001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.activemq.transport.discovery.zeroconf;
018    
019    import java.io.IOException;
020    import java.net.InetAddress;
021    import java.util.HashMap;
022    import java.util.Map;
023    import java.util.concurrent.atomic.AtomicInteger;
024    import org.apache.activemq.jmdns.JmDNS;
025    
026    public final class JmDNSFactory {
027    
028        static Map<InetAddress, UsageTracker> registry = new HashMap<InetAddress, UsageTracker>();
029    
030        static class UsageTracker {
031            AtomicInteger count = new AtomicInteger(0);
032            JmDNS jmDNS;
033        }
034    
035        private JmDNSFactory() {        
036        }
037        
038        static synchronized JmDNS create(final InetAddress address) throws IOException {
039            UsageTracker tracker = registry.get(address);
040            if (tracker == null) {
041                tracker = new UsageTracker();
042                tracker.jmDNS = new JmDNS(address) {
043                    public void close() {
044                        if (onClose(address)) {
045                            super.close();
046                        }
047                    }
048                };
049                registry.put(address, tracker);
050            }
051            tracker.count.incrementAndGet();
052            return tracker.jmDNS;
053        }
054    
055        static synchronized boolean onClose(InetAddress address) {
056            UsageTracker tracker = registry.get(address);
057            if (tracker != null) {
058                if (tracker.count.decrementAndGet() == 0) {
059                    registry.remove(address);
060                    return true;
061                }
062            }
063            return false;
064        }
065    }