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
39 /** Timer instance */
40 private static Timer _timer;
41
42 /** Static usage count tracker */
43 private static int _usageCount;
44
45 /** Prevent instantiation */
46 private EvictionTimer() {
47 // Hide the default constuctor
48 }
49
50 /**
51 * Add the specified eviction task to the timer. Tasks that are added with a
52 * call to this method *must* call {@link #cancel(TimerTask)} to cancel the
53 * task to prevent memory and/or thread leaks in application server
54 * environments.
55 * @param task Task to be scheduled
56 * @param delay Delay in milliseconds before task is executed
57 * @param period Time in milliseconds between executions
58 */
59 static synchronized void schedule(TimerTask task, long delay, long period) {
60 if (null == _timer) {
61 _timer = new Timer(true);
62 }
63 _usageCount++;
64 _timer.schedule(task, delay, period);
65 }
66
67 /**
68 * Remove the specified eviction task from the timer.
69 * @param task Task to be scheduled
70 */
71 static synchronized void cancel(TimerTask task) {
72 task.cancel();
73 _usageCount--;
74 if (_usageCount == 0) {
75 _timer.cancel();
76 _timer = null;
77 }
78 }
79 }