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/*******************************************************************************
* Copyright (c) 2004, 2007 Boeing.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Boeing - initial API and implementation
*******************************************************************************/
package org.eclipse.osee.framework.jini.lease;
import java.rmi.RemoteException;
import java.util.HashMap;
import java.util.Map;
import java.util.Timer;
import java.util.TimerTask;
import java.util.logging.Level;
import net.jini.core.lease.Lease;
import net.jini.core.lease.LeaseDeniedException;
import net.jini.core.lease.UnknownLeaseException;
import org.eclipse.osee.framework.jini.JiniPlugin;
import org.eclipse.osee.framework.logging.OseeLog;
/**
* This class handles the renewal of leases. It is designed such that a lease will be renewed a set amount of time prior
* to expiration, and handles retrying in cases where the renewal fails. Leases are renewed for the maximum amount of
* time the lease will allow. Retries are be scheduled for half of the remaining lease time. For example, if the first
* attempt to renew occurs with 2 minutes left, the first retry will occur with 1 minute, then 30 seconds, until
* STOP_RETRY_TIME is reached.
*
* @author David Diepenbrock
*/
public class OseeLeaseRenewer {
private Timer timer;
private final Map<OseeLease, Renewer> map;
/**
* The amount of time before a lease expires to first attempt renewal. This amount of time should be sufficiently
* large to account for delays in communication (i.e. network delays), and allow for at least a few retries in the
* event the service is not reachable. This time is specified in milliseconds.
*/
private static final long RENEWAL_TIME = 2 * 60 * 1000; // 2 minutes
/**
* When less than this amount of time is remaining in a lease, failed renewal attempts will not be retried. This time
* is specified in milliseconds.
*/
private static final long STOP_RETRY_TIME = 250; // 250 ms
public OseeLeaseRenewer() {
// debug = new Debug(false, true, this.getClass().getName());
map = new HashMap<OseeLease, Renewer>(4);
}
/**
* Attempts to maintain a lease until cancelRenewal is called
*
* @param lease
*/
public synchronized void startRenewal(OseeLease lease) {
if (timer == null) {
timer = new Timer(true);
}
lease.resetStartTime();
Renewer renewer = new Renewer(lease);
map.put(lease, renewer);
// Pick the larger duration - RENEWAL_TIME before the expiration, or half of the total lease
// time.
long duration = Math.max(lease.getDuration() / 2, lease.getDuration() - RENEWAL_TIME);
timer.schedule(renewer, duration, duration);
}
/**
* Prevents the lease from being renewed. This does not cancel the lease, only the renewal attempts.
*
* @param lease
*/
public synchronized void cancelRenewal(OseeLease lease) {
Renewer renewer = map.remove(lease);
if (renewer != null) {
renewer.cancel();
} else {
OseeLog.log(JiniPlugin.class, Level.WARNING,
this.getClass().getName() + ": Lease Cancel Attempt: Lease Not Found!");
}
if (map.isEmpty()) {
timer.cancel();
timer = null;
}
}
private class Renewer extends TimerTask {
private final OseeLease lease;
public Renewer(OseeLease lease) {
super();
this.lease = lease;
}
@Override
public void run() {
try {
// Obtain the longest lease allowed
lease.renew(Lease.FOREVER);
} catch (LeaseDeniedException ex) {
OseeLog.log(JiniPlugin.class, Level.SEVERE, ex);
} catch (UnknownLeaseException ex) {
OseeLog.log(JiniPlugin.class, Level.SEVERE, ex);
}
/*
* If there was a problem with the lease renewal, retry up until there is less than 250 ms
* remaining in the lease, at which point we can give up hope. Assuming leases are renewed
* with 2 minutes remaining & 250 ms for STOP_RETRY_TIME, this will provide 8 attempts.
*/
catch (RemoteException ex) {
long remainingTime = lease.getExpiration() - System.currentTimeMillis();
if (remainingTime > STOP_RETRY_TIME) {
timer.schedule(new Renewer(lease), remainingTime / 2);
} else {
// debug.report("Canceling Renewals Retries");
cancelRenewal(lease);
OseeLog.log(JiniPlugin.class, Level.SEVERE, "Unable to renew lease.", ex);
}
}
}
}
}
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