Interface TransferQueue<E>

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>

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	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 declared in interface BlockingQueue

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

Modifier and Type	Method	Description
boolean	add(E e)	Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning true upon success and throwing an IllegalStateException if no space is currently available.
boolean	contains(Object o)	Returns true if this queue contains the specified element.
int	drainTo(Collection<? super E> c)	Removes all available elements from this queue and adds them to the given collection.
int	drainTo(Collection<? super E> c, int maxElements)	Removes at most the given number of available elements from this queue and adds them to the given collection.
boolean	offer(E e)	Inserts the specified element into this queue if it is possible to do so immediately without violating capacity restrictions, returning true upon success and false if no space is currently available.
boolean	offer(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.
E	poll(long timeout, TimeUnit unit)	Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.
void	put(E e)	Inserts the specified element into this queue, waiting if necessary for space to become available.
int	remainingCapacity()	Returns the number of additional elements that this queue can ideally (in the absence of memory or resource constraints) accept without blocking, or Integer.MAX_VALUE if there is no intrinsic limit.
boolean	remove(Object o)	Removes a single instance of the specified element from this queue, if it is present.
E	take()	Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.

Methods declared in interface Collection

addAll, clear, containsAll, equals, hashCode, isEmpty, iterator, parallelStream, removeAll, removeIf, retainAll, size, spliterator, stream, toArray, toArray, toArray

Modifier and Type	Method	Description
boolean	addAll(Collection<? extends E> c)	Adds all of the elements in the specified collection to this collection (optional operation).
void	clear()	Removes all of the elements from this collection (optional operation).
boolean	containsAll(Collection<?> c)	Returns true if this collection contains all of the elements in the specified collection.
boolean	equals(Object o)	Compares the specified object with this collection for equality.
int	hashCode()	Returns the hash code value for this collection.
boolean	isEmpty()	Returns true if this collection contains no elements.
Iterator<E>	iterator()	Returns an iterator over the elements in this collection.
default Stream<E>	parallelStream()	Returns a possibly parallel Stream with this collection as its source.
boolean	removeAll(Collection<?> c)	Removes all of this collection's elements that are also contained in the specified collection (optional operation).
default boolean	removeIf(Predicate<? super E> filter)	Removes all of the elements of this collection that satisfy the given predicate (optional operation).
boolean	retainAll(Collection<?> c)	Retains only the elements in this collection that are contained in the specified collection (optional operation).
int	size()	Returns the number of elements in this collection.
default Spliterator<E>	spliterator()	Creates a Spliterator over the elements in this collection.
default Stream<E>	stream()	Returns a sequential Stream with this collection as its source.
Object[]	toArray()	Returns an array containing all of the elements in this collection.
default <T> T[]	toArray(IntFunction<T[]> generator)	Returns an array containing all of the elements in this collection, using the provided generator function to allocate the returned array.
<T> T[]	toArray(T[] a)	Returns an array containing all of the elements in this collection; the runtime type of the returned array is that of the specified array.

Methods declared in interface Iterable

forEach

Modifier and Type	Method	Description
default void	forEach(Consumer<? super E> action)	Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception.

Methods declared in interface Queue

element, peek, poll, remove

Modifier and Type	Method	Description
E	element()	Retrieves, but does not remove, the head of this queue.
E	peek()	Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.
E	poll()	Retrieves and removes the head of this queue, or returns null if this queue is empty.
E	remove()	Retrieves and removes the head of this queue.

Method Details

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