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java.util.concurrent
Interface TransferQueue<E>

Type Parameters:

E - the type of elements held in this collection

All Superinterfaces:

BlockingQueue<E>, Collection<E>, Iterable<E>, Queue<E>

All Known Implementing Classes:

LinkedTransferQueue

public interface TransferQueue<E>
extends BlockingQueue<E>

A BlockingQueue in which producers may wait for consumers to receive elements. A TransferQueue may be useful for example in message passing applications in which producers sometimes (using method transfer(E)) await receipt of elements by consumers invoking take or poll, while at other times enqueue elements (via method put) without waiting for receipt. Non-blocking and time-out versions of tryTransfer are also available. A TransferQueue may also be queried, via hasWaitingConsumer(), whether there are any threads waiting for items, which is a converse analogy to a peek operation.

Like other blocking queues, a 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 SynchronousQueue, put and transfer are effectively synonymous.

This interface is a member of the Java Collections Framework.

Since:

1.7

Method Summary

Modifier and Type	Method and Description
int	getWaitingConsumerCount() Returns an estimate of the number of consumers waiting to receive elements via BlockingQueue.take() or timed poll.
boolean	hasWaitingConsumer() Returns true if there is at least one consumer waiting to receive an element via BlockingQueue.take() or timed poll.
void	transfer(E e) Transfers the element to a consumer, waiting if necessary to do so.
boolean	tryTransfer(E e) Transfers the element to a waiting consumer immediately, if possible.
boolean	tryTransfer(E e, long timeout, TimeUnit unit) Transfers the element to a consumer if it is possible to do so before the timeout elapses.

Methods inherited from interface java.util.concurrent.BlockingQueue

add, contains, drainTo, drainTo, offer, offer, poll, put, remainingCapacity, remove, take

Methods inherited from interface java.util.Queue

element, peek, poll, remove

Methods inherited from interface java.util.Collection

addAll, clear, containsAll, equals, hashCode, isEmpty, iterator, removeAll, retainAll, size, toArray, toArray

Method Detail

tryTransfer

boolean tryTransfer(E e)

Transfers the element to a waiting consumer immediately, if possible.

More precisely, transfers the specified element immediately if there exists a consumer already waiting to receive it (in BlockingQueue.take() or timed poll), otherwise returning false without enqueuing the element.

Parameters:

e - the element to transfer

Returns:

true if the element was transferred, else false

Throws:

ClassCastException - if the class of the specified element prevents it from being added to this queue

NullPointerException - if the specified element is null

IllegalArgumentException - if some property of the specified element prevents it from being added to this queue

transfer

void transfer(E e)
              throws InterruptedException

Transfers the element to a consumer, waiting if necessary to do so.

More precisely, transfers the specified element immediately if there exists a consumer already waiting to receive it (in BlockingQueue.take() or timed poll), else waits until the element is received by a consumer.

Parameters:

e - the element to transfer

Throws:

InterruptedException - if interrupted while waiting, in which case the element is not left enqueued

ClassCastException - if the class of the specified element prevents it from being added to this queue

NullPointerException - if the specified element is null

IllegalArgumentException - if some property of the specified element prevents it from being added to this queue

tryTransfer

boolean tryTransfer(E e,
                    long timeout,
                    TimeUnit unit)
                    throws InterruptedException

Transfers the element to a consumer if it is possible to do so before the timeout elapses.

More precisely, transfers the specified element immediately if there exists a consumer already waiting to receive it (in BlockingQueue.take() or timed poll), else waits until the element is received by a consumer, returning false if the specified wait time elapses before the element can be transferred.

Parameters:

e - the element to transfer

timeout - how long to wait before giving up, in units of unit

unit - a TimeUnit determining how to interpret the timeout parameter

Returns:

true if successful, or 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

ClassCastException - if the class of the specified element prevents it from being added to this queue

NullPointerException - if the specified element is null

IllegalArgumentException - if some property of the specified element prevents it from being added to this queue

hasWaitingConsumer

boolean hasWaitingConsumer()

Returns true if there is at least one consumer waiting to receive an element via BlockingQueue.take() or timed poll. The return value represents a momentary state of affairs.

Returns:

true if there is at least one waiting consumer

getWaitingConsumerCount

int getWaitingConsumerCount()

Returns an estimate of the number of consumers waiting to receive elements via BlockingQueue.take() or timed 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 hasWaitingConsumer().

Returns:

the number of consumers waiting to receive elements