fix: Cleans the multiUserChats map.

smack-core/src/main/java/org/jivesoftware/smack/util/CleaningWeakReferenceMap.java

@@ -0,0 +1,94 @@
+/**
+ *
+ * Copyright the original author or authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smack.util;
+
+import java.lang.ref.WeakReference;
+import java.util.HashMap;
+import java.util.Iterator;
+
+/**
+ * Extends a {@link HashMap} with {@link WeakReference} values, so that
+ * weak references which have been cleared are periodically removed from
+ * the map. The cleaning occurs as part of {@link #put}, after a specific
+ * number ({@link #cleanInterval}) of calls to {@link #put}.
+ *
+ * @param <K> The key type.
+ * @param <V> The value type.
+ *
+ * @author Boris Grozev
+ */
+public class CleaningWeakReferenceMap<K, V>
+    extends HashMap<K, WeakReference<V>> {
+    private static final long serialVersionUID = 0L;
+
+    /**
+     * The number of calls to {@link #put} after which to clean this map
+     * (i.e. remove cleared {@link WeakReference}s from it).
+     */
+    private final int cleanInterval;
+
+    /**
+     * The number of times {@link #put} has been called on this instance
+     * since the last time it was {@link #clean}ed.
+     */
+    private int numberOfInsertsSinceLastClean = 0;
+
+    /**
+     * Initializes a new {@link CleaningWeakReferenceMap} instance with the
+     * default clean interval.
+     */
+    public CleaningWeakReferenceMap() {
+        this(50);
+    }
+
+    /**
+     * Initializes a new {@link CleaningWeakReferenceMap} instance with a given
+     * clean interval.
+     * @param cleanInterval the number of calls to {@link #put} after which the
+     * map will clean itself.
+     */
+    public CleaningWeakReferenceMap(int cleanInterval) {
+        this.cleanInterval = cleanInterval;
+    }
+
+    @Override
+    public WeakReference<V> put(K key, WeakReference<V> value) {
+        WeakReference<V> ret = super.put(key, value);
+
+        if (numberOfInsertsSinceLastClean++ > cleanInterval) {
+            numberOfInsertsSinceLastClean = 0;
+            clean();
+        }
+
+        return ret;
+    }
+
+    /**
+     * Removes all cleared entries from this map (i.e. entries whose value
+     * is a cleared {@link WeakReference}).
+     */
+    private void clean() {
+        Iterator<Entry<K, WeakReference<V>>> iter = entrySet().iterator();
+        while (iter.hasNext()) {
+            Entry<K, WeakReference<V>> e = iter.next();
+            if (e != null && e.getValue() != null
+                && e.getValue().get() == null) {
+                iter.remove();
+            }
+        }
+    }
+}

smack-extensions/src/main/java/org/jivesoftware/smackx/muc/MultiUserChatManager.java

@@ -19,7 +19,6 @@ package org.jivesoftware.smackx.muc;
 import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -46,6 +45,7 @@ import org.jivesoftware.smack.filter.StanzaTypeFilter;
 import org.jivesoftware.smack.packet.Message;
 import org.jivesoftware.smack.packet.Stanza;
 import org.jivesoftware.smack.util.Async;
+import org.jivesoftware.smack.util.CleaningWeakReferenceMap;
 
 import org.jivesoftware.smackx.disco.AbstractNodeInformationProvider;
 import org.jivesoftware.smackx.disco.ServiceDiscoveryManager;
@@ -144,7 +144,7 @@ public final class MultiUserChatManager extends Manager {
      * those instances to get garbage collected. Note that MultiUserChat instances can not get garbage collected while
      * the user is joined, because then the MUC will have PacketListeners added to the XMPPConnection.
      */
-    private final Map<EntityBareJid, WeakReference<MultiUserChat>> multiUserChats = new HashMap<>();
+    private final Map<EntityBareJid, WeakReference<MultiUserChat>> multiUserChats = new CleaningWeakReferenceMap<>();
 
     private boolean autoJoinOnReconnect;