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 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:	1.10
Committed:	Sun Aug 2 18:05:53 2009 UTC (14 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.9:	+5 -5 lines
Log Message:	un-@code-ify
#	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	1.10	* capacity bounded. If so, an attempted transfer operation may
27			* initially block waiting for available space, and/or subsequently
28			* block waiting for reception by a consumer. Note that in a queue
29			* with zero capacity, such as {@link SynchronousQueue}, {@code put}
30			* 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	1.9	* Transfers the element to a waiting consumer immediately, if possible.
43			*
44			* <p>More precisely, transfers the specified element immediately
45			* if there exists a consumer already waiting to receive it (in
46			* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
47			* otherwise returning {@code false} without enqueuing the element.
48	dl	1.1	*
49			* @param e the element to transfer
50	jsr166	1.4	* @return {@code true} if the element was transferred, else
51			* {@code false}
52	dl	1.1	* @throws ClassCastException if the class of the specified element
53			* prevents it from being added to this queue
54			* @throws NullPointerException if the specified element is null
55			* @throws IllegalArgumentException if some property of the specified
56			* element prevents it from being added to this queue
57			*/
58			boolean tryTransfer(E e);
59
60			/**
61	jsr166	1.9	* Transfers the element to a consumer, waiting if necessary to do so.
62			*
63			* <p>More precisely, transfers the specified element immediately
64			* if there exists a consumer already waiting to receive it (in
65			* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
66			* else waits until the element is received by a consumer.
67	dl	1.1	*
68			* @param e the element to transfer
69			* @throws InterruptedException if interrupted while waiting,
70	jsr166	1.9	* in which case the element is not left enqueued
71	dl	1.1	* @throws ClassCastException if the class of the specified element
72			* prevents it from being added to this queue
73			* @throws NullPointerException if the specified element is null
74			* @throws IllegalArgumentException if some property of the specified
75			* element prevents it from being added to this queue
76			*/
77			void transfer(E e) throws InterruptedException;
78
79			/**
80	jsr166	1.9	* Transfers the element to a consumer if it is possible to do so
81			* before the timeout elapses.
82			*
83			* <p>More precisely, transfers the specified element immediately
84			* if there exists a consumer already waiting to receive it (in
85			* {@link #take} or timed {@link #poll(long,TimeUnit) poll}),
86			* else waits until the element is received by a consumer,
87			* returning {@code false} if the specified wait time elapses
88			* before the element can be transferred.
89	dl	1.1	*
90			* @param e the element to transfer
91			* @param timeout how long to wait before giving up, in units of
92	jsr166	1.4	* {@code unit}
93			* @param unit a {@code TimeUnit} determining how to interpret the
94			* {@code timeout} parameter
95			* @return {@code true} if successful, or {@code false} if
96	dl	1.1	* the specified waiting time elapses before completion,
97	jsr166	1.9	* in which case the element is not left enqueued
98	dl	1.1	* @throws InterruptedException if interrupted while waiting,
99	jsr166	1.9	* in which case the element is not left enqueued
100	dl	1.1	* @throws ClassCastException if the class of the specified element
101			* prevents it from being added to this queue
102			* @throws NullPointerException if the specified element is null
103			* @throws IllegalArgumentException if some property of the specified
104			* element prevents it from being added to this queue
105			*/
106	jsr166	1.3	boolean tryTransfer(E e, long timeout, TimeUnit unit)
107	dl	1.1	throws InterruptedException;
108
109			/**
110	jsr166	1.4	* Returns {@code true} if there is at least one consumer waiting
111	jsr166	1.7	* to receive an element via {@link #take} or
112	jsr166	1.8	* timed {@link #poll(long,TimeUnit) poll}.
113	jsr166	1.4	* The return value represents a momentary state of affairs.
114			*
115			* @return {@code true} if there is at least one waiting consumer
116	dl	1.1	*/
117			boolean hasWaitingConsumer();
118
119			/**
120			* Returns an estimate of the number of consumers waiting to
121	jsr166	1.8	* receive elements via {@link #take} or timed
122			* {@link #poll(long,TimeUnit) poll}. The return value is an
123			* approximation of a momentary state of affairs, that may be
124			* inaccurate if consumers have completed or given up waiting.
125			* The value may be useful for monitoring and heuristics, but
126			* not for synchronization control. Implementations of this
127	dl	1.2	* method are likely to be noticeably slower than those for
128	jsr166	1.4	* {@link #hasWaitingConsumer}.
129			*
130	jsr166	1.7	* @return the number of consumers waiting to receive elements
131	dl	1.1	*/
132			int getWaitingConsumerCount();
133			}