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root/jsr166/jsr166/src/main/java/util/concurrent/BlockingQueue.java
Revision: 1.54
Committed: Tue Dec 2 05:48:28 2014 UTC (9 years, 6 months ago) by jsr166
Branch: MAIN
Changes since 1.53: +1 -1 lines
Log Message: 
this collection => this XXX

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 jsr166 1.45 * http://creativecommons.org/publicdomain/zero/1.0/
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 1.32 * that wait for the queue to become non-empty when retrieving an
15     * element, and wait for space to become available in the queue when
16 jsr166 1.37 * storing an element.
17     *
18 jsr166 1.51 * <p>{@code BlockingQueue} methods come in four forms, with different ways
19 jsr166 1.37 * of handling operations that cannot be satisfied immediately, but may be
20     * satisfied at some point in the future:
21     * one throws an exception, the second returns a special value (either
22 jsr166 1.51 * {@code null} or {@code false}, depending on the operation), the third
23 jsr166 1.37 * blocks the current thread indefinitely until the operation can succeed,
24     * and the fourth blocks for only a given maximum time limit before giving
25     * up. These methods are summarized in the following table:
26 dl 1.31 *
27 dl 1.32 * <table BORDER CELLPADDING=3 CELLSPACING=1>
28 jsr166 1.52 * <caption>Summary of BlockingQueue methods</caption>
29 dl 1.31 * <tr>
30 dl 1.32 * <td></td>
31     * <td ALIGN=CENTER><em>Throws exception</em></td>
32 jsr166 1.37 * <td ALIGN=CENTER><em>Special value</em></td>
33 dl 1.32 * <td ALIGN=CENTER><em>Blocks</em></td>
34     * <td ALIGN=CENTER><em>Times out</em></td>
35 dl 1.31 * </tr>
36     * <tr>
37 dl 1.32 * <td><b>Insert</b></td>
38     * <td>{@link #add add(e)}</td>
39     * <td>{@link #offer offer(e)}</td>
40     * <td>{@link #put put(e)}</td>
41     * <td>{@link #offer(Object, long, TimeUnit) offer(e, time, unit)}</td>
42 dl 1.31 * </tr>
43     * <tr>
44 dl 1.32 * <td><b>Remove</b></td>
45     * <td>{@link #remove remove()}</td>
46     * <td>{@link #poll poll()}</td>
47     * <td>{@link #take take()}</td>
48     * <td>{@link #poll(long, TimeUnit) poll(time, unit)}</td>
49 dl 1.31 * </tr>
50     * <tr>
51 dl 1.32 * <td><b>Examine</b></td>
52     * <td>{@link #element element()}</td>
53     * <td>{@link #peek peek()}</td>
54     * <td><em>not applicable</em></td>
55     * <td><em>not applicable</em></td>
56 dl 1.31 * </tr>
57 dl 1.32 * </table>
58 dl 1.2 *
59 jsr166 1.51 * <p>A {@code BlockingQueue} does not accept {@code null} elements.
60     * Implementations throw {@code NullPointerException} on attempts
61     * to {@code add}, {@code put} or {@code offer} a {@code null}. A
62     * {@code null} is used as a sentinel value to indicate failure of
63     * {@code poll} operations.
64     *
65     * <p>A {@code BlockingQueue} may be capacity bounded. At any given
66     * time it may have a {@code remainingCapacity} beyond which no
67     * additional elements can be {@code put} without blocking.
68     * A {@code BlockingQueue} without any intrinsic capacity constraints always
69     * reports a remaining capacity of {@code Integer.MAX_VALUE}.
70 dl 1.2 *
71 jsr166 1.51 * <p>{@code BlockingQueue} implementations are designed to be used
72 dl 1.29 * primarily for producer-consumer queues, but additionally support
73     * the {@link java.util.Collection} interface. So, for example, it is
74     * possible to remove an arbitrary element from a queue using
75 jsr166 1.51 * {@code remove(x)}. However, such operations are in general
76 dl 1.18 * <em>not</em> performed very efficiently, and are intended for only
77 dl 1.29 * occasional use, such as when a queued message is cancelled.
78     *
79 jsr166 1.51 * <p>{@code BlockingQueue} implementations are thread-safe. All
80 dl 1.29 * queuing methods achieve their effects atomically using internal
81     * locks or other forms of concurrency control. However, the
82 jsr166 1.51 * <em>bulk</em> Collection operations {@code addAll},
83     * {@code containsAll}, {@code retainAll} and {@code removeAll} are
84 dl 1.29 * <em>not</em> necessarily performed atomically unless specified
85     * otherwise in an implementation. So it is possible, for example, for
86 jsr166 1.51 * {@code addAll(c)} to fail (throwing an exception) after adding
87     * only some of the elements in {@code c}.
88 dl 1.2 *
89 jsr166 1.51 * <p>A {@code BlockingQueue} does <em>not</em> intrinsically support
90 dl 1.2 * any kind of &quot;close&quot; or &quot;shutdown&quot; operation to
91     * indicate that no more items will be added. The needs and usage of
92 brian 1.5 * such features tend to be implementation-dependent. For example, a
93 dl 1.2 * common tactic is for producers to insert special
94     * <em>end-of-stream</em> or <em>poison</em> objects, that are
95     * interpreted accordingly when taken by consumers.
96 tim 1.1 *
97     * <p>
98 brian 1.5 * Usage example, based on a typical producer-consumer scenario.
99 jsr166 1.51 * Note that a {@code BlockingQueue} can safely be used with multiple
100 dholmes 1.7 * producers and multiple consumers.
101 jsr166 1.49 * <pre> {@code
102 tim 1.1 * class Producer implements Runnable {
103     * private final BlockingQueue queue;
104     * Producer(BlockingQueue q) { queue = q; }
105     * public void run() {
106     * try {
107 jsr166 1.37 * while (true) { queue.put(produce()); }
108 tim 1.15 * } catch (InterruptedException ex) { ... handle ...}
109 tim 1.1 * }
110     * Object produce() { ... }
111     * }
112     *
113     * class Consumer implements Runnable {
114     * private final BlockingQueue queue;
115 dl 1.21 * Consumer(BlockingQueue q) { queue = q; }
116 tim 1.1 * public void run() {
117     * try {
118 jsr166 1.37 * while (true) { consume(queue.take()); }
119 tim 1.15 * } catch (InterruptedException ex) { ... handle ...}
120 tim 1.1 * }
121     * void consume(Object x) { ... }
122     * }
123     *
124     * class Setup {
125     * void main() {
126     * BlockingQueue q = new SomeQueueImplementation();
127     * Producer p = new Producer(q);
128 brian 1.5 * Consumer c1 = new Consumer(q);
129     * Consumer c2 = new Consumer(q);
130 tim 1.1 * new Thread(p).start();
131 brian 1.5 * new Thread(c1).start();
132     * new Thread(c2).start();
133 tim 1.1 * }
134 jsr166 1.49 * }}</pre>
135 tim 1.1 *
136 jsr166 1.43 * <p>Memory consistency effects: As with other concurrent
137     * collections, actions in a thread prior to placing an object into a
138     * {@code BlockingQueue}
139     * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
140     * actions subsequent to the access or removal of that element from
141     * the {@code BlockingQueue} in another thread.
142     *
143 dl 1.28 * <p>This interface is a member of the
144 jsr166 1.44 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
145 dl 1.28 * Java Collections Framework</a>.
146 jsr166 1.33 *
147 tim 1.1 * @since 1.5
148 dl 1.6 * @author Doug Lea
149 jsr166 1.54 * @param <E> the type of elements held in this queue
150 tim 1.1 */
151     public interface BlockingQueue<E> extends Queue<E> {
152 jsr166 1.37 /**
153     * Inserts the specified element into this queue if it is possible to do
154     * so immediately without violating capacity restrictions, returning
155 jsr166 1.51 * {@code true} upon success and throwing an
156     * {@code IllegalStateException} if no space is currently available.
157 jsr166 1.37 * When using a capacity-restricted queue, it is generally preferable to
158     * use {@link #offer(Object) offer}.
159     *
160     * @param e the element to add
161 jsr166 1.51 * @return {@code true} (as specified by {@link Collection#add})
162 jsr166 1.37 * @throws IllegalStateException if the element cannot be added at this
163     * time due to capacity restrictions
164     * @throws ClassCastException if the class of the specified element
165     * prevents it from being added to this queue
166     * @throws NullPointerException if the specified element is null
167     * @throws IllegalArgumentException if some property of the specified
168     * element prevents it from being added to this queue
169     */
170     boolean add(E e);
171 dholmes 1.7
172     /**
173 jsr166 1.37 * Inserts the specified element into this queue if it is possible to do
174     * so immediately without violating capacity restrictions, returning
175 jsr166 1.51 * {@code true} upon success and {@code false} if no space is currently
176 jsr166 1.37 * available. When using a capacity-restricted queue, this method is
177     * generally preferable to {@link #add}, which can fail to insert an
178     * element only by throwing an exception.
179     *
180     * @param e the element to add
181 jsr166 1.51 * @return {@code true} if the element was added to this queue, else
182     * {@code false}
183 jsr166 1.37 * @throws ClassCastException if the class of the specified element
184     * prevents it from being added to this queue
185     * @throws NullPointerException if the specified element is null
186     * @throws IllegalArgumentException if some property of the specified
187     * element prevents it from being added to this queue
188 dholmes 1.7 */
189 jsr166 1.35 boolean offer(E e);
190 jsr166 1.33
191 tim 1.1 /**
192 dl 1.20 * Inserts the specified element into this queue, waiting if necessary
193 jsr166 1.37 * for space to become available.
194     *
195 jsr166 1.35 * @param e the element to add
196 jsr166 1.37 * @throws InterruptedException if interrupted while waiting
197     * @throws ClassCastException if the class of the specified element
198     * prevents it from being added to this queue
199     * @throws NullPointerException if the specified element is null
200     * @throws IllegalArgumentException if some property of the specified
201     * element prevents it from being added to this queue
202 tim 1.1 */
203 jsr166 1.37 void put(E e) throws InterruptedException;
204 tim 1.1
205     /**
206 jsr166 1.37 * Inserts the specified element into this queue, waiting up to the
207     * specified wait time if necessary for space to become available.
208     *
209     * @param e the element to add
210 dl 1.6 * @param timeout how long to wait before giving up, in units of
211 jsr166 1.51 * {@code unit}
212     * @param unit a {@code TimeUnit} determining how to interpret the
213     * {@code timeout} parameter
214     * @return {@code true} if successful, or {@code false} if
215 jsr166 1.37 * the specified waiting time elapses before space is available
216     * @throws InterruptedException if interrupted while waiting
217     * @throws ClassCastException if the class of the specified element
218     * prevents it from being added to this queue
219     * @throws NullPointerException if the specified element is null
220     * @throws IllegalArgumentException if some property of the specified
221     * element prevents it from being added to this queue
222 tim 1.1 */
223 jsr166 1.37 boolean offer(E e, long timeout, TimeUnit unit)
224 tim 1.1 throws InterruptedException;
225    
226     /**
227 jsr166 1.37 * Retrieves and removes the head of this queue, waiting if necessary
228     * until an element becomes available.
229     *
230 dholmes 1.7 * @return the head of this queue
231 jsr166 1.37 * @throws InterruptedException if interrupted while waiting
232 tim 1.1 */
233 dholmes 1.7 E take() throws InterruptedException;
234    
235 tim 1.1 /**
236 jsr166 1.37 * Retrieves and removes the head of this queue, waiting up to the
237     * specified wait time if necessary for an element to become available.
238     *
239     * @param timeout how long to wait before giving up, in units of
240 jsr166 1.51 * {@code unit}
241     * @param unit a {@code TimeUnit} determining how to interpret the
242     * {@code timeout} parameter
243     * @return the head of this queue, or {@code null} if the
244 jsr166 1.37 * specified waiting time elapses before an element is available
245     * @throws InterruptedException if interrupted while waiting
246 tim 1.1 */
247 jsr166 1.37 E poll(long timeout, TimeUnit unit)
248     throws InterruptedException;
249 dholmes 1.7
250 dl 1.2 /**
251 jsr166 1.34 * Returns the number of additional elements that this queue can ideally
252     * (in the absence of memory or resource constraints) accept without
253 jsr166 1.51 * blocking, or {@code Integer.MAX_VALUE} if there is no intrinsic
254 jsr166 1.34 * limit.
255     *
256     * <p>Note that you <em>cannot</em> always tell if an attempt to insert
257 jsr166 1.51 * an element will succeed by inspecting {@code remainingCapacity}
258 jsr166 1.34 * because it may be the case that another thread is about to
259 jsr166 1.37 * insert or remove an element.
260 jsr166 1.34 *
261 dl 1.2 * @return the remaining capacity
262 dl 1.6 */
263     int remainingCapacity();
264 tim 1.1
265 dl 1.18 /**
266 jsr166 1.37 * Removes a single instance of the specified element from this queue,
267 jsr166 1.51 * if it is present. More formally, removes an element {@code e} such
268     * that {@code o.equals(e)}, if this queue contains one or more such
269 jsr166 1.38 * elements.
270 jsr166 1.51 * Returns {@code true} if this queue contained the specified element
271 jsr166 1.37 * (or equivalently, if this queue changed as a result of the call).
272 dl 1.18 *
273 jsr166 1.37 * @param o element to be removed from this queue, if present
274 jsr166 1.51 * @return {@code true} if this queue changed as a result of the call
275 jsr166 1.37 * @throws ClassCastException if the class of the specified element
276 dl 1.48 * is incompatible with this queue
277 dl 1.47 * (<a href="../Collection.html#optional-restrictions">optional</a>)
278 dl 1.46 * @throws NullPointerException if the specified element is null
279 dl 1.47 * (<a href="../Collection.html#optional-restrictions">optional</a>)
280 dl 1.18 */
281 jsr166 1.37 boolean remove(Object o);
282    
283     /**
284 jsr166 1.51 * Returns {@code true} if this queue contains the specified element.
285     * More formally, returns {@code true} if and only if this queue contains
286     * at least one element {@code e} such that {@code o.equals(e)}.
287 jsr166 1.37 *
288     * @param o object to be checked for containment in this queue
289 jsr166 1.51 * @return {@code true} if this queue contains the specified element
290 jsr166 1.37 * @throws ClassCastException if the class of the specified element
291 dl 1.48 * is incompatible with this queue
292 dl 1.47 * (<a href="../Collection.html#optional-restrictions">optional</a>)
293 dl 1.46 * @throws NullPointerException if the specified element is null
294 dl 1.47 * (<a href="../Collection.html#optional-restrictions">optional</a>)
295 jsr166 1.37 */
296     public boolean contains(Object o);
297 dholmes 1.7
298 dl 1.18 /**
299 dl 1.22 * Removes all available elements from this queue and adds them
300 jsr166 1.37 * to the given collection. This operation may be more
301 dl 1.22 * efficient than repeatedly polling this queue. A failure
302 jsr166 1.37 * encountered while attempting to add elements to
303 jsr166 1.51 * collection {@code c} may result in elements being in neither,
304 dl 1.22 * either or both collections when the associated exception is
305 jsr166 1.37 * thrown. Attempts to drain a queue to itself result in
306 jsr166 1.51 * {@code IllegalArgumentException}. Further, the behavior of
307 dl 1.22 * this operation is undefined if the specified collection is
308     * modified while the operation is in progress.
309 dl 1.18 *
310 dl 1.22 * @param c the collection to transfer elements into
311 jsr166 1.37 * @return the number of elements transferred
312     * @throws UnsupportedOperationException if addition of elements
313     * is not supported by the specified collection
314     * @throws ClassCastException if the class of an element of this queue
315     * prevents it from being added to the specified collection
316     * @throws NullPointerException if the specified collection is null
317     * @throws IllegalArgumentException if the specified collection is this
318     * queue, or some property of an element of this queue prevents
319     * it from being added to the specified collection
320 dl 1.18 */
321 dl 1.22 int drainTo(Collection<? super E> c);
322 jsr166 1.33
323 dl 1.22 /**
324     * Removes at most the given number of available elements from
325 jsr166 1.37 * this queue and adds them to the given collection. A failure
326     * encountered while attempting to add elements to
327 jsr166 1.51 * collection {@code c} may result in elements being in neither,
328 dl 1.22 * either or both collections when the associated exception is
329 jsr166 1.37 * thrown. Attempts to drain a queue to itself result in
330 jsr166 1.51 * {@code IllegalArgumentException}. Further, the behavior of
331 dl 1.22 * this operation is undefined if the specified collection is
332     * modified while the operation is in progress.
333     *
334     * @param c the collection to transfer elements into
335     * @param maxElements the maximum number of elements to transfer
336 jsr166 1.37 * @return the number of elements transferred
337     * @throws UnsupportedOperationException if addition of elements
338     * is not supported by the specified collection
339     * @throws ClassCastException if the class of an element of this queue
340     * prevents it from being added to the specified collection
341     * @throws NullPointerException if the specified collection is null
342     * @throws IllegalArgumentException if the specified collection is this
343     * queue, or some property of an element of this queue prevents
344     * it from being added to the specified collection
345 dl 1.22 */
346     int drainTo(Collection<? super E> c, int maxElements);
347 dl 1.18 }