/*
* RHQ Management Platform
* Copyright (C) 2005-2008 Red Hat, Inc.
* All rights reserved.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation version 2 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
package org.rhq.enterprise.communications.command.client;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArraySet;
import mazz.i18n.Logger;
import org.rhq.core.util.exception.ThrowableUtil;
import org.rhq.enterprise.communications.command.CommandResponse;
import org.rhq.enterprise.communications.command.impl.identify.IdentifyCommand;
import org.rhq.enterprise.communications.i18n.CommI18NFactory;
import org.rhq.enterprise.communications.i18n.CommI18NResourceKeys;
import org.rhq.enterprise.communications.util.CommUtils;
/**
* An object that runs in a thread whose sole job is to poll the given remote server. When the server's status changes
* (that is, goes down or comes back up), the client sender that owns this thread will be told to stop or start sending
* as appropriate.
*
* @author John Mazzitelli
*/
class ServerPollingThread extends Thread {
/**
* Logger
*/
private static final Logger LOG = CommI18NFactory.getLogger(ServerPollingThread.class);
/**
* The client sender that asked us to poll the server.
*/
private final ClientCommandSender m_clientSender;
/**
* The amount of time in milliseconds that this thread will sleep in between polling the server.
*/
private final long m_interval;
/**
* This is simply a flag to eliminate a flood of log messages that would get dumped each time the server failed to
* be communicated with. We want to warn once in the case the failure is due to a misconfiguration (the log message
* should help diagnose the misconfiguration), but we don't want to continually log warnings in the normal case when
* the server just isn't up yet.
*/
private boolean m_warnedAboutConnectionFailure;
/**
* The list of polling listeners that will be notified when the sender's polling thread polls the server.
*/
private final Set<PollingListener> m_pollingListeners = new CopyOnWriteArraySet<PollingListener>();
/**
* Constructor for {@link ServerPollingThread} making this thread a daemon thread.
*
* @param client the client sender on whose behalf we are polling
* @param polling_interval the amount of time in milliseconds that the thread will pause in between polls
*/
public ServerPollingThread(ClientCommandSender client, long polling_interval) {
super("RHQ Server Polling Thread");
setDaemon(true);
m_clientSender = client;
m_interval = polling_interval;
m_warnedAboutConnectionFailure = false;
}
/**
* @see java.lang.Thread#run()
*/
@Override
public void run() {
LOG.debug(CommI18NResourceKeys.SERVER_POLLING_THREAD_STARTED, m_interval);
// Chapter 7 - Java Concurrency in Practice
// Use interruption to do thread cancellation
try {
while (!isInterrupted()) {
try {
// Send a small, simple identify command to the server and if it succeeds, tell the client
// sender that it is OK to start sending messages, if it is not already sending
IdentifyCommand id_cmd = new IdentifyCommand();
m_clientSender.preprocessCommand(id_cmd);
CommandResponse response = m_clientSender.send(id_cmd);
// let all our listeners know what the results of the poll was
for (PollingListener listener : m_pollingListeners) {
try {
listener.pollResponse(response);
} catch (Throwable t) {
// should never happen, but I'm paranoid
}
}
// there are special cases when we might get a response back but it should be considered "server down".
// 1) when the server replies with a NotProcessedException response
// 2) when our failover mechanism runs out of retries and it can't find a server to process our request,
// the comm layer will reply with a failoverable exception.
// In both cases, our CommUtils will detect this.
if (CommUtils.isExceptionFailoverable(response.getException())) {
throw response.getException();
}
if (m_clientSender.startSending()) {
LOG.info(CommI18NResourceKeys.SERVER_POLLING_THREAD_SERVER_ONLINE);
m_warnedAboutConnectionFailure = false; // if we detect the server is down again, lets log the exception again
}
} catch (InterruptedException e) {
throw e;
} catch (Throwable t) {
// This probably just means that the server isn't online yet
// However, we want to log a warning at least once in case this is a configuration error (in which case
// the connection will never succeed - without this log message, it will be hard to debug the misconfiguration).
if (!m_warnedAboutConnectionFailure) {
m_warnedAboutConnectionFailure = true;
LOG.debug(CommI18NResourceKeys.SERVER_POLL_FAILURE, ThrowableUtil.getAllMessages(t));
}
// Failed to send the command for some reason, make sure the client sender isn't trying to send the server messages.
// Since the server is down, no sense processing commands currently in the queue.
if (m_clientSender.stopSending(false)) {
LOG.warn(CommI18NResourceKeys.SERVER_POLLING_THREAD_SERVER_OFFLINE);
}
}
synchronized (this) {
wait(m_interval); // go to sleep before we poll again
}
}
} catch (InterruptedException e) {
// Thread exiting
}
LOG.debug(CommI18NResourceKeys.SERVER_POLLING_THREAD_STOPPED);
}
/**
* Tells this thread to stop polling. This will block and wait for the thread to die.
*/
public void stopPolling() {
interrupt();
try {
// Not sure why the thread wouldn't die immediately, but you never know
join(m_interval * 2);
} catch (InterruptedException e) {
interrupt();
}
m_pollingListeners.clear();
}
public void addPollingListener(PollingListener listener) {
if (m_pollingListeners.add(listener)) {
LOG.debug(CommI18NResourceKeys.SERVER_POLLING_THREAD_ADDED_POLLING_LISTENER, listener);
}
}
public void removePollingListener(PollingListener listener) {
if (m_pollingListeners.remove(listener)) {
LOG.debug(CommI18NResourceKeys.SERVER_POLLING_THREAD_REMOVED_POLLING_LISTENER, listener);
}
}
}