- Type Parameters:
E
- the type of elements held in this collection
- All Superinterfaces:
BlockingQueue<E>
,Collection<E>
,Iterable<E>
,Queue<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
) 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 any BlockingQueue
, 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
- Author:
- Doug Lea
-
Method Summary
Modifier and TypeMethodDescriptionint
Returns an estimate of the number of consumers waiting to dequeue elements viatake
orpoll
.boolean
Returnstrue
if there is at least one consumer waiting to dequeue an element viatake
orpoll
.void
Inserts the specified element into this queue, waiting if necessary for space to become available and the element to be dequeued by a consumer invokingtake
orpoll
.boolean
tryTransfer
(E e) Transfers the specified element if there exists a consumer already waiting to receive it, otherwise returningfalse
without enqueuing the element.boolean
tryTransfer
(E e, long timeout, TimeUnit unit) 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 invokingtake
orpoll
.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.Collection
addAll, clear, containsAll, equals, hashCode, isEmpty, iterator, parallelStream, removeAll, removeIf, retainAll, size, spliterator, stream, toArray, toArray, toArray
-
Method Details
-
tryTransfer
Transfers the specified element if there exists a consumer already waiting to receive it, 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
-
transfer
Inserts the specified element into this queue, waiting if necessary for space to become available and the element to be dequeued by a consumer invokingtake
orpoll
.- Parameters:
e
- the element to transfer- Throws:
InterruptedException
- if interrupted while waiting, in which case the element is not enqueued.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
-
tryTransfer
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 invokingtake
orpoll
.- 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 enqueued.- Throws:
InterruptedException
- if interrupted while waiting, in which case the element is not enqueued.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
-
hasWaitingConsumer
boolean hasWaitingConsumer()Returnstrue
if there is at least one consumer waiting to dequeue an element viatake
orpoll
. 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 dequeue elements viatake
orpoll
. 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 dequeue elements
-