/*
 * 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.lang.reflect.Constructor;
import java.rmi.NoSuchObjectException;
import java.rmi.RemoteException;
import java.util.Map;

import org.jboss.deployment.DeploymentException;
import org.jboss.ejb.BeanLock;
import org.jboss.ejb.BeanLockExt;
import org.jboss.ejb.Container;
import org.jboss.ejb.EnterpriseContext;
import org.jboss.ejb.InstanceCache;
import org.jboss.logging.Logger;
import org.jboss.metadata.MetaData;
import org.jboss.metadata.XmlLoadable;
import org.jboss.monitor.MetricsConstants;
import org.jboss.monitor.Monitorable;
import org.jboss.monitor.client.BeanCacheSnapshot;
import org.jboss.util.CachePolicy;
import org.w3c.dom.Element;

/**
 * Base class for caches of entity and stateful beans. <p>
 * It manages the cache entries through a {@link CachePolicy} object;
 * the implementation of the cache policy object must respect the following
 * requirements:
 * <ul>
 * <li> Have a public constructor that takes a single argument of type
 * AbstractInstanceCache.class or a subclass
 * </ul>
 *
 * @author <a href="mailto:simone.bordet@compaq.com">Simone Bordet</a>
 * @author <a href="bill@burkecentral.com">Bill Burke</a>
 * @author <a href="marc.fleury@jboss.org">Marc Fleury</a>
 * @author Scott.Stark@jboss.org
 * @version $Revision: 81030 $
 * @jmx:mbean
 */
public abstract class AbstractInstanceCache
   implements InstanceCache, XmlLoadable, Monitorable, MetricsConstants,
      AbstractInstanceCacheMBean
{
   // Constants -----------------------------------------------------

   // Attributes ----------------------------------------------------
   protected static Logger log = Logger.getLogger(AbstractInstanceCache.class);

   /* The object that is delegated to implement the desired caching policy */
   private CachePolicy m_cache;
   /* The mutex object for the cache */
   private final Object m_cacheLock = new Object();

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

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

   // Monitorable implementation ------------------------------------
   public void sample(Object s)
   {
      if( m_cache == null )
         return;

      synchronized (getCacheLock())
      {
         BeanCacheSnapshot snapshot = (BeanCacheSnapshot)s;
         snapshot.m_passivatingBeans = 0;
         CachePolicy policy = getCache();
         if (policy instanceof Monitorable)
         {
            ((Monitorable)policy).sample(s);
         }
      }
   }
   public Map retrieveStatistic()
   {
      return null;
   }
   public void resetStatistic()
   {
   }

   // Public --------------------------------------------------------
   /* From InstanceCache interface */
   public EnterpriseContext get(Object id)
      throws RemoteException, NoSuchObjectException
   {
      if (id == null) throw new IllegalArgumentException("Can't get an object with a null key");

      EnterpriseContext ctx;

      synchronized (getCacheLock())
      {
         CachePolicy cache = getCache();
         ctx = (EnterpriseContext)cache.get(id);
         if (ctx == null)
         {
            try
            {
               ctx = acquireContext();
               setKey(id, ctx);
               if (doActivate(ctx) == false)
                  // This is a recursive activation
                  return ctx;
               logActivation(id);
               // the cache will throw an IllegalStateException if we try to insert
               // something that is in the cache already, so we don't check here
               cache.insert(id, ctx);
            }
            catch (Throwable x)
            {
               log.debug("Activation failure", x);
               throw new NoSuchObjectException(x.getMessage());
            }
         }
      }

      return ctx;
   }

   /* From InstanceCache interface */
   public void insert(EnterpriseContext ctx)
   {
      if (ctx == null) throw new IllegalArgumentException("Can't insert a null object in the cache");

      Object key = getKey(ctx);
      synchronized (getCacheLock())
      {
         // the cache will throw an IllegalStateException if we try to insert
	 // something that is in the cache already, so we don't check here
         getCache().insert(key, ctx);
      }
   }

   /**
    * Tries to passivate the instance. If the instance is in use then the instance
    * will be passivated later according to the container's commit option and max age.
    */
   protected void tryToPassivate(EnterpriseContext ctx)
   {
      tryToPassivate(ctx, false);
   }

   /**
    * Tries to passivate the instance. If the instance is in use and passivateAfterCommit
    * parameter is true then the instance will passivated after the transaction commits.
    * Otherwise, the instance will be passivated later according to the container's
    * commit option and max age.
    */
   protected void tryToPassivate(EnterpriseContext ctx, boolean passivateAfterCommit)
   {
      Object id = ctx.getId();
      if (id == null) return;
      BeanLock lock = getContainer().getLockManager().getLock(id);
      boolean lockedBean = false;
      try
      {
         /* If this is a BeanLockExt only attempt the lock as the call to
         remove is going to have to acquire the cache lock, but this may already
         be held since this method is called by passivation policies without
         the cache lock. This can lead to a deadlock as in the case of a size based
         eviction during a cache get attempts to lock the bean that has been
         locked by an age based background thread as seen in bug 987389 on
         sourceforge.
         */
         if( lock instanceof BeanLockExt )
         {
            BeanLockExt lock2 = (BeanLockExt) lock;
            lockedBean = lock2.attemptSync();
            if( lockedBean == false )
            {
               unableToPassivateDueToCtxLock(ctx, passivateAfterCommit);
               return;
            }
         }
         else
         {
            // Use the blocking sync
            lock.sync();
            lockedBean = true;
         }

         if (canPassivate(ctx))
         {
            try
            {
               remove(id);
               passivate(ctx);
               freeContext(ctx);
            }
            catch (Exception ignored)
            {
               log.warn("failed to passivate, id="+id, ignored);
            }
         }
         else
         {
            // Touch the entry to make it MRU
            synchronized (getCacheLock())
            {
               getCache().get(id);
            }

            unableToPassivateDueToCtxLock(ctx, passivateAfterCommit);
         }
      }
      finally
      {
         if( lockedBean )
            lock.releaseSync();
         getContainer().getLockManager().removeLockRef(id);
      }
   }

   /**
    * Passivates and removes the instance from the cache.
    * If the instance is in use then removal and passivation will be scheduled until
    * after transaction ends
    */
   public void release(EnterpriseContext ctx)
   {
      if (ctx == null) throw new IllegalArgumentException("Can't release a null object");

      // Here I remove the bean; call to remove(id) is wrong
      // cause will remove also the cache lock that is needed
      // by the passivation, that eventually will remove it.
      /* the removal should only be done if the instance is not in use.
         this is taken care of in tryToPassivate
      Object id = getKey(ctx);
      synchronized (getCacheLock())
      {
         if (getCache().peek(id) != null)
            getCache().remove(id);
      }
      */
      tryToPassivate(ctx, true);
   }

   /**
    * From InstanceCache interface
    * @jmx:managed-operation
    */
   public void remove(Object id)
   {
      if (id == null) throw new IllegalArgumentException("Can't remove an object using a null key");

      synchronized (getCacheLock())
      {
         if (getCache().peek(id) != null)
         {
            getCache().remove(id);
         }
      }
   }

   public boolean isActive(Object id)
   {
      // Check whether an object with the given id is available in the cache
      synchronized (getCacheLock())
      {
         return getCache().peek(id) != null;
      }
   }

   /** Get the current cache size
    * @jmx:managed-attribute
    * @return the size of the cache
    */
   public long getCacheSize()
   {
      int cacheSize = m_cache != null ? m_cache.size() : 0;
      return cacheSize;
   }
   /** Flush the cache.
    * @jmx:managed-operation
    */
   public void flush()
   {
      if( m_cache != null )
         m_cache.flush();
   }
   /** Get the passivated count.
    * @jmx:managed-attribute
    * @return the number of passivated instances.
    */
   public long getPassivatedCount()
   {
      return 0;
   }

   /**
    * Display the cache policy.
    * 
    * @jmx:managed-attribute
    * @return the cache policy as a string.
    */
   public String getCachePolicyString()
   {
      return m_cache.toString();
   }
   
   // XmlLoadable implementation ----------------------------------------------
   public void importXml(Element element) throws DeploymentException
   {
      // This one is mandatory
      String p = MetaData.getElementContent(MetaData.getUniqueChild(element, "cache-policy"));
      try
      {
         Class cls = SecurityActions.getContextClassLoader().loadClass(p);
         Constructor ctor = cls.getConstructor(new Class[] {AbstractInstanceCache.class});
         m_cache = (CachePolicy)ctor.newInstance(new Object[] {this});
      }
      catch (Exception x)
      {
         throw new DeploymentException("Can't create cache policy", x);
      }

      Element policyConf = MetaData.getOptionalChild(element, "cache-policy-conf");
      if (policyConf != null)
      {
         if (m_cache instanceof XmlLoadable)
         {
            try
            {
               ((XmlLoadable)m_cache).importXml(policyConf);
            }
            catch (Exception x)
            {
               throw new DeploymentException("Can't import policy configuration", x);
            }
         }
      }
   }

   /* From Service interface*/
   public void create() throws Exception
   {
      getCache().create();
   }
   /* From Service interface*/
   public void start() throws Exception
   {
      getCache().start();
   }
   /* From Service interface*/
   public void stop()
   {
      // Empty the cache
      synchronized (getCacheLock())
      {
         getCache().stop();
      }
   }
   /* From Service interface*/
   public void destroy()
   {
      synchronized (getCacheLock())
      {
         getCache().destroy();
      }
   }

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

   // Package protected ---------------------------------------------

   // Protected -----------------------------------------------------
   protected void logActivation(Object id)
   {
      if( log.isTraceEnabled() )
      {
         StringBuffer m_buffer=new StringBuffer(100);
         m_buffer.append("Activated bean ");
         m_buffer.append(getContainer().getBeanMetaData().getEjbName());
         m_buffer.append(" with id = ");
         m_buffer.append(id);
         log.trace(m_buffer.toString());
      }
   }

   protected void logPassivation(Object id)
   {
      if( log.isTraceEnabled() )
      {
         StringBuffer m_buffer=new StringBuffer(100);
         m_buffer.append("Passivated bean ");
         m_buffer.append(getContainer().getBeanMetaData().getEjbName());
         m_buffer.append(" with id = ");
         m_buffer.append(id);
         log.trace(m_buffer.toString());
      }
   }

   protected void unableToPassivateDueToCtxLock(EnterpriseContext ctx, boolean passivateAfterCommit)
   {
      log.warn("Unable to passivate due to ctx lock, id="+ctx.getId());
   }

   /**
    * Returns the container for this cache.
    */
   protected abstract Container getContainer();
   /**
    * Returns the cache policy used for this cache.
    */
   protected CachePolicy getCache() {return m_cache;}
   /**
    * Returns the mutex used to sync access to the cache policy object
    */
   public Object getCacheLock()
   {
      return m_cacheLock;
   }
   /**
    * Passivates the given EnterpriseContext
    */
   protected abstract void passivate(EnterpriseContext ctx) throws RemoteException;
   /**
    * Activates the given EnterpriseContext
    */
   protected abstract void activate(EnterpriseContext ctx) throws RemoteException;
   /**
    * Activate the given EnterpriseContext
    * 
    * @param ctx the context
    * @return false if we recursively activating
    * @throws RemoteException for any error
    */
   protected boolean doActivate(EnterpriseContext ctx) throws RemoteException
   {
      activate(ctx);
      return true;
   }
   /**
    * Acquires an EnterpriseContext from the pool
    */
   protected abstract EnterpriseContext acquireContext() throws Exception;
   /**
    * Frees the given EnterpriseContext to the pool
    */
   protected abstract void freeContext(EnterpriseContext ctx);
   /**
    * Returns the key used by the cache to map the given context
    */
   protected abstract Object getKey(EnterpriseContext ctx);
   /**
    * Sets the given id as key for the given context
    */
   protected abstract void setKey(Object id, EnterpriseContext ctx);
   /**
    * Returns whether the given context can be passivated or not
    *
    */
   protected abstract boolean canPassivate(EnterpriseContext ctx);

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

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