src/org/sonews/daemon/ChannelReader.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
     1 /*
     2  *   SONEWS News Server
     3  *   see AUTHORS for the list of contributors
     4  *
     5  *   This program is free software: you can redistribute it and/or modify
     6  *   it under the terms of the GNU General Public License as published by
     7  *   the Free Software Foundation, either version 3 of the License, or
     8  *   (at your option) any later version.
     9  *
    10  *   This program is distributed in the hope that it will be useful,
    11  *   but WITHOUT ANY WARRANTY; without even the implied warranty of
    12  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    13  *   GNU General Public License for more details.
    14  *
    15  *   You should have received a copy of the GNU General Public License
    16  *   along with this program.  If not, see <http://www.gnu.org/licenses/>.
    17  */
    18 
    19 package org.sonews.daemon;
    20 
    21 import java.io.IOException;
    22 import java.nio.ByteBuffer;
    23 import java.nio.channels.CancelledKeyException;
    24 import java.nio.channels.SelectionKey;
    25 import java.nio.channels.Selector;
    26 import java.nio.channels.SocketChannel;
    27 import java.util.Iterator;
    28 import java.util.Set;
    29 import java.util.logging.Level;
    30 import org.sonews.util.Log;
    31 
    32 /**
    33  * A Thread task listening for OP_READ events from SocketChannels.
    34  * @author Christian Lins
    35  * @since sonews/0.5.0
    36  */
    37 class ChannelReader extends AbstractDaemon
    38 {
    39 
    40 	private static ChannelReader instance = new ChannelReader();
    41 
    42 	/**
    43 	 * @return Active ChannelReader instance.
    44 	 */
    45 	public static ChannelReader getInstance()
    46 	{
    47 		return instance;
    48 	}
    49 	private Selector selector = null;
    50 
    51 	protected ChannelReader()
    52 	{
    53 	}
    54 
    55 	/**
    56 	 * Sets the selector which is used by this reader to determine the channel
    57 	 * to read from.
    58 	 * @param selector
    59 	 */
    60 	public void setSelector(final Selector selector)
    61 	{
    62 		this.selector = selector;
    63 	}
    64 
    65 	/**
    66 	 * Run loop. Blocks until some data is available in a channel.
    67 	 */
    68 	@Override
    69 	public void run()
    70 	{
    71 		assert selector != null;
    72 
    73 		while (isRunning()) {
    74 			try {
    75 				// select() blocks until some SelectableChannels are ready for
    76 				// processing. There is no need to lock the selector as we have only
    77 				// one thread per selector.
    78 				selector.select();
    79 
    80 				// Get list of selection keys with pending events.
    81 				// Note: the selected key set is not thread-safe
    82 				SocketChannel channel = null;
    83 				NNTPConnection conn = null;
    84 				final Set<SelectionKey> selKeys = selector.selectedKeys();
    85 				SelectionKey selKey = null;
    86 
    87 				synchronized (selKeys) {
    88 					Iterator it = selKeys.iterator();
    89 
    90 					// Process the first pending event
    91 					while (it.hasNext()) {
    92 						selKey = (SelectionKey) it.next();
    93 						channel = (SocketChannel) selKey.channel();
    94 						conn = Connections.getInstance().get(channel);
    95 
    96 						// Because we cannot lock the selKey as that would cause a deadlock
    97 						// we lock the connection. To preserve the order of the received
    98 						// byte blocks a selection key for a connection that has pending
    99 						// read events is skipped.
   100 						if (conn == null || conn.tryReadLock()) {
   101 							// Remove from set to indicate that it's being processed
   102 							it.remove();
   103 							if (conn != null) {
   104 								break; // End while loop
   105 							}
   106 						} else {
   107 							selKey = null;
   108 							channel = null;
   109 							conn = null;
   110 						}
   111 					}
   112 				}
   113 
   114 				// Do not lock the selKeys while processing because this causes
   115 				// a deadlock in sun.nio.ch.SelectorImpl.lockAndDoSelect()
   116 				if (selKey != null && channel != null && conn != null) {
   117 					processSelectionKey(conn, channel, selKey);
   118 					conn.unlockReadLock();
   119 				}
   120 
   121 			} catch (CancelledKeyException ex) {
   122 				Log.get().warning("ChannelReader.run(): " + ex);
   123 				Log.get().log(Level.INFO, "", ex);
   124 			} catch (Exception ex) {
   125 				ex.printStackTrace();
   126 			}
   127 
   128 			// Eventually wait for a register operation
   129 			synchronized (NNTPDaemon.RegisterGate) {
   130 				// Do nothing; FindBugs may warn about an empty synchronized
   131 				// statement, but we cannot use a wait()/notify() mechanism here.
   132 				// If we used something like RegisterGate.wait() we block here
   133 				// until the NNTPDaemon calls notify(). But the daemon only
   134 				// calls notify() if itself is NOT blocked in the listening socket.
   135 			}
   136 		} // while(isRunning())
   137 	}
   138 
   139 	private void processSelectionKey(final NNTPConnection connection,
   140 		final SocketChannel socketChannel, final SelectionKey selKey)
   141 		throws InterruptedException, IOException
   142 	{
   143 		assert selKey != null;
   144 		assert selKey.isReadable();
   145 
   146 		// Some bytes are available for reading
   147 		if (selKey.isValid()) {
   148 			// Lock the channel
   149 			//synchronized(socketChannel)
   150 			{
   151 				// Read the data into the appropriate buffer
   152 				ByteBuffer buf = connection.getInputBuffer();
   153 				int read = -1;
   154 				try {
   155 					read = socketChannel.read(buf);
   156 				} catch (IOException ex) {
   157 					// The connection was probably closed by the remote host
   158 					// in a non-clean fashion
   159 					Log.get().info("ChannelReader.processSelectionKey(): " + ex);
   160 				} catch (Exception ex) {
   161 					Log.get().warning("ChannelReader.processSelectionKey(): " + ex);
   162 				}
   163 
   164 				if (read == -1) // End of stream
   165 				{
   166 					selKey.cancel();
   167 				} else if (read > 0) // If some data was read
   168 				{
   169 					ConnectionWorker.addChannel(socketChannel);
   170 				}
   171 			}
   172 		} else {
   173 			// Should not happen
   174 			Log.get().severe("Should not happen: " + selKey.toString());
   175 		}
   176 	}
   177 }