jaroslav@601
|
1 |
/*
|
jaroslav@601
|
2 |
* Copyright (c) 1997, 2005, Oracle and/or its affiliates. All rights reserved.
|
jaroslav@601
|
3 |
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
|
jaroslav@601
|
4 |
*
|
jaroslav@601
|
5 |
* This code is free software; you can redistribute it and/or modify it
|
jaroslav@601
|
6 |
* under the terms of the GNU General Public License version 2 only, as
|
jaroslav@601
|
7 |
* published by the Free Software Foundation. Oracle designates this
|
jaroslav@601
|
8 |
* particular file as subject to the "Classpath" exception as provided
|
jaroslav@601
|
9 |
* by Oracle in the LICENSE file that accompanied this code.
|
jaroslav@601
|
10 |
*
|
jaroslav@601
|
11 |
* This code is distributed in the hope that it will be useful, but WITHOUT
|
jaroslav@601
|
12 |
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
|
jaroslav@601
|
13 |
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
|
jaroslav@601
|
14 |
* version 2 for more details (a copy is included in the LICENSE file that
|
jaroslav@601
|
15 |
* accompanied this code).
|
jaroslav@601
|
16 |
*
|
jaroslav@601
|
17 |
* You should have received a copy of the GNU General Public License version
|
jaroslav@601
|
18 |
* 2 along with this work; if not, write to the Free Software Foundation,
|
jaroslav@601
|
19 |
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
|
jaroslav@601
|
20 |
*
|
jaroslav@601
|
21 |
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
|
jaroslav@601
|
22 |
* or visit www.oracle.com if you need additional information or have any
|
jaroslav@601
|
23 |
* questions.
|
jaroslav@601
|
24 |
*/
|
jaroslav@601
|
25 |
|
jaroslav@601
|
26 |
package java.lang.ref;
|
jaroslav@601
|
27 |
|
jaroslav@601
|
28 |
/**
|
jaroslav@601
|
29 |
* Reference queues, to which registered reference objects are appended by the
|
jaroslav@601
|
30 |
* garbage collector after the appropriate reachability changes are detected.
|
jaroslav@601
|
31 |
*
|
jaroslav@601
|
32 |
* @author Mark Reinhold
|
jaroslav@601
|
33 |
* @since 1.2
|
jaroslav@601
|
34 |
*/
|
jaroslav@601
|
35 |
|
jaroslav@601
|
36 |
public class ReferenceQueue<T> {
|
jaroslav@601
|
37 |
|
jaroslav@601
|
38 |
/**
|
jaroslav@601
|
39 |
* Constructs a new reference-object queue.
|
jaroslav@601
|
40 |
*/
|
jaroslav@601
|
41 |
public ReferenceQueue() { }
|
jaroslav@601
|
42 |
|
jaroslav@601
|
43 |
private static class Null extends ReferenceQueue {
|
jaroslav@601
|
44 |
boolean enqueue(Reference r) {
|
jaroslav@601
|
45 |
return false;
|
jaroslav@601
|
46 |
}
|
jaroslav@601
|
47 |
}
|
jaroslav@601
|
48 |
|
jaroslav@601
|
49 |
static ReferenceQueue NULL = new Null();
|
jaroslav@601
|
50 |
static ReferenceQueue ENQUEUED = new Null();
|
jaroslav@601
|
51 |
|
jaroslav@601
|
52 |
static private class Lock { };
|
jaroslav@601
|
53 |
private Lock lock = new Lock();
|
jaroslav@601
|
54 |
private volatile Reference<? extends T> head = null;
|
jaroslav@601
|
55 |
private long queueLength = 0;
|
jaroslav@601
|
56 |
|
jaroslav@601
|
57 |
boolean enqueue(Reference<? extends T> r) { /* Called only by Reference class */
|
jaroslav@601
|
58 |
synchronized (r) {
|
jaroslav@601
|
59 |
if (r.queue == ENQUEUED) return false;
|
jaroslav@601
|
60 |
synchronized (lock) {
|
jaroslav@601
|
61 |
r.queue = ENQUEUED;
|
jaroslav@601
|
62 |
r.next = (head == null) ? r : head;
|
jaroslav@601
|
63 |
head = r;
|
jaroslav@601
|
64 |
queueLength++;
|
jaroslav@601
|
65 |
lock.notifyAll();
|
jaroslav@601
|
66 |
return true;
|
jaroslav@601
|
67 |
}
|
jaroslav@601
|
68 |
}
|
jaroslav@601
|
69 |
}
|
jaroslav@601
|
70 |
|
jaroslav@601
|
71 |
private Reference<? extends T> reallyPoll() { /* Must hold lock */
|
jaroslav@601
|
72 |
if (head != null) {
|
jaroslav@601
|
73 |
Reference<? extends T> r = head;
|
jaroslav@601
|
74 |
head = (r.next == r) ? null : r.next;
|
jaroslav@601
|
75 |
r.queue = NULL;
|
jaroslav@601
|
76 |
r.next = r;
|
jaroslav@601
|
77 |
queueLength--;
|
jaroslav@601
|
78 |
return r;
|
jaroslav@601
|
79 |
}
|
jaroslav@601
|
80 |
return null;
|
jaroslav@601
|
81 |
}
|
jaroslav@601
|
82 |
|
jaroslav@601
|
83 |
/**
|
jaroslav@601
|
84 |
* Polls this queue to see if a reference object is available. If one is
|
jaroslav@601
|
85 |
* available without further delay then it is removed from the queue and
|
jaroslav@601
|
86 |
* returned. Otherwise this method immediately returns <tt>null</tt>.
|
jaroslav@601
|
87 |
*
|
jaroslav@601
|
88 |
* @return A reference object, if one was immediately available,
|
jaroslav@601
|
89 |
* otherwise <code>null</code>
|
jaroslav@601
|
90 |
*/
|
jaroslav@601
|
91 |
public Reference<? extends T> poll() {
|
jaroslav@601
|
92 |
if (head == null)
|
jaroslav@601
|
93 |
return null;
|
jaroslav@601
|
94 |
synchronized (lock) {
|
jaroslav@601
|
95 |
return reallyPoll();
|
jaroslav@601
|
96 |
}
|
jaroslav@601
|
97 |
}
|
jaroslav@601
|
98 |
|
jaroslav@601
|
99 |
/**
|
jaroslav@601
|
100 |
* Removes the next reference object in this queue, blocking until either
|
jaroslav@601
|
101 |
* one becomes available or the given timeout period expires.
|
jaroslav@601
|
102 |
*
|
jaroslav@601
|
103 |
* <p> This method does not offer real-time guarantees: It schedules the
|
jaroslav@601
|
104 |
* timeout as if by invoking the {@link Object#wait(long)} method.
|
jaroslav@601
|
105 |
*
|
jaroslav@601
|
106 |
* @param timeout If positive, block for up to <code>timeout</code>
|
jaroslav@601
|
107 |
* milliseconds while waiting for a reference to be
|
jaroslav@601
|
108 |
* added to this queue. If zero, block indefinitely.
|
jaroslav@601
|
109 |
*
|
jaroslav@601
|
110 |
* @return A reference object, if one was available within the specified
|
jaroslav@601
|
111 |
* timeout period, otherwise <code>null</code>
|
jaroslav@601
|
112 |
*
|
jaroslav@601
|
113 |
* @throws IllegalArgumentException
|
jaroslav@601
|
114 |
* If the value of the timeout argument is negative
|
jaroslav@601
|
115 |
*
|
jaroslav@601
|
116 |
* @throws InterruptedException
|
jaroslav@601
|
117 |
* If the timeout wait is interrupted
|
jaroslav@601
|
118 |
*/
|
jaroslav@601
|
119 |
public Reference<? extends T> remove(long timeout)
|
jaroslav@601
|
120 |
throws IllegalArgumentException, InterruptedException
|
jaroslav@601
|
121 |
{
|
jaroslav@601
|
122 |
if (timeout < 0) {
|
jaroslav@601
|
123 |
throw new IllegalArgumentException("Negative timeout value");
|
jaroslav@601
|
124 |
}
|
jaroslav@601
|
125 |
synchronized (lock) {
|
jaroslav@601
|
126 |
Reference<? extends T> r = reallyPoll();
|
jaroslav@601
|
127 |
if (r != null) return r;
|
jaroslav@601
|
128 |
for (;;) {
|
jaroslav@601
|
129 |
lock.wait(timeout);
|
jaroslav@601
|
130 |
r = reallyPoll();
|
jaroslav@601
|
131 |
if (r != null) return r;
|
jaroslav@601
|
132 |
if (timeout != 0) return null;
|
jaroslav@601
|
133 |
}
|
jaroslav@601
|
134 |
}
|
jaroslav@601
|
135 |
}
|
jaroslav@601
|
136 |
|
jaroslav@601
|
137 |
/**
|
jaroslav@601
|
138 |
* Removes the next reference object in this queue, blocking until one
|
jaroslav@601
|
139 |
* becomes available.
|
jaroslav@601
|
140 |
*
|
jaroslav@601
|
141 |
* @return A reference object, blocking until one becomes available
|
jaroslav@601
|
142 |
* @throws InterruptedException If the wait is interrupted
|
jaroslav@601
|
143 |
*/
|
jaroslav@601
|
144 |
public Reference<? extends T> remove() throws InterruptedException {
|
jaroslav@601
|
145 |
return remove(0);
|
jaroslav@601
|
146 |
}
|
jaroslav@601
|
147 |
|
jaroslav@601
|
148 |
}
|