fixes #238: Release references provided by unloaded plugins

When another plugin provides a Statistic instance, that instance should be released when the provider unloads. Failing to do so will prevent that plugin's classloader from being destroyed. This can cause all kinds of unexpected side-effects.

This commit removes references to _all_ Statistic instances whenever _any_ plugin unloads. That's a buckshot, but the effects should be limited to missing stats around the time that a plugin gets unloaded/reloaded - which is expected to be very rare.

Author: guusdk

changelog.html

@@ -48,6 +48,7 @@ <h1>
 <ul>
     <li>[<a href='https://github.com/igniterealtime/openfire-monitoring-plugin/issues/232'>Issue #232</a>] - Fix SQL issue when retrieving archived messages from MSSQL</li>
     <li>[<a href='https://github.com/igniterealtime/openfire-monitoring-plugin/issues/235'>Issue #235</a>] - Plugin compatible with Openfire 4.8.0</li>
+    <li>[<a href='https://github.com/igniterealtime/openfire-monitoring-plugin/issues/238'>Issue #238</a>] - Ensure that Statistics provided by unloaded plugins are no longer referenced.</li>
     <li>[<a href='https://github.com/igniterealtime/openfire-monitoring-plugin/issues/240'>Issue #240</a>] - Stop using javascript libraries that are removed from Openfire 4.8</li>
     <li>[<a href='https://github.com/igniterealtime/openfire-monitoring-plugin/issues/242'>Issue #242</a>] - Fix 'Unable to save XML properties' error</li>
 </ul>

src/java/org/jivesoftware/openfire/plugin/MonitoringPlugin.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008 Jive Software. All rights reserved.
+ * Copyright (C) 2008 Jive Software, 2022 Ignite Realtime Foundation. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -38,6 +38,7 @@
 import org.jivesoftware.openfire.archive.GroupConversationInterceptor;
 import org.jivesoftware.openfire.archive.MonitoringConstants;
 import org.jivesoftware.openfire.container.Plugin;
+import org.jivesoftware.openfire.container.PluginListener;
 import org.jivesoftware.openfire.container.PluginManager;
 import org.jivesoftware.openfire.http.HttpBindManager;
 import org.jivesoftware.openfire.reporting.graph.GraphEngine;
@@ -62,7 +63,8 @@
  *
  * @author Matt Tucker
  */
-public class MonitoringPlugin implements Plugin {
+public class MonitoringPlugin implements Plugin, PluginListener
+{
 
     /**
      * The context root of the URL under which the public web endpoints are exposed.
@@ -200,6 +202,8 @@ public boolean accept(File pathname) {
 
         loadPublicWeb(pluginDirectory);
 
+        manager.addPluginListener(this);
+
         statsEngine.start();
         statisticsModule.start();
         conversationManager.start();
@@ -218,6 +222,8 @@ public void destroyPlugin() {
 
         unloadPublicWeb();
 
+        XMPPServer.getInstance().getPluginManager().removePluginListener(this);
+
         if (messageIndexer != null) {
             messageIndexer.stop();
             messageIndexer = null;
@@ -349,4 +355,17 @@ public GraphEngine getGraphEngine() {
     public StatsViewer getStatsViewer() {
         return statsViewer;
     }
+
+    @Override
+    public void pluginCreated(String s, Plugin plugin)
+    {}
+
+    @Override
+    public void pluginDestroyed(String s, Plugin plugin)
+    {
+        // Restart the statsEngine to get rid of references to classes from the Plugin that's being unloaded. Fixes issue #238.
+        if (statsEngine != null) {
+            statsEngine.purgeDefinitions();
+        }
+    }
 }

src/java/org/jivesoftware/openfire/reporting/stats/StatsEngine.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008 Jive Software. All rights reserved.
+ * Copyright (C) 2008 Jive Software, 2022 Ignite Realtime Foundation. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -98,6 +98,11 @@ public void stop() {
         samplingTask.cancel();
     }
 
+    public void purgeDefinitions() {
+        definitionMap.clear();
+        multiMap.clear();
+    }
+
     private void checkDatabase(StatDefinition[] def) throws RrdException, IOException {
         File directory = new File(getStatsDirectroy());
         if (directory.exists()) {