/*
* Copyright 1999,2004 The Apache Software Foundation.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.catalina.cluster.tcp;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.SocketChannel;
import org.apache.catalina.cluster.io.ObjectReader;
/**
* 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.
*
* @author Filip Hanik
*
* @version $Revision: 380229 $, $Date: 2006-02-23 16:28:29 -0500 (Thu, 23 Feb 2006) $
*/
public class TcpReplicationThread extends WorkerThread {
public static final byte[] ACK_COMMAND = new byte[] {6, 2, 3};
private static org.apache.commons.logging.Log log =
org.apache.commons.logging.LogFactory.getLog( TcpReplicationThread.class );
private ByteBuffer buffer = ByteBuffer.allocate (1024);
private SelectionKey key;
private boolean sendAck=true;
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) {
if(log.isInfoEnabled())
log.info("TCP worker thread interrupted in cluster",e);
// clear interrupt status
Thread.interrupted();
}
if (key == null) {
continue; // just in case
}
try {
drainChannel (key);
} catch (Exception e) {
//this is common, since the sockets on the other
//end expire after a certain time.
if ( e instanceof IOException ) {
//dont spew out stack traces for IO exceptions unless debug is enabled.
if (log.isDebugEnabled()) log.debug ("IOException in replication worker, unable to drain channel. Probable cause: Keep alive socket closed.", e);
else log.warn ("IOException in replication worker, unable to drain channel. Probable cause: Keep alive socket closed.");
} else if ( log.isErrorEnabled() ) {
//this is a real error, log it.
log.error("Exception caught in TcpReplicationThread.drainChannel.",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 sendAck)
{
this.key = key;
this.sendAck=sendAck;
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.
*/
protected 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
reader.append(buffer.array(),0,count);
buffer.clear(); // make buffer empty
}
//check to see if any data is available
int pkgcnt = reader.execute();
if (log.isTraceEnabled()) {
log.trace("sending " + pkgcnt + " ack packages to " + channel.socket().getLocalPort() );
}
if (sendAck) {
while ( pkgcnt > 0 ) {
sendAck(key,channel);
pkgcnt--;
}
}
if (count < 0) {
// close channel on EOF, invalidates the key
channel.close();
return;
}
//acquire the interestOps mutex
Object mutex = this.getPool().getInterestOpsMutex();
synchronized (mutex) {
// cycle the selector so this key is active again
key.selector().wakeup();
// resume interest in OP_READ, OP_WRITE
int resumeOps = key.interestOps() | SelectionKey.OP_READ;
key.interestOps(resumeOps);
}
}
/**
* send a reply-acknowledgement (6,2,3)
* @param key
* @param channel
*/
protected void sendAck(SelectionKey key, SocketChannel channel) {
try {
channel.write(ByteBuffer.wrap(ACK_COMMAND));
if (log.isTraceEnabled()) {
log.trace("ACK sent to " + channel.socket().getPort());
}
} catch ( java.io.IOException x ) {
log.warn("Unable to send ACK back through channel, channel disconnected?: "+x.getMessage());
}
}
}