1 /*
 2  * Copyright (c) 2021, 2022, 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
43     void signal() {
44         lock.notifyAll();
45     }
46     @Override
47     void await() throws InterruptedException {
48         lock.wait();
49     }
50 
51     @Override
52     void await(long timeoutMillis) throws InterruptedException {
53         lock.wait(timeoutMillis);
54     }
55 
56     @Override
57     boolean enqueue(Reference<? extends T> r) {
58         synchronized(lock) {
59             return enqueue0(r);
60         }
61     }
62 
63     @Override
64     public Reference<? extends T> poll() {
65         if (headIsNull())
66             return null;
67 
68         synchronized(lock) {
69             return poll0();
70         }
71     }
72 
73     @Override
74     public Reference<? extends T> remove(long timeout)
75             throws IllegalArgumentException, InterruptedException {
76         if (timeout < 0)
77             throw new IllegalArgumentException("Negative timeout value");
78         if (timeout == 0)
79             return remove();
80 
81         synchronized(lock) {
82             return remove0(timeout);
83         }
84     }
85 
86     @Override
87     public Reference<? extends T> remove() throws InterruptedException {
88         synchronized(lock) {
89             return remove0();
90         }
91     }
92 }