1 /*
 2  * Copyright (c) 2021, 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
 6  * under the terms of the GNU General Public License version 2 only, as
 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
18  * 2 along with this work; if not, write to the Free Software Foundation,
19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20  *
21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22  * or visit www.oracle.com if you need additional information or have any
23  * questions.
24  */
25 
26 package java.lang.ref;
27 
28 /**
29  * An implementation of a ReferenceQueue that uses native monitors.
30  * The use of java.util.concurrent.lock locks interacts with various mechanisms,
31  * such as virtual threads and ForkJoinPool, that might not be appropriate for some
32  * low-level mechanisms, in particular MethodType's weak intern set.
33  */
34 final class NativeReferenceQueue<T> extends ReferenceQueue<T> {
35     public NativeReferenceQueue() {
36         super(0);
37     }
38 
39     private static class Lock { };
40     private final Lock lock = new Lock();
41 
42     @Override void signal() { lock.notifyAll(); }
43     @Override void await() throws InterruptedException { lock.wait(); }
44     @Override void await(long timeoutMillis) throws InterruptedException {
45         lock.wait(timeoutMillis); 
46     }
47 
48     @Override
49     boolean enqueue(Reference<? extends T> r) {
50         synchronized(lock) {
51             return enqueue0(r);
52         }
53     }
54     
55     @Override
56     public Reference<? extends T> poll() {
57         if (headIsNull())
58             return null;
59         
60         synchronized(lock) {
61             return poll0();
62         }
63     }
64 
65     @Override
66     public Reference<? extends T> remove(long timeout) 
67             throws IllegalArgumentException, InterruptedException {
68         if (timeout < 0)
69             throw new IllegalArgumentException("Negative timeout value");
70         if (timeout == 0)
71             return remove();
72 
73         synchronized(lock) {
74             return remove0(timeout);
75         }
76     }
77 
78     @Override
79     public Reference<? extends T> remove() throws InterruptedException {
80         synchronized(lock) {
81             return remove0();
82         }
83     }
84 }