blob: 193df527d596b195a39d2ef877e134d271548f26 (
plain) (
blame)
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
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
|
/*
* %CopyrightBegin%
*
* Copyright Ericsson AB 2000-2009. All Rights Reserved.
*
* Licensed 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.
*
* %CopyrightEnd%
*/
package com.ericsson.otp.erlang;
/**
* This class implements a generic FIFO queue. There is no upper bound on the
* length of the queue, items are linked.
*/
public class GenericQueue {
private static final int open = 0;
private static final int closing = 1;
private static final int closed = 2;
private int status;
private Bucket head;
private Bucket tail;
private int count;
private void init() {
head = null;
tail = null;
count = 0;
}
/** Create an empty queue */
public GenericQueue() {
init();
status = open;
}
/** Clear a queue */
public void flush() {
init();
}
public void close() {
status = closing;
}
/**
* Add an object to the tail of the queue.
*
* @param o
* Object to insert in the queue
*/
public synchronized void put(final Object o) {
final Bucket b = new Bucket(o);
if (tail != null) {
tail.setNext(b);
tail = b;
} else {
// queue was empty but has one element now
head = tail = b;
}
count++;
// notify any waiting tasks
notify();
}
/**
* Retrieve an object from the head of the queue, or block until one
* arrives.
*
* @return The object at the head of the queue.
*/
public synchronized Object get() {
Object o = null;
while ((o = tryGet()) == null) {
try {
this.wait();
} catch (final InterruptedException e) {
}
}
return o;
}
/**
* Retrieve an object from the head of the queue, blocking until one arrives
* or until timeout occurs.
*
* @param timeout
* Maximum time to block on queue, in ms. Use 0 to poll the
* queue.
*
* @exception InterruptedException
* if the operation times out.
*
* @return The object at the head of the queue, or null if none arrived in
* time.
*/
public synchronized Object get(final long timeout)
throws InterruptedException {
if (status == closed) {
return null;
}
long currentTime = System.currentTimeMillis();
final long stopTime = currentTime + timeout;
Object o = null;
while (true) {
if ((o = tryGet()) != null) {
return o;
}
currentTime = System.currentTimeMillis();
if (stopTime <= currentTime) {
throw new InterruptedException("Get operation timed out");
}
try {
this.wait(stopTime - currentTime);
} catch (final InterruptedException e) {
// ignore, but really should retry operation instead
}
}
}
// attempt to retrieve message from queue head
public Object tryGet() {
Object o = null;
if (head != null) {
o = head.getContents();
head = head.getNext();
count--;
if (head == null) {
tail = null;
count = 0;
}
}
return o;
}
public synchronized int getCount() {
return count;
}
/*
* The Bucket class. The queue is implemented as a linked list of Buckets.
* The container holds the queued object and a reference to the next Bucket.
*/
class Bucket {
private Bucket next;
private final Object contents;
public Bucket(final Object o) {
next = null;
contents = o;
}
public void setNext(final Bucket newNext) {
next = newNext;
}
public Bucket getNext() {
return next;
}
public Object getContents() {
return contents;
}
}
}
|
