1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
|
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package java.lang.ref;
/**
* The {@code ReferenceQueue} is the container on which reference objects are
* enqueued when the garbage collector detects the reachability type specified
* for the referent.
*
* @since 1.2
*/
public class ReferenceQueue<T> {
private static final int NANOS_PER_MILLI = 1000000;
private Reference<? extends T> head;
/**
* Constructs a new instance of this class.
*/
public ReferenceQueue() {
}
/**
* Returns the next available reference from the queue, removing it in the
* process. Does not wait for a reference to become available.
*
* @return the next available reference, or {@code null} if no reference is
* immediately available
*/
@SuppressWarnings("unchecked")
public synchronized Reference<? extends T> poll() {
if (head == null) {
return null;
}
Reference<? extends T> ret;
ret = head;
if (head == head.queueNext) {
head = null;
} else {
head = head.queueNext;
}
ret.queueNext = null;
return ret;
}
/**
* Returns the next available reference from the queue, removing it in the
* process. Waits indefinitely for a reference to become available.
*
* @throws InterruptedException if the blocking call was interrupted
*/
public Reference<? extends T> remove() throws InterruptedException {
return remove(0L);
}
/**
* Returns the next available reference from the queue, removing it in the
* process. Waits for a reference to become available or the given timeout
* period to elapse, whichever happens first.
*
* @param timeoutMillis maximum time to spend waiting for a reference object
* to become available. A value of {@code 0} results in the method
* waiting indefinitely.
* @return the next available reference, or {@code null} if no reference
* becomes available within the timeout period
* @throws IllegalArgumentException if {@code timeoutMillis < 0}.
* @throws InterruptedException if the blocking call was interrupted
*/
public synchronized Reference<? extends T> remove(long timeoutMillis)
throws InterruptedException {
if (timeoutMillis < 0) {
throw new IllegalArgumentException("timeout < 0: " + timeoutMillis);
}
if (head != null) {
return poll();
}
// avoid overflow: if total > 292 years, just wait forever
if (timeoutMillis == 0 || (timeoutMillis > Long.MAX_VALUE / NANOS_PER_MILLI)) {
do {
wait(0);
} while (head == null);
return poll();
}
// guaranteed to not overflow
long nanosToWait = timeoutMillis * NANOS_PER_MILLI;
int timeoutNanos = 0;
// wait until notified or the timeout has elapsed
long startTime = System.nanoTime();
while (true) {
wait(timeoutMillis, timeoutNanos);
if (head != null) {
break;
}
long nanosElapsed = System.nanoTime() - startTime;
long nanosRemaining = nanosToWait - nanosElapsed;
if (nanosRemaining <= 0) {
break;
}
timeoutMillis = nanosRemaining / NANOS_PER_MILLI;
timeoutNanos = (int) (nanosRemaining - timeoutMillis * NANOS_PER_MILLI);
}
return poll();
}
/**
* Enqueue the reference object on the receiver.
*
* @param reference
* reference object to be enqueued.
*/
synchronized void enqueue(Reference<? extends T> reference) {
if (head == null) {
reference.queueNext = reference;
} else {
reference.queueNext = head;
}
head = reference;
notify();
}
/** @hide */
public static Reference<?> unenqueued = null;
static void add(Reference<?> list) {
synchronized (ReferenceQueue.class) {
if (unenqueued == null) {
unenqueued = list;
} else {
Reference<?> next = unenqueued.pendingNext;
unenqueued.pendingNext = list.pendingNext;
list.pendingNext = next;
}
ReferenceQueue.class.notifyAll();
}
}
}
|
