Package org.jgroups.util

Class Queue

  • public class Queue
extends java.lang.Object
    Elements are added at the tail and removed from the head. Class is thread-safe in that 1 producer and 1 consumer may add/remove elements concurrently. The class is not explicitely designed for multiple producers or consumers. Implemented as a linked list, so that removal of an element at the head does not cause a right-shift of the remaining elements (as in a Vector-based implementation).
    Author:
    Bela Ban

    • Field Summary

      Fields 
      Modifier and Type Field Description
      protected static org.apache.commons.logging.Log log  

    • Constructor Summary

      Constructors 
      Constructor Description
      Queue()
      creates an empty queue

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void add​(java.lang.Object obj)
      adds an object to the tail of this queue If the queue has been closed with close(true) no exception will be thrown if the queue has not been flushed yet.
      void addAll​(java.util.Collection c)  
      void addAll​(java.util.List<java.lang.Object> list)  
      void addAtHead​(java.lang.Object obj)
      Adds a new object to the head of the queue basically (obj.equals(queue.remove(queue.add(obj)))) returns true If the queue has been closed with close(true) no exception will be thrown if the queue has not been flushed yet.
      void clear()
      Removes all elements from the queue.
      void close​(boolean flush_entries)
      Marks the queues as closed.
      boolean closed()
      returns true if the Queue has been closed however, this method will return false if the queue has been closed using the close(true) method and the last element has yet not been received.
      java.lang.Object getFirst()
      Returns the first element.
      java.lang.Object getLast()
      Returns the last element.
      java.lang.Object peek()
      returns the first object on the queue, without removing it.
      java.lang.Object peek​(long timeout)
      returns the first object on the queue, without removing it.
      java.lang.Object remove()
      Removes 1 element from head or blocks until next element has been added or until queue has been closed
      java.lang.Object remove​(long timeout)
      Removes 1 element from the head.
      void removeElement​(java.lang.Object obj)
      removes a specific object from the queue.
      void reset()
      resets the queue.
      int size()
      returns the number of objects that are currently in the queue
      java.lang.String toString()
      prints the size of the queue
      java.util.LinkedList values()
      Returns all the elements of the queue
      void waitUntilClosed​(long timeout)
      Waits until the queue has been closed.

      • Methods inherited from class java.lang.Object

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

    • Field Detail

      • log

        protected static final org.apache.commons.logging.Log log

    • Constructor Detail

      • Queue

        public Queue()
        creates an empty queue

    • Method Detail

      • getFirst

        public java.lang.Object getFirst()
        Returns the first element. Returns null if no elements are available.

      • getLast

        public java.lang.Object getLast()
        Returns the last element. Returns null if no elements are available.

      • closed

        public boolean closed()
        returns true if the Queue has been closed however, this method will return false if the queue has been closed using the close(true) method and the last element has yet not been received.
        Returns:
        true if the queue has been closed

      • add

        public void add​(java.lang.Object obj)
         throws QueueClosedException
        adds an object to the tail of this queue If the queue has been closed with close(true) no exception will be thrown if the queue has not been flushed yet.
        Parameters:
        obj - - the object to be added to the queue
        Throws:
        QueueClosedException - exception if closed() returns true

      • addAtHead

        public void addAtHead​(java.lang.Object obj)
               throws QueueClosedException
        Adds a new object to the head of the queue basically (obj.equals(queue.remove(queue.add(obj)))) returns true If the queue has been closed with close(true) no exception will be thrown if the queue has not been flushed yet.
        Parameters:
        obj - - the object to be added to the queue
        Throws:
        QueueClosedException - exception if closed() returns true

      • remove

        public java.lang.Object remove()
                        throws QueueClosedException
        Removes 1 element from head or blocks until next element has been added or until queue has been closed
        Returns:
        the first element to be taken of the queue
        Throws:
        QueueClosedException

      • remove

        public java.lang.Object remove​(long timeout)
                        throws QueueClosedException,
                               TimeoutException
        Removes 1 element from the head. If the queue is empty the operation will wait for timeout ms. if no object is added during the timeout time, a Timout exception is thrown
        Parameters:
        timeout - - the number of milli seconds this operation will wait before it times out
        Returns:
        the first object in the queue
        Throws:
        QueueClosedException
        TimeoutException

      • removeElement

        public void removeElement​(java.lang.Object obj)
                   throws QueueClosedException
        removes a specific object from the queue. the object is matched up using the Object.equals method.
        Parameters:
        obj - the actual object to be removed from the queue
        Throws:
        QueueClosedException

      • peek

        public java.lang.Object peek()
                      throws QueueClosedException
        returns the first object on the queue, without removing it. If the queue is empty this object blocks until the first queue object has been added
        Returns:
        the first object on the queue
        Throws:
        QueueClosedException

      • peek

        public java.lang.Object peek​(long timeout)
                      throws QueueClosedException,
                             TimeoutException
        returns the first object on the queue, without removing it. If the queue is empty this object blocks until the first queue object has been added or the operation times out
        Parameters:
        timeout - how long in milli seconds will this operation wait for an object to be added to the queue before it times out
        Returns:
        the first object on the queue
        Throws:
        QueueClosedException
        TimeoutException

      • clear

        public void clear()
        Removes all elements from the queue. This method can succeed even when the queue is closed

      • close

        public void close​(boolean flush_entries)
        Marks the queues as closed. When an add or remove operation is attempted on a closed queue, an exception is thrown.
        Parameters:
        flush_entries - When true, a end-of-entries marker is added to the end of the queue. Entries may be added and removed, but when the end-of-entries marker is encountered, the queue is marked as closed. This allows to flush pending messages before closing the queue.

      • waitUntilClosed

        public void waitUntilClosed​(long timeout)
        Waits until the queue has been closed. Returns immediately if already closed
        Parameters:
        timeout - Number of milliseconds to wait. A value <= 0 means to wait forever

      • reset

        public void reset()
        resets the queue. This operation removes all the objects in the queue and marks the queue open

      • values

        public java.util.LinkedList values()
        Returns all the elements of the queue
        Returns:
        A copy of the queue

      • size

        public int size()
        returns the number of objects that are currently in the queue

      • toString

        public java.lang.String toString()
        prints the size of the queue
        Overrides:
        toString in class java.lang.Object