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, 1 month ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	fork jdk8 maintenance branch for source and jtreg tests
#	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 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	}