckpointIDCounter implements CheckpointIDCounter {
+
+ private static final Logger LOG =
LoggerFactory.getLogger(ZooKeeperCheckpointIDCounter.class);
+
+ /** Curator ZooKeeper client */
+ private final CuratorFramework client;
+
+ /** Path of the shared count */
+ private final String counterPath;
+
+ /** Curator recipe for shared counts */
+ private final SharedCount sharedCount;
+
+ /** Connection state listener to monitor the client connection */
+ private final SharedCountConnectionStateListener connStateListener =
+ new SharedCountConnectionStateListener();
+
+ /**
+ * Creates a {@link ZooKeeperCheckpointIDCounter} instance.
+ *
+ * @param client Curator ZooKeeper client
+ * @param counterPath ZooKeeper path for the counter. It's sufficient
to have a path per-job.
+ * @throws Exception
+ */
+ public ZooKeeperCheckpointIDCounter(CuratorFramework client, String
counterPath) throws Exception {
+ this.client = checkNotNull(client, "Curator client");
+ this.counterPath = checkNotNull(counterPath, "Counter path");
+ this.sharedCount = new SharedCount(client, counterPath, 1);
+ }
+
+ @Override
+ public void start() throws Exception {
+ sharedCount.start();
+
client.getConnectionStateListenable().addListener(connStateListener);
+ }
+
+ @Override
+ public void stop() throws Exception {
+ sharedCount.close();
+
client.getConnectionStateListenable().removeListener(connStateListener);
+
+ LOG.info("Removing {} from ZooKeeper", counterPath);
+
client.delete().deletingChildrenIfNeeded().inBackground().forPath(counterPath);
+ }
+
+ @Override
+ public long getAndIncrement() throws Exception {
+ while (true) {
+ ConnectionState connState =
connStateListener.getLastState();
+
+ if (connState != null) {
+ throw new IllegalStateException("Connection
state: " + connState);
+ }
+
+ VersionedValue<Integer> current =
sharedCount.getVersionedValue();
+
+ Integer newCount = current.getValue() + 1;
+
+ if (sharedCount.trySetCount(current, newCount)) {
+ return current.getValue();
+ }
+ }
+ }
+
+ /**
+ * Connection state listener. In case of {@link
ConnectionState#SUSPENDED} or {@link
+ * ConnectionState#LOST} we are not guaranteed to read a current count
from ZooKeeper.
+ */
+ private class SharedCountConnectionStateListener implements
ConnectionStateListener {
+
+ private volatile ConnectionState lastState;
+
+ @Override
+ public void stateChanged(CuratorFramework client,
ConnectionState newState) {
+ if (newState == ConnectionState.SUSPENDED || newState
== ConnectionState.LOST) {
--- End diff --
Yes, good idea!
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