package org.apache.jcs.auxiliary.lateral;
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
import java.util.Iterator;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.jcs.auxiliary.lateral.behavior.ILateralCacheManager;
import org.apache.jcs.engine.CacheConstants;
/**
* Used to monitor and repair any failed connection for the lateral cache
* service. By default the monitor operates in a failure driven mode. That is,
* it goes into a wait state until there is an error. Upon the notification of a
* connection error, the monitor changes to operate in a time driven mode. That
* is, it attempts to recover the connections on a periodic basis. When all
* failed connections are restored, it changes back to the failure driven mode.
*
*/
public class LateralCacheMonitor
implements Runnable
{
private final static Log log = LogFactory.getLog( LateralCacheMonitor.class );
private static long idlePeriod = 20 * 1000;
// minimum 20 seconds.
//private static long idlePeriod = 3*1000; // for debugging.
// Must make sure LateralCacheMonitor is started before any lateral error
// can be detected!
private boolean alright = true;
private final static int ERROR = 1;
private static int mode = ERROR;
private ILateralCacheManager manager;
/**
* Configures the idle period between repairs.
*
* @param idlePeriod
* The new idlePeriod value
*/
public static void setIdlePeriod( long idlePeriod )
{
if ( idlePeriod > LateralCacheMonitor.idlePeriod )
{
LateralCacheMonitor.idlePeriod = idlePeriod;
}
}
/**
* Allows close classes, ie testers to set the idle period to something
* testable.
*
* @param idlePeriod
*/
protected static void forceShortIdlePeriod( long idlePeriod )
{
LateralCacheMonitor.idlePeriod = idlePeriod;
}
/** Constructor for the LateralCacheMonitor object
* <p>
* It's the clients responsibility to decide how many
* of these there will be.
*
* @param manager
*/
public LateralCacheMonitor( ILateralCacheManager manager )
{
this.manager = manager;
}
/**
* Notifies the cache monitor that an error occurred, and kicks off the
* error recovery process.
*/
public void notifyError()
{
bad();
synchronized ( this )
{
notify();
}
}
/**
* Main processing method for the LateralCacheMonitor object
*/
public void run()
{
do
{
if ( mode == ERROR )
{
if ( log.isDebugEnabled() )
{
if ( alright )
{
log.debug( "ERROR DRIVEN MODE: alright = " + alright
+ ", connection monitor will wait for an error." );
}
else
{
log.debug( "ERROR DRIVEN MODE: alright = " + alright + " connection monitor running." );
}
}
if ( alright )
{
synchronized ( this )
{
if ( alright )
{
// Failure driven mode.
try
{
wait();
// wake up only if there is an error.
}
catch ( InterruptedException ignore )
{
//no op, this is expected
}
}
}
}
}
else
{
log.debug( "TIME DRIVEN MODE: connection monitor will sleep for " + idlePeriod + " after this run." );
// Time driven mode: sleep between each round of recovery
// attempt.
// will need to test not just check status
}
// The "alright" flag must be false here.
// Simply presume we can fix all the errors until proven otherwise.
synchronized ( this )
{
alright = true;
}
if ( log.isDebugEnabled() )
{
log.debug( "Cache monitor running." );
}
// Monitor each LateralCacheManager instance one after the other.
// Each LateralCacheManager corresponds to one lateral connection.
log.info( "LateralCacheManager.instances.size() = " + manager.getInstances().size() );
//for
int cnt = 0;
Iterator itr = manager.getInstances().values().iterator();
while ( itr.hasNext() )
{
cnt++;
ILateralCacheManager mgr = (ILateralCacheManager) itr.next();
try
{
// If any cache is in error, it strongly suggests all caches
// managed by the
// same LateralCacheManager instance are in error. So we fix
// them once and for all.
//for
//log.info( "\n " + cnt + "- mgr.lca.getTcpServer() = " + mgr.lca.getTcpServer() + " mgr = " + mgr );
log.info( "\n " + cnt + "- mgr.getCaches().size() = " + mgr.getCaches().size() );
if ( mgr.getCaches().size() == 0 )
{
// there is probably a problem.
// monitor may be running when we just started up and
// there
// is not a cache yet.
// if this is error driven mode, mark as bad,
// otherwise we will come back around argain.
if ( mode == ERROR )
{
bad();
}
}
Iterator itr2 = mgr.getCaches().values().iterator();
while ( itr2.hasNext() )
{
LateralCacheNoWait c = (LateralCacheNoWait) itr2.next();
if ( c.getStatus() == CacheConstants.STATUS_ERROR )
{
log.info( "found LateralCacheNoWait in error, " + c.toString() );
LateralCacheRestore repairer = new LateralCacheRestore( mgr );
// If we can't fix them, just skip and re-try in the
// next round.
if ( repairer.canFix() )
{
repairer.fix();
}
else
{
bad();
}
//break;
}
else
{
log.info( "Lateral Cache No Wait not in error" );
}
}
}
catch ( Exception ex )
{
bad();
// Problem encountered in fixing the caches managed by a
// LateralCacheManager instance.
// Soldier on to the next LateralCacheManager instance.
log.error( "Problem encountered in fixing the caches", ex );
}
}
try
{
// don't want to sleep after waking from an error
// run immediately and sleep here.
if ( log.isDebugEnabled() )
{
log.debug( "Lateral cache monitor sleeping for " + idlePeriod + " between runs." );
}
Thread.sleep( idlePeriod );
}
catch ( InterruptedException ex )
{
// ignore;
}
}
while ( true );
}
/**
* Sets the "alright" flag to false in a critial section.
*/
private void bad()
{
if ( alright )
{
synchronized ( this )
{
alright = false;
}
}
}
}