/**
    * 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.master;
  
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.TreeMap;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HTableDescriptor;
  import org.apache.hadoop.hbase.MetaTableAccessor;
  import org.apache.hadoop.hbase.RegionTransition;
  import org.apache.hadoop.hbase.ServerLoad;
  import org.apache.hadoop.hbase.ServerName;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.TableStateManager;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.client.RegionReplicaUtil;
  import org.apache.hadoop.hbase.master.RegionState.State;
  import org.apache.hadoop.hbase.protobuf.generated.ZooKeeperProtos;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.ConfigUtil;
  import org.apache.hadoop.hbase.util.FSUtils;
  import org.apache.hadoop.hbase.util.Pair;
  import org.apache.hadoop.hbase.zookeeper.ZKAssign;
  import org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher;
  import org.apache.zookeeper.KeeperException;
  
  import com.google.common.annotations.VisibleForTesting;
  import com.google.common.base.Preconditions;
  
  /**
   * Region state accountant. It holds the states of all regions in the memory.
   * In normal scenario, it should match the meta table and the true region states.
   *
   * This map is used by AssignmentManager to track region states.
   */
  @InterfaceAudience.Private
  public class RegionStates {
    private static final Log LOG = LogFactory.getLog(RegionStates.class);
  
    /**
     * Regions currently in transition.
     */
    final HashMap<String, RegionState> regionsInTransition =
      new HashMap<String, RegionState>();
  
    /**
     * Region encoded name to state map.
     * All the regions should be in this map.
     */
    private final Map<String, RegionState> regionStates =
      new HashMap<String, RegionState>();
  
    /**
     * Holds mapping of table -> region state
     */
    private final Map<TableName, Map<String, RegionState>> regionStatesTableIndex =
        new HashMap<TableName, Map<String, RegionState>>();
  
    /**
     * Server to regions assignment map.
     * Contains the set of regions currently assigned to a given server.
     */
    private final Map<ServerName, Set<HRegionInfo>> serverHoldings =
      new HashMap<ServerName, Set<HRegionInfo>>();
  
    /**
     * Maintains the mapping from the default region to the replica regions.
     */
    private final Map<HRegionInfo, Set<HRegionInfo>> defaultReplicaToOtherReplicas =
      new HashMap<HRegionInfo, Set<HRegionInfo>>();
  
   /**
    * Region to server assignment map.
    * Contains the server a given region is currently assigned to.
    */
   private final TreeMap<HRegionInfo, ServerName> regionAssignments =
     new TreeMap<HRegionInfo, ServerName>();
 
   /**
    * Encoded region name to server assignment map for re-assignment
    * purpose. Contains the server a given region is last known assigned
    * to, which has not completed log splitting, so not assignable.
    * If a region is currently assigned, this server info in this
    * map should be the same as that in regionAssignments.
    * However the info in regionAssignments is cleared when the region
    * is offline while the info in lastAssignments is cleared when
    * the region is closed or the server is dead and processed.
    */
   private final HashMap<String, ServerName> lastAssignments =
     new HashMap<String, ServerName>();
 
   /**
    * Encoded region name to server assignment map for the
    * purpose to clean up serverHoldings when a region is online
    * on a new server. When the region is offline from the previous
    * server, we cleaned up regionAssignments so that it has the
    * latest assignment map. But we didn't clean up serverHoldings
    * to match the meta. We need this map to find out the old server
    * whose serverHoldings needs cleanup, given a moved region.
    */
   private final HashMap<String, ServerName> oldAssignments =
     new HashMap<String, ServerName>();
 
   /**
    * Map a host port pair string to the latest start code
    * of a region server which is known to be dead. It is dead
    * to us, but server manager may not know it yet.
    */
   private final HashMap<String, Long> deadServers =
     new HashMap<String, Long>();
 
   /**
    * Map a dead servers to the time when log split is done.
    * Since log splitting is not ordered, we have to remember
    * all processed instances. The map is cleaned up based
    * on a configured time. By default, we assume a dead
    * server should be done with log splitting in two hours.
    */
   private final HashMap<ServerName, Long> processedServers =
     new HashMap<ServerName, Long>();
   private long lastProcessedServerCleanTime;
 
   private final TableStateManager tableStateManager;
   private final RegionStateStore regionStateStore;
   private final ServerManager serverManager;
   private final MasterServices server;
   private final boolean useZK; // Is it ZK based assignment?
 
   // The maximum time to keep a log split info in region states map
   static final String LOG_SPLIT_TIME = "hbase.master.maximum.logsplit.keeptime";
   static final long DEFAULT_LOG_SPLIT_TIME = 7200000L; // 2 hours
 
   RegionStates(final MasterServices master, final TableStateManager tableStateManager,
       final ServerManager serverManager, final RegionStateStore regionStateStore) {
     this.tableStateManager = tableStateManager;
     this.regionStateStore = regionStateStore;
     this.serverManager = serverManager;
     this.server = master;
     this.useZK = ConfigUtil.useZKForAssignment(server.getConfiguration());
   }
 
   /**
    * @return a copy of the region assignment map
    */
   public synchronized Map<HRegionInfo, ServerName> getRegionAssignments() {
     return new TreeMap<HRegionInfo, ServerName>(regionAssignments);
   }
 
   /**
    * Return the replicas (including default) for the regions grouped by ServerName
    * @param regions
    * @return a pair containing the groupings as a map
    */
   synchronized Map<ServerName, List<HRegionInfo>> getRegionAssignments(
     Collection<HRegionInfo> regions) {
     Map<ServerName, List<HRegionInfo>> map = new HashMap<ServerName, List<HRegionInfo>>();
     for (HRegionInfo region : regions) {
       HRegionInfo defaultReplica = RegionReplicaUtil.getRegionInfoForDefaultReplica(region);
       Set<HRegionInfo> allReplicas = defaultReplicaToOtherReplicas.get(defaultReplica);
       if (allReplicas != null) {
         for (HRegionInfo hri : allReplicas) {
           ServerName server = regionAssignments.get(hri);
           if (server != null) {
             List<HRegionInfo> regionsOnServer = map.get(server);
             if (regionsOnServer == null) {
               regionsOnServer = new ArrayList<HRegionInfo>(1);
               map.put(server, regionsOnServer);
             }
             regionsOnServer.add(hri);
           }
         }
       }
     }
     return map;
   }
 
   public synchronized ServerName getRegionServerOfRegion(HRegionInfo hri) {
     return regionAssignments.get(hri);
   }
 
   /**
    * Get regions in transition and their states
    */
   @SuppressWarnings("unchecked")
   public synchronized Map<String, RegionState> getRegionsInTransition() {
     return (Map<String, RegionState>)regionsInTransition.clone();
   }
 
   /**
    * @return True if specified region in transition.
    */
   public synchronized boolean isRegionInTransition(final HRegionInfo hri) {
     return regionsInTransition.containsKey(hri.getEncodedName());
   }
 
   /**
    * @return True if specified region in transition.
    */
   public synchronized boolean isRegionInTransition(final String encodedName) {
     return regionsInTransition.containsKey(encodedName);
   }
 
   /**
    * @return True if any region in transition.
    */
   public synchronized boolean isRegionsInTransition() {
     return !regionsInTransition.isEmpty();
   }
 
   /**
    * @return True if hbase:meta table region is in transition.
    */
   public synchronized boolean isMetaRegionInTransition() {
     for (RegionState state : regionsInTransition.values()) {
       if (state.getRegion().isMetaRegion()) return true;
     }
     return false;
   }
 
   /**
    * @return True if specified region assigned, and not in transition.
    */
   public synchronized boolean isRegionOnline(final HRegionInfo hri) {
     return !isRegionInTransition(hri) && regionAssignments.containsKey(hri);
   }
 
   /**
    * @return True if specified region offline/closed, but not in transition.
    * If the region is not in the map, it is offline to us too.
    */
   public synchronized boolean isRegionOffline(final HRegionInfo hri) {
     return getRegionState(hri) == null || (!isRegionInTransition(hri)
       && isRegionInState(hri, State.OFFLINE, State.CLOSED));
   }
 
   /**
    * @return True if specified region is in one of the specified states.
    */
   public boolean isRegionInState(
       final HRegionInfo hri, final State... states) {
     return isRegionInState(hri.getEncodedName(), states);
   }
 
   /**
    * @return True if specified region is in one of the specified states.
    */
   public boolean isRegionInState(
       final String encodedName, final State... states) {
     RegionState regionState = getRegionState(encodedName);
     return isOneOfStates(regionState, states);
   }
 
   /**
    * Wait for the state map to be updated by assignment manager.
    */
   public synchronized void waitForUpdate(
       final long timeout) throws InterruptedException {
     this.wait(timeout);
   }
 
   /**
    * Get region transition state
    */
   public RegionState getRegionTransitionState(final HRegionInfo hri) {
     return getRegionTransitionState(hri.getEncodedName());
   }
 
   /**
    * Get region transition state
    */
   public synchronized RegionState
       getRegionTransitionState(final String encodedName) {
     return regionsInTransition.get(encodedName);
   }
 
   /**
    * Add a list of regions to RegionStates. If a region is split
    * and offline, its state will be SPLIT. Otherwise, its state will
    * be OFFLINE. Region already in RegionStates will be skipped.
    */
   public void createRegionStates(
       final List<HRegionInfo> hris) {
     for (HRegionInfo hri: hris) {
       createRegionState(hri);
     }
   }
 
   /**
    * Add a region to RegionStates. If the region is split
    * and offline, its state will be SPLIT. Otherwise, its state will
    * be OFFLINE. If it is already in RegionStates, this call has
    * no effect, and the original state is returned.
    */
   public RegionState createRegionState(final HRegionInfo hri) {
     return createRegionState(hri, null, null, null);
   }
 
   /**
    * Add a region to RegionStates with the specified state.
    * If the region is already in RegionStates, this call has
    * no effect, and the original state is returned.
    *
    * @param hri the region info to create a state for
    * @param newState the state to the region in set to
    * @param serverName the server the region is transitioning on
    * @param lastHost the last server that hosts the region
    * @return the current state
    */
   public synchronized RegionState createRegionState(final HRegionInfo hri,
       State newState, ServerName serverName, ServerName lastHost) {
     if (newState == null || (newState == State.OPEN && serverName == null)) {
       newState =  State.OFFLINE;
     }
     if (hri.isOffline() && hri.isSplit()) {
       newState = State.SPLIT;
       serverName = null;
     }
     String encodedName = hri.getEncodedName();
     RegionState regionState = regionStates.get(encodedName);
     if (regionState != null) {
       LOG.warn("Tried to create a state for a region already in RegionStates, "
         + "used existing: " + regionState + ", ignored new: " + newState);
     } else {
       regionState = new RegionState(hri, newState, serverName);
       putRegionState(regionState);
       if (newState == State.OPEN) {
         if (!serverName.equals(lastHost)) {
           LOG.warn("Open region's last host " + lastHost
             + " should be the same as the current one " + serverName
             + ", ignored the last and used the current one");
           lastHost = serverName;
         }
         lastAssignments.put(encodedName, lastHost);
         regionAssignments.put(hri, lastHost);
       } else if (!regionState.isUnassignable()) {
         regionsInTransition.put(encodedName, regionState);
       }
       if (lastHost != null && newState != State.SPLIT) {
         addToReplicaMapping(hri);
         addToServerHoldings(lastHost, hri);
         if (newState != State.OPEN) {
           oldAssignments.put(encodedName, lastHost);
         }
       }
     }
     return regionState;
   }
 
   private RegionState putRegionState(RegionState regionState) {
     HRegionInfo hri = regionState.getRegion();
     String encodedName = hri.getEncodedName();
     TableName table = hri.getTable();
     RegionState oldState = regionStates.put(encodedName, regionState);
     Map<String, RegionState> map = regionStatesTableIndex.get(table);
     if (map == null) {
       map = new HashMap<String, RegionState>();
       regionStatesTableIndex.put(table, map);
     }
     map.put(encodedName, regionState);
     return oldState;
   }
 
   /**
    * Set the region state to CLOSED
    */
   public RegionState setRegionStateTOCLOSED(
       final byte[] regionName,
       final ServerName serverName) {
     HRegionInfo regionInfo = getRegionInfo(regionName);
     return setRegionStateTOCLOSED(regionInfo, serverName);
   }
 
   /**
    * Set the region state to CLOSED
    */
   public RegionState setRegionStateTOCLOSED(
       final HRegionInfo regionInfo,
       final ServerName serverName) {
     ServerName sn = serverName;
     if (sn == null) {
       RegionState regionState = getRegionState(regionInfo.getEncodedName());
       if (regionState != null) {
         sn = regionState.getServerName();
       }
       // TODO: if sn is null, should we dig into
       // lastAssignments.get(regionInfo.getEncodedName() to get the server name?
       // For now, I just keep the same logic that works in the past
     }
     // We have to make sure that the last region server is set to be the same as the
     // current RS.  If we don't do that, we could run into situation that both AM and SSH
     // think other would do the assignment work; at the end, neither does the work and
     // region remains RIT.
     // See HBASE-13330 and HBASE-17023
     setLastRegionServerOfRegion(sn, regionInfo.getEncodedName());
     return updateRegionState(regionInfo, State.CLOSED, sn);
   }
 
   /**
    * Update a region state. It will be put in transition if not already there.
    */
   public RegionState updateRegionState(
       final HRegionInfo hri, final State state) {
     RegionState regionState = getRegionState(hri.getEncodedName());
     return updateRegionState(hri, state,
       regionState == null ? null : regionState.getServerName());
   }
 
   /**
    * Update a region state. It will be put in transition if not already there.
    *
    * If we can't find the region info based on the region name in
    * the transition, log a warning and return null.
    */
   public RegionState updateRegionState(
       final RegionTransition transition, final State state) {
     byte [] regionName = transition.getRegionName();
     HRegionInfo regionInfo = getRegionInfo(regionName);
     if (regionInfo == null) {
       String prettyRegionName = HRegionInfo.prettyPrint(
         HRegionInfo.encodeRegionName(regionName));
       LOG.warn("Failed to find region " + prettyRegionName
         + " in updating its state to " + state
         + " based on region transition " + transition);
       return null;
     }
     return updateRegionState(regionInfo, state,
       transition.getServerName());
   }
 
   /**
    * Transition a region state to OPEN from OPENING/PENDING_OPEN
    */
   public synchronized RegionState transitionOpenFromPendingOpenOrOpeningOnServer(
       final RegionTransition transition, final RegionState fromState, final ServerName sn) {
     if(fromState.isPendingOpenOrOpeningOnServer(sn)){
       return updateRegionState(transition, State.OPEN);
     }
     return null;
   }
 
   /**
    * Update a region state. It will be put in transition if not already there.
    */
   public RegionState updateRegionState(
       final HRegionInfo hri, final State state, final ServerName serverName) {
     return updateRegionState(hri, state, serverName, HConstants.NO_SEQNUM);
   }
 
   public void regionOnline(final HRegionInfo hri, final ServerName serverName) {
     regionOnline(hri, serverName, HConstants.NO_SEQNUM);
   }
 
   /**
    * A region is online, won't be in transition any more.
    * We can't confirm it is really online on specified region server
    * because it hasn't been put in region server's online region list yet.
    */
   public void regionOnline(final HRegionInfo hri, final ServerName serverName, long openSeqNum) {
     String encodedName = hri.getEncodedName();
     if (!serverManager.isServerOnline(serverName)) {
       // This is possible if the region server dies before master gets a
       // chance to handle ZK event in time. At this time, if the dead server
       // is already processed by SSH, we should ignore this event.
       // If not processed yet, ignore and let SSH deal with it.
       LOG.warn("Ignored, " + encodedName + " was opened on a dead server: " + serverName);
       return;
     }
     updateRegionState(hri, State.OPEN, serverName, openSeqNum);
 
     synchronized (this) {
       RegionState regionState = regionsInTransition.remove(encodedName);
       // When region is online and remove from regionsInTransition,
       // update the RIT duration to assignment manager metrics
       if (regionState != null && this.server.getAssignmentManager() != null) {
         long ritDuration = System.currentTimeMillis() - regionState.getStamp()
             + regionState.getRitDuration();
         this.server.getAssignmentManager().getAssignmentManagerMetrics()
             .updateRitDuration(ritDuration);
       }
       ServerName oldServerName = regionAssignments.put(hri, serverName);
       if (!serverName.equals(oldServerName)) {
         if (LOG.isDebugEnabled()) {
           LOG.debug("Onlined " + hri.getShortNameToLog() + " on " + serverName);
         }
         addToServerHoldings(serverName, hri);
         addToReplicaMapping(hri);
         if (oldServerName == null) {
           oldServerName = oldAssignments.remove(encodedName);
         }
         if (oldServerName != null
             && !oldServerName.equals(serverName)
             && serverHoldings.containsKey(oldServerName)) {
           LOG.info("Offlined " + hri.getShortNameToLog() + " from " + oldServerName);
           removeFromServerHoldings(oldServerName, hri);
         }
       }
     }
   }
 
   private void addToServerHoldings(ServerName serverName, HRegionInfo hri) {
     Set<HRegionInfo> regions = serverHoldings.get(serverName);
     if (regions == null) {
       regions = new HashSet<HRegionInfo>();
       serverHoldings.put(serverName, regions);
     }
     regions.add(hri);
   }
 
   private void addToReplicaMapping(HRegionInfo hri) {
     HRegionInfo defaultReplica = RegionReplicaUtil.getRegionInfoForDefaultReplica(hri);
     Set<HRegionInfo> replicas =
         defaultReplicaToOtherReplicas.get(defaultReplica);
     if (replicas == null) {
       replicas = new HashSet<HRegionInfo>();
       defaultReplicaToOtherReplicas.put(defaultReplica, replicas);
     }
     replicas.add(hri);
   }
 
   private void removeFromServerHoldings(ServerName serverName, HRegionInfo hri) {
     Set<HRegionInfo> oldRegions = serverHoldings.get(serverName);
     oldRegions.remove(hri);
     if (oldRegions.isEmpty()) {
       serverHoldings.remove(serverName);
     }
   }
 
   private void removeFromReplicaMapping(HRegionInfo hri) {
     HRegionInfo defaultReplica = RegionReplicaUtil.getRegionInfoForDefaultReplica(hri);
     Set<HRegionInfo> replicas = defaultReplicaToOtherReplicas.get(defaultReplica);
     if (replicas != null) {
       replicas.remove(hri);
       if (replicas.isEmpty()) {
         defaultReplicaToOtherReplicas.remove(defaultReplica);
       }
     }
   }
 
   /**
    * Used in some unit tests
    */
   @VisibleForTesting
   synchronized boolean existsInServerHoldings(final ServerName serverName,
       final HRegionInfo hri) {
     Set<HRegionInfo> oldRegions = serverHoldings.get(serverName);
     if (oldRegions != null) {
       return oldRegions.contains(hri);
     }
     return false;
   }
 
   /**
    * A dead server's wals have been split so that all the regions
    * used to be open on it can be safely assigned now. Mark them assignable.
    */
   public synchronized void logSplit(final ServerName serverName) {
     for (Iterator<Map.Entry<String, ServerName>> it
         = lastAssignments.entrySet().iterator(); it.hasNext();) {
       Map.Entry<String, ServerName> e = it.next();
       if (e.getValue().equals(serverName)) {
         it.remove();
       }
     }
     long now = System.currentTimeMillis();
     if (LOG.isDebugEnabled()) {
       LOG.debug("Adding to log splitting servers " + serverName);
     }
     processedServers.put(serverName, Long.valueOf(now));
     Configuration conf = server.getConfiguration();
     long obsoleteTime = conf.getLong(LOG_SPLIT_TIME, DEFAULT_LOG_SPLIT_TIME);
     // Doesn't have to be very accurate about the clean up time
     if (now > lastProcessedServerCleanTime + obsoleteTime) {
       lastProcessedServerCleanTime = now;
       long cutoff = now - obsoleteTime;
       for (Iterator<Map.Entry<ServerName, Long>> it
           = processedServers.entrySet().iterator(); it.hasNext();) {
         Map.Entry<ServerName, Long> e = it.next();
         if (e.getValue().longValue() < cutoff) {
           if (LOG.isDebugEnabled()) {
             LOG.debug("Removed from log splitting servers " + e.getKey());
           }
           it.remove();
         }
       }
     }
   }
 
   /**
    * Log split is done for a given region, so it is assignable now.
    */
   public void logSplit(final HRegionInfo region) {
     clearLastAssignment(region);
   }
 
   public synchronized void clearLastAssignment(final HRegionInfo region) {
     lastAssignments.remove(region.getEncodedName());
   }
 
   /**
    * A region is offline, won't be in transition any more.
    */
   public void regionOffline(final HRegionInfo hri) {
     regionOffline(hri, null);
   }
 
   /**
    * A region is offline, won't be in transition any more. Its state
    * should be the specified expected state, which can only be
    * Split/Merged/Offline/null(=Offline)/SplittingNew/MergingNew.
    */
   public void regionOffline(
       final HRegionInfo hri, final State expectedState) {
     Preconditions.checkArgument(expectedState == null
       || RegionState.isUnassignable(expectedState),
         "Offlined region should not be " + expectedState);
     if (isRegionInState(hri, State.SPLITTING_NEW, State.MERGING_NEW)) {
       // Remove it from all region maps
       deleteRegion(hri);
       return;
     }
 
     /*
      * One tricky case, if region here is a replica region and its parent is at
      * SPLIT state, its newState should be same as its parent, not OFFLINE.
      */
     State newState =
         expectedState == null ? State.OFFLINE : expectedState;
 
     if ((expectedState == null) && !RegionReplicaUtil.isDefaultReplica(hri)) {
       RegionState primateState = getRegionState(
           RegionReplicaUtil.getRegionInfoForDefaultReplica(hri));
       if ((primateState != null) && (primateState.getState() == State.SPLIT)) {
         if (LOG.isDebugEnabled()) {
           LOG.debug("Update region " + hri + "to SPLIT, from primary region " +
               RegionReplicaUtil.getRegionInfoForDefaultReplica(hri));
         }
         newState = State.SPLIT;
       }
     }
 
     updateRegionState(hri, newState);
     String encodedName = hri.getEncodedName();
     synchronized (this) {
       regionsInTransition.remove(encodedName);
       ServerName oldServerName = regionAssignments.remove(hri);
       if (oldServerName != null && serverHoldings.containsKey(oldServerName)) {
         if (newState == State.MERGED || newState == State.SPLIT
             || hri.isMetaRegion() || tableStateManager.isTableState(hri.getTable(),
               ZooKeeperProtos.Table.State.DISABLED, ZooKeeperProtos.Table.State.DISABLING)) {
           // Offline the region only if it's merged/split, or the table is disabled/disabling.
           // Otherwise, offline it from this server only when it is online on a different server.
           LOG.info("Offlined " + hri.getShortNameToLog() + " from " + oldServerName);
           removeFromServerHoldings(oldServerName, hri);
           removeFromReplicaMapping(hri);
         } else {
           // Need to remember it so that we can offline it from this
           // server when it is online on a different server.
           oldAssignments.put(encodedName, oldServerName);
         }
       }
     }
   }
 
   /**
    * A server is offline, all regions on it are dead.
    */
   public List<HRegionInfo> serverOffline(final ZooKeeperWatcher watcher, final ServerName sn) {
     // Offline all regions on this server not already in transition.
     List<HRegionInfo> rits = new ArrayList<HRegionInfo>();
     Set<HRegionInfo> regionsToClean = new HashSet<HRegionInfo>();
     // Offline regions outside the loop and synchronized block to avoid
     // ConcurrentModificationException and deadlock in case of meta anassigned,
     // but RegionState a blocked.
     Set<HRegionInfo> regionsToOffline = new HashSet<HRegionInfo>();
     synchronized (this) {
       Set<HRegionInfo> assignedRegions = serverHoldings.get(sn);
       if (assignedRegions == null) {
         assignedRegions = new HashSet<HRegionInfo>();
       }
 
       for (HRegionInfo region : assignedRegions) {
         // Offline open regions, no need to offline if SPLIT/MERGED/OFFLINE
         if (isRegionOnline(region)) {
           regionsToOffline.add(region);
         } else if (isRegionInState(region, State.SPLITTING, State.MERGING)) {
           LOG.debug("Offline splitting/merging region " + getRegionState(region));
           try {
             // Delete the ZNode if exists
             ZKAssign.deleteNodeFailSilent(watcher, region);
             regionsToOffline.add(region);
           } catch (KeeperException ke) {
             server.abort("Unexpected ZK exception deleting node " + region, ke);
           }
         }
       }
 
       for (RegionState state : regionsInTransition.values()) {
         HRegionInfo hri = state.getRegion();
         if (assignedRegions.contains(hri)) {
           // Region is open on this region server, but in transition.
           // This region must be moving away from this server, or splitting/merging.
           // SSH will handle it, either skip assigning, or re-assign.
           LOG.info("Transitioning " + state + " will be handled by ServerCrashProcedure for " + sn);
         } else if (sn.equals(state.getServerName())) {
           // Region is in transition on this region server, and this
           // region is not open on this server. So the region must be
           // moving to this server from another one (i.e. opening or
           // pending open on this server, was open on another one.
           // Offline state is also kind of pending open if the region is in
           // transition. The region could be in failed_close state too if we have
           // tried several times to open it while this region server is not reachable)
           if (state.isPendingOpenOrOpening() || state.isFailedClose() || state.isOffline()) {
             LOG.info("Found region in " + state +
               " to be reassigned by ServerCrashProcedure for " + sn);
             rits.add(hri);
           } else if(state.isSplittingNew() || state.isMergingNew()) {
             LOG.info("Offline/Cleanup region if no meta entry exists, hri: " + hri +
                 " state: " + state);
             regionsToClean.add(state.getRegion());
           } else {
             LOG.warn("THIS SHOULD NOT HAPPEN: unexpected " + state);
           }
         }
       }
       this.notifyAll();
     }
 
     for (HRegionInfo hri : regionsToOffline) {
       regionOffline(hri);
     }
 
     cleanFailedSplitMergeRegions(regionsToClean);
     return rits;
   }
 
   /**
    * This method does an RPC to hbase:meta. Do not call this method with a lock/synchronize held.
    * In ZK mode we rollback and hence cleanup daughters/merged region. We also cleanup if
    * meta doesn't have these regions.
    *
    * @param hris The hris to check if empty in hbase:meta and if so, clean them up.
    */
   private void cleanFailedSplitMergeRegions(Set<HRegionInfo> hris) {
     if (hris.isEmpty()) {
       return;
     }
 
     for (HRegionInfo hri : hris) {
       // This is RPC to meta table. It is done while we have a synchronize on
       // regionstates. No progress will be made if meta is not available at this time.
       // This is a cleanup task. Not critical.
       try {
         Pair<HRegionInfo, ServerName> regionPair =
             MetaTableAccessor.getRegion(server.getConnection(), hri.getRegionName());
         if (regionPair == null || useZK) {
           regionOffline(hri);
 
           // If we use ZK, then we can cleanup entries from meta, since we roll back.
           if (regionPair != null) {
             MetaTableAccessor.deleteRegion(this.server.getConnection(), hri);
           }
           LOG.debug("Cleaning up HDFS since no meta entry exists, hri: " + hri);
           FSUtils.deleteRegionDir(server.getConfiguration(), hri);
         }
       } catch (IOException e) {
         LOG.warn("Got exception while cleaning up region " + hri, e);
       }
     }
   }
 
   /**
    * Gets the online regions of the specified table.
    * This method looks at the in-memory state.  It does not go to <code>hbase:meta</code>.
    * Only returns <em>online</em> regions.  If a region on this table has been
    * closed during a disable, etc., it will be included in the returned list.
    * So, the returned list may not necessarily be ALL regions in this table, its
    * all the ONLINE regions in the table.
    * @param tableName
    * @return Online regions from <code>tableName</code>
    */
   public synchronized List<HRegionInfo> getRegionsOfTable(TableName tableName) {
     List<HRegionInfo> tableRegions = new ArrayList<HRegionInfo>();
     // boundary needs to have table's name but regionID 0 so that it is sorted
     // before all table's regions.
     HRegionInfo boundary = new HRegionInfo(tableName, null, null, false, 0L);
     for (HRegionInfo hri: regionAssignments.tailMap(boundary).keySet()) {
       if(!hri.getTable().equals(tableName)) break;
       tableRegions.add(hri);
     }
     return tableRegions;
   }
 
   /**
    * Gets current state of all regions of the table.
    * This method looks at the in-memory state.  It does not go to <code>hbase:meta</code>.
    * Method guaranteed to return keys for all states
    * in {@link org.apache.hadoop.hbase.master.RegionState.State}
    *
    * @param tableName
    * @return Online regions from <code>tableName</code>
    */
   public synchronized Map<RegionState.State, List<HRegionInfo>>
   getRegionByStateOfTable(TableName tableName) {
     Map<RegionState.State, List<HRegionInfo>> tableRegions =
         new HashMap<State, List<HRegionInfo>>();
     for (State state : State.values()) {
       tableRegions.put(state, new ArrayList<HRegionInfo>());
     }
     Map<String, RegionState> indexMap = regionStatesTableIndex.get(tableName);
     if (indexMap == null)
       return tableRegions;
     for (RegionState regionState : indexMap.values()) {
       tableRegions.get(regionState.getState()).add(regionState.getRegion());
     }
     return tableRegions;
   }
 
   /**
    * Wait on region to clear regions-in-transition.
    * <p>
    * If the region isn't in transition, returns immediately.  Otherwise, method
    * blocks until the region is out of transition.
    */
   public synchronized void waitOnRegionToClearRegionsInTransition(
       final HRegionInfo hri) throws InterruptedException {
     if (!isRegionInTransition(hri)) return;
 
     while(!server.isStopped() && isRegionInTransition(hri)) {
       RegionState rs = getRegionState(hri);
       LOG.info("Waiting on " + rs + " to clear regions-in-transition");
       waitForUpdate(100);
     }
 
     if (server.isStopped()) {
       LOG.info("Giving up wait on region in " +
         "transition because stoppable.isStopped is set");
     }
   }
 
   /**
    * A table is deleted. Remove its regions from all internal maps.
    * We loop through all regions assuming we don't delete tables too much.
    */
   public void tableDeleted(final TableName tableName) {
     Set<HRegionInfo> regionsToDelete = new HashSet<HRegionInfo>();
     synchronized (this) {
       for (RegionState state: regionStates.values()) {
         HRegionInfo region = state.getRegion();
         if (region.getTable().equals(tableName)) {
           regionsToDelete.add(region);
         }
       }
     }
     for (HRegionInfo region: regionsToDelete) {
       deleteRegion(region);
     }
   }
 
   /**
    * Get a copy of all regions assigned to a server
    */
   public synchronized Set<HRegionInfo> getServerRegions(ServerName serverName) {
     Set<HRegionInfo> regions = serverHoldings.get(serverName);
     if (regions == null) return null;
     return new HashSet<HRegionInfo>(regions);
   }
 
   /**
    * Remove a region from all state maps.
    */
   @VisibleForTesting
   public synchronized void deleteRegion(final HRegionInfo hri) {
     String encodedName = hri.getEncodedName();
     regionsInTransition.remove(encodedName);
     regionStates.remove(encodedName);
     TableName table = hri.getTable();
     Map<String, RegionState> indexMap = regionStatesTableIndex.get(table);
     indexMap.remove(encodedName);
     if (indexMap.size() == 0)
       regionStatesTableIndex.remove(table);
     lastAssignments.remove(encodedName);
     ServerName sn = regionAssignments.remove(hri);
     if (sn != null) {
       Set<HRegionInfo> regions = serverHoldings.get(sn);
       regions.remove(hri);
     }
   }
 
   @VisibleForTesting
   public boolean isRegionInRegionStates(final HRegionInfo hri) {
     return (getRegionState(hri) != null || isRegionOnline(hri)) || isRegionInTransition(hri)
         || isRegionInState(hri, State.OFFLINE, State.CLOSED);
      }
 
   /**
    * Checking if a region was assigned to a server which is not online now.
    * If so, we should hold re-assign this region till SSH has split its wals.
    * Once logs are split, the last assignment of this region will be reset,
    * which means a null last assignment server is ok for re-assigning.
    *
    * A region server could be dead but we don't know it yet. We may
    * think it's online falsely. Therefore if a server is online, we still
    * need to confirm it reachable and having the expected start code.
    */
   synchronized boolean wasRegionOnDeadServer(final String encodedName) {
     ServerName server = lastAssignments.get(encodedName);
     return isServerDeadAndNotProcessed(server);
   }
 
   synchronized boolean isServerDeadAndNotProcessed(ServerName server) {
     if (server == null) return false;
     if (serverManager.isServerOnline(server)) {
       String hostAndPort = server.getHostAndPort();
       long startCode = server.getStartcode();
       Long deadCode = deadServers.get(hostAndPort);
       if (deadCode == null || startCode > deadCode.longValue()) {
         if (serverManager.isServerReachable(server)) {
           return false;
         }
         // The size of deadServers won't grow unbounded.
         deadServers.put(hostAndPort, Long.valueOf(startCode));
       }
       // Watch out! If the server is not dead, the region could
       // remain unassigned. That's why ServerManager#isServerReachable
       // should use some retry.
       //
       // We cache this info since it is very unlikely for that
       // instance to come back up later on. We don't want to expire
       // the server since we prefer to let it die naturally.
       LOG.warn("Couldn't reach online server " + server);
     }
     // Now, we know it's dead. Check if it's processed
     return !processedServers.containsKey(server);
   }
 
  /**
    * Get the last region server a region was on for purpose of re-assignment,
    * i.e. should the re-assignment be held back till log split is done?
    */
   synchronized ServerName getLastRegionServerOfRegion(final String encodedName) {
     return lastAssignments.get(encodedName);
   }
 
   synchronized void setLastRegionServerOfRegions(
       final ServerName serverName, final List<HRegionInfo> regionInfos) {
     for (HRegionInfo hri: regionInfos) {
       setLastRegionServerOfRegion(serverName, hri.getEncodedName());
     }
   }
 
   synchronized void setLastRegionServerOfRegion(
       final ServerName serverName, final String encodedName) {
     lastAssignments.put(encodedName, serverName);
   }
 
   void splitRegion(HRegionInfo p,
       HRegionInfo a, HRegionInfo b, ServerName sn) throws IOException {
 
     regionStateStore.splitRegion(p, a, b, sn, getRegionReplication(p));
     synchronized (this) {
       // After PONR, split is considered to be done.
       // Update server holdings to be aligned with the meta.
       Set<HRegionInfo> regions = serverHoldings.get(sn);
       if (regions == null) {
         throw new IllegalStateException(sn + " should host some regions");
       }
       regions.remove(p);
       regions.add(a);
       regions.add(b);
     }
   }
 
   void mergeRegions(HRegionInfo p,
       HRegionInfo a, HRegionInfo b, ServerName sn) throws IOException {
     regionStateStore.mergeRegions(p, a, b, sn, getRegionReplication(a));
     synchronized (this) {
       // After PONR, merge is considered to be done.
       // Update server holdings to be aligned with the meta.
       Set<HRegionInfo> regions = serverHoldings.get(sn);
       if (regions == null) {
         throw new IllegalStateException(sn + " should host some regions");
       }
       regions.remove(a);
       regions.remove(b);
       regions.add(p);
     }
   }
 
   private int getRegionReplication(HRegionInfo r) throws IOException {
     if (tableStateManager != null) {
       HTableDescriptor htd = ((MasterServices)server).getTableDescriptors().get(r.getTable());
       if (htd != null) {
         return htd.getRegionReplication();
       }
     }
     return 1;
   }
 
   /**
    * At cluster clean re/start, mark all user regions closed except those of tables
    * that are excluded, such as disabled/disabling/enabling tables. All user regions
    * and their previous locations are returned.
    */
   synchronized Map<HRegionInfo, ServerName> closeAllUserRegions(Set<TableName> excludedTables) {
     boolean noExcludeTables = excludedTables == null || excludedTables.isEmpty();
     Set<HRegionInfo> toBeClosed = new HashSet<HRegionInfo>(regionStates.size());
     for(RegionState state: regionStates.values()) {
       HRegionInfo hri = state.getRegion();
       if (state.isSplit() || hri.isSplit()) {
         continue;
       }
       TableName tableName = hri.getTable();
       if (!TableName.META_TABLE_NAME.equals(tableName)
           && (noExcludeTables || !excludedTables.contains(tableName))) {
         toBeClosed.add(hri);
       }
     }
     Map<HRegionInfo, ServerName> allUserRegions =
       new HashMap<HRegionInfo, ServerName>(toBeClosed.size());
     for (HRegionInfo hri: toBeClosed) {
       RegionState regionState = updateRegionState(hri, State.CLOSED);
       allUserRegions.put(hri, regionState.getServerName());
     }
     return allUserRegions;
   }
 
   /**
    * Compute the average load across all region servers.
    * Currently, this uses a very naive computation - just uses the number of
    * regions being served, ignoring stats about number of requests.
    * @return the average load
    */
   protected synchronized double getAverageLoad() {
     int numServers = 0, totalLoad = 0;
     for (Map.Entry<ServerName, Set<HRegionInfo>> e: serverHoldings.entrySet()) {
       Set<HRegionInfo> regions = e.getValue();
       ServerName serverName = e.getKey();
       int regionCount = regions.size();
       if (serverManager.isServerOnline(serverName)) {
         totalLoad += regionCount;
         numServers++;
       }
     }
     if (numServers > 1) {
       // The master region server holds only a couple regions.
       // Don't consider this server in calculating the average load
       // if there are other region servers to avoid possible confusion.
       Set<HRegionInfo> hris = serverHoldings.get(server.getServerName());
       if (hris != null) {
         totalLoad -= hris.size();
         numServers--;
       }
     }
     return numServers == 0 ? 0.0 :
       (double)totalLoad / (double)numServers;
   }
 
   /**
    * This is an EXPENSIVE clone.  Cloning though is the safest thing to do.
    * Can't let out original since it can change and at least the load balancer
    * wants to iterate this exported list.  We need to synchronize on regions
    * since all access to this.servers is under a lock on this.regions.
    *
    * @return A clone of current assignments by table.
    */
   protected Map<TableName, Map<ServerName, List<HRegionInfo>>>
       getAssignmentsByTable() {
     Map<TableName, Map<ServerName, List<HRegionInfo>>> result =
       new HashMap<TableName, Map<ServerName,List<HRegionInfo>>>();
     synchronized (this) {
       if (!server.getConfiguration().getBoolean(
             HConstants.HBASE_MASTER_LOADBALANCE_BYTABLE, false)) {
         Map<ServerName, List<HRegionInfo>> svrToRegions =
           new HashMap<ServerName, List<HRegionInfo>>(serverHoldings.size());
         for (Map.Entry<ServerName, Set<HRegionInfo>> e: serverHoldings.entrySet()) {
           svrToRegions.put(e.getKey(), new ArrayList<HRegionInfo>(e.getValue()));
         }
         result.put(TableName.valueOf(HConstants.ENSEMBLE_TABLE_NAME), svrToRegions);
       } else {
         for (Map.Entry<ServerName, Set<HRegionInfo>> e: serverHoldings.entrySet()) {
           for (HRegionInfo hri: e.getValue()) {
             if (hri.isMetaRegion()) continue;
             TableName tablename = hri.getTable();
             Map<ServerName, List<HRegionInfo>> svrToRegions = result.get(tablename);
             if (svrToRegions == null) {
               svrToRegions = new HashMap<ServerName, List<HRegionInfo>>(serverHoldings.size());
               result.put(tablename, svrToRegions);
             }
             List<HRegionInfo> regions = svrToRegions.get(e.getKey());
             if (regions == null) {
               regions = new ArrayList<HRegionInfo>();
               svrToRegions.put(e.getKey(), regions);
             }
             regions.add(hri);
           }
         }
       }
     }
 
     Map<ServerName, ServerLoad>
       onlineSvrs = serverManager.getOnlineServers();
     // Take care of servers w/o assignments, and remove servers in draining mode
     List<ServerName> drainingServers = this.serverManager.getDrainingServersList();
     for (Map<ServerName, List<HRegionInfo>> map: result.values()) {
       for (ServerName svr: onlineSvrs.keySet()) {
         if (!map.containsKey(svr)) {
           map.put(svr, new ArrayList<HRegionInfo>());
         }
       }
       map.keySet().removeAll(drainingServers);
     }
     return result;
   }
 
   protected RegionState getRegionState(final HRegionInfo hri) {
     return getRegionState(hri.getEncodedName());
   }
 
   /**
    * Returns a clone of region assignments per server
    * @return a Map of ServerName to a List of HRegionInfo's
    */
   protected synchronized Map<ServerName, List<HRegionInfo>> getRegionAssignmentsByServer() {
     Map<ServerName, List<HRegionInfo>> regionsByServer =
         new HashMap<ServerName, List<HRegionInfo>>(serverHoldings.size());
     for (Map.Entry<ServerName, Set<HRegionInfo>> e: serverHoldings.entrySet()) {
       regionsByServer.put(e.getKey(), new ArrayList<HRegionInfo>(e.getValue()));
     }
     return regionsByServer;
   }
 
   protected synchronized RegionState getRegionState(final String encodedName) {
     return regionStates.get(encodedName);
   }
 
   /**
    * Get the HRegionInfo from cache, if not there, from the hbase:meta table
    * @param  regionName
    * @return HRegionInfo for the region
    */
   @SuppressWarnings("deprecation")
   protected HRegionInfo getRegionInfo(final byte [] regionName) {
     String encodedName = HRegionInfo.encodeRegionName(regionName);
     RegionState regionState = getRegionState(encodedName);
     if (regionState != null) {
       return regionState.getRegion();
     }
 
     try {
       Pair<HRegionInfo, ServerName> p =
         MetaTableAccessor.getRegion(server.getConnection(), regionName);
       HRegionInfo hri = p == null ? null : p.getFirst();
       if (hri != null) {
         createRegionState(hri);
       }
       return hri;
     } catch (IOException e) {
       server.abort("Aborting because error occurred while reading "
         + Bytes.toStringBinary(regionName) + " from hbase:meta", e);
       return null;
     }
   }
 
   static boolean isOneOfStates(RegionState regionState, State... states) {
     State s = regionState != null ? regionState.getState() : null;
     for (State state: states) {
       if (s == state) return true;
     }
     return false;
   }
 
   /**
    * Update a region state. It will be put in transition if not already there.
    */
   private RegionState updateRegionState(final HRegionInfo hri,
       final State state, final ServerName serverName, long openSeqNum) {
     if (state == State.FAILED_CLOSE || state == State.FAILED_OPEN) {
       LOG.warn("Failed to open/close " + hri.getShortNameToLog()
         + " on " + serverName + ", set to " + state);
     }
 
     String encodedName = hri.getEncodedName();
     RegionState regionState = new RegionState(
       hri, state, System.currentTimeMillis(), serverName);
     RegionState oldState = getRegionState(encodedName);
     if (!regionState.equals(oldState)) {
       LOG.info("Transition " + oldState + " to " + regionState);
       // Persist region state before updating in-memory info, if needed
       regionStateStore.updateRegionState(openSeqNum, regionState, oldState);
     }
 
     synchronized (this) {
       RegionState oldRegionState = regionsInTransition.put(encodedName, regionState);
       // When region transform old region state to new region state,
       // accumulate the RIT duration to new region state.
       if (oldRegionState != null) {
         regionState.updateRitDuration(oldRegionState.getStamp());
       }
       putRegionState(regionState);
 
       // For these states, region should be properly closed.
       // There should be no log splitting issue.
       if ((state == State.CLOSED || state == State.MERGED
           || state == State.SPLIT) && lastAssignments.containsKey(encodedName)) {
         ServerName last = lastAssignments.get(encodedName);
         if (last.equals(serverName)) {
           lastAssignments.remove(encodedName);
         } else {
           LOG.warn(encodedName + " moved to " + state + " on "
             + serverName + ", expected " + last);
         }
       }
 
       // Once a region is opened, record its last assignment right away.
       if (serverName != null && state == State.OPEN) {
         ServerName last = lastAssignments.get(encodedName);
         if (!serverName.equals(last)) {
           lastAssignments.put(encodedName, serverName);
           if (last != null && isServerDeadAndNotProcessed(last)) {
             LOG.warn(encodedName + " moved to " + serverName
               + ", while it's previous host " + last
               + " is dead but not processed yet");
           }
         }
       }
 
       // notify the change
       this.notifyAll();
     }
     return regionState;
   }
 }