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 package com.sun.grizzly.async;

 import java.util.Map;

 import java.util.concurrent.ConcurrentHashMap;

 import java.util.concurrent.ConcurrentLinkedQueue;

 import java.util.concurrent.atomic.AtomicReference;

 import java.util.concurrent.locks.ReentrantLock;

 /**

  * Class implements {@link Map}-like collection, maps keys to values, where

  * single key could have queue of correspondent values.

  *

  * @author Alexey Stashok

  */

 public class AsyncQueue<K, E> {

     private Map<K, AsyncQueueEntry> queueMap =

             new ConcurrentHashMap<K, AsyncQueueEntry>();

     /**

      * Add data to the {@link AsyncQueue}, corresponding to the given

      * <code>E</code> key

      * 

      * @param key <code>E</code>

      * @param queueRecord data unit

      */

     public void offer(K key, E queueRecord) {

         AsyncQueueEntry entry = obtainAsyncQueueEntry(key);

         entry.queue.offer(queueRecord);

     }

     /**

      * Get head element of <code>E</code> key related queue.

      * Element will not be removed from queue.

      * 

      * @param key <code>K</code>

      *

      * @return <code>E</code> data unit

      */

     public E peek(K key) {

         AsyncQueueEntry entry = queueMap.get(key);

         if (entry != null) {

             return entry.queue.peek();

         }

         return null;

     }

     /**

      * Get head element of <code>K</code> key related queue.

      * Element will be removed from queue.

      * 

      * @param key <code>K</code>

      *

      * @return <code>E</code> data unit

      */

     public E poll(K key) {

         AsyncQueueEntry entry = queueMap.get(key);

         if (entry != null) {

             return entry.queue.poll();

         }

         return null;

     }

     /**

      * Remove head element of <code>K</code> key related queue.

      * 

      * @param key <code>K</code>

      */

     public void removeEntry(K key) {

         queueMap.remove(key);

     }

     /**

      * Get the size of <code>K</code> key related queue.

      * 

      * @param key <code>K</code>

      * @return size of <code>K</code> key related queue.

      */

     public int size(K key) {

         AsyncQueueEntry entry = queueMap.get(key);

         return entry == null ? 0 : entry.queue.size();

     }

     /**

      * Checks if <code>K</code> key related queue is empty.

      * 

      * @param key <code>K</code>

      * @return true, if <code>K</code> key related queue is empty, false otherwise

      */

     public boolean isEmpty(K key) {

         AsyncQueueEntry entry = queueMap.get(key);

         return entry == null || entry.queue.isEmpty();

     }

     public void clear() {

         queueMap.clear();

     }

     protected AsyncQueueEntry obtainAsyncQueueEntry(K key) {

         AsyncQueueEntry entry = queueMap.get(key);

         if (entry == null) {

             synchronized(key) {

                 entry = queueMap.get(key);

                 if (entry == null) {

                     entry = new AsyncQueueEntry();

                     queueMap.put(key, entry);

                 }

             }

         }

         return entry;

     }

     protected AsyncQueueEntry getAsyncQueueEntry(K key) {

         return queueMap.get(key);

     }

     /**

      * {@link AsyncQueue} data unit

      */

     protected class AsyncQueueEntry {

         public ConcurrentLinkedQueue<E> queue;

         public AtomicReference<E> currentElement;

         public ReentrantLock queuedActionLock;

         public AsyncQueueEntry() {

             queue = new ConcurrentLinkedQueue<E>();

             currentElement = new AtomicReference<E>();

             queuedActionLock = new ReentrantLock();

         }

     }    

 }