001    /*
002     * Copyright 2010 the original author or authors.
003     * 
004     *  Licensed under the Apache License, Version 2.0 (the "License");
005     *  you may not use this file except in compliance with the License.
006     *  You may obtain a copy of the License at
007     *
008     *      http://www.apache.org/licenses/LICENSE-2.0
009     *
010     *  Unless required by applicable law or agreed to in writing, software
011     *  distributed under the License is distributed on an "AS IS" BASIS,
012     *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013     *  See the License for the specific language governing permissions and
014     *  limitations under the License.
015     */
016    package com.hs.mail.util;
017    
018    import java.util.NoSuchElementException;
019    import java.util.TreeSet;
020    
021    /**
022     * 
023     * @author Won Chul Doh
024     * @since Dec 12, 2005
025     *
026     */
027    public class ObjectLocker {
028    
029        public static final long DEFAULT_MAX_WAIT = 3L * 1000L;
030        public static final long DEFAULT_MIN_EVICTABLE_TIME_MILLIS = 5L * 60L * 1000L;
031        public static final int DEFAULT_QUEUE_SIZE = 100;
032            
033            static TreeSet _locks = new TreeSet();
034    
035        public ObjectLocker() {
036            super();
037        }
038        
039        protected long _maxWait = DEFAULT_MAX_WAIT;
040        protected long _minEvictableTimeMillis = DEFAULT_MIN_EVICTABLE_TIME_MILLIS;
041        protected int _queueSize = DEFAULT_QUEUE_SIZE;
042    
043            public void lock(Object o) throws Exception {
044            long starttime = System.currentTimeMillis();
045            for (;;) {
046                if (_locks.contains(o)) {
047                    synchronized (this) {
048                            try {
049                                wait(_maxWait);
050                            } catch (InterruptedException e) {
051                                // ignored
052                            }
053                    }
054                    if ((System.currentTimeMillis() - starttime) >= _maxWait) {
055                        throw new NoSuchElementException("Timeout waiting for idle object " + o);
056                    } else {
057                        continue; // keep looping
058                    }
059                } else {
060                    synchronized (this) {
061                        _locks.add(o);
062                    }
063                    return;
064                }
065            }
066        }
067        
068        public void unlock(Object o) {
069            synchronized (this) {
070                _locks.remove(o);
071                if (_locks.size() >= _queueSize) {
072                    evict();
073                }
074                notifyAll();
075            }
076        }
077        
078        private void evict() {
079        }
080        
081    }