Module java.base
Package java.util.concurrent

Class LinkedTransferQueue<E>

java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractQueue<E>
java.util.concurrent.LinkedTransferQueue<E>
Type Parameters:
E - the type of elements held in this queue
All Implemented Interfaces:
Serializable, Iterable<E>, Collection<E>, BlockingQueue<E>, TransferQueue<E>, Queue<E>
public class LinkedTransferQueue<E> extends AbstractQueue<E> implements TransferQueue<E>, 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, 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(java.util.Collection<? extends E>), removeIf(java.util.function.Predicate<? super E>) or forEach(java.util.function.Consumer<? super E>), 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
See Also:
Serialized Form

  • Constructor Summary

    Constructors
    Constructor
    Description
    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

    Modifier and Type
    Method
    Description
    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.
    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 class java.util.AbstractQueue

    addAll, clear, element, remove

    Methods declared in class java.util.AbstractCollection

    containsAll, toString

    Methods declared in class java.lang.Object

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

    Methods declared in interface java.util.Collection

    addAll, containsAll, equals, hashCode, parallelStream, stream, toArray

    Methods declared in interface java.util.Queue

    element, remove

  • Constructor Details

    • 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 Details

    • 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.

      Specified by:
      spliterator in interface Collection<E>
      Specified by:
      spliterator in interface Iterable<E>
      Implementation Note:
      The Spliterator implements trySplit to permit limited parallelism.
      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 BlockingQueue<E>
      Specified by:
      offer in interface Queue<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 BlockingQueue<E>
      Specified by:
      add in interface Collection<E>
      Specified by:
      add in interface Queue<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.

      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:
      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>
      Specified by:
      iterator in interface Iterable<E>
      Specified by:
      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>
      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 BlockingQueue<E>
      Specified by:
      remove in interface Collection<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 BlockingQueue<E>
      Specified by:
      contains in interface Collection<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
      See Also:
      AbstractCollection.remove(Object), AbstractCollection.contains(Object)

    • retainAll

      public boolean retainAll​(Collection<?> c)
      Description copied from class: AbstractCollection
      Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.
      Specified by:
      retainAll in interface Collection<E>
      Overrides:
      retainAll in class AbstractCollection<E>
      Parameters:
      c - collection containing elements to be retained in 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 permit null elements (optional), or if the specified collection is null
      See Also:
      AbstractCollection.remove(Object), AbstractCollection.contains(Object)

    • clear

      public void clear()
      Description copied from class: AbstractQueue
      Removes all of the elements from this queue. The queue will be empty after this call returns.

      This implementation repeatedly invokes poll until it returns null.

      Specified by:
      clear in interface Collection<E>
      Overrides:
      clear in class AbstractQueue<E>

    • forEach

      public void forEach​(Consumer<? super E> action)
      Description copied from interface: Iterable
      Performs the given action for each element of the Iterable until all elements have been processed or the action throws an exception. Actions are performed in the order of iteration, if that order is specified. Exceptions thrown by the action are relayed to the caller.

      The behavior of this method is unspecified if the action performs side-effects that modify the underlying source of elements, unless an overriding class has specified a concurrent modification policy.

      Specified by:
      forEach in interface Iterable<E>
      Parameters:
      action - The action to be performed for each element
      Throws:
      NullPointerException - if the specified action is null