/**
    *
    * 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 org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
  import org.apache.hadoop.hbase.util.HasThread;
  
  import java.util.ConcurrentModificationException;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.Delayed;
  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.
   */
  @InterfaceAudience.Private
  public class Leases extends HasThread {
    private static final Log LOG = LogFactory.getLog(Leases.class.getName());
    public static final int MIN_WAIT_TIME = 100;
    private final Map<String, Lease> leases = new ConcurrentHashMap<String, Lease>();
  
    protected final int leaseCheckFrequency;
    protected volatile boolean stopRequested = false;
  
    /**
     * Creates a lease monitor
     * 
     * @param leaseCheckFrequency - how often the lease should be checked
     *          (milliseconds)
     */
    public Leases(final int leaseCheckFrequency) {
      super("RegionServerLeases");  // thread name
      this.leaseCheckFrequency = leaseCheckFrequency;
      setDaemon(true);
    }
  
    /**
     * @see Thread#run()
     */
    @Override
    public void run() {
      long toWait = leaseCheckFrequency;
      Lease nextLease = null;
      long nextLeaseDelay = Long.MAX_VALUE;
  
      while (!stopRequested || (stopRequested && !leases.isEmpty()) ) {
  
        try {
          if (nextLease != null) {
            toWait = nextLease.getDelay(TimeUnit.MILLISECONDS);
          }
  
          toWait = Math.min(leaseCheckFrequency, toWait);
          toWait = Math.max(MIN_WAIT_TIME, toWait);
  
          Thread.sleep(toWait);
        } catch (InterruptedException e) {
          continue;
        } catch (ConcurrentModificationException e) {
          continue;
       } catch (Throwable e) {
         LOG.fatal("Unexpected exception killed leases thread", e);
         break;
       }
 
       nextLease = null;
       nextLeaseDelay = Long.MAX_VALUE;
       for (Iterator<Map.Entry<String, Lease>> it = leases.entrySet().iterator(); it.hasNext();) {
         Map.Entry<String, Lease> entry = it.next();
         Lease lease = entry.getValue();
         long thisLeaseDelay = lease.getDelay(TimeUnit.MILLISECONDS);
         if ( thisLeaseDelay > 0) {
           if (nextLease == null || thisLeaseDelay < nextLeaseDelay) {
             nextLease = lease;
             nextLeaseDelay = thisLeaseDelay;
           }
         } else {
           // A lease expired.  Run the expired code before removing from map
           // since its presence in map 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();
           }
           it.remove();
         }
       }
     }
     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 lose 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;
     leases.clear();
     LOG.info(Thread.currentThread().getName() + " closed leases");
   }
 
   /**
    * Create a lease and insert it to the map of leases.
    *
    * @param leaseName name of the lease
    * @param leaseTimeoutPeriod length of the lease in milliseconds
    * @param listener listener that will process lease expirations
    * @throws LeaseStillHeldException
    */
   public void createLease(String leaseName, int leaseTimeoutPeriod, final LeaseListener listener)
       throws LeaseStillHeldException {
     addLease(new Lease(leaseName, leaseTimeoutPeriod, listener));
   }
 
   /**
    * Inserts lease.  Resets expiration before insertion.
    * @param lease
    * @throws LeaseStillHeldException
    */
   public void addLease(final Lease lease) throws LeaseStillHeldException {
     if (this.stopRequested) {
       return;
     }
     if (leases.containsKey(lease.getLeaseName())) {
       throw new LeaseStillHeldException(lease.getLeaseName());
     }
     lease.resetExpirationTime();
     leases.put(lease.getLeaseName(), lease);
   }
 
   /**
    * Renew a lease
    *
    * @param leaseName name of lease
    * @throws LeaseException
    */
   public void renewLease(final String leaseName) throws LeaseException {
     if (this.stopRequested) {
       return;
     }
     Lease lease = leases.get(leaseName);
 
     if (lease == null ) {
       throw new LeaseException("lease '" + leaseName +
           "' does not exist or has already expired");
     }
     lease.resetExpirationTime();
   }
 
   /**
    * Client explicitly cancels a lease.
    * @param leaseName name of lease
    * @throws org.apache.hadoop.hbase.regionserver.LeaseException
    */
   public void cancelLease(final String leaseName) throws LeaseException {
     removeLease(leaseName);
   }
 
   /**
    * Remove named lease.
    * Lease is removed from the map of leases.
    * Lease can be reinserted using {@link #addLease(Lease)}
    *
    * @param leaseName name of lease
    * @throws org.apache.hadoop.hbase.regionserver.LeaseException
    * @return Removed lease
    */
   Lease removeLease(final String leaseName) throws LeaseException {
     Lease lease = leases.remove(leaseName);
     if (lease == null) {
       throw new LeaseException("lease '" + leaseName + "' does not exist");
     }
     return lease;
   }
 
   /**
    * Thrown if we are asked to 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;
     }
   }
 
   /** This class tracks a single Lease. */
   static class Lease implements Delayed {
     private final String leaseName;
     private final LeaseListener listener;
     private int leaseTimeoutPeriod;
     private long expirationTime;
 
     Lease(final String leaseName, int leaseTimeoutPeriod, LeaseListener listener) {
       this.leaseName = leaseName;
       this.listener = listener;
       this.leaseTimeoutPeriod = leaseTimeoutPeriod;
       this.expirationTime = 0;
     }
 
     /** @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() == obj.hashCode();
     }
 
     @Override
     public int hashCode() {
       return this.leaseName.hashCode();
     }
 
     public long getDelay(TimeUnit unit) {
       return unit.convert(this.expirationTime - EnvironmentEdgeManager.currentTime(),
           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);
     }
 
     /**
      * Resets the expiration time of the lease.
      */
     public void resetExpirationTime() {
       this.expirationTime = EnvironmentEdgeManager.currentTime() + this.leaseTimeoutPeriod;
     }
   }
 }