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/licenses/publicdomain
 */

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 {@code 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 specified element immediately if there exists a
     * consumer already waiting to receive it (in {@link #take} or
     * timed {@link #poll(Object,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);

    /**
     * Inserts the specified element into this queue, waiting if
     * necessary for space to become available and the element to be
     * received by a consumer invoking {@code take} or {@code poll}.
     *
     * @param e the element to transfer
     * @throws InterruptedException if interrupted while waiting,
     *         in which case the element is not 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;

    /**
     * Inserts the specified element into this queue, waiting up to
     * the specified wait time if necessary for space to become
     * available and the element to be received by a consumer invoking
     * {@code take} or {@code poll}.
     *
     * @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 enqueued
     * @throws InterruptedException if interrupted while waiting,
     *         in which case the element is not 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(Object,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(Object,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:	1.7
Committed:	Thu Jul 30 22:45:39 2009 UTC (14 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.6:	+11 -8 lines
Log Message:	TransferQueue spec improvements
#	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/licenses/publicdomain
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. {@linkplain
18	* #tryTransfer(Object) Non-blocking} and {@linkplain
19	* #tryTransfer(Object,long,TimeUnit) time-out} versions of {@code
20	* tryTransfer} are also available. A {@code TransferQueue} may also
21	* be queried, via {@link #hasWaitingConsumer}, whether there are any
22	* threads waiting for items, which is a converse analogy to a {@code
23	* peek} operation.
24	*
25	* <p>Like other blocking queues, a {@code TransferQueue} may be
26	* capacity bounded. If so, an attempted {@code transfer} operation
27	* may initially block waiting for available space, and/or
28	* subsequently block waiting for reception by a consumer. Note that
29	* in a queue with zero capacity, such as {@link SynchronousQueue},
30	* {@code put} 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 specified element immediately if there exists a
43	* consumer already waiting to receive it (in {@link #take} or
44	* timed {@link #poll(Object,long,TimeUnit) poll}), otherwise
45	* returning {@code false} without enqueuing the element.
46	*
47	* @param e the element to transfer
48	* @return {@code true} if the element was transferred, else
49	* {@code false}
50	* @throws ClassCastException if the class of the specified element
51	* prevents it from being added to this queue
52	* @throws NullPointerException if the specified element is null
53	* @throws IllegalArgumentException if some property of the specified
54	* element prevents it from being added to this queue
55	*/
56	boolean tryTransfer(E e);
57
58	/**
59	* Inserts the specified element into this queue, waiting if
60	* necessary for space to become available and the element to be
61	* received by a consumer invoking {@code take} or {@code poll}.
62	*
63	* @param e the element to transfer
64	* @throws InterruptedException if interrupted while waiting,
65	* in which case the element is not enqueued
66	* @throws ClassCastException if the class of the specified element
67	* prevents it from being added to this queue
68	* @throws NullPointerException if the specified element is null
69	* @throws IllegalArgumentException if some property of the specified
70	* element prevents it from being added to this queue
71	*/
72	void transfer(E e) throws InterruptedException;
73
74	/**
75	* Inserts the specified element into this queue, waiting up to
76	* the specified wait time if necessary for space to become
77	* available and the element to be received by a consumer invoking
78	* {@code take} or {@code poll}.
79	*
80	* @param e the element to transfer
81	* @param timeout how long to wait before giving up, in units of
82	* {@code unit}
83	* @param unit a {@code TimeUnit} determining how to interpret the
84	* {@code timeout} parameter
85	* @return {@code true} if successful, or {@code false} if
86	* the specified waiting time elapses before completion,
87	* in which case the element is not enqueued
88	* @throws InterruptedException if interrupted while waiting,
89	* in which case the element is not enqueued
90	* @throws ClassCastException if the class of the specified element
91	* prevents it from being added to this queue
92	* @throws NullPointerException if the specified element is null
93	* @throws IllegalArgumentException if some property of the specified
94	* element prevents it from being added to this queue
95	*/
96	boolean tryTransfer(E e, long timeout, TimeUnit unit)
97	throws InterruptedException;
98
99	/**
100	* Returns {@code true} if there is at least one consumer waiting
101	* to receive an element via {@link #take} or
102	* timed {@link #poll(Object,long,TimeUnit) poll}.
103	* The return value represents a momentary state of affairs.
104	*
105	* @return {@code true} if there is at least one waiting consumer
106	*/
107	boolean hasWaitingConsumer();
108
109	/**
110	* Returns an estimate of the number of consumers waiting to
111	* receive elements via {@link #take} or
112	* timed {@link #poll(Object,long,TimeUnit) poll}. The return
113	* value is an approximation of a momentary state of affairs, that
114	* may be inaccurate if consumers have completed or given up
115	* waiting. The value may be useful for monitoring and heuristics,
116	* but not for synchronization control. Implementations of this
117	* method are likely to be noticeably slower than those for
118	* {@link #hasWaitingConsumer}.
119	*
120	* @return the number of consumers waiting to receive elements
121	*/
122	int getWaitingConsumerCount();
123	}