OF-1424: Use weakly consistent impl to prevent CME.

src/java/org/jivesoftware/openfire/group/Group.java

@@ -28,6 +28,7 @@ import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.ConcurrentSkipListSet;
 
 import org.jivesoftware.openfire.XMPPServer;
 import org.jivesoftware.openfire.event.GroupEventDispatcher;
@@ -62,8 +63,8 @@ public class Group implements Cacheable, Externalizable {
 
     private String name;
     private String description;
-    private Set<JID> members;
-    private Set<JID> administrators;
+    private ConcurrentSkipListSet<JID> members;
+    private ConcurrentSkipListSet<JID> administrators;
 
     /**
      * Constructor added for Externalizable. Do not use this constructor.
@@ -88,8 +89,8 @@ public class Group implements Cacheable, Externalizable {
         this.provider = groupManager.getProvider();
         this.name = name;
         this.description = description;
-        this.members = new HashSet<>(members);
-        this.administrators = new HashSet<>(administrators);
+        this.members = new ConcurrentSkipListSet<>(members);
+        this.administrators = new ConcurrentSkipListSet<>(administrators);
     }
 
     /**
@@ -110,8 +111,8 @@ public class Group implements Cacheable, Externalizable {
         this.provider = groupManager.getProvider();
         this.name = name;
         this.description = description;
-        this.members = new HashSet<>(members);
-        this.administrators = new HashSet<>(administrators);
+        this.members = new ConcurrentSkipListSet<>(members);
+        this.administrators = new ConcurrentSkipListSet<>(administrators);
 
         this.properties = provider.loadProperties(this);
 
@@ -502,8 +503,8 @@ public class Group implements Cacheable, Externalizable {
         if (ExternalizableUtil.getInstance().readBoolean(in)) {
             description = ExternalizableUtil.getInstance().readSafeUTF(in);
         }
-        members= new HashSet<>();
-        administrators = new HashSet<>();
+        members= new ConcurrentSkipListSet<>();
+        administrators = new ConcurrentSkipListSet<>();
         ExternalizableUtil.getInstance().readSerializableCollection(in, members, getClass().getClassLoader());
         ExternalizableUtil.getInstance().readSerializableCollection(in, administrators, getClass().getClassLoader());
     }