org/sonews/daemon/ChannelReader.java
author cli
Wed Aug 12 13:03:23 2009 +0200 (2009-08-12)
changeset 7 0b76e099eb96
parent 1 6fceb66e1ad7
child 15 f2293e8566f5
permissions -rw-r--r--
PullFeeder sends an addition "MODE READER" to peers.
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/*
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 *   SONEWS News Server
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 *   see AUTHORS for the list of contributors
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 *
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 *   This program is free software: you can redistribute it and/or modify
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 *   it under the terms of the GNU General Public License as published by
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 *   the Free Software Foundation, either version 3 of the License, or
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 *   (at your option) any later version.
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 *
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 *   This program is distributed in the hope that it will be useful,
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 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
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 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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 *   GNU General Public License for more details.
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 *
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 *   You should have received a copy of the GNU General Public License
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 *   along with this program.  If not, see <http://www.gnu.org/licenses/>.
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 */
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package org.sonews.daemon;
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import java.io.IOException;
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import java.nio.ByteBuffer;
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import java.nio.channels.CancelledKeyException;
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import java.nio.channels.SelectionKey;
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import java.nio.channels.Selector;
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import java.nio.channels.SocketChannel;
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import java.util.Iterator;
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import java.util.Set;
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import org.sonews.util.Log;
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/**
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 * A Thread task listening for OP_READ events from SocketChannels.
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 * @author Christian Lins
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 * @since sonews/0.5.0
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 */
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class ChannelReader extends AbstractDaemon
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{
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  private static ChannelReader instance = new ChannelReader();
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  /**
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   * @return Active ChannelReader instance.
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   */
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  public static ChannelReader getInstance()
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  {
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    return instance;
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  }
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  private Selector selector = null;
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  protected ChannelReader()
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  {
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  }
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  /**
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   * Sets the selector which is used by this reader to determine the channel
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   * to read from.
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   * @param selector
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   */
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  public void setSelector(final Selector selector)
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  {
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    this.selector = selector;
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  }
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  /**
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   * Run loop. Blocks until some data is available in a channel.
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   */
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  @Override
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  public void run()
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  {
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    assert selector != null;
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    while(isRunning())
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    {
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      try
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      {
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        // select() blocks until some SelectableChannels are ready for
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        // processing. There is no need to lock the selector as we have only
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        // one thread per selector.
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        selector.select();
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        // Get list of selection keys with pending events.
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        // Note: the selected key set is not thread-safe
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        SocketChannel channel = null;
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        NNTPConnection conn = null;
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        final Set<SelectionKey> selKeys = selector.selectedKeys();
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        SelectionKey selKey = null;
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        synchronized (selKeys)
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        {
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          Iterator it = selKeys.iterator();
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          // Process the first pending event
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          while (it.hasNext())
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          {
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            selKey = (SelectionKey) it.next();
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            channel = (SocketChannel) selKey.channel();
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            conn = Connections.getInstance().get(channel);
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            // Because we cannot lock the selKey as that would cause a deadlock
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            // we lock the connection. To preserve the order of the received
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            // byte blocks a selection key for a connection that has pending
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            // read events is skipped.
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            if (conn == null || conn.tryReadLock())
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            {
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              // Remove from set to indicate that it's being processed
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              it.remove();
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              if (conn != null)
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              {
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                break; // End while loop
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              }
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            }
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            else
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            {
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              selKey = null;
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              channel = null;
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              conn = null;
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            }
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          }
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        }
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        // Do not lock the selKeys while processing because this causes
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        // a deadlock in sun.nio.ch.SelectorImpl.lockAndDoSelect()
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        if (selKey != null && channel != null && conn != null)
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        {
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          processSelectionKey(conn, channel, selKey);
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          conn.unlockReadLock();
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        }
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      }
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      catch(CancelledKeyException ex)
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      {
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        Log.msg("ChannelReader.run(): " + ex, false);
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        if(Log.isDebug())
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        {
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          ex.printStackTrace();
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        }
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      }
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      catch(Exception ex)
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      {
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        ex.printStackTrace();
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      }
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      // Eventually wait for a register operation
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      synchronized (NNTPDaemon.RegisterGate)
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      {
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      // Do nothing; FindBugs may warn about an empty synchronized 
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      // statement, but we cannot use a wait()/notify() mechanism here.
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      // If we used something like RegisterGate.wait() we block here
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      // until the NNTPDaemon calls notify(). But the daemon only
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      // calls notify() if itself is NOT blocked in the listening socket.
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      }
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    } // while(isRunning())
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  }
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  private void processSelectionKey(final NNTPConnection connection,
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    final SocketChannel socketChannel, final SelectionKey selKey)
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    throws InterruptedException, IOException
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  {
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    assert selKey != null;
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    assert selKey.isReadable();
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    // Some bytes are available for reading
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    if(selKey.isValid())
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    {   
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      // Lock the channel
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      //synchronized(socketChannel)
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      {
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        // Read the data into the appropriate buffer
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        ByteBuffer buf = connection.getInputBuffer();
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        int read = -1;
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        try 
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        {
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          read = socketChannel.read(buf);
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        }
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        catch(IOException ex)
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        {
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          // The connection was probably closed by the remote host
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          // in a non-clean fashion
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          Log.msg("ChannelReader.processSelectionKey(): " + ex, true);
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        }
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        catch(Exception ex) 
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        {
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          Log.msg("ChannelReader.processSelectionKey(): " + ex, false);
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          if(Log.isDebug())
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          {
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            ex.printStackTrace();
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          }
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        }
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        if(read == -1) // End of stream
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        {
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          selKey.cancel();
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        }
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        else if(read > 0) // If some data was read
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        {
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          ConnectionWorker.addChannel(socketChannel);
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        }
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      }
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    }
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    else
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    {
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      // Should not happen
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      Log.msg(selKey, false);
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    }
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  }
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}