LinkedTransferQueue (FlexDoc/Javadoc 2.0 Demo)

An unbounded TransferQueue based on linked nodes. This queue orders elements FIFO (first-in-first-out) with respect to any given producer. The head of the queue is that element that has been on the queue the longest time for some producer. The tail of the queue is that element that has been on the queue the shortest time for some producer.

Beware that, unlike in most collections, the size method is NOT a constant-time operation. Because of the asynchronous nature of these queues, determining the current number of elements requires a traversal of the elements, and so may report inaccurate results if this collection is modified during traversal.

Bulk operations that add, remove, or examine multiple elements, such as AbstractQueue.addAll(Collection), removeIf(Predicate) or forEach(Consumer), are not guaranteed to be performed atomically. For example, a forEach traversal concurrent with an addAll operation might observe only some of the added elements.

This class and its iterator implement all of the optional methods of the Collection and Iterator interfaces.

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a LinkedTransferQueue happen-before actions subsequent to the access or removal of that element from the LinkedTransferQueue in another thread.

This class is a member of the Java Collections Framework.

Since:

1.7

Author:

Doug Lea

See Also:

Serialized Form

Constructor Summary
LinkedTransferQueue() Creates an initially empty LinkedTransferQueue.
LinkedTransferQueue(Collection<? extends E> c) Creates a LinkedTransferQueue initially containing the elements of the given collection, added in traversal order of the collection's iterator.

Method Summary
boolean	add(E e) Inserts the specified element at the tail of this queue.
void	clear() Removes all of the elements from this queue.
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.
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.
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.
boolean	isEmpty() Returns true if this queue contains no elements.
Iterator<E>	iterator() Returns an iterator over the elements in this queue in proper sequence.
boolean	offer(E e) Inserts the specified element at the tail of this queue.
boolean	offer(E e, long timeout, TimeUnit unit) Inserts the specified element at the tail 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	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 at the tail of this queue.
int	remainingCapacity() Always returns Integer.MAX_VALUE because a LinkedTransferQueue is not capacity constrained.
boolean	remove(Object o) Removes a single instance of the specified element from this queue, if it is present.
boolean	removeAll(Collection<?> c) Removes all of this collection's elements that are also contained in the specified collection (optional operation).
boolean	removeIf(Predicate<? super E> filter) Removes all of the elements of this collection that satisfy the given predicate.
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 queue.
Spliterator<E>	spliterator() Returns a Spliterator over the elements in this queue.
E	take() Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.
Object[]	toArray() Returns an array containing all of the elements in this queue, in proper sequence.
<T> T[]	toArray(T[] a) Returns an array containing all of the elements in this queue, in proper sequence; the runtime type of the returned array is that of the specified array.
String	toString() Returns a string representation of this collection.
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 inherited from class java.util.AbstractQueue

addAll, element, remove

Methods inherited from class java.util.AbstractCollection

containsAll

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Collection

parallelStream, stream, toArray

Constructor Detail

LinkedTransferQueue

public LinkedTransferQueue

()

Creates an initially empty LinkedTransferQueue.

LinkedTransferQueue

public LinkedTransferQueue

(Collection<? extends E> c)

Creates a LinkedTransferQueue initially containing the elements of the given collection, added in traversal order of the collection's iterator.

Parameters:

c - the collection of elements to initially contain

Throws:

NullPointerException - if the specified collection or any of its elements are null

Method Detail

toString

public String toString

()

Description copied from class: AbstractCollection

Returns a string representation of this collection. The string representation consists of a list of the collection's elements in the order they are returned by its iterator, enclosed in square brackets ("[]"). Adjacent elements are separated by the characters ", " (comma and space). Elements are converted to strings as by String.valueOf(Object).

Overrides:

toString in class AbstractCollection<E>

Returns:

a string representation of this collection

toArray

public Object[] toArray

()

Returns an array containing all of the elements in this queue, in proper sequence.

The returned array will be "safe" in that no references to it are maintained by this queue. (In other words, this method must allocate a new array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

Specified by:

toArray in interface Collection<E>

Overrides:

toArray in class AbstractCollection<E>

Returns:

an array containing all of the elements in this queue

toArray

public <T> T[] toArray

(T[] a)

Returns an array containing all of the elements in this queue, in proper sequence; the runtime type of the returned array is that of the specified array. If the queue fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this queue.

If this queue fits in the specified array with room to spare (i.e., the array has more elements than this queue), the element in the array immediately following the end of the queue is set to null.

Like the toArray() method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs.

Suppose x is a queue known to contain only strings. The following code can be used to dump the queue into a newly allocated array of String:

 String[] y = x.toArray(new String[0]);

Note that toArray(new Object[0]) is identical in function to toArray().

Specified by:

toArray in interface Collection<E>

Overrides:

toArray in class AbstractCollection<E>

Type Parameters:

T - the component type of the array to contain the collection

Parameters:

a - the array into which the elements of the queue are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose

Returns:

an array containing all of the elements in this queue

Throws:

ArrayStoreException - if the runtime type of the specified array is not a supertype of the runtime type of every element in this queue

NullPointerException - if the specified array is null

spliterator

public Spliterator<E> spliterator

()

Returns a Spliterator over the elements in this queue.

The returned spliterator is weakly consistent.

The Spliterator reports Spliterator.CONCURRENT, Spliterator.ORDERED, and Spliterator.NONNULL.

Implementation Note:

The Spliterator implements trySplit to permit limited parallelism.

Specified by:

spliterator in interface Collection<E>

spliterator in interface Iterable<E>

Returns:

a Spliterator over the elements in this queue

Since:

1.8

put

public void put

(E e)

Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never block.

Specified by:

put in interface BlockingQueue<E>

Parameters:

e - the element to add

Throws:

NullPointerException - if the specified element is null

offer

public boolean offer

(E e,
long timeout,
TimeUnit unit)

Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never block or return false.

Specified by:

offer in interface BlockingQueue<E>

Parameters:

e - the element to add

timeout - how long to wait before giving up, in units of unit

unit - a TimeUnit determining how to interpret the timeout parameter

Returns:

true (as specified by BlockingQueue.offer)

Throws:

NullPointerException - if the specified element is null

offer

public boolean offer

(E e)

Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never return false.

Specified by:

offer in interface Queue<E>

offer in interface BlockingQueue<E>

Parameters:

e - the element to add

Returns:

true (as specified by Queue.offer(E))

Throws:

NullPointerException - if the specified element is null

add

public boolean add

(E e)

Inserts the specified element at the tail of this queue. As the queue is unbounded, this method will never throw IllegalStateException or return false.

Specified by:

add in interface Collection<E>

add in interface Queue<E>

add in interface BlockingQueue<E>

Overrides:

add in class AbstractQueue<E>

Parameters:

e - the element to add

Returns:

true (as specified by Collection.add(E))

Throws:

NullPointerException - if the specified element is null

tryTransfer

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.

Specified by:

tryTransfer in interface TransferQueue<E>

Parameters:

e - the element to transfer

Returns:

true if the element was transferred, else false

Throws:

NullPointerException - if the specified element is null

transfer

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 inserts the specified element at the tail of this queue and waits until the element is received by a consumer.

Specified by:

transfer in interface TransferQueue<E>

Parameters:

e - the element to transfer

Throws:

NullPointerException - if the specified element is null

InterruptedException - if interrupted while waiting, in which case the element is not left enqueued

tryTransfer

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.

Specified by:

tryTransfer in interface TransferQueue<E>

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:

NullPointerException - if the specified element is null

InterruptedException - if interrupted while waiting, in which case the element is not left enqueued

take

public E take	()
throws	InterruptedException

Description copied from interface: BlockingQueue

Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.

Specified by:

take in interface BlockingQueue<E>

Returns:

the head of this queue

Throws:

InterruptedException - if interrupted while waiting

poll

public E poll	(long timeout, TimeUnit unit)
throws	InterruptedException

Description copied from interface: BlockingQueue

Retrieves and removes the head of this queue, waiting up to the specified wait time if necessary for an element to become available.

Specified by:

poll in interface BlockingQueue<E>

Parameters:

timeout - how long to wait before giving up, in units of unit

unit - a TimeUnit determining how to interpret the timeout parameter

Returns:

the head of this queue, or null if the specified waiting time elapses before an element is available

Throws:

InterruptedException - if interrupted while waiting

poll

public E poll

()

Description copied from interface: Queue

Retrieves and removes the head of this queue, or returns null if this queue is empty.

Specified by:

poll in interface Queue<E>

Returns:

the head of this queue, or null if this queue is empty

drainTo

public int drainTo

(Collection<? super E> c)

Description copied from interface: BlockingQueue

Removes all available elements from this queue and adds them to the given collection. This operation may be more efficient than repeatedly polling this queue. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

drainTo in interface BlockingQueue<E>

Parameters:

c - the collection to transfer elements into

Returns:

the number of elements transferred

Throws:

NullPointerException - if the specified collection is null

IllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection

drainTo

public int drainTo

(Collection<? super E> c,
int maxElements)

Description copied from interface: BlockingQueue

Removes at most the given number of available elements from this queue and adds them to the given collection. A failure encountered while attempting to add elements to collection c may result in elements being in neither, either or both collections when the associated exception is thrown. Attempts to drain a queue to itself result in IllegalArgumentException. Further, the behavior of this operation is undefined if the specified collection is modified while the operation is in progress.

Specified by:

drainTo in interface BlockingQueue<E>

Parameters:

c - the collection to transfer elements into

maxElements - the maximum number of elements to transfer

Returns:

the number of elements transferred

Throws:

NullPointerException - if the specified collection is null

IllegalArgumentException - if the specified collection is this queue, or some property of an element of this queue prevents it from being added to the specified collection

iterator

public Iterator<E> iterator

()

Returns an iterator over the elements in this queue in proper sequence. The elements will be returned in order from first (head) to last (tail).

The returned iterator is weakly consistent.

Specified by:

iterator in interface Collection<E>

iterator in interface Iterable<E>

Overrides:

iterator in class AbstractCollection<E>

Returns:

an iterator over the elements in this queue in proper sequence

peek

public E peek

()

Description copied from interface: Queue

Retrieves, but does not remove, the head of this queue, or returns null if this queue is empty.

Specified by:

peek in interface Queue<E>

Returns:

the head of this queue, or null if this queue is empty

isEmpty

public boolean isEmpty

()

Returns true if this queue contains no elements.

Specified by:

isEmpty in interface Collection<E>

Overrides:

isEmpty in class AbstractCollection<E>

Returns:

true if this queue contains no elements

hasWaitingConsumer

public boolean hasWaitingConsumer

()

Description copied from interface: TransferQueue

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.

Specified by:

hasWaitingConsumer in interface TransferQueue<E>

Returns:

true if there is at least one waiting consumer

size

public int size

()

Returns the number of elements in this queue. If this queue contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.

Beware that, unlike in most collections, this method is NOT a constant-time operation. Because of the asynchronous nature of these queues, determining the current number of elements requires an O(n) traversal.

Specified by:

size in interface Collection<E>

Overrides:

size in class AbstractCollection<E>

Returns:

the number of elements in this queue

getWaitingConsumerCount

public int getWaitingConsumerCount

()

Description copied from interface: TransferQueue

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 TransferQueue.hasWaitingConsumer().

Specified by:

getWaitingConsumerCount in interface TransferQueue<E>

Returns:

the number of consumers waiting to receive elements

remove

public boolean remove

(Object o)

Removes a single instance of the specified element from this queue, if it is present. More formally, removes an element e such that o.equals(e), if this queue contains one or more such elements. Returns true if this queue contained the specified element (or equivalently, if this queue changed as a result of the call).

Specified by:

remove in interface Collection<E>

remove in interface BlockingQueue<E>

Overrides:

remove in class AbstractCollection<E>

Parameters:

o - element to be removed from this queue, if present

Returns:

true if this queue changed as a result of the call

contains

public boolean contains

(Object o)

Returns true if this queue contains the specified element. More formally, returns true if and only if this queue contains at least one element e such that o.equals(e).

Specified by:

contains in interface Collection<E>

contains in interface BlockingQueue<E>

Overrides:

contains in class AbstractCollection<E>

Parameters:

o - object to be checked for containment in this queue

Returns:

true if this queue contains the specified element

remainingCapacity

public int remainingCapacity

()

Always returns Integer.MAX_VALUE because a LinkedTransferQueue is not capacity constrained.

Specified by:

remainingCapacity in interface BlockingQueue<E>

Returns:

Integer.MAX_VALUE (as specified by BlockingQueue.remainingCapacity())

removeIf

public boolean removeIf

(Predicate<? super E> filter)

Description copied from interface: Collection

Removes all of the elements of this collection that satisfy the given predicate. Errors or runtime exceptions thrown during iteration or by the predicate are relayed to the caller.

Specified by:

removeIf in interface Collection<E>

Parameters:

filter - a predicate which returns true for elements to be removed

Returns:

true if any elements were removed

Throws:

NullPointerException - if the specified filter is null

removeAll

public boolean removeAll

(Collection<?> c)

Description copied from class: AbstractCollection

Removes all of this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.

Specified by:

removeAll in interface Collection<E>

Overrides:

removeAll in class AbstractCollection<E>

Parameters:

c - collection containing elements to be removed from this collection

Returns:

true if this collection changed as a result of the call

Throws:

NullPointerException - if this collection contains one or more null elements and the specified collection does not support null elements (optional), or if the specified collection is null