//
//  ========================================================================
//  Copyright (c) 1995-2014 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.io.nio;

import java.io.IOException;
import java.nio.channels.CancelledKeyException;
import java.nio.channels.Channel;
import java.nio.channels.ClosedSelectorException;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.util.ArrayList;
import java.util.List;
import java.util.Collections;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

import org.eclipse.jetty.io.AsyncEndPoint;
import org.eclipse.jetty.io.ConnectedEndPoint;
import org.eclipse.jetty.io.Connection;
import org.eclipse.jetty.io.EndPoint;
import org.eclipse.jetty.util.TypeUtil;
import org.eclipse.jetty.util.component.AbstractLifeCycle;
import org.eclipse.jetty.util.component.AggregateLifeCycle;
import org.eclipse.jetty.util.component.Dumpable;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/* ------------------------------------------------------------ */
/**
 * The Selector Manager manages and number of SelectSets to allow
 * NIO scheduling to scale to large numbers of connections.
 * <p>
 */
public abstract class SelectorManager extends AbstractLifeCycle implements Dumpable
{
	public static final Logger LOG=LoggerFactory.getLogger("org.eclipse.jetty.io.nio");

	private static final int __MONITOR_PERIOD=Integer.getInteger("org.eclipse.jetty.io.nio.MONITOR_PERIOD",1000).intValue();
	private static final int __MAX_SELECTS=Integer.getInteger("org.eclipse.jetty.io.nio.MAX_SELECTS",100000).intValue();
	private static final int __BUSY_PAUSE=Integer.getInteger("org.eclipse.jetty.io.nio.BUSY_PAUSE",50).intValue();
	private static final int __IDLE_TICK=Integer.getInteger("org.eclipse.jetty.io.nio.IDLE_TICK",400).intValue();

	private int _maxIdleTime;
	private long _lowResourcesConnections;
	private SelectSet[] _selectSet;
	private int _selectSets=1;
	private volatile int _set=0;

	/* ------------------------------------------------------------ */
	/**
	 * @param maxIdleTime The maximum period in milli seconds that a connection may be idle before it is closed.
	 * @see #setLowResourcesMaxIdleTime(long)
	 */
	public void setMaxIdleTime(long maxIdleTime)
	{
		_maxIdleTime=(int)maxIdleTime;
	}

	/* ------------------------------------------------------------ */
	/**
	 * @param selectSets number of select sets to create
	 */
	public void setSelectSets(int selectSets)
	{
		long lrc = _lowResourcesConnections * _selectSets;
		_selectSets=selectSets;
		_lowResourcesConnections=lrc/_selectSets;
	}

	/* ------------------------------------------------------------ */
	/** Register a channel
	 * @param channel
	 */
	public void register(SocketChannel channel)
	{
		// The ++ increment here is not atomic, but it does not matter.
		// so long as the value changes sometimes, then connections will
		// be distributed over the available sets.

		int s = _set++;
		if (s<0)
			s=-s;
		s=s%_selectSets;
		SelectSet[] sets = _selectSet;
		if (sets!=null)
		{
			SelectSet set=sets[s];
			set.addChange(channel);
			set.wakeup();
		}
	}

	/* ------------------------------------------------------------ */
	/**
	 * @return the lowResourcesConnections
	 */
	public long getLowResourcesConnections()
	{
		return _lowResourcesConnections*_selectSets;
	}

	/* ------------------------------------------------------------ */
	/**
	 * Set the number of connections, which if exceeded places this manager in low resources state.
	 * This is not an exact measure as the connection count is averaged over the select sets.
	 * @param lowResourcesConnections the number of connections
	 * @see #setLowResourcesMaxIdleTime(long)
	 */
	public void setLowResourcesConnections(long lowResourcesConnections)
	{
		_lowResourcesConnections=(lowResourcesConnections+_selectSets-1)/_selectSets;
	}


	public abstract void execute(Runnable task);

	/* ------------------------------------------------------------ */
	/* (non-Javadoc)
	 * @see org.eclipse.component.AbstractLifeCycle#doStart()
	 */
	@Override
	protected void doStart() throws Exception
	{
		_selectSet = new SelectSet[_selectSets];
		for (int i=0;i<_selectSet.length;i++)
			_selectSet[i]= new SelectSet(i);

		super.doStart();

		// start a thread to Select
		for (int i=0;i<_selectSets;i++)
		{
			final int id=i;
			execute(new Runnable()
			{
				public void run()
				{
					String name=Thread.currentThread().getName();
					try
					{
						SelectSet[] sets=_selectSet;
						if (sets==null)
							return;
						SelectSet set=sets[id];

						Thread.currentThread().setName(name+" Selector"+id);
						LOG.debug("Starting {} on {}",Thread.currentThread(),this);
						while (isRunning())
						{
							try
							{
								set.doSelect();
							}
							catch(IOException e)
							{
								LOG.trace("",e);
							}
							catch(Exception e)
							{
								LOG.warn("",e);
							}
						}
					}
					finally
					{
						LOG.debug("Stopped {} on {}",Thread.currentThread(),this);
						Thread.currentThread().setName(name);
					}
				}

			});
		}
	}


	/* ------------------------------------------------------------------------------- */
	@Override
	protected void doStop() throws Exception
	{
		SelectSet[] sets= _selectSet;
		_selectSet=null;
		if (sets!=null)
		{
			for (SelectSet set : sets)
			{
				if (set!=null)
					set.stop();
			}
		}
		super.doStop();
	}

	/* ------------------------------------------------------------------------------- */
	public abstract AsyncConnection newConnection(SocketChannel channel, AsyncEndPoint endpoint, Object attachment);

	public String dump()
	{
		return AggregateLifeCycle.dump(this);
	}

	public void dump(Appendable out, String indent) throws IOException
	{
		AggregateLifeCycle.dumpObject(out,this);
		AggregateLifeCycle.dump(out,indent,TypeUtil.asList(_selectSet));
	}


	public class SelectSet implements Dumpable
	{
		private final int _setID;
		private volatile long _now = System.currentTimeMillis();

		private volatile Selector _selector;

		private volatile Thread _selecting;
		private int _busySelects;
		private long _monitorNext;
		private boolean _pausing;
		private boolean _paused;
		private volatile long _idleTick;
		private ConcurrentMap<SelectChannelEndPoint,Object> _endPoints = new ConcurrentHashMap<SelectChannelEndPoint, Object>();

		SelectSet(int acceptorID) throws Exception
		{
			_setID=acceptorID;

			_idleTick = System.currentTimeMillis();

			// create a selector;
			_selector = Selector.open();
			_monitorNext=System.currentTimeMillis()+__MONITOR_PERIOD;
		}

		private void addChange(SocketChannel channel)
		{
			try {
				SelectionKey key = channel.register(_selector,SelectionKey.OP_READ,null);
				SelectChannelEndPoint endpoint = createEndPoint(channel,key);
				key.attach(endpoint);
				endpoint.schedule();
			} catch(IOException e) {
				LOG.warn("",e);
				try {
					channel.close();
				} catch(IOException e2) {
					LOG.warn("",e2);
				}
			}
		}
		/* ------------------------------------------------------------ */
		/**
		 * Select and dispatch tasks found from changes and the selector.
		 *
		 * @throws IOException
		 */
		public void doSelect() throws IOException
		{
			try
			{
				_selecting=Thread.currentThread();
				final Selector selector=_selector;
				// Stopped concurrently ?
				if (selector == null)
					return;

				// Do and instant select to see if any connections can be handled.
				int selected=selector.selectNow();

				_now = System.currentTimeMillis();

				// if no immediate things to do
				if (selected==0 && selector.selectedKeys().isEmpty())
				{
					// If we are in pausing mode
					if (_pausing)
					{
						try
						{
							Thread.sleep(__BUSY_PAUSE); // pause to reduce impact of  busy loop
						}
						catch(InterruptedException e)
						{
							LOG.trace("",e);
						}
						_now = System.currentTimeMillis();
					}

					// workout how long to wait in select
					long wait = __IDLE_TICK;

					// If we should wait with a select
					if (wait>0)
					{
						long before = _now;
						selector.select(wait);
						_now = System.currentTimeMillis();

						// If we are monitoring for busy selector
						// and this select did not wait more than 1ms
						if (__MONITOR_PERIOD>0 && _now-before <=1)
						{
							// count this as a busy select and if there have been too many this monitor cycle
							if (++_busySelects>__MAX_SELECTS)
							{
								// Start injecting pauses
								_pausing=true;

								// if this is the first pause
								if (!_paused)
								{
									// Log and dump some status
									_paused=true;
									LOG.warn("Selector {} is too busy, pausing!",this);
								}
							}
						}
					}
				}

				// have we been destroyed while sleeping
				if (_selector==null || !selector.isOpen())
					return;

				// Look for things to do
				for (SelectionKey key: selector.selectedKeys())
				{
					SocketChannel channel=null;

					try
					{
						if (!key.isValid())
						{
							key.cancel();
							SelectChannelEndPoint endpoint = (SelectChannelEndPoint)key.attachment();
							if (endpoint != null)
								endpoint.doUpdateKey();
							continue;
						}

						Object att = key.attachment();
						if (att instanceof SelectChannelEndPoint)
						{
							if (key.isReadable()||key.isWritable())
								((SelectChannelEndPoint)att).schedule();
						}
						else if (key.isConnectable())
						{
							// Complete a connection of a registered channel
							channel = (SocketChannel)key.channel();
							boolean connected=false;
							try
							{
								connected=channel.finishConnect();
							}
							catch(Exception e)
							{
								LOG.warn(e+","+channel+","+att);
								LOG.debug("",e);
							}
							finally
							{
								if (connected)
								{
									key.interestOps(SelectionKey.OP_READ);
									SelectChannelEndPoint endpoint = createEndPoint(channel,key);
									key.attach(endpoint);
									endpoint.schedule();
								}
								else
								{
									key.cancel();
									channel.close();
								}
							}
						}
						else
						{
							// Wrap readable registered channel in an endpoint
							channel = (SocketChannel)key.channel();
							SelectChannelEndPoint endpoint = createEndPoint(channel,key);
							key.attach(endpoint);
							if (key.isReadable())
								endpoint.schedule();
						}
						key = null;
					}
					catch (CancelledKeyException e)
					{
						LOG.trace("",e);
					}
					catch (Exception e)
					{
						if (isRunning())
							LOG.warn("",e);
						else
							LOG.trace("",e);

						try
						{
							if (channel!=null)
								channel.close();
						}
						catch(IOException e2)
						{
							LOG.debug("",e2);
						}

						if (key != null && !(key.channel() instanceof ServerSocketChannel) && key.isValid())
							key.cancel();
					}
				}

				// Everything always handled
				selector.selectedKeys().clear();

				_now = System.currentTimeMillis();

				// Idle tick
				if (_now-_idleTick>__IDLE_TICK)
				{
					_idleTick = _now;

					final long idle_now=((_lowResourcesConnections>0 && selector.keys().size()>_lowResourcesConnections))
						?(_now+_maxIdleTime)
						:_now;

					execute(new Runnable()
					{
						public void run()
						{
							for (SelectChannelEndPoint endp:_endPoints.keySet())
							{
								endp.checkIdleTimestamp(idle_now);
							}
						}
						public String toString() {return "Idle-"+super.toString();}
					});

				}

				// Reset busy select monitor counts
				if (__MONITOR_PERIOD>0 && _now>_monitorNext)
				{
					_busySelects=0;
					_pausing=false;
					_monitorNext=_now+__MONITOR_PERIOD;

				}
			}
			catch (ClosedSelectorException e)
			{
				if (isRunning())
					LOG.warn("",e);
				else
					LOG.trace("",e);
			}
			catch (CancelledKeyException e)
			{
				LOG.trace("",e);
			}
			finally
			{
				_selecting=null;
			}
		}

		public SelectorManager getManager()
		{
			return SelectorManager.this;
		}

		public long getNow()
		{
			return _now;
		}

		public void wakeup()
		{
			Selector selector = _selector;
			if (selector!=null)
				selector.wakeup();
		}

		private SelectChannelEndPoint createEndPoint(SocketChannel channel, SelectionKey sKey) throws IOException
		{
			SelectChannelEndPoint endp = new SelectChannelEndPoint(channel,this,sKey, _maxIdleTime);
			endp.setConnection(getManager().newConnection(channel,endp, sKey.attachment()));
			LOG.debug("created {}",endp);
			_endPoints.put(endp,this);
			return endp;
		}

		public void destroyEndPoint(SelectChannelEndPoint endp)
		{
			LOG.debug("destroyEndPoint {}",endp);
			_endPoints.remove(endp);
			endp.getConnection().onClose();
		}

		Selector getSelector()
		{
			return _selector;
		}

		void stop() throws Exception
		{
			// Spin for a while waiting for selector to complete
			// to avoid unneccessary closed channel exceptions
			try
			{
				for (int i=0;i<100 && _selecting!=null;i++)
				{
					wakeup();
					Thread.sleep(10);
				}
			}
			catch(Exception e)
			{
				LOG.warn("",e);
			}

			// close endpoints and selector
			synchronized (this)
			{
				Selector selector=_selector;
				for (SelectionKey key:selector.keys())
				{
					if (key==null)
						continue;
					Object att=key.attachment();
					if (att instanceof EndPoint)
					{
						EndPoint endpoint = (EndPoint)att;
						try
						{
							endpoint.close();
						}
						catch(IOException e)
						{
							LOG.trace("",e);
						}
					}
				}

				try
				{
					selector=_selector;
					if (selector != null)
						selector.close();
				}
				catch (IOException e)
				{
					LOG.trace("",e);
				}
				_selector = null;
			}
		}

		public String dump()
		{
			return AggregateLifeCycle.dump(this);
		}

		public void dump(Appendable out, String indent) throws IOException
		{
			out.append(String.valueOf(this)).append(" id=").append(String.valueOf(_setID)).append("\n");
			AggregateLifeCycle.dump(out,indent,Collections.emptyList());
		}

		public String toString()
		{
			Selector selector=_selector;
			return String.format("%s keys=%d selected=%d",
					super.toString(),
					selector != null && selector.isOpen() ? selector.keys().size() : -1,
					selector != null && selector.isOpen() ? selector.selectedKeys().size() : -1);
		}
	}

}