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3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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7  * published by the Free Software Foundation.  Oracle designates this
8  * particular file as subject to the "Classpath" exception as provided
9  * by Oracle in the LICENSE file that accompanied this code.
10  *
11  * This code is distributed in the hope that it will be useful, but WITHOUT
12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14  * version 2 for more details (a copy is included in the LICENSE file that
15  * accompanied this code).
16  *
17  * You should have received a copy of the GNU General Public License version
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19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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24  */
25 
26 package com.sun.imageio.stream;
27 
28 import sun.awt.util.ThreadGroupUtils;
29 
30 import java.io.IOException;
31 import java.security.AccessController;
32 import java.security.PrivilegedAction;
33 import java.util.Set;
34 import java.util.WeakHashMap;
35 import javax.imageio.stream.ImageInputStream;
36 
37 /**
38  * This class provide means to properly close hanging
39  * image input/output streams on VM shutdown.
40  * This might be useful for proper cleanup such as removal
41  * of temporary files.
42  *
43  * Addition of stream do not prevent it from being garbage collected
44  * if no other references to it exists. Stream can be closed
45  * explicitly without removal from StreamCloser queue.
46  * Explicit removal from the queue only helps to save some memory.
47  */
48 public class StreamCloser {
49 
50     private static WeakHashMap<CloseAction, Object> toCloseQueue;
51     private static Thread streamCloser;
52 
addToQueue(CloseAction ca)53     public static void addToQueue(CloseAction ca) {
54         synchronized (StreamCloser.class) {
55             if (toCloseQueue == null) {
56                 toCloseQueue =
57                     new WeakHashMap<CloseAction, Object>();
58             }
59 
60             toCloseQueue.put(ca, null);
61 
62             if (streamCloser == null) {
63                 final Runnable streamCloserRunnable = new Runnable() {
64                     public void run() {
65                         if (toCloseQueue != null) {
66                             synchronized (StreamCloser.class) {
67                                 Set<CloseAction> set =
68                                     toCloseQueue.keySet();
69                                 // Make a copy of the set in order to avoid
70                                 // concurrent modification (the is.close()
71                                 // will in turn call removeFromQueue())
72                                 CloseAction[] actions =
73                                     new CloseAction[set.size()];
74                                 actions = set.toArray(actions);
75                                 for (CloseAction ca : actions) {
76                                     if (ca != null) {
77                                         try {
78                                             ca.performAction();
79                                         } catch (IOException e) {
80                                         }
81                                     }
82                                 }
83                             }
84                         }
85                     }
86                 };
87 
88                 AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
89                     /* The thread must be a member of a thread group
90                      * which will not get GCed before VM exit.
91                      * Make its parent the top-level thread group.
92                      */
93                     ThreadGroup tg = ThreadGroupUtils.getRootThreadGroup();
94                     streamCloser = new Thread(tg, streamCloserRunnable,
95                                               "StreamCloser", 0, false);
96                     /* Set context class loader to null in order to avoid
97                      * keeping a strong reference to an application classloader.
98                      */
99                     streamCloser.setContextClassLoader(null);
100                     Runtime.getRuntime().addShutdownHook(streamCloser);
101                     return null;
102                 });
103             }
104         }
105     }
106 
removeFromQueue(CloseAction ca)107     public static void removeFromQueue(CloseAction ca) {
108         synchronized (StreamCloser.class) {
109             if (toCloseQueue != null) {
110                 toCloseQueue.remove(ca);
111             }
112         }
113     }
114 
createCloseAction(ImageInputStream iis)115     public static CloseAction createCloseAction(ImageInputStream iis) {
116         return new CloseAction(iis);
117     }
118 
119     public static final class CloseAction {
120         private ImageInputStream iis;
121 
CloseAction(ImageInputStream iis)122         private CloseAction(ImageInputStream iis) {
123             this.iis = iis;
124         }
125 
performAction()126         public void performAction() throws IOException {
127             if (iis != null) {
128                 iis.close();
129             }
130         }
131     }
132 }
133