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/*
 * $Header: /cvs/glassfish/admin/mbeanapi-impl/src/java/com/sun/enterprise/management/support/NotificationBuffer.java,v 1.7 2007/05/05 05:23:42 tcfujii Exp $
 * $Revision: 1.7 $
 * $Date: 2007/05/05 05:23:42 $
 */

package com.sun.enterprise.management.support;

import java.util.Map;
import java.util.HashMap;

import javax.management.Notification;
import javax.management.NotificationFilter;

import com.sun.appserv.management.base.NotificationService;
import com.sun.appserv.management.util.misc.CircularList;
import com.sun.appserv.management.util.misc.OverflowHandler;



/**
	A circular buffer for Notifications.
 */
final class NotificationBuffer
{
	private final CircularList<Notification> mNotifications;
	private final NotificationFilter	mFilter;
	private final int					mBufferSize;
	long								mNextSequenceNumber;
	private OverflowHandler				mOverflowHandler;
	
	
		protected synchronized long
	nextSequenceNumber( )
	{
		return( mNextSequenceNumber++ );
	}
	
		protected synchronized long
	getNextSequenceNumber( )
	{
		return( mNextSequenceNumber );
	}
	
		public
	NotificationBuffer(
		final int					bufferSize,
		final NotificationFilter	filter,
		final OverflowHandler		handler )
	{
		mFilter					= filter;
		mBufferSize				= bufferSize;
		mNotifications			= new CircularList<Notification>( Notification.class, bufferSize );
		mNextSequenceNumber		= 1;
		mOverflowHandler		= handler;
	}

	/**
		Buffer the Notification if it matches the filter.
	 */
		public void
	bufferNotification( final Notification	notif ) 
	{
		if ( mFilter == null || mFilter.isNotificationEnabled( notif ) )
		{
			synchronized( mNotifications )
			{
				mNotifications.add( notif );
				nextSequenceNumber();
			}
		}
	}
	
	
	/**
		Get the number of Notifications available.  Once the buffer is full, it will stay
		full until cleared, so that getSize() will return the same number as getCapacity().
	 */
		public int
	getBufferSize()
	{
		return( mBufferSize );
	}
	
		public void
	clear()
	{
		synchronized( mNotifications )
		{
			mNotifications.clear();
		}
	}


	private final Notification[]	EMPTY_NOTIFS	= new Notification[ 0 ];
	private final Long				LONG_ZERO		= Long.valueOf(0);
	
	/**
		Key within the Map returned by getNotifications() that yields the Long
		for the next sequence number.
	 */
	public static final String	NEXT_SEQUENCE_NUMBER_KEY	=
		NotificationService.NEXT_SEQUENCE_NUMBER_KEY;
	
	/**
		Key within the Map returned by getNotifications() that yields the
		Notifications[].
	 */
	public static final String	NOTIFICATIONS_KEY	=
		NotificationService.NOTIFICATIONS_KEY;
	
	/**
		Get all outstanding Notifications which have a sequence number
		that is equal to or greater than the specified one.  The sequence
		number in this case is the overarching one maintained by this buffer,
		and has nothing to do with the sequence number within any particular
		Notification.
		<p>
		A sequence number of 0 means all Notifications.
		<p>
		The array returned contains the following:
		<nl>
		<li>result[ 0 ] is the next sequence number (for the next call)</li>
		<li>result[ 1 ] a Notification[] of the available Notifications</li>
		</nl>
		
		@return result[ 0 ] = next sequence number, result[ 1 ] = Notification[]
	 */
		public Map<String,Object>
	getNotifications( final long sequenceNumberIn ) 
	{
		if ( sequenceNumberIn < 0 )
		{
			throw new IllegalArgumentException( "" + sequenceNumberIn );
		}
		
		final Map<String,Object>	result	= new HashMap<String,Object>();
		result.put( NEXT_SEQUENCE_NUMBER_KEY, LONG_ZERO );
		result.put( NOTIFICATIONS_KEY, EMPTY_NOTIFS );
		
		synchronized( mNotifications )
		{
			final int	numNotifsAvailable	= mNotifications.size();
			final long	nextAvailSequenceNumber	= getNextSequenceNumber();
			result.put(NEXT_SEQUENCE_NUMBER_KEY,
                                    Long.valueOf(nextAvailSequenceNumber));
			
			if ( numNotifsAvailable != 0 )
			{
				final long	lastAvailSequenceNumber		= nextAvailSequenceNumber - 1;
				final long	firstAvailSequenceNumber	= 1 + (lastAvailSequenceNumber - numNotifsAvailable);
				
				assert( firstAvailSequenceNumber >= 1 );
				
				final long	requestedSequenceNumber	= sequenceNumberIn == 0 ?
					firstAvailSequenceNumber : sequenceNumberIn;
					
				if ( requestedSequenceNumber >= firstAvailSequenceNumber &&
					requestedSequenceNumber <= lastAvailSequenceNumber)
				{
					final int	numMatches	= 1 +
						(int)(lastAvailSequenceNumber - requestedSequenceNumber);
					
					final Notification[]	notifs	= new Notification[ numMatches ];
					
					final int	startIndex	= (int)
						(requestedSequenceNumber - firstAvailSequenceNumber);
					for( int i = 0 ; i < numMatches; ++i )
					{
						notifs[ i ]	= (Notification)
							mNotifications.get( startIndex + i );
					}
					
					result.put( NOTIFICATIONS_KEY, notifs );
				}
			}
		}
		
		assert( result.get( NOTIFICATIONS_KEY ) instanceof Notification[] );
		assert( result.get( NEXT_SEQUENCE_NUMBER_KEY ) instanceof Long );
		
		return( result );
	}
}