/*
 * JBoss, Home of Professional Open Source.
 * Copyright 2008, Red Hat Middleware LLC, and individual contributors
 * as indicated by the @author tags. See the copyright.txt file in the
 * distribution for a full listing of individual contributors.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.jboss.ejb.plugins;

import java.security.AccessController;
import java.util.ArrayList;
import java.util.Timer;
import java.util.TimerTask;

import org.jboss.deployment.DeploymentException;
import org.jboss.ejb.EnterpriseContext;
import org.jboss.logging.Logger;
import org.jboss.metadata.MetaData;
import org.jboss.metadata.XmlLoadable;
import org.jboss.monitor.Monitorable;
import org.jboss.monitor.client.BeanCacheSnapshot;
import org.jboss.util.LRUCachePolicy;
import org.jboss.util.loading.ContextClassLoaderSwitcher;
import org.w3c.dom.Element;

/**
 * Least Recently Used cache policy for EnterpriseContexts.
 *
 * @see AbstractInstanceCache
 * @author <a href="mailto:simone.bordet@compaq.com">Simone Bordet</a>
 * @author <a href="mailto:bill@jboss.org">Bill Burke</a>
 * @version $Revision: 81030 $
 */
public class LRUEnterpriseContextCachePolicy extends LRUCachePolicy
   implements XmlLoadable, Monitorable
{
   // Constants -----------------------------------------------------

   // Attributes ----------------------------------------------------
   protected static Logger log = Logger.getLogger(LRUEnterpriseContextCachePolicy.class);
   protected static Timer tasksTimer;
   static
   {
      // Don't leak the TCCL to the tasksTimer thread
      ContextClassLoaderSwitcher clSwitcher = (ContextClassLoaderSwitcher) AccessController.doPrivileged(ContextClassLoaderSwitcher.INSTANTIATOR);
      ContextClassLoaderSwitcher.SwitchContext clSwitchContext = null;
      try
      {
         // Switches the TCCL to this class' classloader
         clSwitchContext = clSwitcher.getSwitchContext(LRUEnterpriseContextCachePolicy.class.getClassLoader());
         tasksTimer = new Timer(true);
      }
      finally
      {
         // Restores the TCCL
         if (clSwitchContext != null)
            clSwitchContext.reset();
      }
      
      log.debug("Cache policy timer started, tasksTimer="+tasksTimer);
   }

   /** The AbstractInstanceCache that uses this cache policy */
   private AbstractInstanceCache m_cache;

   /** The period of the resizer's runs */
   private long m_resizerPeriod;

   /** The period of the overager's runs */
   private long m_overagerPeriod;

   /** The age after which a bean is automatically passivated */
   private long m_maxBeanAge;

   /**
    * Enlarge cache capacity if there is a cache miss every or less
    * this member's value
    */
   private long m_minPeriod;

   /**
    * Shrink cache capacity if there is a cache miss every or more
    * this member's value
    */
   private long m_maxPeriod;

   /**
    * The resizer will always try to keep the cache capacity so
    * that the cache is this member's value loaded of cached objects
    */
   private double m_factor;

   /** The overager timer task */
   private TimerTask m_overager;

   /** The resizer timer task */
   private TimerTask m_resizer;

   /** Useful for log messages */
   private StringBuffer m_buffer = new StringBuffer();


   // Static --------------------------------------------------------

   // Constructors --------------------------------------------------

   /**
    * Creates a LRU cache policy object given the instance cache that use
    * this policy object.
    */
   public LRUEnterpriseContextCachePolicy(AbstractInstanceCache eic)
   {
      if (eic == null)
         throw new IllegalArgumentException
            ("Instance cache argument cannot be null");

      m_cache = eic;
   }

   // Public --------------------------------------------------------

   // Monitorable implementation ------------------------------------

   public void sample(Object s)
   {
      if( m_cache == null )
         return;

      BeanCacheSnapshot snapshot = (BeanCacheSnapshot)s;
      LRUList list = getList();
      synchronized (m_cache.getCacheLock())
      {
         snapshot.m_cacheMinCapacity = list.m_minCapacity;
         snapshot.m_cacheMaxCapacity = list.m_maxCapacity;
         snapshot.m_cacheCapacity = list.m_capacity;
         snapshot.m_cacheSize = list.m_count;
      }
   }

   // Z implementation ----------------------------------------------

   public void start()
   {
      if (m_resizerPeriod > 0)
      {
         m_resizer = new ResizerTask(m_resizerPeriod);
         long delay = (long) (Math.random() * m_resizerPeriod);
         tasksTimer.schedule(m_resizer, delay, m_resizerPeriod);
      }

      if (m_overagerPeriod > 0)
      {
         m_overager = new OveragerTask(m_overagerPeriod);
         long delay = (long) (Math.random() * m_overagerPeriod);
         tasksTimer.schedule(m_overager, delay, m_overagerPeriod);
      }
   }

   public void stop()
   {
      if (m_resizer != null) {m_resizer.cancel();}
      if (m_overager != null) {m_overager.cancel();}
      super.stop();
   }

   public void destroy()
   {
      m_overager = null;
      m_resizer = null;
      super.destroy();
   }

   /**
    * Reads from the configuration the parameters for this cache policy, that are
    * all optionals.
    * FIXME 20010626 marcf:
    *  Simone seriously arent' all the options overkill? give it another 6 month .
    *	 Remember you are exposing the guts of this to the end user, also provide defaults
    *  so that if an entry is not specified you can still work and it looks _much_ better in
    *  the configuration files.
    *
    */
   public void importXml(Element element) throws DeploymentException
   {
      String min = MetaData.getElementContent(MetaData.getOptionalChild(element, "min-capacity"));
      String max = MetaData.getElementContent(MetaData.getOptionalChild(element, "max-capacity"));
      String op = MetaData.getElementContent(MetaData.getOptionalChild(element, "overager-period"));
      String rp = MetaData.getElementContent(MetaData.getOptionalChild(element, "resizer-period"));
      String ma = MetaData.getElementContent(MetaData.getOptionalChild(element, "max-bean-age"));
      String map = MetaData.getElementContent(MetaData.getOptionalChild(element, "max-cache-miss-period"));
      String mip = MetaData.getElementContent(MetaData.getOptionalChild(element, "min-cache-miss-period"));
      String fa = MetaData.getElementContent(MetaData.getOptionalChild(element, "cache-load-factor"));
      try
      {
         if (min != null)
         {
            int s = Integer.parseInt(min);
            if (s <= 0)
            {
               throw new DeploymentException("Min cache capacity can't be <= 0");
            }
            m_minCapacity = s;
         }
         if (max != null)
         {
            int s = Integer.parseInt(max);
            if (s <= 0)
            {
               throw new DeploymentException("Max cache capacity can't be <= 0");
            }
            m_maxCapacity = s;
         }
         if (op != null)
         {
            int p = Integer.parseInt(op);
            if (p <= 0) {throw new DeploymentException("Overager period can't be <= 0");}
            m_overagerPeriod = p * 1000;
         }
         if (rp != null)
         {
            int p = Integer.parseInt(rp);
            if (p <= 0) {throw new DeploymentException("Resizer period can't be <= 0");}
            m_resizerPeriod = p * 1000;
         }
         if (ma != null)
         {
            int a = Integer.parseInt(ma);
            if (a <= 0) {throw new DeploymentException("Max bean age can't be <= 0");}
            m_maxBeanAge = a * 1000;
         }
         if (map != null)
         {
            int p = Integer.parseInt(map);
            if (p <= 0) {throw new DeploymentException("Max cache miss period can't be <= 0");}
            m_maxPeriod = p * 1000;
         }
         if (mip != null)
         {
            int p = Integer.parseInt(mip);
            if (p <= 0) {throw new DeploymentException("Min cache miss period can't be <= 0");}
            m_minPeriod = p * 1000;
         }
         if (fa != null)
         {
            double f = Double.parseDouble(fa);
            if (f <= 0.0) {throw new DeploymentException("Cache load factor can't be <= 0");}
            m_factor = f;
         }
      }
      catch (NumberFormatException x)
      {
         throw new DeploymentException("Can't parse policy configuration", x);
      }
   }

   // Y overrides ---------------------------------------------------

   /**
    * Flush is overriden here because in this policy impl
    * flush might not actually remove all the instances from the cache.
    * Those instances that are in use (associated with a transaction) should not
    * be removed from the cache. So, the iteration is done not until the cache is empty
    * but until we tried to age-out every instance in the cache.
    */
   public void flush()
   {
      int i = size();
      LRUCacheEntry entry = null;
      while (i-- > 0 && (entry = m_list.m_tail) != null)
      {
         ageOut(entry);
      }
   }
   
   // Package protected ---------------------------------------------

   // Protected -----------------------------------------------------

   protected LRUList createList()
   {
      return new ContextLRUList();
   }


   protected void ageOut(LRUCacheEntry entry)
   {
      if( m_cache == null )
         return;

      if (entry == null)
      {
         throw new IllegalArgumentException
            ("Cannot remove a null cache entry");
      }

      if( log.isTraceEnabled() )
      {
         m_buffer.setLength(0);
         m_buffer.append("Aging out from cache bean ");
         m_buffer.append(m_cache.getContainer().getBeanMetaData().getEjbName());
         m_buffer.append("with id = ");
         m_buffer.append(entry.m_key);
         m_buffer.append("; cache size = ");
         m_buffer.append(getList().m_count);
         log.trace(m_buffer.toString());
      }

      // This will schedule the passivation
      m_cache.release((EnterpriseContext)entry.m_object);
   }
   protected void cacheMiss()
   {
      LRUList list = getList();
      ++list.m_cacheMiss;
   }

   // Private -------------------------------------------------------

   private LRUList getList()
   {
      return m_list;
   }

   // Inner classes -------------------------------------------------

   /**
    * This TimerTask resizes the cache capacity using the cache miss frequency
    * algorithm, that is the more cache misses we have, the more the cache size
    * is enlarged, and viceversa. <p>
    * Of course, the maximum and minimum capacity are the bounds that this
    * resizer never passes.
    */
   protected class ResizerTask extends TimerTask
   {
      private String m_message;
      private StringBuffer m_buffer;
      private long resizerPeriod;

      protected ResizerTask(long resizerPeriod)
      {
         this.resizerPeriod = resizerPeriod;
         m_message = "Resized cache for bean " +
            m_cache.getContainer().getBeanMetaData().getEjbName() +
            ": old capacity = ";
         m_buffer = new StringBuffer();
      }

      public void run()
      {
         // For now implemented as a Cache Miss Frequency algorithm
         if( m_cache == null )
         {
            cancel();
            return;
         }

         LRUList list = getList();

         // Sync with the cache, since it is accessed also by another thread
         synchronized (m_cache.getCacheLock())
         {
            int period = list.m_cacheMiss == 0 ? Integer.MAX_VALUE : (int)(resizerPeriod / list.m_cacheMiss);
            int cap = list.m_capacity;
            if (period <= m_minPeriod && cap < list.m_maxCapacity)
            {
               // Enlarge cache capacity: if period == m_minPeriod then
               // the capacity is increased of the (1-m_factor)*100 %.
               double factor = 1.0 + ((double)m_minPeriod / period) * (1.0 - m_factor);
               int newCap = (int)(cap * factor);
               list.m_capacity = newCap < list.m_maxCapacity ? newCap : list.m_maxCapacity;
               log(cap, list.m_capacity);
            }
            else if (period >= m_maxPeriod &&
                     cap > list.m_minCapacity &&
                     list.m_count < (cap * m_factor))
            {
               // Shrink cache capacity
               int newCap = (int)(list.m_count / m_factor);
               list.m_capacity = newCap > list.m_minCapacity ? newCap : list.m_minCapacity;
               log(cap, list.m_capacity);
            }
            list.m_cacheMiss = 0;
         }
      }

      private void log(int oldCapacity, int newCapacity)
      {
         if( log.isTraceEnabled() )
         {
            m_buffer.setLength(0);
            m_buffer.append(m_message);
            m_buffer.append(oldCapacity);
            m_buffer.append(", new capacity = ");
            m_buffer.append(newCapacity);
            log.trace(m_buffer.toString());
         }
      }
   }

   /**
    * This TimerTask passivates cached beans that have not been called for a while.
    */
   protected class OveragerTask extends TimerTask
   {
      private String m_message;
      private StringBuffer m_buffer;

      protected OveragerTask(long period)
      {
         m_message = getTaskLogMessage() + " " +
            m_cache.getContainer().getBeanMetaData().getEjbName() +
            " with id = ";
         m_buffer = new StringBuffer();
      }

      public void run()
      {
         if( m_cache == null )
         {
            cancel();
            return;
         }

         LRUList list = getList();
         long now = System.currentTimeMillis();
         ArrayList passivateEntries = null;
         synchronized (m_cache.getCacheLock())
         {
            for (LRUCacheEntry entry = list.m_tail; entry != null; entry = entry.m_prev)
            {
               if (now - entry.m_time >= getMaxAge())
               {
                  // Attempt to remove this entry from cache
                  if (passivateEntries == null) passivateEntries = new ArrayList();
                  passivateEntries.add(entry);
               }
               else
               {
                  break;
               }
            }
         }
         // We need to do this outside of cache lock because of deadlock possibilities
         // with EntityInstanceInterceptor and Stateful. This is because tryToPassivate
         // calls lock.synch and other interceptor call lock.synch and after call a cache method that locks
         if (passivateEntries != null)
         {
            for (int i = 0; i < passivateEntries.size(); i++)
            {
               LRUCacheEntry entry = (LRUCacheEntry) passivateEntries.get(i);
               try
               {
                  m_cache.tryToPassivate((EnterpriseContext) entry.m_object);
               }
               catch (Throwable t)
               {
                  log.debug("Ignored error while trying to passivate ctx", t);
               }
            }
         }
      }

      private void log(Object key, int count)
      {
         if( log.isTraceEnabled() )
         {
            m_buffer.setLength(0);
            m_buffer.append(m_message);
            m_buffer.append(key);
            m_buffer.append(" - Cache size = ");
            m_buffer.append(count);
            log.trace(m_buffer.toString());
         }
      }

      protected String getTaskLogMessage()
      {
         return "Scheduling for passivation overaged bean";
      }

      protected String getJMSTaskType()
      {
         return "OVERAGER";
      }

      protected long getMaxAge()
      {
         return m_maxBeanAge;
      }
   }

   /**
    * Subclass that logs list activity events.
    */
   protected class ContextLRUList extends LRUList
   {
      boolean trace = log.isTraceEnabled();
      protected void entryPromotion(LRUCacheEntry entry)
      {
         if (trace)
            log.trace("entryPromotion, entry="+entry);
            
         // The cache is full, temporarily increase it
         if (m_count == m_capacity && m_capacity >= m_maxCapacity)
         {
            ++m_capacity;
            log.warn("Cache has reached maximum capacity for container " +
                     m_cache.getContainer().getJmxName() +
                     " - probably because all instances are in use. " + 
                     "Temporarily increasing the size to " + m_capacity);
         }
      }
      protected void entryAdded(LRUCacheEntry entry)
      {
         if (trace)
            log.trace("entryAdded, entry="+entry);
      }
      protected void entryRemoved(LRUCacheEntry entry)
      {
         if (trace)
            log.trace("entryRemoved, entry="+entry);
      }
      protected void capacityChanged(int oldCapacity)
      {
         if (trace)
            log.trace("capacityChanged, oldCapacity="+oldCapacity);
      }
   }

}
