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/*
* Copyright 2007 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the LICENSE file that accompanied this code.
*
* This code 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
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*/
package com.sun.jmx.event;
import com.sun.jmx.remote.util.ClassLogger;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
/**
* <p>Manage a renewable lease. The lease can be renewed indefinitely
* but if the lease runs to its current expiry date without being renewed
* then the expiry callback is invoked. If the lease has already expired
* when renewal is attempted then the lease method returns zero.</p>
* @author sjiang
* @author emcmanus
*/
// The synchronization logic of this class is tricky to deal correctly with the
// case where the lease expires at the same time as the |lease| or |stop| method
// is called. If the lease is active then the field |scheduled| represents
// the expiry task; otherwise |scheduled| is null. Renewing or stopping the
// lease involves canceling this task and setting |scheduled| either to a new
// task (to renew) or to null (to stop).
//
// Suppose the expiry task runs at the same time as the |lease| method is called.
// If the task enters its synchronized block before the method starts, then
// it will set |scheduled| to null and the method will return 0. If the method
// starts before the task enters its synchronized block, then the method will
// cancel the task which will see that when it later enters the block.
// Similar reasoning applies to the |stop| method. It is not expected that
// different threads will call |lease| or |stop| simultaneously, although the
// logic should be correct then too.
public class LeaseManager {
public LeaseManager(Runnable callback) {
this(callback, EventParams.getLeaseTimeout());
}
public LeaseManager(Runnable callback, long timeout) {
if (logger.traceOn()) {
logger.trace("LeaseManager", "new manager with lease: "+timeout);
}
if (callback == null) {
throw new NullPointerException("Null callback.");
}
if (timeout <= 0)
throw new IllegalArgumentException("Timeout must be positive: " + timeout);
this.callback = callback;
schedule(timeout);
}
/**
* <p>Renew the lease for the given time. The new time can be shorter
* than the previous one, in which case the lease will expire earlier
* than it would have.</p>
*
* <p>Calling this method after the lease has expired will return zero
* immediately and have no other effect.</p>
*
* @param timeout the new lifetime. If zero, the lease
* will expire immediately.
*/
public synchronized long lease(long timeout) {
if (logger.traceOn()) {
logger.trace("lease", "new lease to: "+timeout);
}
if (timeout < 0)
throw new IllegalArgumentException("Negative lease: " + timeout);
if (scheduled == null)
return 0L;
scheduled.cancel(false);
if (logger.traceOn())
logger.trace("lease", "start lease: "+timeout);
schedule(timeout);
return timeout;
}
private class Expire implements Runnable {
ScheduledFuture<?> task;
public void run() {
synchronized (LeaseManager.this) {
if (task.isCancelled())
return;
scheduled = null;
}
callback.run();
executor.shutdown();
}
}
private synchronized void schedule(long timeout) {
Expire expire = new Expire();
scheduled = executor.schedule(expire, timeout, TimeUnit.MILLISECONDS);
expire.task = scheduled;
}
/**
* <p>Cancel the lease without calling the expiry callback.</p>
*/
public synchronized void stop() {
logger.trace("stop", "canceling lease");
scheduled.cancel(false);
scheduled = null;
try {
executor.shutdown();
} catch (SecurityException e) {
// OK: caller doesn't have RuntimePermission("modifyThread")
// which is unlikely in reality but triggers a test failure otherwise
logger.trace("stop", "exception from executor.shutdown", e);
}
}
private final Runnable callback;
private ScheduledFuture scheduled; // If null, the lease has expired.
private final ScheduledExecutorService executor
= Executors.newScheduledThreadPool(1,
new DaemonThreadFactory("JMX LeaseManager %d"));
private static final ClassLogger logger =
new ClassLogger("javax.management.event", "LeaseManager");
}
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