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:	1.13
Committed:	Sun Jan 18 20:17:33 2015 UTC (9 years, 3 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.12:	+1 -0 lines
Log Message:	exactly one blank line before and after package statements
#	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
9	import java.util.concurrent.*;
10
11	/**
12	* A {@link BlockingQueue} in which producers may wait for consumers
13	* to receive elements. A {@code TransferQueue} may be useful for
14	* example in message passing applications in which producers
15	* sometimes (using method {@link #transfer}) await receipt of
16	* elements by consumers invoking {@code take} or {@code poll}, while
17	* at other times enqueue elements (via method {@code put}) without
18	* waiting for receipt.
19	* {@linkplain #tryTransfer(Object) Non-blocking} and
20	* {@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of
21	* {@code tryTransfer} are also available.
22	* A {@code TransferQueue} may also be queried, via {@link
23	* #hasWaitingConsumer}, whether there are any threads waiting for
24	* items, which is a converse analogy to a {@code peek} operation.
25	*
26	* <p>Like other blocking queues, a {@code TransferQueue} may be
27	* capacity bounded. If so, an attempted transfer operation may
28	* initially block waiting for available space, and/or subsequently
29	* block waiting for reception by a consumer. Note that in a queue
30	* with zero capacity, such as {@link SynchronousQueue}, {@code put}
31	* and {@code transfer} are effectively synonymous.
32	*
33	* <p>This interface is a member of the
34	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
35	* Java Collections Framework</a>.
36	*
37	* @since 1.7
38	* @author Doug Lea
39	* @param <E> the type of elements held in this collection
40	*/
41	public interface TransferQueue<E> extends BlockingQueue<E> {
42	/**
43	* Transfers the element to a waiting consumer immediately, if possible.
44	*
45	* <p>More precisely, transfers the specified element immediately
46	* if there exists a consumer already waiting to receive it (in
47	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
48	* otherwise returning {@code false} without enqueuing the element.
49	*
50	* @param e the element to transfer
51	* @return {@code true} if the element was transferred, else
52	* {@code false}
53	* @throws ClassCastException if the class of the specified element
54	* prevents it from being added to this queue
55	* @throws NullPointerException if the specified element is null
56	* @throws IllegalArgumentException if some property of the specified
57	* element prevents it from being added to this queue
58	*/
59	boolean tryTransfer(E e);
60
61	/**
62	* Transfers the element to a consumer, waiting if necessary to do so.
63	*
64	* <p>More precisely, transfers the specified element immediately
65	* if there exists a consumer already waiting to receive it (in
66	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
67	* else waits until the element is received by a consumer.
68	*
69	* @param e the element to transfer
70	* @throws InterruptedException if interrupted while waiting,
71	* in which case the element is not left enqueued
72	* @throws ClassCastException if the class of the specified element
73	* prevents it from being added to this queue
74	* @throws NullPointerException if the specified element is null
75	* @throws IllegalArgumentException if some property of the specified
76	* element prevents it from being added to this queue
77	*/
78	void transfer(E e) throws InterruptedException;
79
80	/**
81	* Transfers the element to a consumer if it is possible to do so
82	* before the timeout elapses.
83	*
84	* <p>More precisely, transfers the specified element immediately
85	* if there exists a consumer already waiting to receive it (in
86	* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
87	* else waits until the element is received by a consumer,
88	* returning {@code false} if the specified wait time elapses
89	* before the element can be transferred.
90	*
91	* @param e the element to transfer
92	* @param timeout how long to wait before giving up, in units of
93	* {@code unit}
94	* @param unit a {@code TimeUnit} determining how to interpret the
95	* {@code timeout} parameter
96	* @return {@code true} if successful, or {@code false} if
97	* the specified waiting time elapses before completion,
98	* in which case the element is not left enqueued
99	* @throws InterruptedException if interrupted while waiting,
100	* in which case the element is not left enqueued
101	* @throws ClassCastException if the class of the specified element
102	* prevents it from being added to this queue
103	* @throws NullPointerException if the specified element is null
104	* @throws IllegalArgumentException if some property of the specified
105	* element prevents it from being added to this queue
106	*/
107	boolean tryTransfer(E e, long timeout, TimeUnit unit)
108	throws InterruptedException;
109
110	/**
111	* Returns {@code true} if there is at least one consumer waiting
112	* to receive an element via {@link #take} or
113	* timed {@link #poll(long,TimeUnit) poll}.
114	* The return value represents a momentary state of affairs.
115	*
116	* @return {@code true} if there is at least one waiting consumer
117	*/
118	boolean hasWaitingConsumer();
119
120	/**
121	* Returns an estimate of the number of consumers waiting to
122	* receive elements via {@link #take} or timed
123	* {@link #poll(long,TimeUnit) poll}. The return value is an
124	* approximation of a momentary state of affairs, that may be
125	* inaccurate if consumers have completed or given up waiting.
126	* The value may be useful for monitoring and heuristics, but
127	* not for synchronization control. Implementations of this
128	* method are likely to be noticeably slower than those for
129	* {@link #hasWaitingConsumer}.
130	*
131	* @return the number of consumers waiting to receive elements
132	*/
133	int getWaitingConsumerCount();
134	}