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(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(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:	1.8
Committed:	Fri Jul 31 07:30:29 2009 UTC (14 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.7:	+9 -9 lines
Log Message:	*TransferQueue spec improvements
#	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			* 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	jsr166	1.4	* to receive elements. A {@code TransferQueue} may be useful for
13	dl	1.1	* example in message passing applications in which producers
14	jsr166	1.6	* 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	dl	1.1	*
25	jsr166	1.6	* <p>Like other blocking queues, a {@code TransferQueue} may be
26	jsr166	1.4	* capacity bounded. If so, an attempted {@code transfer} operation
27	dl	1.1	* 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	jsr166	1.4	* {@code put} and {@code transfer} are effectively synonymous.
31	dl	1.1	*
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	jsr166	1.7	* Transfers the specified element immediately if there exists a
43			* consumer already waiting to receive it (in {@link #take} or
44	jsr166	1.8	* timed {@link #poll(long,TimeUnit) poll}), otherwise returning
45			* {@code false} without enqueuing the element.
46	dl	1.1	*
47			* @param e the element to transfer
48	jsr166	1.4	* @return {@code true} if the element was transferred, else
49			* {@code false}
50	dl	1.1	* @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	jsr166	1.7	* received by a consumer invoking {@code take} or {@code poll}.
62	dl	1.1	*
63			* @param e the element to transfer
64			* @throws InterruptedException if interrupted while waiting,
65	jsr166	1.5	* in which case the element is not enqueued
66	dl	1.1	* @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	jsr166	1.7	* available and the element to be received by a consumer invoking
78	jsr166	1.4	* {@code take} or {@code poll}.
79	dl	1.1	*
80			* @param e the element to transfer
81			* @param timeout how long to wait before giving up, in units of
82	jsr166	1.4	* {@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	dl	1.1	* the specified waiting time elapses before completion,
87	jsr166	1.5	* in which case the element is not enqueued
88	dl	1.1	* @throws InterruptedException if interrupted while waiting,
89	jsr166	1.5	* in which case the element is not enqueued
90	dl	1.1	* @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	jsr166	1.3	boolean tryTransfer(E e, long timeout, TimeUnit unit)
97	dl	1.1	throws InterruptedException;
98
99			/**
100	jsr166	1.4	* Returns {@code true} if there is at least one consumer waiting
101	jsr166	1.7	* to receive an element via {@link #take} or
102	jsr166	1.8	* timed {@link #poll(long,TimeUnit) poll}.
103	jsr166	1.4	* The return value represents a momentary state of affairs.
104			*
105			* @return {@code true} if there is at least one waiting consumer
106	dl	1.1	*/
107			boolean hasWaitingConsumer();
108
109			/**
110			* Returns an estimate of the number of consumers waiting to
111	jsr166	1.8	* receive elements via {@link #take} or timed
112			* {@link #poll(long,TimeUnit) poll}. The return value is an
113			* approximation of a momentary state of affairs, that may be
114			* inaccurate if consumers have completed or given up waiting.
115			* The value may be useful for monitoring and heuristics, but
116			* not for synchronization control. Implementations of this
117	dl	1.2	* method are likely to be noticeably slower than those for
118	jsr166	1.4	* {@link #hasWaitingConsumer}.
119			*
120	jsr166	1.7	* @return the number of consumers waiting to receive elements
121	dl	1.1	*/
122			int getWaitingConsumerCount();
123			}