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package com.sun.xml.ws.transport.tcp.connectioncache.spi.concurrent;

/** A class that provides a very simply unbounded queue.
 * The main requirement here is that the class support constant time (very fast)
 * deletion of arbitrary elements.  An instance of this class must be thread safe,
 * either by locking or by using a wait-free algorithm (preferred).
 * The interface is made as simple is possible to make it easier to produce
 * a wait-free implementation.
 */
public interface ConcurrentQueue<V> {
    /** A Handle provides the capability to delete an element of a ConcurrentQueue
     * very quickly.  Typically, the handle is stored in the element, so that an
     * element located from another data structure can be quickly deleted from 
     * a ConcurrentQueue.
     */
    public interface Handle<V> {
	/** Return the value that corresponds to this handle.
	 */
	V value() ;

	/** Delete the element corresponding to this handle 
	 * from the queue.  Takes constant time.  Returns
	 * true if the removal succeeded, or false if it failed.
	 * which can occur if another thread has already called
	 * poll or remove on this element.
	 */
	boolean remove() ;
    }

    /** Return the number of elements in the queue.
     */
    int size() ;

    /** Add a new element to the tail of the queue.
     * Returns a handle for the element in the queue.
     */
    Handle<V> offer( V arg ) ;

    /** Return an element from the head of the queue.
     * The element is removed from the queue.
     */
    V poll() ;
}