Remove license state listeners on closables (#36308)

We have a few places where we register license state listeners on
transient components (i.e., resources that can be open and closed during
the lifecycle of the server). In one case (the opt-out query cache) we
were never removing the registered listener, effectively a terrible
memory leak. In another case, we were not un-registered the listener
that we registered, since we were not referencing the same instance of
Runnable. This commit does two things:
  - introduces a marker interface LicenseStateListener so that it is
    easier to identify these listeners in the codebase and avoid classes
    that need to register a license state listener from having to
    implement Runnable which carries a different semantic meaning than
    we want here
  - fixes the two places where we are currently leaking license state
    listeners

x-pack/plugin/core/src/main/java/org/elasticsearch/license/LicenseStateListener.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+package org.elasticsearch.license;
+
+import org.elasticsearch.Version;
+
+/**
+ * Marker interface for callbacks that are invoked when the license state changes.
+ */
+@FunctionalInterface
+public interface LicenseStateListener {
+
+    /**
+     * Callback when the license state changes. See {@link XPackLicenseState#update(License.OperationMode, boolean, Version)}.
+     */
+    void licenseStateChanged();
+
+}

x-pack/plugin/core/src/main/java/org/elasticsearch/license/XPackLicenseState.java

@@ -266,7 +266,7 @@ private static class Status {
         }
     }
 
-    private final List<Runnable> listeners;
+    private final List<LicenseStateListener> listeners;
     private final boolean isSecurityEnabled;
     private final boolean isSecurityExplicitlyEnabled;
 
@@ -315,17 +315,17 @@ void update(OperationMode mode, boolean active, @Nullable Version mostRecentTria
                 }
             }
         }
-        listeners.forEach(Runnable::run);
+        listeners.forEach(LicenseStateListener::licenseStateChanged);
     }
 
     /** Add a listener to be notified on license change */
-    public void addListener(Runnable runnable) {
-        listeners.add(Objects.requireNonNull(runnable));
+    public void addListener(final LicenseStateListener listener) {
+        listeners.add(Objects.requireNonNull(listener));
     }
 
     /** Remove a listener */
-    public void removeListener(Runnable runnable) {
-        listeners.remove(runnable);
+    public void removeListener(final LicenseStateListener listener) {
+        listeners.remove(Objects.requireNonNull(listener));
     }
 
     /** Return the current license type. */

x-pack/plugin/monitoring/src/main/java/org/elasticsearch/xpack/monitoring/exporter/local/LocalExporter.java

@@ -35,6 +35,7 @@
 import org.elasticsearch.index.IndexNotFoundException;
 import org.elasticsearch.ingest.IngestMetadata;
 import org.elasticsearch.ingest.PipelineConfiguration;
+import org.elasticsearch.license.LicenseStateListener;
 import org.elasticsearch.license.XPackLicenseState;
 import org.elasticsearch.protocol.xpack.watcher.DeleteWatchRequest;
 import org.elasticsearch.protocol.xpack.watcher.PutWatchRequest;
@@ -78,7 +79,7 @@
 import static org.elasticsearch.xpack.core.monitoring.exporter.MonitoringTemplateUtils.pipelineName;
 import static org.elasticsearch.xpack.monitoring.Monitoring.CLEAN_WATCHER_HISTORY;
 
-public class LocalExporter extends Exporter implements ClusterStateListener, CleanerService.Listener {
+public class LocalExporter extends Exporter implements ClusterStateListener, CleanerService.Listener, LicenseStateListener {
 
     private static final Logger logger = Loggers.getLogger(LocalExporter.class);
 
@@ -106,9 +107,10 @@ public LocalExporter(Exporter.Config config, Client client, CleanerService clean
         this.clusterAlertBlacklist = ClusterAlertsUtil.getClusterAlertsBlacklist(config);
         this.cleanerService = cleanerService;
         this.dateTimeFormatter = dateTimeFormatter(config);
+        // if additional listeners are added here, adjust LocalExporterTests#testLocalExporterRemovesListenersOnClose accordingly
         clusterService.addListener(this);
         cleanerService.add(this);
-        licenseState.addListener(this::licenseChanged);
+        licenseState.addListener(this);
     }
 
     @Override
@@ -121,7 +123,8 @@ public void clusterChanged(ClusterChangedEvent event) {
     /**
      * When the license changes, we need to ensure that Watcher is setup properly.
      */
-    private void licenseChanged() {
+    @Override
+    public void licenseStateChanged() {
         watcherSetup.set(false);
     }
 
@@ -152,7 +155,7 @@ public void doClose() {
             // we also remove the listener in resolveBulk after we get to RUNNING, but it's okay to double-remove
             clusterService.removeListener(this);
             cleanerService.remove(this);
-            licenseState.removeListener(this::licenseChanged);
+            licenseState.removeListener(this);
         }
     }
 

x-pack/plugin/monitoring/src/test/java/org/elasticsearch/xpack/monitoring/exporter/local/LocalExporterTests.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+package org.elasticsearch.xpack.monitoring.exporter.local;
+
+import org.elasticsearch.client.Client;
+import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.license.XPackLicenseState;
+import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.xpack.monitoring.cleaner.CleanerService;
+import org.elasticsearch.xpack.monitoring.exporter.Exporter;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+
+public class LocalExporterTests extends ESTestCase {
+
+    public void testLocalExporterRemovesListenersOnClose() throws Exception {
+        final ClusterService clusterService = mock(ClusterService.class);
+        final XPackLicenseState licenseState = mock(XPackLicenseState.class);
+        final Exporter.Config config = new Exporter.Config("name", "type", Settings.EMPTY, clusterService, licenseState);
+        final CleanerService cleanerService = mock(CleanerService.class);
+        final LocalExporter exporter = new LocalExporter(config, mock(Client.class), cleanerService);
+        verify(clusterService).addListener(exporter);
+        verify(cleanerService).add(exporter);
+        verify(licenseState).addListener(exporter);
+        exporter.close();
+        verify(clusterService).removeListener(exporter);
+        verify(cleanerService).remove(exporter);
+        verify(licenseState).removeListener(exporter);
+    }
+
+}

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authz/accesscontrol/OptOutQueryCache.java

@@ -14,6 +14,7 @@
 import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.index.cache.query.QueryCache;
 import org.elasticsearch.indices.IndicesQueryCache;
+import org.elasticsearch.license.LicenseStateListener;
 import org.elasticsearch.license.XPackLicenseState;
 import org.elasticsearch.xpack.core.security.authz.AuthorizationServiceField;
 import org.elasticsearch.xpack.core.security.authz.accesscontrol.IndicesAccessControl;
@@ -26,7 +27,7 @@
  * Opts out of the query cache if field level security is active for the current request,
  * and its unsafe to cache.
  */
-public final class OptOutQueryCache extends AbstractIndexComponent implements QueryCache {
+public final class OptOutQueryCache extends AbstractIndexComponent implements LicenseStateListener, QueryCache {
 
     private final IndicesQueryCache indicesQueryCache;
     private final ThreadContext context;
@@ -43,14 +44,20 @@ public OptOutQueryCache(
         this.context = Objects.requireNonNull(context, "threadContext must not be null");
         this.indexName = indexSettings.getIndex().getName();
         this.licenseState = Objects.requireNonNull(licenseState, "licenseState");
-        licenseState.addListener(() -> this.clear("license state changed"));
+        licenseState.addListener(this);
     }
 
     @Override
     public void close() throws ElasticsearchException {
+        licenseState.removeListener(this);
         clear("close");
     }
 
+    @Override
+    public void licenseStateChanged() {
+        clear("license state changed");
+    }
+
     @Override
     public void clear(String reason) {
         logger.debug("full cache clear, reason [{}]", reason);

x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/authz/accesscontrol/OptOutQueryCacheTests.java

@@ -183,6 +183,22 @@ public void testOptOutQueryCacheIndexDoesNotHaveFieldLevelSecurity() {
         verify(indicesQueryCache).doCache(same(weight), same(policy));
     }
 
+    public void testOptOutQueryCacheRemovesLicenseStateListenerOnClose() {
+        final Settings.Builder settings = Settings.builder()
+                .put("index.version.created", Version.CURRENT)
+                .put("index.number_of_shards", 1)
+                .put("index.number_of_replicas", 0);
+        final IndexMetaData indexMetaData = IndexMetaData.builder("index").settings(settings).build();
+        final IndexSettings indexSettings = new IndexSettings(indexMetaData, Settings.EMPTY);
+        final IndicesQueryCache indicesQueryCache = mock(IndicesQueryCache.class);
+        final ThreadContext threadContext = new ThreadContext(Settings.EMPTY);
+        final XPackLicenseState licenseState = mock(XPackLicenseState.class);
+        final OptOutQueryCache cache = new OptOutQueryCache(indexSettings, indicesQueryCache, threadContext, licenseState);
+        verify(licenseState).addListener(cache);
+        cache.close();
+        verify(licenseState).removeListener(cache);
+    }
+
     private static FieldPermissionsDefinition fieldPermissionDef(String[] granted, String[] denied) {
         return new FieldPermissionsDefinition(granted, denied);
     }