Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/1620#discussion_r52626379
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/GenericExactlyOnceSink.java
---
@@ -0,0 +1,173 @@
+/**
+ * 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
+ * <p/>
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * <p/>
+ * 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.streaming.runtime.operators;
+
+import org.apache.flink.api.common.ExecutionConfig;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
+import org.apache.flink.api.common.typeutils.TypeSerializer;
+import org.apache.flink.api.java.tuple.Tuple;
+import org.apache.flink.api.java.typeutils.TypeExtractor;
+import org.apache.flink.core.memory.DataInputView;
+import org.apache.flink.runtime.state.AbstractStateBackend;
+import org.apache.flink.runtime.state.StateHandle;
+import org.apache.flink.streaming.api.operators.AbstractStreamOperator;
+import org.apache.flink.streaming.api.operators.OneInputStreamOperator;
+import org.apache.flink.streaming.api.watermark.Watermark;
+import org.apache.flink.streaming.runtime.streamrecord.StreamRecord;
+import org.apache.flink.streaming.runtime.tasks.StreamTaskState;
+
+import java.io.IOException;
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * Generic Sink that emits its input elements into an arbitrary backend.
This sink is integrated with the checkpointing
+ * mechanism to provide exactly once semantics.
+ *
+ * Incoming records are stored within a {@link
org.apache.flink.runtime.state.AbstractStateBackend}, and only committed if a
+ * checkpoint is completed. Should a job fail while the data is being
committed, no exactly once guarantee can be made.
+ * @param <IN>
+ */
+public abstract class GenericExactlyOnceSink<IN extends Tuple> extends
AbstractStreamOperator<IN> implements OneInputStreamOperator<IN, IN> {
+ private AbstractStateBackend.CheckpointStateOutputView out;
+ private TypeSerializer<IN> serializer;
+ protected TypeInformation<IN> typeInfo;
+
+ private ExactlyOnceState state = new ExactlyOnceState();
+
+ /**
+ * Saves a handle in the state.
+ * @param checkpointId
+ * @throws IOException
+ */
+ private void saveHandleInState(final long checkpointId) throws
IOException {
+ //only add handle if a new OperatorState was created since the
last snapshot/notify
+ if (out != null) {
+ out.writeByte(0); //EOF-byte
+ StateHandle<DataInputView> handle =
out.closeAndGetHandle();
+ if (state.pendingHandles.containsKey(checkpointId)) {
+
state.pendingHandles.get(checkpointId).add(handle);
+ } else {
+ ArrayList<StateHandle<DataInputView>> list =
new ArrayList<>();
+ list.add(handle);
+ state.pendingHandles.put(checkpointId, list);
+ }
+ out = null;
+ }
+ }
+
+ @Override
+ public StreamTaskState snapshotOperatorState(final long checkpointId,
final long timestamp) throws Exception {
+ StreamTaskState taskState =
super.snapshotOperatorState(checkpointId, timestamp);
+ saveHandleInState(checkpointId);
+ taskState.setFunctionState(state);
+ return taskState;
+ }
+
+ @Override
+ public void restoreState(StreamTaskState state, long recoveryTimestamp)
throws Exception {
+ super.restoreState(state, recoveryTimestamp);
+ this.state = (ExactlyOnceState) state.getFunctionState();
+ out = null;
+ }
+
+ @Override
+ public void notifyOfCompletedCheckpoint(long checkpointId) throws
Exception {
+ super.notifyOfCompletedCheckpoint(checkpointId);
+ saveHandleInState(checkpointId);
+
+ synchronized (state.pendingHandles) {
+ Set<Long> pastCheckpointIds =
state.pendingHandles.keySet();
+ Set<Long> checkpointsToRemove = new HashSet<>();
+ for (Long pastCheckpointId : pastCheckpointIds) {
+ if (pastCheckpointId <= checkpointId) {
+ List<StateHandle<DataInputView>>
handles = state.pendingHandles.get(pastCheckpointId);
+ for (StateHandle<DataInputView> handle
: handles) {
+ DataInputView in =
handle.getState(getUserCodeClassloader());
+ while (in.readByte() == 1) {
+ IN value =
serializer.deserialize(in);
+ sendValue(value);
+ }
+
checkpointsToRemove.add(pastCheckpointId);
+ }
+ }
+ }
+ for (Long toRemove : checkpointsToRemove) {
+ state.pendingHandles.remove(toRemove);
+ }
+ }
+ }
+
+ /**
+ * Write the given element into the backend.
+ * @param value value to be written
+ * @throws Exception
+ */
+ protected abstract void sendValue(IN value) throws Exception;
+
+ @Override
+ public void processElement(StreamRecord<IN> element) throws Exception {
+ IN value = element.getValue();
+ if (serializer == null) {
+ typeInfo = TypeExtractor.getForObject(value);
+ serializer = typeInfo.createSerializer(new
ExecutionConfig());
+ }
+ //generate initial operator state
+ if (out == null) {
+ out =
getStateBackend().createCheckpointStateOutputView(0, 0);
+ }
+ out.writeByte(1);
+ serializer.serialize(value, out);
+ }
+
+ @Override
+ public void processWatermark(Watermark mark) throws Exception {
+ //don't do anything, since no are a sink
+ }
+
+ /**
+ * This state is used to keep a list of all StateHandles (essentially
references to past OperatorStates) that were
+ * used since the last completed checkpoint.
+ **/
+ public class ExactlyOnceState implements StateHandle<Serializable> {
+ protected HashMap<Long, ArrayList<StateHandle<DataInputView>>>
pendingHandles;
+
+ public ExactlyOnceState() {
+ pendingHandles = new HashMap<>();
+ }
+
+ @Override
+ public HashMap<Long, ArrayList<StateHandle<DataInputView>>>
getState(ClassLoader userCodeClassLoader) throws Exception {
+ return pendingHandles;
+ }
+
+ @Override
+ public void discardState() throws Exception {
+ pendingHandles = new HashMap<>();
--- End diff --
What about the `StateHandles` in the `pendingHandles` map? Shouldn't we
call discard on them as well?
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