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From StephanEwen <...@git.apache.org>
Subject [GitHub] flink pull request #3524: [FLINK-6014][checkpoint] Allow the registration of...
Date Wed, 29 Mar 2017 13:16:02 GMT
Github user StephanEwen commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3524#discussion_r108671962
  
    --- 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<>();
    +
    +	/** All state objects that are not referenced any more */
    +	private transient final List<StateObject> discardedStates = new ArrayList<>();
    +
    +	/**
    +	 * Register the state in the registry
    +	 *
    +	 * @param key The key of the state to register
    +	 * @param state The state to register
    +	 */
    +	public void register(String key, StateObject state) {
    +		Tuple2<StateObject, Integer> stateAndRefCnt = registeredStates.get(key);
    +
    +		if (stateAndRefCnt == null) {
    +			registeredStates.put(key, new Tuple2<>(state, 1));
    +		} else {
    +			if (!stateAndRefCnt.f0.equals(state)) {
    --- End diff --
    
    This is a nice idea, but I think that `equals()` on state objects does not always work
very well. On `ByteStreamHandle`, it is a bit expensive (compare all bytes, which may be up
to a few megabytes) and on `FileStreamHandle` it assumes that the paths are normalized (upper/lower
case, slashes, authority or no authority, ...). That's why I suggested to have a dedicated
key. Then we only requite the key to be "normalized" so it behaved well for `equals()`.


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