KAFKA-9480: Fix bug that prevented to measure task-level process-rate (#8018)

Reviewers: Guozhang Wang <guozhang@confluent.io>, Matthias J. Sax <matthias@confluent.io>

streams/src/main/java/org/apache/kafka/streams/processor/internals/SourceNode.java

@@ -66,14 +66,19 @@ public class SourceNode<K, V> extends ProcessorNode<K, V> {
     @SuppressWarnings("unchecked")
     @Override
     public void init(final InternalProcessorContext context) {
-        super.init(context);
-        this.context = context;
+        // It is important to first create the sensor before calling init on the
+        // parent object. Otherwise due to backwards compatibility an empty sensor
+        // without parent is created with the same name.
+        // Once the backwards compatibility is not needed anymore it might be possible to
+        // change this.
         processAtSourceSensor = ProcessorNodeMetrics.processorAtSourceSensorOrForwardSensor(
             Thread.currentThread().getName(),
             context.taskId().toString(),
             context.currentNode().name(),
             context.metrics()
         );
+        super.init(context);
+        this.context = context;
 
         // if deserializers are null, get the default ones from the context
         if (this.keyDeserializer == null) {

streams/src/test/java/org/apache/kafka/common/metrics/SensorAccessor.java

@@ -0,0 +1,35 @@
+/*
+ * 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.kafka.common.metrics;
+
+import java.util.List;
+
+/**
+ * This class allows unit tests to access package-private members in class {@link Sensor}.
+ */
+public class SensorAccessor {
+
+    public final Sensor sensor;
+
+    public SensorAccessor(final Sensor sensor) {
+        this.sensor = sensor;
+    }
+
+    public List<Sensor> parents() {
+        return sensor.parents();
+    }
+}

streams/src/test/java/org/apache/kafka/streams/processor/internals/SourceNodeTest.java

@@ -19,6 +19,8 @@ package org.apache.kafka.streams.processor.internals;
 import org.apache.kafka.common.header.Headers;
 import org.apache.kafka.common.header.internals.RecordHeaders;
 import org.apache.kafka.common.metrics.Metrics;
+import org.apache.kafka.common.metrics.Sensor;
+import org.apache.kafka.common.metrics.SensorAccessor;
 import org.apache.kafka.common.serialization.Deserializer;
 import org.apache.kafka.streams.StreamsConfig;
 import org.apache.kafka.streams.processor.internals.metrics.StreamsMetricsImpl;
@@ -30,11 +32,13 @@ import org.junit.Test;
 import java.nio.charset.StandardCharsets;
 import java.util.Collections;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import static org.apache.kafka.common.utils.Utils.mkEntry;
 import static org.apache.kafka.common.utils.Utils.mkMap;
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.contains;
 import static org.junit.Assert.assertTrue;
 
 public class SourceNodeTest {
@@ -112,6 +116,15 @@ public class SourceNodeTest {
             final String parentGroupName = "stream-task-metrics";
             assertTrue(StreamsTestUtils.containsMetric(metrics, "process-rate", parentGroupName, metricTags));
             assertTrue(StreamsTestUtils.containsMetric(metrics, "process-total", parentGroupName, metricTags));
+
+            final String sensorNamePrefix = "internal." + threadId + ".task." + context.taskId().toString();
+            final Sensor processSensor =
+                metrics.getSensor(sensorNamePrefix + ".node." + context.currentNode().name() + ".s.process");
+            final SensorAccessor sensorAccessor = new SensorAccessor(processSensor);
+            assertThat(
+                sensorAccessor.parents().stream().map(Sensor::name).collect(Collectors.toList()),
+                contains(sensorNamePrefix + ".s.process")
+            );
         }
     }
 }