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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  package org.apache.commons.pool.impl;
19  
20  import java.util.Timer;
21  import java.util.TimerTask;
22  
23  /***
24   * <p>
25   * Provides a shared idle object eviction timer for all pools. This class wraps
26   * the standard {@link Timer} and keeps track of how many pools are using it.
27   * If no pools are using the timer, it is canceled. This prevents a thread
28   * being left running which, in application server environments, can lead to
29   * memory leads and/or prevent applications from shutting down or reloading
30   * cleanly.
31   * </p>
32   * <p>
33   * This class has package scope to prevent its inclusion in the pool public API.
34   * The class declaration below should *not* be changed to public.
35   * </p> 
36   */
37  class EvictionTimer {
38      private static Timer _timer;
39      private static int _usageCount;
40      
41      private EvictionTimer() {
42          // Hide the default constuctor
43      }
44      
45      /***
46       * Add the specified eviction task to the timer. Tasks that are added with a
47       * call to this method *must* call {@link #cancel(TimerTask)} to cancel the
48       * task to prevent memory and/or thread leaks in application server
49       * environments.
50       * @param task      Task to be scheduled
51       * @param delay     Delay in milliseconds before task is executed
52       * @param period    Time in milliseconds between executions
53       */
54      static synchronized void schedule(TimerTask task, long delay, long period) {
55          if (null == _timer) {
56              _timer = new Timer(true);
57          }
58          _usageCount++;
59          _timer.schedule(task, delay, period);
60      }
61      
62      /***
63       * Remove the specified eviction task from the timer.
64       * @param task      Task to be scheduled
65       */
66      static synchronized void cancel(TimerTask task) {
67          task.cancel();
68          _usageCount--;
69          if (_usageCount == 0) {
70              _timer.cancel();
71              _timer = null;
72          }
73      }
74  }