/**
* Copyright 2007 The Apache Software Foundation
*
* 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.
*/
package org.apache.hadoop.hbase.regionserver;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import java.util.ConcurrentModificationException;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.Delayed;
import java.util.concurrent.DelayQueue;
import java.util.concurrent.TimeUnit;
import java.io.IOException;
/**
* Leases
*
* There are several server classes in HBase that need to track external
* clients that occasionally send heartbeats.
*
* <p>These external clients hold resources in the server class.
* Those resources need to be released if the external client fails to send a
* heartbeat after some interval of time passes.
*
* <p>The Leases class is a general reusable class for this kind of pattern.
* An instance of the Leases class will create a thread to do its dirty work.
* You should close() the instance if you want to clean up the thread properly.
*
* <p>
* NOTE: This class extends Thread rather than Chore because the sleep time
* can be interrupted when there is something to do, rather than the Chore
* sleep time which is invariant.
*/
public class Leases extends Thread {
private static final Log LOG = LogFactory.getLog(Leases.class.getName());
private final int leasePeriod;
private final int leaseCheckFrequency;
private volatile DelayQueue<Lease> leaseQueue = new DelayQueue<Lease>();
protected final Map<String, Lease> leases = new HashMap<String, Lease>();
private volatile boolean stopRequested = false;
/**
* Creates a lease monitor
*
* @param leasePeriod - length of time (milliseconds) that the lease is valid
* @param leaseCheckFrequency - how often the lease should be checked
* (milliseconds)
*/
public Leases(final int leasePeriod, final int leaseCheckFrequency) {
this.leasePeriod = leasePeriod;
this.leaseCheckFrequency = leaseCheckFrequency;
setDaemon(true);
}
/**
* @see java.lang.Thread#run()
*/
@Override
public void run() {
while (!stopRequested || (stopRequested && leaseQueue.size() > 0) ) {
Lease lease = null;
try {
lease = leaseQueue.poll(leaseCheckFrequency, TimeUnit.MILLISECONDS);
} catch (InterruptedException e) {
continue;
} catch (ConcurrentModificationException e) {
continue;
} catch (Throwable e) {
LOG.fatal("Unexpected exception killed leases thread", e);
break;
}
if (lease == null) {
continue;
}
// A lease expired. Run the expired code before removing from queue
// since its presence in queue is used to see if lease exists still.
if (lease.getListener() == null) {
LOG.error("lease listener is null for lease " + lease.getLeaseName());
} else {
lease.getListener().leaseExpired();
}
synchronized (leaseQueue) {
leases.remove(lease.getLeaseName());
}
}
close();
}
/**
* Shuts down this lease instance when all outstanding leases expire.
* Like {@link #close()} but rather than violently end all leases, waits
* first on extant leases to finish. Use this method if the lease holders
* could loose data, leak locks, etc. Presumes client has shutdown
* allocation of new leases.
*/
public void closeAfterLeasesExpire() {
this.stopRequested = true;
}
/**
* Shut down this Leases instance. All pending leases will be destroyed,
* without any cancellation calls.
*/
public void close() {
LOG.info(Thread.currentThread().getName() + " closing leases");
this.stopRequested = true;
synchronized (leaseQueue) {
leaseQueue.clear();
leases.clear();
leaseQueue.notifyAll();
}
LOG.info(Thread.currentThread().getName() + " closed leases");
}
/**
* Obtain a lease
*
* @param leaseName name of the lease
* @param listener listener that will process lease expirations
* @throws LeaseStillHeldException
*/
public void createLease(String leaseName, final LeaseListener listener)
throws LeaseStillHeldException {
if (stopRequested) {
return;
}
Lease lease = new Lease(leaseName, listener,
System.currentTimeMillis() + leasePeriod);
synchronized (leaseQueue) {
if (leases.containsKey(leaseName)) {
throw new LeaseStillHeldException(leaseName);
}
leases.put(leaseName, lease);
leaseQueue.add(lease);
}
}
/**
* Thrown if we are asked create a lease but lease on passed name already
* exists.
*/
@SuppressWarnings("serial")
public static class LeaseStillHeldException extends IOException {
private final String leaseName;
/**
* @param name
*/
public LeaseStillHeldException(final String name) {
this.leaseName = name;
}
/** @return name of lease */
public String getName() {
return this.leaseName;
}
}
/**
* Renew a lease
*
* @param leaseName name of lease
* @throws LeaseException
*/
public void renewLease(final String leaseName) throws LeaseException {
synchronized (leaseQueue) {
Lease lease = leases.get(leaseName);
// We need to check to see if the remove is successful as the poll in the run()
// method could have completed between the get and the remove which will result
// in a corrupt leaseQueue.
if (lease == null || !leaseQueue.remove(lease)) {
throw new LeaseException("lease '" + leaseName +
"' does not exist or has already expired");
}
lease.setExpirationTime(System.currentTimeMillis() + leasePeriod);
leaseQueue.add(lease);
}
}
/**
* Client explicitly cancels a lease.
*
* @param leaseName name of lease
* @throws LeaseException
*/
public void cancelLease(final String leaseName) throws LeaseException {
synchronized (leaseQueue) {
Lease lease = leases.remove(leaseName);
if (lease == null) {
throw new LeaseException("lease '" + leaseName + "' does not exist");
}
leaseQueue.remove(lease);
}
}
/** This class tracks a single Lease. */
private static class Lease implements Delayed {
private final String leaseName;
private final LeaseListener listener;
private long expirationTime;
Lease(final String leaseName, LeaseListener listener, long expirationTime) {
this.leaseName = leaseName;
this.listener = listener;
this.expirationTime = expirationTime;
}
/** @return the lease name */
public String getLeaseName() {
return leaseName;
}
/** @return listener */
public LeaseListener getListener() {
return this.listener;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
return this.hashCode() == ((Lease) obj).hashCode();
}
@Override
public int hashCode() {
return this.leaseName.hashCode();
}
public long getDelay(TimeUnit unit) {
return unit.convert(this.expirationTime - System.currentTimeMillis(),
TimeUnit.MILLISECONDS);
}
public int compareTo(Delayed o) {
long delta = this.getDelay(TimeUnit.MILLISECONDS) -
o.getDelay(TimeUnit.MILLISECONDS);
return this.equals(o) ? 0 : (delta > 0 ? 1 : -1);
}
/** @param expirationTime the expirationTime to set */
public void setExpirationTime(long expirationTime) {
this.expirationTime = expirationTime;
}
/**
* Get the expiration time for that lease
* @return expiration time
*/
public long getExpirationTime() {
return this.expirationTime;
}
}
}