KAFKA-7660: fix streams and Metrics memory leaks

clients/src/main/java/org/apache/kafka/common/metrics/Metrics.java

@@ -446,6 +446,12 @@ public void removeSensor(String name) {
                             removeMetric(metric.metricName());
                         log.debug("Removed sensor with name {}", name);
                         childSensors = childrenSensors.remove(sensor);
+                        for (final Sensor parent : sensor.parents()) {
+                            final List<Sensor> peers = childrenSensors.get(parent);
+                            if (peers != null) {
+                                peers.remove(sensor);
+                            }
+                        }
                     }
                 }
             }

clients/src/main/java/org/apache/kafka/common/metrics/Sensor.java

@@ -22,13 +22,15 @@
 import org.apache.kafka.common.utils.Utils;
 
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 
+import static java.util.Arrays.asList;
+import static java.util.Collections.unmodifiableList;
+
 /**
  * A sensor applies a continuous sequence of numerical values to a set of associated metrics. For example a sensor on
  * message size would record a sequence of message sizes using the {@link #record(double)} api and would maintain a set
@@ -132,6 +134,10 @@ public String name() {
         return this.name;
     }
 
+    List<Sensor> parents() {
+        return unmodifiableList(asList(parents));
+    }
+
     /**
      * Record an occurrence, this is just short-hand for {@link #record(double) record(1.0)}
      */
@@ -267,6 +273,6 @@ public boolean hasExpired() {
     }
 
     synchronized List<KafkaMetric> metrics() {
-        return Collections.unmodifiableList(this.metrics);
+        return unmodifiableList(this.metrics);
     }
 }

clients/src/test/java/org/apache/kafka/common/metrics/MetricsTest.java

@@ -16,6 +16,8 @@
  */
 package org.apache.kafka.common.metrics;
 
+import static java.util.Collections.emptyList;
+import static java.util.Collections.singletonList;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotNull;
@@ -177,6 +179,20 @@ public void testBadSensorHierarchy() {
         metrics.sensor("gc", c1, c2); // should fail
     }
 
+    @Test
+    public void testRemoveChildSensor() {
+        final Metrics metrics = new Metrics();
+
+        final Sensor parent = metrics.sensor("parent");
+        final Sensor child = metrics.sensor("child", parent);
+
+        assertEquals(singletonList(child), metrics.childrenSensors().get(parent));
+
+        metrics.removeSensor("child");
+
+        assertEquals(emptyList(), metrics.childrenSensors().get(parent));
+    }
+
     @Test
     public void testRemoveSensor() {
         int size = metrics.metrics().size();

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

@@ -222,10 +222,9 @@ public void removeSensor(Sensor sensor) {
         Objects.requireNonNull(sensor, "Sensor is null");
         metrics.removeSensor(sensor.name());
 
-        final Sensor parent = parentSensors.get(sensor);
+        final Sensor parent = parentSensors.remove(sensor);
         if (parent != null) {
             metrics.removeSensor(parent.name());
-            parentSensors.remove(sensor);
         }
 
     }