1 /*
2  * Copyright (c) 2014, 2018, Oracle and/or its affiliates. All rights reserved.
3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4  *
5  * This code is free software; you can redistribute it and/or modify it
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7  * published by the Free Software Foundation.
8  *
9  * This code is distributed in the hope that it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12  * version 2 for more details (a copy is included in the LICENSE file that
13  * accompanied this code).
14  *
15  * You should have received a copy of the GNU General Public License version
16  * 2 along with this work; if not, write to the Free Software Foundation,
17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18  *
19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20  * or visit www.oracle.com if you need additional information or have any
21  * questions.
22  */
23 package gc.g1.unloading.keepref;
24 
25 import gc.g1.unloading.check.cleanup.CleanupAction;
26 import gc.g1.unloading.loading.LibLoader;
27 
28 /**
29  * This holder keeps reference through JNI local reference.
30  */
31 public class JNILocalRefHolder implements RefHolder {
32 
33     static {
34         //Force loading library
35         new LibLoader().hashCode();
36     }
37 
38     // We use this field to transfer object into native JNI call. Idea is to avoid transferring link through method
39     // arguments.
40     private Object objectToKeep;
41 
holdWithJNILocalReference(Object syncObject)42     private native void holdWithJNILocalReference(Object syncObject);
43 
44     @Override
hold(Object object)45     public Object hold(Object object) {
46         objectToKeep = object;
47         final Object syncObject = new Object();
48         Thread keepingThread = new Thread(new Runnable() {
49             @Override
50             public void run() {
51                 synchronized (syncObject) {
52                     holdWithJNILocalReference(syncObject);
53                 }
54             }
55         });
56         keepingThread.setDaemon(true);
57         keepingThread.start();
58         return new CleanupAction() {
59             @Override
60             public void cleanup() throws Exception {
61                 synchronized (syncObject) {
62                     syncObject.notify();
63                 }
64             }
65         };
66     }
67 
68 
69 }
70