Github user StephanEwen commented on a diff in the pull request:
https://github.com/apache/flink/pull/3524#discussion_r108671268
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/state/SharedStateRegistry.java
---
@@ -0,0 +1,192 @@
+/*
+ * 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.state;
+
+import org.apache.flink.annotation.VisibleForTesting;
+import org.apache.flink.api.java.tuple.Tuple2;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * A {@code SharedStateRegistry} will be deployed in the
+ * {@link org.apache.flink.runtime.checkpoint.CheckpointCoordinator} to
+ * maintain the reference count of those state objects shared among
different
+ * checkpoints. Each shared state object must be identified by a unique
key.
+ */
+public class SharedStateRegistry implements Serializable {
+
+ private static final long serialVersionUID = -8357254413007773970L;
+
+ /** All registered state objects */
+ private final Map<String, Tuple2<StateObject, Integer>>
registeredStates = new HashMap<>();
--- End diff --
I think we can be a bit more efficient by having a `StateObjectAndCount`
class, rather than a tuple 2. Safes the reference for the Integer.
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