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root/jsr166/jsr166/src/main/java/util/concurrent/BlockingQueue.java
Revision: 1.31
Committed: Sun Nov 21 01:40:53 2004 UTC (19 years, 6 months ago) by dl
Branch: MAIN
Changes since 1.30: +33 -1 lines
Log Message: 
Changes for maintenance/RFE phase

File Contents

# User Rev Content
1 dl 1.2 /*
2     * Written by Doug Lea with assistance from members of JCP JSR-166
3 dl 1.26 * Expert Group and released to the public domain, as explained at
4     * http://creativecommons.org/licenses/publicdomain
5 dl 1.2 */
6    
7 tim 1.1 package java.util.concurrent;
8 tim 1.9
9     import java.util.Collection;
10 tim 1.1 import java.util.Queue;
11    
12     /**
13 dl 1.4 * A {@link java.util.Queue} that additionally supports operations
14 dl 1.27 * that wait for the queue to become non-empty when retrieving an element,
15     * and wait for space to become available in the queue when storing an
16 dl 1.31 * element. The names
17     * of the operations vary with their policies:
18     *
19     *<table BORDER CELLPADDING=3 CELLSPACING=1>
20     * <tr>
21     * <td><em>Operation</em></td>
22     * <td ALIGN=CENTER><em>Attempt</em></td>
23     * <td ALIGN=CENTER><em>Throw</em></td>
24     * <td ALIGN=CENTER><em>Block</em></td>
25     * <td ALIGN=CENTER><em>Timeout</em></td>
26     * </tr>
27     * <tr>
28     * <td><em>insert</em></td>
29     * <td>offer(x)</td>
30     * <td>add(x)</td>
31     * <td>put(x)</td>
32     * <td>offer(x,time,unit)</td>
33     * </tr>
34     * <tr>
35     * <td><em>extract</em></td>
36     * <td>poll()</td>
37     * <td>remove()</td>
38     * <td>take()</td>
39     * <td>poll(time,unit)</td>
40     * </tr>
41     * <tr>
42     * <td><em>inspect</em></td>
43     * <td>peek()</td>
44     * <td>element()</td>
45     * <td></td>
46     * <td></td>
47     * </tr>
48     *</table>
49 dl 1.2 *
50 dholmes 1.7 * <p>A <tt>BlockingQueue</tt> does not accept <tt>null</tt> elements.
51 dholmes 1.10 * Implementations throw <tt>NullPointerException</tt> on attempts
52 dl 1.2 * to <tt>add</tt>, <tt>put</tt> or <tt>offer</tt> a <tt>null</tt>. A
53     * <tt>null</tt> is used as a sentinel value to indicate failure of
54     * <tt>poll</tt> operations.
55     *
56 dholmes 1.7 * <p>A <tt>BlockingQueue</tt> may be capacity bounded. At any given
57     * time it may have a <tt>remainingCapacity</tt> beyond which no
58 dl 1.2 * additional elements can be <tt>put</tt> without blocking.
59 dholmes 1.7 * A <tt>BlockingQueue</tt> without any intrinsic capacity constraints always
60     * reports a remaining capacity of <tt>Integer.MAX_VALUE</tt>.
61 dl 1.2 *
62 dl 1.29 * <p> <tt>BlockingQueue</tt> implementations are designed to be used
63     * primarily for producer-consumer queues, but additionally support
64     * the {@link java.util.Collection} interface. So, for example, it is
65     * possible to remove an arbitrary element from a queue using
66 dl 1.6 * <tt>remove(x)</tt>. However, such operations are in general
67 dl 1.18 * <em>not</em> performed very efficiently, and are intended for only
68 dl 1.29 * occasional use, such as when a queued message is cancelled.
69     *
70     * <p> <tt>BlockingQueue</tt> implementations are thread-safe. All
71     * queuing methods achieve their effects atomically using internal
72     * locks or other forms of concurrency control. However, the
73     * <em>bulk</em> Collection operations <tt>addAll</tt>,
74     * <tt>containsAll</tt>, <tt>retainAll</tt> and <tt>removeAll</tt> are
75     * <em>not</em> necessarily performed atomically unless specified
76     * otherwise in an implementation. So it is possible, for example, for
77     * <tt>addAll(c)</tt> to fail (throwing an exception) after adding
78 dl 1.18 * only some of the elements in <tt>c</tt>.
79 dl 1.2 *
80 dholmes 1.7 * <p>A <tt>BlockingQueue</tt> does <em>not</em> intrinsically support
81 dl 1.2 * any kind of &quot;close&quot; or &quot;shutdown&quot; operation to
82     * indicate that no more items will be added. The needs and usage of
83 brian 1.5 * such features tend to be implementation-dependent. For example, a
84 dl 1.2 * common tactic is for producers to insert special
85     * <em>end-of-stream</em> or <em>poison</em> objects, that are
86     * interpreted accordingly when taken by consumers.
87 tim 1.1 *
88     * <p>
89 brian 1.5 * Usage example, based on a typical producer-consumer scenario.
90 tim 1.9 * Note that a <tt>BlockingQueue</tt> can safely be used with multiple
91 dholmes 1.7 * producers and multiple consumers.
92 tim 1.1 * <pre>
93     * class Producer implements Runnable {
94     * private final BlockingQueue queue;
95     * Producer(BlockingQueue q) { queue = q; }
96     * public void run() {
97     * try {
98     * while(true) { queue.put(produce()); }
99 tim 1.15 * } catch (InterruptedException ex) { ... handle ...}
100 tim 1.1 * }
101     * Object produce() { ... }
102     * }
103     *
104     * class Consumer implements Runnable {
105     * private final BlockingQueue queue;
106 dl 1.21 * Consumer(BlockingQueue q) { queue = q; }
107 tim 1.1 * public void run() {
108     * try {
109     * while(true) { consume(queue.take()); }
110 tim 1.15 * } catch (InterruptedException ex) { ... handle ...}
111 tim 1.1 * }
112     * void consume(Object x) { ... }
113     * }
114     *
115     * class Setup {
116     * void main() {
117     * BlockingQueue q = new SomeQueueImplementation();
118     * Producer p = new Producer(q);
119 brian 1.5 * Consumer c1 = new Consumer(q);
120     * Consumer c2 = new Consumer(q);
121 tim 1.1 * new Thread(p).start();
122 brian 1.5 * new Thread(c1).start();
123     * new Thread(c2).start();
124 tim 1.1 * }
125     * }
126     * </pre>
127     *
128 dl 1.28 * <p>This interface is a member of the
129     * <a href="{@docRoot}/../guide/collections/index.html">
130     * Java Collections Framework</a>.
131     *
132 tim 1.1 * @since 1.5
133 dl 1.6 * @author Doug Lea
134 dl 1.24 * @param <E> the type of elements held in this collection
135 tim 1.1 */
136     public interface BlockingQueue<E> extends Queue<E> {
137 dholmes 1.7
138     /**
139 dl 1.20 * Inserts the specified element into this queue, if possible. When
140 dl 1.18 * using queues that may impose insertion restrictions (for
141     * example capacity bounds), method <tt>offer</tt> is generally
142     * preferable to method {@link Collection#add}, which can fail to
143 dl 1.19 * insert an element only by throwing an exception.
144 dl 1.18 *
145 dl 1.19 * @param o the element to add.
146 dl 1.18 * @return <tt>true</tt> if it was possible to add the element to
147 dl 1.19 * this queue, else <tt>false</tt>
148     * @throws NullPointerException if the specified element is <tt>null</tt>
149 dholmes 1.7 */
150 tim 1.14 boolean offer(E o);
151 dl 1.20
152 tim 1.1 /**
153 dl 1.20 * Inserts the specified element into this queue, waiting if necessary
154 dl 1.18 * up to the specified wait time for space to become available.
155 dholmes 1.10 * @param o the element to add
156 dholmes 1.7 * @param timeout how long to wait before giving up, in units of
157     * <tt>unit</tt>
158 tim 1.9 * @param unit a <tt>TimeUnit</tt> determining how to interpret the
159 dholmes 1.7 * <tt>timeout</tt> parameter
160     * @return <tt>true</tt> if successful, or <tt>false</tt> if
161     * the specified waiting time elapses before space is available.
162 tim 1.1 * @throws InterruptedException if interrupted while waiting.
163 dholmes 1.11 * @throws NullPointerException if the specified element is <tt>null</tt>.
164 tim 1.1 */
165 dholmes 1.10 boolean offer(E o, long timeout, TimeUnit unit)
166 dholmes 1.7 throws InterruptedException;
167 tim 1.1
168     /**
169 dholmes 1.12 * Retrieves and removes the head of this queue, waiting
170 dholmes 1.7 * if necessary up to the specified wait time if no elements are
171     * present on this queue.
172 dl 1.6 * @param timeout how long to wait before giving up, in units of
173     * <tt>unit</tt>
174 tim 1.9 * @param unit a <tt>TimeUnit</tt> determining how to interpret the
175 dholmes 1.7 * <tt>timeout</tt> parameter
176 tim 1.9 * @return the head of this queue, or <tt>null</tt> if the
177 dholmes 1.7 * specified waiting time elapses before an element is present.
178 tim 1.1 * @throws InterruptedException if interrupted while waiting.
179     */
180 tim 1.9 E poll(long timeout, TimeUnit unit)
181 tim 1.1 throws InterruptedException;
182    
183     /**
184 dholmes 1.12 * Retrieves and removes the head of this queue, waiting
185 dholmes 1.7 * if no elements are present on this queue.
186     * @return the head of this queue
187 tim 1.1 * @throws InterruptedException if interrupted while waiting.
188     */
189 dholmes 1.7 E take() throws InterruptedException;
190    
191 tim 1.1 /**
192 dholmes 1.12 * Adds the specified element to this queue, waiting if necessary for
193 dholmes 1.7 * space to become available.
194 dholmes 1.10 * @param o the element to add
195 tim 1.1 * @throws InterruptedException if interrupted while waiting.
196 dholmes 1.13 * @throws NullPointerException if the specified element is <tt>null</tt>.
197 tim 1.1 */
198 dholmes 1.10 void put(E o) throws InterruptedException;
199 dholmes 1.7
200 dl 1.2 /**
201 dholmes 1.12 * Returns the number of elements that this queue can ideally (in
202 dl 1.2 * the absence of memory or resource constraints) accept without
203     * blocking, or <tt>Integer.MAX_VALUE</tt> if there is no
204 tim 1.9 * intrinsic limit.
205 dholmes 1.7 * <p>Note that you <em>cannot</em> always tell if
206 dl 1.2 * an attempt to <tt>add</tt> an element will succeed by
207     * inspecting <tt>remainingCapacity</tt> because it may be the
208 dl 1.30 * case that another thread is about to <tt>put</tt> or <tt>take</tt> an
209     * element.
210 dl 1.2 * @return the remaining capacity
211 dl 1.6 */
212     int remainingCapacity();
213 tim 1.1
214 dl 1.18 /**
215     * Adds the specified element to this queue if it is possible to
216     * do so immediately, returning <tt>true</tt> upon success, else
217     * throwing an IllegalStateException.
218     * @param o the element
219     * @return <tt>true</tt> (as per the general contract of
220     * <tt>Collection.add</tt>).
221     *
222     * @throws NullPointerException if the specified element is <tt>null</tt>
223     * @throws IllegalStateException if element cannot be added
224     */
225     boolean add(E o);
226 dholmes 1.7
227 dl 1.18 /**
228 dl 1.22 * Removes all available elements from this queue and adds them
229     * into the given collection. This operation may be more
230     * efficient than repeatedly polling this queue. A failure
231     * encountered while attempting to <tt>add</tt> elements to
232     * collection <tt>c</tt> may result in elements being in neither,
233     * either or both collections when the associated exception is
234     * thrown. Attempts to drain a queue to itself result in
235     * <tt>IllegalArgumentException</tt>. Further, the behavior of
236     * this operation is undefined if the specified collection is
237     * modified while the operation is in progress.
238 dl 1.18 *
239 dl 1.22 * @param c the collection to transfer elements into
240     * @return the number of elements transferred.
241     * @throws NullPointerException if c is null
242     * @throws IllegalArgumentException if c is this queue
243 dl 1.18 *
244     */
245 dl 1.22 int drainTo(Collection<? super E> c);
246    
247     /**
248     * Removes at most the given number of available elements from
249     * this queue and adds them into the given collection. A failure
250     * encountered while attempting to <tt>add</tt> elements to
251     * collection <tt>c</tt> may result in elements being in neither,
252     * either or both collections when the associated exception is
253     * thrown. Attempts to drain a queue to itself result in
254     * <tt>IllegalArgumentException</tt>. Further, the behavior of
255     * this operation is undefined if the specified collection is
256     * modified while the operation is in progress.
257     *
258     * @param c the collection to transfer elements into
259     * @param maxElements the maximum number of elements to transfer
260     * @return the number of elements transferred.
261     * @throws NullPointerException if c is null
262     * @throws IllegalArgumentException if c is this queue
263     */
264     int drainTo(Collection<? super E> c, int maxElements);
265 dl 1.18 }