OpenJDK 1.23 · java.util.concurrent.TransferQueue · APIdia, the JavaDoc alternative

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 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.

Method Summary

Modifier and Type	Method and Description
public int	Returns: the number of consumers waiting to receive elements getWaitingConsumerCount() Returns an estimate of the number of consumers waiting to receive elements via `take` or timed `poll`.
public boolean	Returns: `true` if there is at least one waiting consumer hasWaitingConsumer() Returns `true` if there is at least one consumer waiting to receive an element via `take` or timed `poll`.
public void	transfer(E the element to transfer e) Transfers the element to a consumer, waiting if necessary to do so.
public boolean	Returns: `true` if the element was transferred, else `false` tryTransfer(E the element to transfer e) Transfers the element to a waiting consumer immediately, if possible.
public boolean	Returns: `true` if successful, or `false` if the specified waiting time elapses before completion, in which case the element is not left enqueued tryTransfer(E the element to transfer e, long how long to wait before giving up, in units of `unit` timeout, TimeUnit a `TimeUnit` determining how to interpret the `timeout` parameter unit) Transfers the element to a consumer if it is possible to do so before the timeout elapses.

Inherited from java.util.concurrent.BlockingQueue:: add contains drainTo drainTo offer offer poll put remainingCapacity remove take

Method Detail

getWaitingConsumerCount back to summary

getWaitingConsumerCount	back to summary
public int getWaitingConsumerCount() Returns an estimate of the number of consumers waiting to receive elements via `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:int the number of consumers waiting to receive elements

public int getWaitingConsumerCount()

Returns an estimate of the number of consumers waiting to receive elements via 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:int: the number of consumers waiting to receive elements

hasWaitingConsumer back to summary

hasWaitingConsumer	back to summary
public boolean hasWaitingConsumer() Returns `true` if there is at least one consumer waiting to receive an element via `take` or timed `poll`. The return value represents a momentary state of affairs. Returns:boolean `true` if there is at least one waiting consumer

public boolean hasWaitingConsumer()

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

Returns:boolean: true if there is at least one waiting consumer

transfer back to summary

transfer	back to summary
public 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 `take` or timed `poll`), else waits until the element is received by a consumer. Parameters e:E the element to transfer Exceptions 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

public void transfer(E e) throws InterruptedException

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

Parameters

e:E: the element to transfer

Exceptions

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 back to summary

tryTransfer	back to summary
public 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 `take` or timed `poll`), otherwise returning `false` without enqueuing the element. Parameters e:E the element to transfer Returns:boolean `true` if the element was transferred, else `false` Exceptions 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

public 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 take or timed poll), otherwise returning false without enqueuing the element.

Parameters

e:E: the element to transfer

Returns:boolean

true if the element was transferred, else false

Exceptions

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 back to summary

tryTransfer	back to summary
public 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 `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:E the element to transfer timeout:long how long to wait before giving up, in units of `unit` unit:TimeUnit a `TimeUnit` determining how to interpret the `timeout` parameter Returns:boolean `true` if successful, or `false` if the specified waiting time elapses before completion, in which case the element is not left enqueued Exceptions 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

public 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 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:E: the element to transfer
timeout:long: how long to wait before giving up, in units of unit
unit:TimeUnit: a TimeUnit determining how to interpret the timeout parameter

Returns:boolean

true if successful, or false if the specified waiting time elapses before completion, in which case the element is not left enqueued

Exceptions

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

public Interface TransferQueue<E>

Method Summary

Method Detail