yunfengzhou-hub commented on code in PR #20275:
URL: https://github.com/apache/flink/pull/20275#discussion_r935026305


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flink-streaming-java/src/test/java/org/apache/flink/streaming/runtime/tasks/CoordinatorEventsToStreamOperatorRecipientExactlyOnceITCase.java:
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@@ -0,0 +1,385 @@
+/*
+ * 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.streaming.runtime.tasks;
+
+import org.apache.flink.api.common.JobExecutionResult;
+import org.apache.flink.api.common.accumulators.LongCounter;
+import org.apache.flink.api.common.state.ListState;
+import org.apache.flink.api.common.state.ListStateDescriptor;
+import org.apache.flink.api.common.typeinfo.BasicTypeInfo;
+import org.apache.flink.api.common.typeinfo.TypeInformation;
+import org.apache.flink.runtime.jobgraph.OperatorID;
+import org.apache.flink.runtime.jobgraph.tasks.AbstractInvokable;
+import 
org.apache.flink.runtime.operators.coordination.CoordinatorEventsExactlyOnceITCase;
+import org.apache.flink.runtime.operators.coordination.OperatorCoordinator;
+import org.apache.flink.runtime.operators.coordination.OperatorEvent;
+import org.apache.flink.runtime.operators.coordination.OperatorEventHandler;
+import org.apache.flink.runtime.state.StateInitializationContext;
+import org.apache.flink.runtime.state.StateSnapshotContext;
+import org.apache.flink.streaming.api.datastream.DataStream;
+import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
+import org.apache.flink.streaming.api.functions.sink.DiscardingSink;
+import org.apache.flink.streaming.api.functions.source.ParallelSourceFunction;
+import org.apache.flink.streaming.api.functions.source.RichSourceFunction;
+import org.apache.flink.streaming.api.graph.StreamConfig;
+import org.apache.flink.streaming.api.operators.AbstractStreamOperator;
+import org.apache.flink.streaming.api.operators.AbstractStreamOperatorFactory;
+import org.apache.flink.streaming.api.operators.CoordinatedOperatorFactory;
+import org.apache.flink.streaming.api.operators.OneInputStreamOperator;
+import org.apache.flink.streaming.api.operators.OneInputStreamOperatorFactory;
+import org.apache.flink.streaming.api.operators.Output;
+import org.apache.flink.streaming.api.operators.StreamOperator;
+import org.apache.flink.streaming.api.operators.StreamOperatorParameters;
+import org.apache.flink.streaming.runtime.streamrecord.StreamRecord;
+import org.apache.flink.util.Preconditions;
+import org.apache.flink.util.SerializedValue;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.Random;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration test case that validates the exactly-once mechanism for 
operator events sent around
+ * checkpoint. This class is an extension to {@link 
CoordinatorEventsExactlyOnceITCase}, further
+ * verifying the exactly-once semantics of events in the following conditions:
+ *
+ * <h2>Stream operator recipient</h2>
+ *
+ * <p>In {@link CoordinatorEventsExactlyOnceITCase}, the test cases focus on 
verifying the
+ * correctness of operator coordinator's behavior. It uses a custom {@link 
AbstractInvokable}
+ * subclass that mocks the behavior of coordinator's recipients. This test 
class uses actual stream
+ * operators as the recipient of coordinator events, verifying that stream 
operators can correctly
+ * handle received operator events and inform coordinators of completing 
checkpoint.
+ *
+ * <h2>Non-source stream task</h2>
+ *
+ * <p>In {@link CoordinatorEventsExactlyOnceITCase}, the two tested tasks are 
executed independently
+ * of each other. They do not have the upstream-downstream relationship as 
operators usually do in a
+ * streaming job, and thus both of them are treated as source tasks. This test 
class further
+ * verifies situations when the tested operators are not sources, which means 
when checkpoint
+ * barriers are injected into sources, these operators may not have started 
checkpoint yet.
+ *
+ * <h2>Unaligned checkpoint</h2>
+ *
+ * <p>This class tests both aligned and unaligned checkpoints to verify that 
the correctness of the
+ * event delivery behavior around checkpoint is not affected by this condition.
+ *
+ * <h2>Non-global failure</h2>
+ *
+ * <p>In {@link CoordinatorEventsExactlyOnceITCase}, failures occur at the 
coordinators' side, so
+ * they will cause the whole Flink job to fail over. In this class, test cases 
are added when there
+ * might only be fail-overs on the subtasks' side, while the coordinators are 
not affected. In this
+ * case the production infrastructure code needs to work together with user 
code (implementations
+ * inside the coordinator and operator subclass) to ensure the exactly-once 
semantics of operator
+ * event delivery.
+ */
+public class CoordinatorEventsToStreamOperatorRecipientExactlyOnceITCase
+        extends CoordinatorEventsExactlyOnceITCase {
+    private static final AtomicBoolean shouldCloseSource = new 
AtomicBoolean(false);
+
+    private static final int numEvents = 100;
+
+    private static final int delay = 1;
+
+    private StreamExecutionEnvironment env;
+
+    @Before
+    public void setup() {
+        env = StreamExecutionEnvironment.getExecutionEnvironment();
+        env.setParallelism(1);
+        env.enableCheckpointing(100);
+        shouldCloseSource.set(false);
+    }
+
+    @Test
+    public void testCoordinatorSendEvents() throws Exception {
+        executeAndVerifyResults(
+                env, new EventReceivingOperatorFactory<>("eventReceiving", 
numEvents, delay));
+    }
+
+    @Test
+    public void testUnalignedCheckpoint() throws Exception {
+        env.getCheckpointConfig().enableUnalignedCheckpoints();
+        executeAndVerifyResults(
+                env, new EventReceivingOperatorFactory<>("eventReceiving", 
numEvents, delay));
+    }
+
+    @Test
+    public void testFailingCheckpoint() throws Exception {
+        executeAndVerifyResults(
+                env, new 
FailingCheckpointOperatorFactory<>("failingCheckpoint", numEvents, delay));
+    }
+
+    private void executeAndVerifyResults(
+            StreamExecutionEnvironment env, 
OneInputStreamOperatorFactory<Long, Long> factory)
+            throws Exception {
+        // Differs the parallelism of source operators from that of tested 
operators, so that when
+        // checkpoint barriers are injected into sources, the tested operators 
have not started
+        // checkpoint yet.
+        DataStream<Long> stream =
+                env.addSource(new IdlingSourceFunction<>(), 
TypeInformation.of(Long.class))
+                        .setParallelism(2);
+        stream =
+                stream.transform("eventReceiving", 
TypeInformation.of(Long.class), factory)
+                        .setParallelism(1);
+        stream.addSink(new DiscardingSink<>());
+
+        JobExecutionResult executionResult =
+                MINI_CLUSTER
+                        .getMiniCluster()
+                        
.executeJobBlocking(env.getStreamGraph().getJobGraph());
+
+        long count = 
executionResult.getAccumulatorResult(EventReceivingOperator.COUNTER_NAME);
+        assertThat(count).isEqualTo(numEvents);
+    }
+
+    /** A mock source function that does not collect any stream record and 
finishes on demand. */
+    private static class IdlingSourceFunction<T> extends RichSourceFunction<T>
+            implements ParallelSourceFunction<T> {
+        private boolean isCancelled = false;
+
+        @Override
+        public void run(SourceContext<T> ctx) throws Exception {
+            while (!isCancelled && !shouldCloseSource.get()) {
+                Thread.sleep(100);
+            }
+        }
+
+        @Override
+        public void cancel() {
+            isCancelled = true;
+        }
+    }
+
+    /**
+     * A wrapper operator factory for {@link EventReceivingOperator} and {@link
+     * EventSendingCoordinator}.
+     */
+    private static class EventReceivingOperatorFactory<IN, OUT>
+            extends AbstractStreamOperatorFactory<OUT>
+            implements CoordinatedOperatorFactory<OUT>, 
OneInputStreamOperatorFactory<IN, OUT> {
+        private final String name;
+        protected final int numEvents;
+        private final int delay;
+
+        public EventReceivingOperatorFactory(String name, int numEvents, int 
delay) {
+            this.name = name;
+            this.numEvents = numEvents;
+            this.delay = delay;
+        }
+
+        @Override
+        public OperatorCoordinator.Provider getCoordinatorProvider(
+                String operatorName, OperatorID operatorID) {
+            return new OperatorCoordinator.Provider() {
+
+                @Override
+                public OperatorID getOperatorId() {
+                    return operatorID;
+                }
+
+                @Override
+                public OperatorCoordinator create(OperatorCoordinator.Context 
context) {
+                    return new EventSendingCoordinator(context, name, 
numEvents, delay);
+                }
+            };
+        }
+
+        @Override
+        public <T extends StreamOperator<OUT>> T createStreamOperator(
+                StreamOperatorParameters<OUT> parameters) {
+            EventReceivingOperator<OUT> operator = new 
EventReceivingOperator<>();
+            operator.setup(
+                    parameters.getContainingTask(),
+                    parameters.getStreamConfig(),
+                    parameters.getOutput());
+            parameters
+                    .getOperatorEventDispatcher()
+                    
.registerEventHandler(parameters.getStreamConfig().getOperatorID(), operator);
+            return (T) operator;
+        }
+
+        @Override
+        public Class<? extends StreamOperator> 
getStreamOperatorClass(ClassLoader classLoader) {
+            return EventReceivingOperator.class;
+        }
+    }
+
+    /**
+     * The stream operator that receives the events and accumulates the 
numbers. The task is
+     * stateful and checkpoints the accumulator.
+     */
+    private static class EventReceivingOperator<T> extends 
AbstractStreamOperator<T>
+            implements OneInputStreamOperator<T, T>, OperatorEventHandler {
+        protected static final String COUNTER_NAME = "numEvents";
+
+        protected final LongCounter counter = new LongCounter();
+
+        protected ListState<Long> state;
+
+        @Override
+        public void open() throws Exception {
+            super.open();
+            getRuntimeContext().addAccumulator(COUNTER_NAME, counter);
+        }
+
+        @Override
+        public void processElement(StreamRecord<T> element) throws Exception {
+            throw new UnsupportedOperationException();
+        }
+
+        @Override
+        public void handleOperatorEvent(OperatorEvent evt) {
+            if (evt instanceof IntegerEvent) {
+                counter.add(1L);
+            } else if (evt instanceof EndEvent) {
+                try {
+                    
state.update(Collections.singletonList(counter.getLocalValue()));
+                } catch (Exception e) {
+                    throw new RuntimeException(e);
+                }
+                shouldCloseSource.set(true);
+            } else {
+                throw new UnsupportedOperationException();
+            }
+        }
+
+        @Override
+        public void snapshotState(StateSnapshotContext context) throws 
Exception {
+            super.snapshotState(context);
+            state.update(Collections.singletonList(counter.getLocalValue()));
+        }
+
+        @Override
+        public void initializeState(StateInitializationContext context) throws 
Exception {
+            super.initializeState(context);
+
+            state =
+                    context.getOperatorStateStore()
+                            .getListState(
+                                    new ListStateDescriptor<>(
+                                            "counterState", 
BasicTypeInfo.LONG_TYPE_INFO));
+
+            counter.resetLocal();
+            Iterator<Long> iterator = state.get().iterator();
+            if (iterator.hasNext()) {
+                counter.add(iterator.next());
+            }
+            Preconditions.checkArgument(!iterator.hasNext());
+
+            // signal the coordinator to start
+            getContainingTask()
+                    .getEnvironment()
+                    .getOperatorCoordinatorEventGateway()
+                    .sendOperatorEventToCoordinator(
+                            getOperatorID(),
+                            new SerializedValue<>(
+                                    new 
StartEvent(counter.getLocalValue().intValue() - 1)));
+        }
+    }
+
+    /**
+     * A wrapper operator factory for {@link FailingCheckpointOperator} and 
{@link
+     * EventSendingCoordinator}.
+     */
+    private static class FailingCheckpointOperatorFactory<IN, OUT>
+            extends EventReceivingOperatorFactory<IN, OUT> {
+        public FailingCheckpointOperatorFactory(String name, int numEvents, 
int delay) {
+            super(name, numEvents, delay);
+        }
+
+        @Override
+        public <T extends StreamOperator<OUT>> T createStreamOperator(
+                StreamOperatorParameters<OUT> parameters) {
+            EventReceivingOperator<OUT> operator = new 
FailingCheckpointOperator<>(numEvents);
+            operator.setup(
+                    parameters.getContainingTask(),
+                    parameters.getStreamConfig(),
+                    parameters.getOutput());
+            parameters
+                    .getOperatorEventDispatcher()
+                    
.registerEventHandler(parameters.getStreamConfig().getOperatorID(), operator);
+            return (T) operator;
+        }
+    }
+
+    /**
+     * A subclass of {@link EventReceivingOperator} whose subtask would fail 
during a specific
+     * checkpoint.
+     */
+    private static class FailingCheckpointOperator<T> extends 
EventReceivingOperator<T> {
+
+        private final int failAtCheckpointAfterMessage;
+
+        private TestScript testScript;
+
+        private FailingCheckpointOperator(int numEvents) {
+            this.failAtCheckpointAfterMessage =
+                    numEvents * 2 / 3 + new Random().nextInt(numEvents / 6);
+        }
+
+        @Override
+        public void setup(
+                StreamTask<?, ?> containingTask,
+                StreamConfig config,
+                Output<StreamRecord<T>> output) {
+            super.setup(containingTask, config, output);
+            if (containingTask.getIndexInSubtaskGroup() == 0) {
+                this.testScript = TestScript.getForOperator(getOperatorID() + 
"-subtask0");
+            } else {
+                this.testScript = null;
+            }
+        }
+
+        @Override
+        public void handleOperatorEvent(OperatorEvent evt) {
+            if (evt instanceof IntegerEvent) {
+                counter.add(1L);
+            } else if (evt instanceof EndEvent) {
+                try {
+                    
state.update(Collections.singletonList(counter.getLocalValue()));
+                } catch (Exception e) {
+                    throw new RuntimeException(e);
+                }
+                if (testScript.hasAlreadyFailed()) {

Review Comment:
   It seems that the parallelism of this operator has to be 1 in order to work 
correctly, thus `testScript` must have been assigned a value during setup. I'll 
modify the logic here.



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