src/org/sonews/daemon/ChannelWriter.java
author František Kučera <franta-hg@frantovo.cz>
Thu Jul 05 13:19:19 2012 +0200 (2012-07-05)
changeset 119 f5b57e221e38
parent 35 ed84c8bdd87b
permissions -rwxr-xr-x
mezery, tabulátory
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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 org.sonews.util.Log;
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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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/**
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 * A Thread task that processes OP_WRITE events for 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 ChannelWriter extends AbstractDaemon
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{
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	private static ChannelWriter instance = new ChannelWriter();
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	/**
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	 * @return Returns the active ChannelWriter instance.
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	 */
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	public static ChannelWriter 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 ChannelWriter()
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	{
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	}
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	/**
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	 * @return Selector associated with this instance.
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	 */
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	public Selector getSelector()
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	{
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		return this.selector;
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	}
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	/**
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	 * Sets the selector that is used by this ChannelWriter.
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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.
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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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			try {
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				SelectionKey selKey = null;
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				SocketChannel socketChannel = null;
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				NNTPConnection connection = null;
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				// select() blocks until some SelectableChannels are ready for
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				// processing. There is no need to synchronize the selector as we
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				// have only one thread per selector.
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				selector.select(); // The return value of select can be ignored
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				// Get list of selection keys with pending OP_WRITE events.
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				// The keySET is not thread-safe whereas the keys itself are.
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				Iterator it = selector.selectedKeys().iterator();
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				while (it.hasNext()) {
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					// We remove the first event from the set and store it for
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					// later processing.
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					selKey = (SelectionKey) it.next();
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					socketChannel = (SocketChannel) selKey.channel();
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					connection = Connections.getInstance().get(socketChannel);
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					it.remove();
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					if (connection != null) {
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						break;
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					} else {
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						selKey = null;
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					}
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				}
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				if (selKey != null) {
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					try {
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						// Process the selected key.
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						// As there is only one OP_WRITE key for a given channel, we need
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						// not to synchronize this processing to retain the order.
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						processSelectionKey(connection, socketChannel, selKey);
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					} catch (IOException ex) {
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						Log.get().warning("Error writing to channel: " + ex);
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						// Cancel write events for this channel
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						selKey.cancel();
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						connection.shutdownInput();
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						connection.shutdownOutput();
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					}
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				}
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				// Eventually wait for a register operation
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				synchronized (NNTPDaemon.RegisterGate) { /* do nothing */ }
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			} catch (CancelledKeyException ex) {
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				Log.get().info("ChannelWriter.run(): " + ex);
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			} catch (Exception ex) {
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				ex.printStackTrace();
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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 connection != null;
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		assert socketChannel != null;
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		assert selKey != null;
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		assert selKey.isWritable();
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		// SocketChannel is ready for writing
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		if (selKey.isValid()) {
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			// Lock the socket channel
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			synchronized (socketChannel) {
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				// Get next output buffer
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				ByteBuffer buf = connection.getOutputBuffer();
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				if (buf == null) {
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					// Currently we have nothing to write, so we stop the writeable
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					// events until we have something to write to the socket channel
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					//selKey.cancel();
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					selKey.interestOps(0);
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					// Update activity timestamp to prevent too early disconnects
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					// on slow client connections
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					connection.setLastActivity(System.currentTimeMillis());
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					return;
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				}
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				while (buf != null) // There is data to be send
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				{
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					// Write buffer to socket channel; this method does not block
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					if (socketChannel.write(buf) <= 0) {
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						// Perhaps there is data to be written, but the SocketChannel's
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						// buffer is full, so we stop writing to until the next event.
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						break;
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					} else {
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						// Retrieve next buffer if available; method may return the same
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						// buffer instance if it still have some bytes remaining
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						buf = connection.getOutputBuffer();
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					}
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				}
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			}
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		} else {
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			Log.get().warning("Invalid OP_WRITE key: " + selKey);
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			if (socketChannel.socket().isClosed()) {
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				connection.shutdownInput();
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				connection.shutdownOutput();
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				socketChannel.close();
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				Log.get().info("Connection closed.");
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			}
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		}
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	}
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}