src/jsr166y/TransferQueue.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package jsr166y;
import java.util.concurrent.*;

/**
 * A {@link BlockingQueue} in which producers may wait for consumers
 * to receive elements.  A {@code TransferQueue} may be useful for
 * example in message passing applications in which producers
 * sometimes (using method {@link #transfer}) await receipt of
 * elements by consumers invoking {@code take} or {@code poll}, while
 * at other times enqueue elements (via method {@code put}) without
 * waiting for receipt.
 * {@linkplain #tryTransfer(Object) Non-blocking} and
 * {@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of
 * {@code tryTransfer} are also available.
 * A {@code TransferQueue} may also be queried, via {@link
 * #hasWaitingConsumer}, whether there are any threads waiting for
 * items, which is a converse analogy to a {@code peek} operation.
 *
 * <p>Like other blocking queues, a {@code TransferQueue} may be
 * capacity bounded.  If so, an attempted transfer operation may
 * initially block waiting for available space, and/or subsequently
 * block waiting for reception by a consumer.  Note that in a queue
 * with zero capacity, such as {@link SynchronousQueue}, {@code put}
 * and {@code transfer} are effectively synonymous.
 *
 * <p>This interface is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @since 1.7
 * @author Doug Lea
 * @param <E> the type of elements held in this collection
 */
public interface TransferQueue<E> extends BlockingQueue<E> {
    /**
     * Transfers the element to a waiting consumer immediately, if possible.
     *
     * <p>More precisely, transfers the specified element immediately
     * if there exists a consumer already waiting to receive it (in
     * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
     * otherwise returning {@code false} without enqueuing the element.
     *
     * @param e the element to transfer
     * @return {@code true} if the element was transferred, else
     *         {@code false}
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    boolean tryTransfer(E e);

    /**
     * Transfers the element to a consumer, waiting if necessary to do so.
     *
     * <p>More precisely, transfers the specified element immediately
     * if there exists a consumer already waiting to receive it (in
     * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
     * else waits until the element is received by a consumer.
     *
     * @param e the element to transfer
     * @throws InterruptedException if interrupted while waiting,
     *         in which case the element is not left enqueued
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    void transfer(E e) throws InterruptedException;

    /**
     * Transfers the element to a consumer if it is possible to do so
     * before the timeout elapses.
     *
     * <p>More precisely, transfers the specified element immediately
     * if there exists a consumer already waiting to receive it (in
     * {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
     * else waits until the element is received by a consumer,
     * returning {@code false} if the specified wait time elapses
     * before the element can be transferred.
     *
     * @param e the element to transfer
     * @param timeout how long to wait before giving up, in units of
     *        {@code unit}
     * @param unit a {@code TimeUnit} determining how to interpret the
     *        {@code timeout} parameter
     * @return {@code true} if successful, or {@code false} if
     *         the specified waiting time elapses before completion,
     *         in which case the element is not left enqueued
     * @throws InterruptedException if interrupted while waiting,
     *         in which case the element is not left enqueued
     * @throws ClassCastException if the class of the specified element
     *         prevents it from being added to this queue
     * @throws NullPointerException if the specified element is null
     * @throws IllegalArgumentException if some property of the specified
     *         element prevents it from being added to this queue
     */
    boolean tryTransfer(E e, long timeout, TimeUnit unit)
        throws InterruptedException;

    /**
     * Returns {@code true} if there is at least one consumer waiting
     * to receive an element via {@link #take} or
     * timed {@link #poll(long,TimeUnit) poll}.
     * The return value represents a momentary state of affairs.
     *
     * @return {@code true} if there is at least one waiting consumer
     */
    boolean hasWaitingConsumer();

    /**
     * Returns an estimate of the number of consumers waiting to
     * receive elements via {@link #take} or timed
     * {@link #poll(long,TimeUnit) poll}.  The return value is an
     * approximation of a momentary state of affairs, that may be
     * inaccurate if consumers have completed or given up waiting.
     * The value may be useful for monitoring and heuristics, but
     * not for synchronization control.  Implementations of this
     * method are likely to be noticeably slower than those for
     * {@link #hasWaitingConsumer}.
     *
     * @return the number of consumers waiting to receive elements
     */
    int getWaitingConsumerCount();
}
Revision:	1.12
Committed:	Tue Mar 15 19:47:02 2011 UTC (13 years, 2 months ago) by jsr166
Branch:	MAIN
CVS Tags:	jdk7-compat, release-1_7_0
Changes since 1.11:	+1 -1 lines
Log Message:	Update Creative Commons license URL in legal notices
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/publicdomain/zero/1.0/
5	*/
6
7	package jsr166y;
8	import java.util.concurrent.*;
9
10	/**
11	* A {@link BlockingQueue} in which producers may wait for consumers
12	* to receive elements. A {@code TransferQueue} may be useful for
13	* example in message passing applications in which producers
14	* sometimes (using method {@link #transfer}) await receipt of
15	* elements by consumers invoking {@code take} or {@code poll}, while
16	* at other times enqueue elements (via method {@code put}) without
17	* waiting for receipt.
18	* {@linkplain #tryTransfer(Object) Non-blocking} and
19	* {@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of
20	* {@code tryTransfer} are also available.
21	* A {@code TransferQueue} may also be queried, via {@link
22	* #hasWaitingConsumer}, whether there are any threads waiting for
23	* items, which is a converse analogy to a {@code peek} operation.
24	*
25	* <p>Like other blocking queues, a {@code TransferQueue} may be
26	* capacity bounded. If so, an attempted transfer operation may
27	* initially block waiting for available space, and/or subsequently
28	* block waiting for reception by a consumer. Note that in a queue
29	* with zero capacity, such as {@link SynchronousQueue}, {@code put}
30	* and {@code transfer} are effectively synonymous.
31	*
32	* <p>This interface is a member of the
33	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
34	* Java Collections Framework</a>.
35	*
36	* @since 1.7
37	* @author Doug Lea
38	* @param <E> the type of elements held in this collection
39	*/
40	public interface TransferQueue<E> extends BlockingQueue<E> {
41	/**
42	* Transfers the element to a waiting consumer immediately, if possible.
43	*
44	* <p>More precisely, transfers the specified element immediately
45	* if there exists a consumer already waiting to receive it (in
46	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
47	* otherwise returning {@code false} without enqueuing the element.
48	*
49	* @param e the element to transfer
50	* @return {@code true} if the element was transferred, else
51	* {@code false}
52	* @throws ClassCastException if the class of the specified element
53	* prevents it from being added to this queue
54	* @throws NullPointerException if the specified element is null
55	* @throws IllegalArgumentException if some property of the specified
56	* element prevents it from being added to this queue
57	*/
58	boolean tryTransfer(E e);
59
60	/**
61	* Transfers the element to a consumer, waiting if necessary to do so.
62	*
63	* <p>More precisely, transfers the specified element immediately
64	* if there exists a consumer already waiting to receive it (in
65	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
66	* else waits until the element is received by a consumer.
67	*
68	* @param e the element to transfer
69	* @throws InterruptedException if interrupted while waiting,
70	* in which case the element is not left enqueued
71	* @throws ClassCastException if the class of the specified element
72	* prevents it from being added to this queue
73	* @throws NullPointerException if the specified element is null
74	* @throws IllegalArgumentException if some property of the specified
75	* element prevents it from being added to this queue
76	*/
77	void transfer(E e) throws InterruptedException;
78
79	/**
80	* Transfers the element to a consumer if it is possible to do so
81	* before the timeout elapses.
82	*
83	* <p>More precisely, transfers the specified element immediately
84	* if there exists a consumer already waiting to receive it (in
85	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
86	* else waits until the element is received by a consumer,
87	* returning {@code false} if the specified wait time elapses
88	* before the element can be transferred.
89	*
90	* @param e the element to transfer
91	* @param timeout how long to wait before giving up, in units of
92	* {@code unit}
93	* @param unit a {@code TimeUnit} determining how to interpret the
94	* {@code timeout} parameter
95	* @return {@code true} if successful, or {@code false} if
96	* the specified waiting time elapses before completion,
97	* in which case the element is not left enqueued
98	* @throws InterruptedException if interrupted while waiting,
99	* in which case the element is not left enqueued
100	* @throws ClassCastException if the class of the specified element
101	* prevents it from being added to this queue
102	* @throws NullPointerException if the specified element is null
103	* @throws IllegalArgumentException if some property of the specified
104	* element prevents it from being added to this queue
105	*/
106	boolean tryTransfer(E e, long timeout, TimeUnit unit)
107	throws InterruptedException;
108
109	/**
110	* Returns {@code true} if there is at least one consumer waiting
111	* to receive an element via {@link #take} or
112	* timed {@link #poll(long,TimeUnit) poll}.
113	* The return value represents a momentary state of affairs.
114	*
115	* @return {@code true} if there is at least one waiting consumer
116	*/
117	boolean hasWaitingConsumer();
118
119	/**
120	* Returns an estimate of the number of consumers waiting to
121	* receive elements via {@link #take} or timed
122	* {@link #poll(long,TimeUnit) poll}. The return value is an
123	* approximation of a momentary state of affairs, that may be
124	* inaccurate if consumers have completed or given up waiting.
125	* The value may be useful for monitoring and heuristics, but
126	* not for synchronization control. Implementations of this
127	* method are likely to be noticeably slower than those for
128	* {@link #hasWaitingConsumer}.
129	*
130	* @return the number of consumers waiting to receive elements
131	*/
132	int getWaitingConsumerCount();
133	}