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, 4 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
#	User	Rev	Content
1	dl	1.1	/*
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	jsr166	1.12	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.1	*/
6
7			package jsr166y;
8	jsr166	1.13
9	dl	1.1	import java.util.concurrent.*;
10
11			/**
12			* A {@link BlockingQueue} in which producers may wait for consumers
13	jsr166	1.4	* to receive elements. A {@code TransferQueue} may be useful for
14	dl	1.1	* example in message passing applications in which producers
15	jsr166	1.6	* 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	jsr166	1.11	* 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	dl	1.1	*
26	jsr166	1.6	* <p>Like other blocking queues, a {@code TransferQueue} may be
27	jsr166	1.10	* 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	dl	1.1	*
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	jsr166	1.9	* 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	dl	1.1	*
50			* @param e the element to transfer
51	jsr166	1.4	* @return {@code true} if the element was transferred, else
52			* {@code false}
53	dl	1.1	* @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	jsr166	1.9	* 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	dl	1.1	*
69			* @param e the element to transfer
70			* @throws InterruptedException if interrupted while waiting,
71	jsr166	1.9	* in which case the element is not left enqueued
72	dl	1.1	* @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	jsr166	1.9	* 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	dl	1.1	*
91			* @param e the element to transfer
92			* @param timeout how long to wait before giving up, in units of
93	jsr166	1.4	* {@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	dl	1.1	* the specified waiting time elapses before completion,
98	jsr166	1.9	* in which case the element is not left enqueued
99	dl	1.1	* @throws InterruptedException if interrupted while waiting,
100	jsr166	1.9	* in which case the element is not left enqueued
101	dl	1.1	* @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	jsr166	1.3	boolean tryTransfer(E e, long timeout, TimeUnit unit)
108	dl	1.1	throws InterruptedException;
109
110			/**
111	jsr166	1.4	* Returns {@code true} if there is at least one consumer waiting
112	jsr166	1.7	* to receive an element via {@link #take} or
113	jsr166	1.8	* timed {@link #poll(long,TimeUnit) poll}.
114	jsr166	1.4	* The return value represents a momentary state of affairs.
115			*
116			* @return {@code true} if there is at least one waiting consumer
117	dl	1.1	*/
118			boolean hasWaitingConsumer();
119
120			/**
121			* Returns an estimate of the number of consumers waiting to
122	jsr166	1.8	* 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	dl	1.2	* method are likely to be noticeably slower than those for
129	jsr166	1.4	* {@link #hasWaitingConsumer}.
130			*
131	jsr166	1.7	* @return the number of consumers waiting to receive elements
132	dl	1.1	*/
133			int getWaitingConsumerCount();
134			}