IT. Expert System.

Java Standard Edition (SE)

LinkedTransferQueue


compact1, compact2, compact3
java.util.concurrent

Class LinkedTransferQueue<E>

  • Type Parameters:
    E - the type of elements held in this collection
    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. Additionally, the bulk operations addAll, removeAll, retainAll, containsAll, equals, and toArray are not guaranteed to be performed atomically. For example, an iterator operating concurrently with an addAll operation might view 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 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

      • 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
      • 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
      • 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 Iterable<E>
        Specified by:
        iterator in interface Collection<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>
        Specified by:
        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>
        Specified by:
        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>
        Specified by:
        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


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