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- Type Parameters:
E
- the type of elements held in this queue
- All Superinterfaces:
BlockingQueue<E>
,Collection<E>
,Iterable<E>
,Queue<E>
- All Known Implementing Classes:
LinkedTransferQueue
public interface TransferQueue<E> extends BlockingQueue<E>
ABlockingQueue
in which producers may wait for consumers to receive elements. ATransferQueue
may be useful for example in message passing applications in which producers sometimes (using methodtransfer(E)
) await receipt of elements by consumers invokingtake
orpoll
, while at other times enqueue elements (via methodput
) without waiting for receipt. Non-blocking and time-out versions oftryTransfer
are also available. ATransferQueue
may also be queried, viahasWaitingConsumer()
, whether there are any threads waiting for items, which is a converse analogy to apeek
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 asSynchronousQueue
,put
andtransfer
are effectively synonymous.This interface is a member of the Java Collections Framework.
- Since:
- 1.7
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description int
getWaitingConsumerCount()
Returns an estimate of the number of consumers waiting to receive elements viaBlockingQueue.take()
or timedpoll
.boolean
hasWaitingConsumer()
Returnstrue
if there is at least one consumer waiting to receive an element viaBlockingQueue.take()
or timedpoll
.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 declared in interface java.util.concurrent.BlockingQueue
add, contains, drainTo, drainTo, offer, offer, poll, put, remainingCapacity, remove, take
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Methods declared in interface java.util.Collection
addAll, clear, containsAll, equals, hashCode, isEmpty, iterator, parallelStream, removeAll, removeIf, retainAll, size, spliterator, stream, toArray, toArray, toArray
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Method Detail
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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 timedpoll
), otherwise returningfalse
without enqueuing the element.- Parameters:
e
- the element to transfer- Returns:
true
if the element was transferred, elsefalse
- Throws:
ClassCastException
- if the class of the specified element prevents it from being added to this queueNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this queue
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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 timedpoll
), 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 enqueuedClassCastException
- if the class of the specified element prevents it from being added to this queueNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this queue
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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 timedpoll
), else waits until the element is received by a consumer, returningfalse
if the specified wait time elapses before the element can be transferred.- Parameters:
e
- the element to transfertimeout
- how long to wait before giving up, in units ofunit
unit
- aTimeUnit
determining how to interpret thetimeout
parameter- Returns:
true
if successful, orfalse
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 enqueuedClassCastException
- if the class of the specified element prevents it from being added to this queueNullPointerException
- if the specified element is nullIllegalArgumentException
- if some property of the specified element prevents it from being added to this queue
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hasWaitingConsumer
boolean hasWaitingConsumer()
Returnstrue
if there is at least one consumer waiting to receive an element viaBlockingQueue.take()
or timedpoll
. The return value represents a momentary state of affairs.- Returns:
true
if there is at least one waiting consumer
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getWaitingConsumerCount
int getWaitingConsumerCount()
Returns an estimate of the number of consumers waiting to receive elements viaBlockingQueue.take()
or timedpoll
. 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 forhasWaitingConsumer()
.- Returns:
- the number of consumers waiting to receive elements
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