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 {@code 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. Non-blocking and time-out versions of
 * {@code tryTransfer} are also available.  A TransferQueue may also
 * be queried via {@code hasWaitingConsumer} whether there are any
 * threads waiting for items, which is a converse analogy to a
 * {@code peek} operation.
 *
 * <p>Like any {@code BlockingQueue}, 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 if there exists a consumer
     * already waiting to receive it, 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
     * dequeued 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 dequeued 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 dequeue an element via {@code take} or {@code 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
     * dequeue elements via {@code take} or {@code 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 dequeue elements
     */
    int getWaitingConsumerCount();
}
Revision:	1.5
Committed:	Tue Jul 21 00:15:14 2009 UTC (14 years, 10 months ago) by jsr166
Branch:	MAIN
Changes since 1.4:	+3 -3 lines
Log Message:	j.u.c. coding standards
#	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	1.4	* sometimes (using method {@code transfer}) await receipt of
15			* elements by consumers invoking {@code take} or {@code poll},
16			* while at other times enqueue elements (via method {@code put})
17	dl	1.2	* without waiting for receipt. Non-blocking and time-out versions of
18	jsr166	1.4	* {@code tryTransfer} are also available. A TransferQueue may also
19			* be queried via {@code hasWaitingConsumer} whether there are any
20	dl	1.2	* threads waiting for items, which is a converse analogy to a
21	jsr166	1.4	* {@code peek} operation.
22	dl	1.1	*
23	jsr166	1.4	* <p>Like any {@code BlockingQueue}, a {@code TransferQueue} may be
24			* capacity bounded. If so, an attempted {@code transfer} operation
25	dl	1.1	* may initially block waiting for available space, and/or
26			* subsequently block waiting for reception by a consumer. Note that
27			* in a queue with zero capacity, such as {@link SynchronousQueue},
28	jsr166	1.4	* {@code put} and {@code transfer} are effectively synonymous.
29	dl	1.1	*
30			* <p>This interface is a member of the
31			* <a href="{@docRoot}/../technotes/guides/collections/index.html">
32			* Java Collections Framework</a>.
33			*
34			* @since 1.7
35			* @author Doug Lea
36			* @param <E> the type of elements held in this collection
37			*/
38			public interface TransferQueue<E> extends BlockingQueue<E> {
39			/**
40			* Transfers the specified element if there exists a consumer
41	jsr166	1.4	* already waiting to receive it, otherwise returning {@code false}
42	dl	1.1	* without enqueuing the element.
43			*
44			* @param e the element to transfer
45	jsr166	1.4	* @return {@code true} if the element was transferred, else
46			* {@code false}
47	dl	1.1	* @throws ClassCastException if the class of the specified element
48			* prevents it from being added to this queue
49			* @throws NullPointerException if the specified element is null
50			* @throws IllegalArgumentException if some property of the specified
51			* element prevents it from being added to this queue
52			*/
53			boolean tryTransfer(E e);
54
55			/**
56			* Inserts the specified element into this queue, waiting if
57			* necessary for space to become available and the element to be
58	jsr166	1.4	* dequeued by a consumer invoking {@code take} or {@code poll}.
59	dl	1.1	*
60			* @param e the element to transfer
61			* @throws InterruptedException if interrupted while waiting,
62	jsr166	1.5	* in which case the element is not enqueued
63	dl	1.1	* @throws ClassCastException if the class of the specified element
64			* prevents it from being added to this queue
65			* @throws NullPointerException if the specified element is null
66			* @throws IllegalArgumentException if some property of the specified
67			* element prevents it from being added to this queue
68			*/
69			void transfer(E e) throws InterruptedException;
70
71			/**
72			* Inserts the specified element into this queue, waiting up to
73			* the specified wait time if necessary for space to become
74			* available and the element to be dequeued by a consumer invoking
75	jsr166	1.4	* {@code take} or {@code poll}.
76	dl	1.1	*
77			* @param e the element to transfer
78			* @param timeout how long to wait before giving up, in units of
79	jsr166	1.4	* {@code unit}
80			* @param unit a {@code TimeUnit} determining how to interpret the
81			* {@code timeout} parameter
82			* @return {@code true} if successful, or {@code false} if
83	dl	1.1	* the specified waiting time elapses before completion,
84	jsr166	1.5	* in which case the element is not enqueued
85	dl	1.1	* @throws InterruptedException if interrupted while waiting,
86	jsr166	1.5	* in which case the element is not enqueued
87	dl	1.1	* @throws ClassCastException if the class of the specified element
88			* prevents it from being added to this queue
89			* @throws NullPointerException if the specified element is null
90			* @throws IllegalArgumentException if some property of the specified
91			* element prevents it from being added to this queue
92			*/
93	jsr166	1.3	boolean tryTransfer(E e, long timeout, TimeUnit unit)
94	dl	1.1	throws InterruptedException;
95
96			/**
97	jsr166	1.4	* Returns {@code true} if there is at least one consumer waiting
98			* to dequeue an element via {@code take} or {@code poll}.
99			* The return value represents a momentary state of affairs.
100			*
101			* @return {@code true} if there is at least one waiting consumer
102	dl	1.1	*/
103			boolean hasWaitingConsumer();
104
105			/**
106			* Returns an estimate of the number of consumers waiting to
107	jsr166	1.4	* dequeue elements via {@code take} or {@code poll}. The return
108	dl	1.2	* value is an approximation of a momentary state of affairs, that
109			* may be inaccurate if consumers have completed or given up
110			* waiting. The value may be useful for monitoring and heuristics,
111			* but not for synchronization control. Implementations of this
112			* method are likely to be noticeably slower than those for
113	jsr166	1.4	* {@link #hasWaitingConsumer}.
114			*
115	dl	1.1	* @return the number of consumers waiting to dequeue elements
116			*/
117			int getWaitingConsumerCount();
118			}