org.elasticsearch.util.concurrent.jsr166y
Class LinkedTransferQueue<E>

java.lang.Object
  java.util.AbstractCollection<E>
      java.util.AbstractQueue<E>
          org.elasticsearch.util.concurrent.jsr166y.LinkedTransferQueue<E>

Type Parameters:

E - the type of elements held in this collection

All Implemented Interfaces:

java.io.Serializable, java.lang.Iterable<E>, java.util.Collection<E>, java.util.concurrent.BlockingQueue<E>, java.util.Queue<E>, TransferQueue<E>

public class LinkedTransferQueue<E>
extends java.util.AbstractQueue<E>
implements TransferQueue<E>, java.io.Serializable

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.

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

See Also:

Serialized Form

Constructor Summary

LinkedTransferQueue()
Creates an initially empty LinkedTransferQueue.

LinkedTransferQueue(java.util.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.
int	drainTo(java.util.Collection<? super E> c)
int	drainTo(java.util.Collection<? super E> c, int maxElements)
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.
java.util.Iterator<E>	iterator() Returns an iterator over the elements in this queue in proper sequence, from head to tail.
boolean	offer(E e) Inserts the specified element at the tail of this queue.
boolean	offer(E e, long timeout, java.util.concurrent.TimeUnit unit) Inserts the specified element at the tail of this queue.
E	peek()
E	poll()
E	poll(long timeout, java.util.concurrent.TimeUnit unit)
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(java.lang.Object o) Removes a single instance of the specified element from this queue, if it is present.
int	size() Returns the number of elements in this queue.
E	take()
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, java.util.concurrent.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, clear, element, remove

Methods inherited from class java.util.AbstractCollection

contains, containsAll, removeAll, retainAll, toArray, toArray, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.concurrent.BlockingQueue

contains

Methods inherited from interface java.util.Queue

element, remove

Methods inherited from interface java.util.Collection

addAll, clear, containsAll, equals, hashCode, removeAll, retainAll, toArray, toArray

Constructor Detail

LinkedTransferQueue

public LinkedTransferQueue()

Creates an initially empty LinkedTransferQueue.

LinkedTransferQueue

public LinkedTransferQueue(java.util.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:

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

Method Detail

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 java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.NullPointerException - if the specified element is null

offer

public boolean offer(E e,
                     long timeout,
                     java.util.concurrent.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 java.util.concurrent.BlockingQueue<E>

Returns:

true (as specified by BlockingQueue.offer)

Throws:

java.lang.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 java.util.concurrent.BlockingQueue<E>

Specified by:

offer in interface java.util.Queue<E>

Returns:

true (as specified by BlockingQueue.offer)

Throws:

java.lang.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 java.util.Collection<E>

Specified by:

add in interface java.util.concurrent.BlockingQueue<E>

Specified by:

add in interface java.util.Queue<E>

Overrides:

add in class java.util.AbstractQueue<E>

Returns:

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

Throws:

java.lang.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:

java.lang.NullPointerException - if the specified element is null

transfer

public void transfer(E e)
              throws java.lang.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:

java.lang.NullPointerException - if the specified element is null

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

tryTransfer

public boolean tryTransfer(E e,
                           long timeout,
                           java.util.concurrent.TimeUnit unit)
                    throws java.lang.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 inserts the specified element at the tail of this queue and waits until the element is received by a consumer, returning false if the specified wait time elapses before the element can be transferred.

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:

java.lang.NullPointerException - if the specified element is null

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

take

public E take()
       throws java.lang.InterruptedException

Specified by:

take in interface java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.InterruptedException

poll

public E poll(long timeout,
              java.util.concurrent.TimeUnit unit)
       throws java.lang.InterruptedException

Specified by:

poll in interface java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.InterruptedException

poll

public E poll()

Specified by:

poll in interface java.util.Queue<E>

drainTo

public int drainTo(java.util.Collection<? super E> c)

Specified by:

drainTo in interface java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.NullPointerException

java.lang.IllegalArgumentException

drainTo

public int drainTo(java.util.Collection<? super E> c,
                   int maxElements)

Specified by:

drainTo in interface java.util.concurrent.BlockingQueue<E>

Throws:

java.lang.NullPointerException

java.lang.IllegalArgumentException

iterator

public java.util.Iterator<E> iterator()

Returns an iterator over the elements in this queue in proper sequence, from head to tail.

The returned iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException, and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

Specified by:

iterator in interface java.lang.Iterable<E>

Specified by:

iterator in interface java.util.Collection<E>

Specified by:

iterator in class java.util.AbstractCollection<E>

Returns:

an iterator over the elements in this queue in proper sequence

peek

public E peek()

Specified by:

peek in interface java.util.Queue<E>

isEmpty

public boolean isEmpty()

Returns true if this queue contains no elements.

Specified by:

isEmpty in interface java.util.Collection<E>

Overrides:

isEmpty in class java.util.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 java.util.Collection<E>

Specified by:

size in class java.util.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(java.lang.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 java.util.Collection<E>

Specified by:

remove in interface java.util.concurrent.BlockingQueue<E>

Overrides:

remove in class java.util.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

remainingCapacity

public int remainingCapacity()

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

Specified by:

remainingCapacity in interface java.util.concurrent.BlockingQueue<E>

Returns:

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