util/concurrent/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 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 queue
 */
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:	1.1
Committed:	Sat Mar 26 06:22:50 2016 UTC (8 years, 2 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	fork jdk8 maintenance branch for source and jtreg tests
#	User	Rev	Content
1	jsr166	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			* http://creativecommons.org/publicdomain/zero/1.0/
5			*/
6
7			package java.util.concurrent;
8
9			/**
10			* A {@link BlockingQueue} in which producers may wait for consumers
11			* to receive elements. A {@code TransferQueue} may be useful for
12			* example in message passing applications in which producers
13			* sometimes (using method {@link #transfer}) await receipt of
14			* elements by consumers invoking {@code take} or {@code poll}, while
15			* at other times enqueue elements (via method {@code put}) without
16			* waiting for receipt.
17			* {@linkplain #tryTransfer(Object) Non-blocking} and
18			* {@linkplain #tryTransfer(Object,long,TimeUnit) time-out} versions of
19			* {@code tryTransfer} are also available.
20			* A {@code TransferQueue} may also be queried, via {@link
21			* #hasWaitingConsumer}, whether there are any threads waiting for
22			* items, which is a converse analogy to a {@code peek} operation.
23			*
24			* <p>Like other blocking queues, a {@code TransferQueue} may be
25			* capacity bounded. If so, an attempted transfer operation may
26			* initially block waiting for available space, and/or subsequently
27			* block waiting for reception by a consumer. Note that in a queue
28			* with zero capacity, such as {@link SynchronousQueue}, {@code put}
29			* and {@code transfer} are effectively synonymous.
30			*
31			* <p>This interface is a member of the
32			* <a href="{@docRoot}/../technotes/guides/collections/index.html">
33			* Java Collections Framework</a>.
34			*
35			* @since 1.7
36			* @author Doug Lea
37			* @param <E> the type of elements held in this queue
38			*/
39			public interface TransferQueue<E> extends BlockingQueue<E> {
40			/**
41			* Transfers the element to a waiting consumer immediately, if possible.
42			*
43			* <p>More precisely, transfers the specified element immediately
44			* if there exists a consumer already waiting to receive it (in
45			* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
46			* otherwise returning {@code false} without enqueuing the element.
47			*
48			* @param e the element to transfer
49			* @return {@code true} if the element was transferred, else
50			* {@code false}
51			* @throws ClassCastException if the class of the specified element
52			* prevents it from being added to this queue
53			* @throws NullPointerException if the specified element is null
54			* @throws IllegalArgumentException if some property of the specified
55			* element prevents it from being added to this queue
56			*/
57			boolean tryTransfer(E e);
58
59			/**
60			* Transfers the element to a consumer, waiting if necessary to do so.
61			*
62			* <p>More precisely, transfers the specified element immediately
63			* if there exists a consumer already waiting to receive it (in
64			* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
65			* else waits until the element is received by a consumer.
66			*
67			* @param e the element to transfer
68			* @throws InterruptedException if interrupted while waiting,
69			* in which case the element is not left enqueued
70			* @throws ClassCastException if the class of the specified element
71			* prevents it from being added to this queue
72			* @throws NullPointerException if the specified element is null
73			* @throws IllegalArgumentException if some property of the specified
74			* element prevents it from being added to this queue
75			*/
76			void transfer(E e) throws InterruptedException;
77
78			/**
79			* Transfers the element to a consumer if it is possible to do so
80			* before the timeout elapses.
81			*
82			* <p>More precisely, transfers the specified element immediately
83			* if there exists a consumer already waiting to receive it (in
84			* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
85			* else waits until the element is received by a consumer,
86			* returning {@code false} if the specified wait time elapses
87			* before the element can be transferred.
88			*
89			* @param e the element to transfer
90			* @param timeout how long to wait before giving up, in units of
91			* {@code unit}
92			* @param unit a {@code TimeUnit} determining how to interpret the
93			* {@code timeout} parameter
94			* @return {@code true} if successful, or {@code false} if
95			* the specified waiting time elapses before completion,
96			* in which case the element is not left enqueued
97			* @throws InterruptedException if interrupted while waiting,
98			* in which case the element is not left enqueued
99			* @throws ClassCastException if the class of the specified element
100			* prevents it from being added to this queue
101			* @throws NullPointerException if the specified element is null
102			* @throws IllegalArgumentException if some property of the specified
103			* element prevents it from being added to this queue
104			*/
105			boolean tryTransfer(E e, long timeout, TimeUnit unit)
106			throws InterruptedException;
107
108			/**
109			* Returns {@code true} if there is at least one consumer waiting
110			* to receive an element via {@link #take} or
111			* timed {@link #poll(long,TimeUnit) poll}.
112			* The return value represents a momentary state of affairs.
113			*
114			* @return {@code true} if there is at least one waiting consumer
115			*/
116			boolean hasWaitingConsumer();
117
118			/**
119			* Returns an estimate of the number of consumers waiting to
120			* receive elements via {@link #take} or timed
121			* {@link #poll(long,TimeUnit) poll}. The return value is an
122			* approximation of a momentary state of affairs, that may be
123			* inaccurate if consumers have completed or given up waiting.
124			* The value may be useful for monitoring and heuristics, but
125			* not for synchronization control. Implementations of this
126			* method are likely to be noticeably slower than those for
127			* {@link #hasWaitingConsumer}.
128			*
129			* @return the number of consumers waiting to receive elements
130			*/
131			int getWaitingConsumerCount();
132			}