E - the type of elements held in this collectionpublic interface TransferQueue<E> extends BlockingQueue<E>
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.
| 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.
|
boolean tryTransfer(E e)
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.
e - the element to transfertrue if the element was transferred, else
falseClassCastException - 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 queuevoid transfer(E e) throws InterruptedException
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.
e - the element to transferInterruptedException - 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 queueboolean tryTransfer(E e, long timeout, TimeUnit unit) throws InterruptedException
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.
e - the element to transfertimeout - how long to wait before giving up, in units of
unitunit - a TimeUnit determining how to interpret the
timeout parametertrue if successful, or false if
the specified waiting time elapses before completion,
in which case the element is not left enqueuedInterruptedException - 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 queueboolean hasWaitingConsumer()
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.true if there is at least one waiting consumerint getWaitingConsumerCount()
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(). Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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