Exit


1   /*
2    * Copyright (c) 1998-2006 Caucho Technology -- all rights reserved
3    *
4    * This file is part of Resin(R) Open Source
5    *
6    * Each copy or derived work must preserve the copyright notice and this
7    * notice unmodified.
8    *
9    * Resin Open Source is free software; you can redistribute it and/or modify
10   * it under the terms of the GNU General Public License as published by
11   * the Free Software Foundation; either version 2 of the License, or
12   * (at your option) any later version.
13   *
14   * Resin Open Source is distributed in the hope that it will be useful,
15   * but WITHOUT ANY WARRANTY; without even the implied warranty of
16   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE, or any warranty
17   * of NON-INFRINGEMENT.  See the GNU General Public License for more
18   * details.
19   *
20   * You should have received a copy of the GNU General Public License
21   * along with Resin Open Source; if not, write to the
22   *   Free SoftwareFoundation, Inc.
23   *   59 Temple Place, Suite 330
24   *   Boston, MA 02111-1307  USA
25   *
26   * @author Scott Ferguson
27   */
28  
29  package com.caucho.util;
30  
31  import java.util.ArrayList  ;
32  
33  /**
34   * The exit class is used to automatically clean state.  For example,
35   * Resin JavaScript will close open files when the script exits.
36   *
37   * Here's a sample use:
38   * <pre>
39   *   boolean isExit = addExit();
40   *   try {
41   *     ...
42   *   } finally {
43   *     if (isExit)
44   *       exit();
45   *   }
46   * </pre>
47   *
48   * <p>Objects register for the exit callback by calling
49   * <code>addExit(listener, object)</code>.
50   *
51   * <p>Exits are intrinsically tied to a thread.
52   */
53  public class Exit {
54    static private ThreadLocal  <Queue> _waiting = new ThreadLocal  <Queue>();
55  
56    private Exit() {}
57  
58    /**
59     * Registers the object and listener.  The listener will be called when
60     * the thread exits the scope.
61     *
62     * <p>If there is no protection scope, i.e. addExit() hasn't been called,
63     * then this function does nothing.
64     *
65     * @param listener the exit handler
66     * @param object the object which needs cleanup
67     */
68    static public void addExit(ExitListener listener, Object   object)
69    {
70      Queue queue = _waiting.get();
71  
72      if (queue != null)
73        queue.add(listener, object);
74    }
75  
76    /**
77     * Starts a protection scope.  Only the outermost scope is important, so
78     * protecting routines must check the return value to see if they are the
79     * outermost scope.
80     *
81     * @return true if this is the outermost scope.
82     */
83    static public boolean addExit()
84    {
85      Queue queue = _waiting.get();
86  
87      if (queue == null) {
88        queue = Queue.allocate();
89        _waiting.set(queue);
90        return true;
91      } else 
92        return false;
93    }
94  
95    /**
96     * Calls all registered listeners.
97     */
98    static public void exit()
99    {
100     Queue queue = null;
101 
102     queue = _waiting.get();
103     _waiting.set(null);
104 
105     if (queue == null)
106       return;
107     
108     int size = queue._listeners.size();
109     for (int i = 0; i < size; i++) {
110       ExitListener listener = queue._listeners.get(i);
111       Object   object = queue._objects.get(i);
112 
113       if (listener != null) {
114     try {
115       listener.handleExit(object);
116     } catch (Exception   e) {
117     }
118       }
119     }
120 
121     queue.free();
122   }
123 
124   private static class Queue {
125     static Queue _freeList;
126 
127     Queue _next;
128     ArrayList  <ExitListener> _listeners = new ArrayList  <ExitListener>();
129     ArrayList  <Object  > _objects = new ArrayList  <Object  >();
130 
131     private Queue()
132     {
133     }
134 
135     void add(ExitListener listener, Object   object)
136     {
137       _listeners.add(listener);
138       _objects.add(object);
139     }
140 
141     static Queue allocate()
142     {
143       if (_freeList == null) 
144     return new Queue();
145 
146       Queue queue = _freeList;
147       _freeList = _freeList._next;
148 
149       return queue;
150     }
151 
152     void free()
153     {
154       _listeners.clear();
155       _objects.clear();
156       _next = _freeList;
157       _freeList = this;
158     }
159   }
160 }
161
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