package org.apache.jcs.engine;
   
   /*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  
  import java.io.IOException;
  import java.io.Serializable;
  import java.util.ArrayList;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.jcs.engine.behavior.ICacheElement;
  import org.apache.jcs.engine.behavior.ICacheEventQueue;
  import org.apache.jcs.engine.behavior.ICacheListener;
  import org.apache.jcs.engine.stats.StatElement;
  import org.apache.jcs.engine.stats.Stats;
  import org.apache.jcs.engine.stats.behavior.IStatElement;
  import org.apache.jcs.engine.stats.behavior.IStats;
  
  /***
   * An event queue is used to propagate ordered cache events to one and only one target listener.
   * <p>
   * This is a modified version of the experimental version. It should lazy initilaize the processor
   * thread, and kill the thread if the queue goes emtpy for a specified period, now set to 1 minute.
   * If something comes in after that a new processor thread should be created.
   */
  public class CacheEventQueue
      implements ICacheEventQueue
  {
      /*** The logger. */
      private static final Log log = LogFactory.getLog( CacheEventQueue.class );
  
      /*** The type of queue -- there are pooled and single */
      private static final String queueType = SINGLE_QUEUE_TYPE;
  
      /*** default */
      private static final int DEFAULT_WAIT_TO_DIE_MILLIS = 10000;
  
      /***
       * time to wait for an event before snuffing the background thread if the queue is empty. make
       * configurable later
       */
      private int waitToDieMillis = DEFAULT_WAIT_TO_DIE_MILLIS;
  
      /***
       * When the events are pulled off the queue, the tell the listener to handle the specific event
       * type. The work is done by the listener.
       */
      private ICacheListener listener;
  
      /*** Id of the listener registed with this queue */
      private long listenerId;
  
      /*** The cache region name, if applicable. */
      private String cacheName;
  
      /*** Maximum number of failures before we buy the farm. */
      private int maxFailure;
  
      /*** in milliseconds */
      private int waitBeforeRetry;
  
      /*** this is true if there is no worker thread. */
      private boolean destroyed = true;
  
      /***
       * This means that the queue is functional. If we reached the max number of failures, the queue
       * is marked as non functional and will never work again.
       */
      private boolean working = true;
  
      /*** the thread that works the queue. */
      private Thread processorThread;
  
      /*** sync */
      private Object queueLock = new Object();
  
      /*** the head of the queue */
      private Node head = new Node();
  
      /*** the end of the queue */
      private Node tail = head;
  
     /*** Number of items in the queue */
     private int size = 0;
 
     /***
      * Constructs with the specified listener and the cache name.
      * <p>
      * @param listener
      * @param listenerId
      * @param cacheName
      */
     public CacheEventQueue( ICacheListener listener, long listenerId, String cacheName )
     {
         this( listener, listenerId, cacheName, 10, 500 );
     }
 
     /***
      * Constructor for the CacheEventQueue object
      * <p>
      * @param listener
      * @param listenerId
      * @param cacheName
      * @param maxFailure
      * @param waitBeforeRetry
      */
     public CacheEventQueue( ICacheListener listener, long listenerId, String cacheName, int maxFailure,
                             int waitBeforeRetry )
     {
         initialize( listener, listenerId, cacheName, maxFailure, waitBeforeRetry, null );
     }
 
     /***
      * Initializes the queue.
      * <p>
      * @param listener
      * @param listenerId
      * @param cacheName
      * @param maxFailure
      * @param waitBeforeRetry
      * @param threadPoolName
      */
     public void initialize( ICacheListener listener, long listenerId, String cacheName, int maxFailure,
                             int waitBeforeRetry, String threadPoolName )
     {
         if ( listener == null )
         {
             throw new IllegalArgumentException( "listener must not be null" );
         }
 
         this.listener = listener;
         this.listenerId = listenerId;
         this.cacheName = cacheName;
         this.maxFailure = maxFailure <= 0 ? 3 : maxFailure;
         this.waitBeforeRetry = waitBeforeRetry <= 0 ? 500 : waitBeforeRetry;
 
         if ( log.isDebugEnabled() )
         {
             log.debug( "Constructed: " + this );
         }
     }
     
     /***
      * What type of queue is this.
      * <p>
      * @return queueType
      */
     public String getQueueType()
     {
         return queueType;
     }
 
     /***
      * Kill the processor thread and indicate that the queue is detroyed and no longer alive, but it
      * can still be working.
      */
     public synchronized void stopProcessing()
     {
         destroyed = true;
         processorThread = null;
     }
 
     /***
      * Returns the time to wait for events before killing the background thread.
      * <p>
      * @return int
      */
     public int getWaitToDieMillis()
     {
         return waitToDieMillis;
     }
 
     /***
      * Sets the time to wait for events before killing the background thread.
      * <p>
      * @param wtdm the ms for the q to sit idle.
      */
     public void setWaitToDieMillis( int wtdm )
     {
         waitToDieMillis = wtdm;
     }
 
     /***
      * Creates a brief string identifying the listener and the region.
      * <p>
      * @return String debugging info.
      */
     public String toString()
     {
         return "CacheEventQueue [listenerId=" + listenerId + ", cacheName=" + cacheName + "]";
     }
 
     /***
      * If they queue has an active thread it is considered alive.
      * <p>
      * @return The alive value
      */
     public synchronized boolean isAlive()
     {
         return ( !destroyed );
     }
 
     /***
      * Sets whether the queue is actively processing -- if there are working threads.
      * <p>
      * @param aState
      */
     public synchronized void setAlive( boolean aState )
     {
         destroyed = !aState;
     }
 
     /***
      * @return The listenerId value
      */
     public long getListenerId()
     {
         return listenerId;
     }
 
     /***
      * Event Q is emtpy.
      * <p>
      * Calling destroy interupts the processor thread.
      */
     public synchronized void destroy()
     {
         if ( !destroyed )
         {
             destroyed = true;
 
             if ( log.isInfoEnabled() )
             {
                 log.info( "Destroying queue, stats =  " + getStatistics() );
             }
 
             // Synchronize on queue so the thread will not wait forever,
             // and then interrupt the QueueProcessor
 
             if ( processorThread != null )
             {
                 synchronized ( queueLock )
                 {
                     processorThread.interrupt();
                 }
             }
             processorThread = null;
 
             if ( log.isInfoEnabled() )
             {
                 log.info( "Cache event queue destroyed: " + this );
             }
         }
         else
         {
             if ( log.isInfoEnabled() )
             {
                 log.info( "Destroy was called after queue was destroyed.  Doing nothing.  Stats =  " + getStatistics() );
             }
         }
     }
 
     /***
      * This adds a put event to the queue. When it is processed, the element will be put to the
      * listener.
      * <p>
      * @param ce The feature to be added to the PutEvent attribute
      * @exception IOException
      */
     public synchronized void addPutEvent( ICacheElement ce )
         throws IOException
     {
         if ( isWorking() )
         {
             put( new PutEvent( ce ) );
         }
         else
         {
             if ( log.isWarnEnabled() )
             {
                 log.warn( "Not enqueuing Put Event for [" + this + "] because it's non-functional." );
             }
         }
     }
 
     /***
      * This adds a remove event to the queue. When processed the listener's remove method will be
      * called for the key.
      * <p>
      * @param key The feature to be added to the RemoveEvent attribute
      * @exception IOException
      */
     public synchronized void addRemoveEvent( Serializable key )
         throws IOException
     {
         if ( isWorking() )
         {
             put( new RemoveEvent( key ) );
         }
         else
         {
             if ( log.isWarnEnabled() )
             {
                 log.warn( "Not enqueuing Remove Event for [" + this + "] because it's non-functional." );
             }
         }
     }
 
     /***
      * This adds a remove all event to the queue. When it is processed, all elements will be removed
      * from the cache.
      * <p>
      * @exception IOException
      */
     public synchronized void addRemoveAllEvent()
         throws IOException
     {
         if ( isWorking() )
         {
             put( new RemoveAllEvent() );
         }
         else
         {
             if ( log.isWarnEnabled() )
             {
                 log.warn( "Not enqueuing RemoveAll Event for [" + this + "] because it's non-functional." );
             }
         }
     }
 
     /***
      * @exception IOException
      */
     public synchronized void addDisposeEvent()
         throws IOException
     {
         if ( isWorking() )
         {
             put( new DisposeEvent() );
         }
         else
         {
             if ( log.isWarnEnabled() )
             {
                 log.warn( "Not enqueuing Dispose Event for [" + this + "] because it's non-functional." );
             }
         }
     }
 
     /***
      * Adds an event to the queue.
      * <p>
      * @param event
      */
     private void put( AbstractCacheEvent event )
     {
         Node newNode = new Node();
         if ( log.isDebugEnabled() )
         {
             log.debug( "Event entering Queue for " + cacheName + ": " + event );
         }
 
         newNode.event = event;
 
         synchronized ( queueLock )
         {
             size++;
             tail.next = newNode;
             tail = newNode;
             if ( isWorking() )
             {
                 if ( !isAlive() )
                 {
                     destroyed = false;
                     processorThread = new QProcessor( this );
                     processorThread.start();
                     if ( log.isInfoEnabled() )
                     {
                         log.info( "Cache event queue created: " + this );
                     }
                 }
                 else
                 {
                     queueLock.notify();
                 }
             }
         }
     }
 
     /***
      * Returns the next cache event from the queue or null if there are no events in the queue.
      * <p>
      * We have an empty node at the head and the tail. When we take an item from the queue we move
      * the next node to the head and then clear the value from that node. This value is returned.
      * <p>
      * When the queue is empty the head node is the same as the tail node.
      * <p>
      * @return An event to process.
      */
     private AbstractCacheEvent take()
     {
         synchronized ( queueLock )
         {
             // wait until there is something to read
             if ( head == tail )
             {
                 return null;
             }
 
             Node node = head.next;
 
             AbstractCacheEvent value = node.event;
 
             if ( log.isDebugEnabled() )
             {
                 log.debug( "head.event = " + head.event );
                 log.debug( "node.event = " + node.event );
             }
 
             // Node becomes the new head (head is always empty)
 
             node.event = null;
             head = node;
 
             size--;
             return value;
         }
     }
 
     /***
      * This method returns semi-structured data on this queue.
      * <p>
      * @see org.apache.jcs.engine.behavior.ICacheEventQueue#getStatistics()
      * @return information on the status and history of the queue
      */
     public IStats getStatistics()
     {
         IStats stats = new Stats();
         stats.setTypeName( "Cache Event Queue" );
 
         ArrayList elems = new ArrayList();
 
         IStatElement se = null;
 
         se = new StatElement();
         se.setName( "Working" );
         se.setData( "" + this.working );
         elems.add( se );
 
         se = new StatElement();
         se.setName( "Alive" );
         se.setData( "" + this.isAlive() );
         elems.add( se );
 
         se = new StatElement();
         se.setName( "Empty" );
         se.setData( "" + this.isEmpty() );
         elems.add( se );
 
         int size = 0;
         synchronized ( queueLock )
         {
             // wait until there is something to read
             if ( head == tail )
             {
                 size = 0;
             }
             else
             {
                 Node n = head;
                 while ( n != null )
                 {
                     n = n.next;
                     size++;
                 }
             }
 
             se = new StatElement();
             se.setName( "Size" );
             se.setData( "" + size );
             elems.add( se );
         }
 
         // get an array and put them in the Stats object
         IStatElement[] ses = (IStatElement[]) elems.toArray( new StatElement[0] );
         stats.setStatElements( ses );
 
         return stats;
     }
 
     // /////////////////////////// Inner classes /////////////////////////////
 
     /*** The queue is composed of nodes. */
     private static class Node
     {
         /*** Next node in the singly linked list. */
         Node next = null;
 
         /*** The payload. */
         CacheEventQueue.AbstractCacheEvent event = null;
     }
 
     /***
      * This is the thread that works the queue.
      * <p>
      * @author asmuts
      * @created January 15, 2002
      */
     private class QProcessor
         extends Thread
     {
         /*** The queue to work */
         CacheEventQueue queue;
 
         /***
          * Constructor for the QProcessor object
          * <p>
          * @param aQueue the event queue to take items from.
          */
         QProcessor( CacheEventQueue aQueue )
         {
             super( "CacheEventQueue.QProcessor-" + aQueue.cacheName );
 
             setDaemon( true );
             queue = aQueue;
         }
 
         /***
          * Main processing method for the QProcessor object.
          * <p>
          * Waits for a specified time (waitToDieMillis) for something to come in and if no new
          * events come in during that period the run method can exit and the thread is dereferenced.
          */
         public void run()
         {
             AbstractCacheEvent event = null;
 
             while ( queue.isAlive() )
             {
                 event = queue.take();
 
                 if ( log.isDebugEnabled() )
                 {
                     log.debug( "Event from queue = " + event );
                 }
 
                 if ( event == null )
                 {
                     synchronized ( queueLock )
                     {
                         try
                         {
                             queueLock.wait( queue.getWaitToDieMillis() );
                         }
                         catch ( InterruptedException e )
                         {
                             log.warn( "Interrupted while waiting for another event to come in before we die." );
                             return;
                         }
                         event = queue.take();
                         if ( log.isDebugEnabled() )
                         {
                             log.debug( "Event from queue after sleep = " + event );
                         }
                     }
                     if ( event == null )
                     {
                         queue.stopProcessing();
                     }
                 }
 
                 if ( queue.isWorking() && queue.isAlive() && event != null )
                 {
                     event.run();
                 }
             }
             if ( log.isDebugEnabled() )
             {
                 log.debug( "QProcessor exiting for " + queue );
             }
         }
     }
 
     /***
      * Retries before declaring failure.
      * <p>
      * @author asmuts
      * @created January 15, 2002
      */
     private abstract class AbstractCacheEvent
         implements Runnable
     {
         /*** Number of failures encountered processing this event. */
         int failures = 0;
 
         /*** Have we finished the job */
         boolean done = false;
 
         /***
          * Main processing method for the AbstractCacheEvent object
          */
         public void run()
         {
             try
             {
                 doRun();
             }
             catch ( IOException e )
             {
                 if ( log.isWarnEnabled() )
                 {
                     log.warn( e );
                 }
                 if ( ++failures >= maxFailure )
                 {
                     if ( log.isWarnEnabled() )
                     {
                         log.warn( "Error while running event from Queue: " + this
                             + ". Dropping Event and marking Event Queue as non-functional." );
                     }
                     setWorking( false );
                     setAlive( false );
                     return;
                 }
                 if ( log.isInfoEnabled() )
                 {
                     log.info( "Error while running event from Queue: " + this + ". Retrying..." );
                 }
                 try
                 {
                     Thread.sleep( waitBeforeRetry );
                     run();
                 }
                 catch ( InterruptedException ie )
                 {
                     if ( log.isErrorEnabled() )
                     {
                         log.warn( "Interrupted while sleeping for retry on event " + this + "." );
                     }
                     // TODO consider if this is best. maybe we shoudl just
                     // destroy
                     setWorking( false );
                     setAlive( false );
                 }
             }
         }
 
         /***
          * @exception IOException
          */
         protected abstract void doRun()
             throws IOException;
     }
 
     /***
      * An element should be put in the cache.
      * <p>
      * @author asmuts
      * @created January 15, 2002
      */
     private class PutEvent
         extends AbstractCacheEvent
     {
         /*** The element to put to the listener */
         private ICacheElement ice;
 
         /***
          * Constructor for the PutEvent object.
          * <p>
          * @param ice
          * @exception IOException
          */
         PutEvent( ICacheElement ice )
             throws IOException
         {
             this.ice = ice;
         }
 
         /***
          * Call put on the listener.
          * <p>
          * @exception IOException
          */
         protected void doRun()
             throws IOException
         {
             listener.handlePut( ice );
         }
 
         /***
          * For debugging.
          * <p>
          * @return Info on the key and value.
          */
         public String toString()
         {
             return new StringBuffer( "PutEvent for key: " ).append( ice.getKey() ).append( " value: " )
                 .append( ice.getVal() ).toString();
         }
 
     }
 
     /***
      * An element should be removed from the cache.
      * <p>
      * @author asmuts
      * @created January 15, 2002
      */
     private class RemoveEvent
         extends AbstractCacheEvent
     {
         /*** The key to remove from the listener */
         private Serializable key;
 
         /***
          * Constructor for the RemoveEvent object
          * <p>
          * @param key
          * @exception IOException
          */
         RemoveEvent( Serializable key )
             throws IOException
         {
             this.key = key;
         }
 
         /***
          * Call remove on the listener.
          * <p>
          * @exception IOException
          */
         protected void doRun()
             throws IOException
         {
             listener.handleRemove( cacheName, key );
         }
 
         /***
          * For debugging.
          * <p>
          * @return Info on the key to remove.
          */
         public String toString()
         {
             return new StringBuffer( "RemoveEvent for " ).append( key ).toString();
         }
 
     }
 
     /***
      * All elements should be removed from the cache when this event is processed.
      * <p>
      * @author asmuts
      * @created January 15, 2002
      */
     private class RemoveAllEvent
         extends AbstractCacheEvent
     {
         /***
          * Call removeAll on the listener.
          * <p>
          * @exception IOException
          */
         protected void doRun()
             throws IOException
         {
             listener.handleRemoveAll( cacheName );
         }
 
         /***
          * For debugging.
          * <p>
          * @return The name of the event.
          */
         public String toString()
         {
             return "RemoveAllEvent";
         }
 
     }
 
     /***
      * The cache should be disposed when this event is processed.
      * <p>
      * @author asmuts
      * @created January 15, 2002
      */
     private class DisposeEvent
         extends AbstractCacheEvent
     {
         /***
          * Called when gets to the end of the queue
          * <p>
          * @exception IOException
          */
         protected void doRun()
             throws IOException
         {
             listener.handleDispose( cacheName );
         }
 
         /***
          * For debugging.
          * <p>
          * @return The name of the event.
          */
         public String toString()
         {
             return "DisposeEvent";
         }
     }
 
     /***
      * @return whether the queue is functional.
      */
     public boolean isWorking()
     {
         return working;
     }
 
     /***
      * This means that the queue is functional. If we reached the max number of failures, the queue
      * is marked as non functional and will never work again.
      * <p>
      * @param b
      */
     public void setWorking( boolean b )
     {
         working = b;
     }
 
     /***
      * @return whether there are any items in the queue.
      */
     public boolean isEmpty()
     {
         return tail == head;
     }
 
     /***
      * Returns the number of elements in the queue.
      * <p>
      * @return number of items in the queue.
      */
     public int size()
     {
         return size;
     }
 }