Java tutorial
/* * $Header: /home/cvs/jakarta-tomcat-catalina/modules/cluster/src/share/org/apache/catalina/cluster/tcp/TcpReplicationThread.java,v 1.7 2004/01/09 23:24:09 fhanik Exp $ * $Revision: 1.7 $ * $Date: 2004/01/09 23:24:09 $ * * ==================================================================== * * The Apache Software License, Version 1.1 * * Copyright (c) 1999 The Apache Software Foundation. All rights * reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * 3. The end-user documentation included with the redistribution, if * any, must include the following acknowlegement: * "This product includes software developed by the * Apache Software Foundation (http://www.apache.org/)." * Alternately, this acknowlegement may appear in the software itself, * if and wherever such third-party acknowlegements normally appear. * * 4. The names "The Jakarta Project", "Tomcat", and "Apache Software * Foundation" must not be used to endorse or promote products derived * from this software without prior written permission. For written * permission, please contact apache@apache.org. * * 5. Products derived from this software may not be called "Apache" * nor may "Apache" appear in their names without prior written * permission of the Apache Group. * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * ==================================================================== * * This software consists of voluntary contributions made by many * individuals on behalf of the Apache Software Foundation. For more * information on the Apache Software Foundation, please see * <http://www.apache.org/>. * * [Additional notices, if required by prior licensing conditions] * */ package org.apache.catalina.cluster.tcp; import java.nio.ByteBuffer; import java.nio.channels.SelectionKey; import java.nio.channels.Selector; import java.util.List; import java.io.IOException; import java.nio.channels.SocketChannel; import org.apache.catalina.cluster.io.ObjectReader; import java.util.LinkedList; /** * A worker thread class which can drain channels and echo-back * the input. Each instance is constructed with a reference to * the owning thread pool object. When started, the thread loops * forever waiting to be awakened to service the channel associated * with a SelectionKey object. * The worker is tasked by calling its serviceChannel() method * with a SelectionKey object. The serviceChannel() method stores * the key reference in the thread object then calls notify() * to wake it up. When the channel has been drained, the worker * thread returns itself to its parent pool. */ public class TcpReplicationThread extends WorkerThread { private static org.apache.commons.logging.Log log = org.apache.commons.logging.LogFactory .getLog(SimpleTcpCluster.class); private ByteBuffer buffer = ByteBuffer.allocate(1024); private SelectionKey key; private boolean synchronous = false; TcpReplicationThread() { } // loop forever waiting for work to do public synchronized void run() { while (doRun) { try { // sleep and release object lock this.wait(); } catch (InterruptedException e) { log.info("TCP worker thread interrupted in cluster", e); // clear interrupt status this.interrupted(); } if (key == null) { continue; // just in case } try { drainChannel(key); } catch (Exception e) { log.error("TCP Worker thread in cluster caught '" + e + "' closing channel", e); // close channel and nudge selector try { key.channel().close(); } catch (IOException ex) { log.error("Unable to close channel.", ex); } key.selector().wakeup(); } key = null; // done, ready for more, return to pool this.pool.returnWorker(this); } } /** * Called to initiate a unit of work by this worker thread * on the provided SelectionKey object. This method is * synchronized, as is the run() method, so only one key * can be serviced at a given time. * Before waking the worker thread, and before returning * to the main selection loop, this key's interest set is * updated to remove OP_READ. This will cause the selector * to ignore read-readiness for this channel while the * worker thread is servicing it. */ synchronized void serviceChannel(SelectionKey key, boolean synchronous) { this.key = key; this.synchronous = synchronous; key.interestOps(key.interestOps() & (~SelectionKey.OP_READ)); key.interestOps(key.interestOps() & (~SelectionKey.OP_WRITE)); this.notify(); // awaken the thread } /** * The actual code which drains the channel associated with * the given key. This method assumes the key has been * modified prior to invocation to turn off selection * interest in OP_READ. When this method completes it * re-enables OP_READ and calls wakeup() on the selector * so the selector will resume watching this channel. */ private void drainChannel(SelectionKey key) throws Exception { boolean packetReceived = false; SocketChannel channel = (SocketChannel) key.channel(); int count; buffer.clear(); // make buffer empty ObjectReader reader = (ObjectReader) key.attachment(); // loop while data available, channel is non-blocking while ((count = channel.read(buffer)) > 0) { buffer.flip(); // make buffer readable int pkgcnt = reader.append(buffer.array(), 0, count); buffer.clear(); // make buffer empty } //check to see if any data is available int pkgcnt = reader.execute(); while (pkgcnt > 0) { if (synchronous) { sendAck(key, channel); } //end if pkgcnt--; } if (count < 0) { // close channel on EOF, invalidates the key channel.close(); return; } // resume interest in OP_READ, OP_WRITE key.interestOps(key.interestOps() | SelectionKey.OP_READ); // cycle the selector so this key is active again key.selector().wakeup(); } private void sendAck(SelectionKey key, SocketChannel channel) { //send a reply-acknowledgement try { channel.write(ByteBuffer.wrap(new byte[] { 6, 2, 3 })); } catch (java.io.IOException x) { log.warn("Unable to send ACK back through channel, channel disconnected?: " + x.getMessage()); } } }