fixes #122: Avoid potential deadlock when loading plugin

If this plugin is being loaded when Openfire has already started, avoid initializing `initializeClustering` as part of the plugin initialization.

The plugin initialization locks the plugin manager. `initializeClustering` needs to obtain resources from the plugin manager (which it can't get while it's locked).

By making the `initializeClustering` method asynchronous, it no longer prevents the plugin initialization from completing, thus breaking the deadlock.

Author: guusdk

changelog.html

@@ -45,6 +45,7 @@ <h1>
 </h1>
 <p><b>5.5.0 Release 2</b> -- tbd</p>
 <ul>
+    <li>[<a href='https://github.com/igniterealtime/openfire-hazelcast-plugin/issues/122'>Issue #122</a>] - Guard against deadlock on plugin initialization</li>
     <li>[<a href='https://github.com/igniterealtime/openfire-hazelcast-plugin/issues/117'>Issue #117</a>] - Fix cluster node page cannot open</li>
     <li>[<a href='https://github.com/igniterealtime/openfire-hazelcast-plugin/issues/112'>Issue #112</a>] - Support locks in SerializingCache</li>
 </ul>

plugin.xml

@@ -6,7 +6,7 @@
     <description>${project.description}</description>
     <author>Ignite Realtime</author>
     <version>${project.version}</version>
-    <date>2025-06-12</date>
+    <date>2026-02-18</date>
     <minServerVersion>5.0.0</minServerVersion>
     <minJavaVersion>17</minJavaVersion>
 </plugin>

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2004-2009 Jive Software, 2022-2024 Ignite Realtime Foundation. All rights reserved.
+ * Copyright (C) 2004-2009 Jive Software, 2022-2026 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.
@@ -21,6 +21,7 @@
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.util.concurrent.CompletableFuture;
 
 import org.jivesoftware.openfire.XMPPServer;
 import org.jivesoftware.openfire.cluster.ClusterManager;
@@ -55,7 +56,7 @@ public void initializePlugin(final PluginManager manager, final File pluginDirec
             @Override
             public void pluginsMonitored() {
                 manager.removePluginManagerListener(this);
-                initializeClustering(pluginDirectory);
+                CompletableFuture.runAsync(() -> initializeClustering(pluginDirectory)) ;
             }
         });