/*
    *
    * 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.client;
  
  import java.io.IOException;
  import java.io.InterruptedIOException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Date;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.ConcurrentMap;
  import java.util.concurrent.ConcurrentSkipListMap;
  import java.util.concurrent.ExecutorService;
  import java.util.concurrent.RejectedExecutionException;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicInteger;
  import java.util.concurrent.atomic.AtomicLong;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.RetryImmediatelyException;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.DoNotRetryIOException;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.HRegionInfo;
  import org.apache.hadoop.hbase.HRegionLocation;
  import org.apache.hadoop.hbase.RegionLocations;
  import org.apache.hadoop.hbase.ServerName;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.client.backoff.ServerStatistics;
  import org.apache.hadoop.hbase.client.coprocessor.Batch;
  import org.apache.hadoop.hbase.exceptions.ClientExceptionsUtil;
  import org.apache.hadoop.hbase.ipc.RpcControllerFactory;
  import org.apache.hadoop.hbase.protobuf.generated.ClientProtos;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
  import org.apache.htrace.Trace;
  
  import com.google.common.annotations.VisibleForTesting;
  
  /**
   * This class  allows a continuous flow of requests. It's written to be compatible with a
   * synchronous caller such as HTable.
   * <p>
   * The caller sends a buffer of operation, by calling submit. This class extract from this list
   * the operations it can send, i.e. the operations that are on region that are not considered
   * as busy. The process is asynchronous, i.e. it returns immediately when if has finished to
   * iterate on the list. If, and only if, the maximum number of current task is reached, the call
   * to submit will block. Alternatively, the caller can call submitAll, in which case all the
   * operations will be sent. Each call to submit returns a future-like object that can be used
   * to track operation progress.
   * </p>
   * <p>
   * The class manages internally the retries.
   * </p>
   * <p>
   * The class can be constructed in regular mode, or "global error" mode. In global error mode,
   * AP tracks errors across all calls (each "future" also has global view of all errors). That
   * mode is necessary for backward compat with HTable behavior, where multiple submissions are
   * made and the errors can propagate using any put/flush call, from previous calls.
   * In "regular" mode, the errors are tracked inside the Future object that is returned.
   * The results are always tracked inside the Future object and can be retrieved when the call
   * has finished. Partial results can also be retrieved if some part of multi-request failed.
   * </p>
   * <p>
   * This class is thread safe in regular mode; in global error code, submitting operations and
   * retrieving errors from different threads may be not thread safe.
   * Internally, the class is thread safe enough to manage simultaneously new submission and results
   * arising from older operations.
   * </p>
   * <p>
   * Internally, this class works with {@link Row}, this mean it could be theoretically used for
   * gets as well.
   * </p>
   */
 @InterfaceAudience.Private
 class AsyncProcess {
   private static final Log LOG = LogFactory.getLog(AsyncProcess.class);
   protected static final AtomicLong COUNTER = new AtomicLong();
 
   public static final String PRIMARY_CALL_TIMEOUT_KEY = "hbase.client.primaryCallTimeout.multiget";
 
   /**
    * Configure the number of failures after which the client will start logging. A few failures
    * is fine: region moved, then is not opened, then is overloaded. We try to have an acceptable
    * heuristic for the number of errors we don't log. 9 was chosen because we wait for 1s at
    * this stage.
    */
   public static final String START_LOG_ERRORS_AFTER_COUNT_KEY =
       "hbase.client.start.log.errors.counter";
   public static final int DEFAULT_START_LOG_ERRORS_AFTER_COUNT = 9;
 
   /**
    * Configuration to decide whether to log details for batch error
    */
   public static final String LOG_DETAILS_FOR_BATCH_ERROR = "hbase.client.log.batcherrors.details";
 
   private final int thresholdToLogUndoneTaskDetails;
   private static final String THRESHOLD_TO_LOG_UNDONE_TASK_DETAILS =
       "hbase.client.threshold.log.details";
   private static final int DEFAULT_THRESHOLD_TO_LOG_UNDONE_TASK_DETAILS = 10;
   private final int THRESHOLD_TO_LOG_REGION_DETAILS = 2;
 
   /**
    * The context used to wait for results from one submit call.
    * 1) If AsyncProcess is set to track errors globally, and not per call (for HTable puts),
    *    then errors and failed operations in this object will reflect global errors.
    * 2) If submit call is made with needResults false, results will not be saved.
    *  */
   public static interface AsyncRequestFuture {
     public boolean hasError();
     public RetriesExhaustedWithDetailsException getErrors();
     public List<? extends Row> getFailedOperations();
     public Object[] getResults() throws InterruptedIOException;
     /** Wait until all tasks are executed, successfully or not. */
     public void waitUntilDone() throws InterruptedIOException;
   }
 
   /**
    * Return value from a submit that didn't contain any requests.
    */
   private static final AsyncRequestFuture NO_REQS_RESULT = new AsyncRequestFuture() {
 
     final Object[] result = new Object[0];
 
     @Override
     public boolean hasError() {
       return false;
     }
 
     @Override
     public RetriesExhaustedWithDetailsException getErrors() {
       return null;
     }
 
     @Override
     public List<? extends Row> getFailedOperations() {
       return null;
     }
 
     @Override
     public Object[] getResults() {
       return result;
     }
 
     @Override
     public void waitUntilDone() throws InterruptedIOException {
     }
   };
 
   /** Sync point for calls to multiple replicas for the same user request (Get).
    * Created and put in the results array (we assume replica calls require results) when
    * the replica calls are launched. See results for details of this process.
    * POJO, all fields are public. To modify them, the object itself is locked. */
   private static class ReplicaResultState {
     public ReplicaResultState(int callCount) {
       this.callCount = callCount;
     }
 
     /** Number of calls outstanding, or 0 if a call succeeded (even with others outstanding). */
     int callCount;
     /** Errors for which it is not decided whether we will report them to user. If one of the
      * calls succeeds, we will discard the errors that may have happened in the other calls. */
     BatchErrors replicaErrors = null;
 
     @Override
     public String toString() {
       return "[call count " + callCount + "; errors " + replicaErrors + "]";
     }
   }
 
 
   // TODO: many of the fields should be made private
   protected final long id;
 
   protected final ClusterConnection connection;
   protected final RpcRetryingCallerFactory rpcCallerFactory;
   protected final RpcControllerFactory rpcFactory;
   protected final BatchErrors globalErrors;
   protected final ExecutorService pool;
 
   protected final AtomicLong tasksInProgress = new AtomicLong(0);
   protected final ConcurrentMap<byte[], AtomicInteger> taskCounterPerRegion =
       new ConcurrentSkipListMap<byte[], AtomicInteger>(Bytes.BYTES_COMPARATOR);
   protected final ConcurrentMap<ServerName, AtomicInteger> taskCounterPerServer =
       new ConcurrentHashMap<ServerName, AtomicInteger>();
 
   // Start configuration settings.
   private final int startLogErrorsCnt;
 
   /**
    * The number of tasks simultaneously executed on the cluster.
    */
   protected final int maxTotalConcurrentTasks;
 
   /**
    * The number of tasks we run in parallel on a single region.
    * With 1 (the default) , we ensure that the ordering of the queries is respected: we don't start
    * a set of operations on a region before the previous one is done. As well, this limits
    * the pressure we put on the region server.
    */
   protected final int maxConcurrentTasksPerRegion;
 
   /**
    * The number of task simultaneously executed on a single region server.
    */
   protected final int maxConcurrentTasksPerServer;
   protected final long pause;
   protected int numTries;
   protected int serverTrackerTimeout;
   protected int rpcTimeout;
   protected int operationTimeout;
   protected long primaryCallTimeoutMicroseconds;
   // End configuration settings.
 
   protected static class BatchErrors {
     private final List<Throwable> throwables = new ArrayList<Throwable>();
     private final List<Row> actions = new ArrayList<Row>();
     private final List<String> addresses = new ArrayList<String>();
 
     public synchronized void add(Throwable ex, Row row, ServerName serverName) {
       if (row == null){
         throw new IllegalArgumentException("row cannot be null. location=" + serverName);
       }
 
       throwables.add(ex);
       actions.add(row);
       addresses.add(serverName != null ? serverName.toString() : "null");
     }
 
     public boolean hasErrors() {
       return !throwables.isEmpty();
     }
 
     private synchronized RetriesExhaustedWithDetailsException makeException() {
       return new RetriesExhaustedWithDetailsException(
           new ArrayList<Throwable>(throwables),
           new ArrayList<Row>(actions), new ArrayList<String>(addresses));
     }
 
     public synchronized void clear() {
       throwables.clear();
       actions.clear();
       addresses.clear();
     }
 
     public synchronized void merge(BatchErrors other) {
       throwables.addAll(other.throwables);
       actions.addAll(other.actions);
       addresses.addAll(other.addresses);
     }
   }
 
   public AsyncProcess(ClusterConnection hc, Configuration conf, ExecutorService pool,
       RpcRetryingCallerFactory rpcCaller, boolean useGlobalErrors, RpcControllerFactory rpcFactory,
       int rpcTimeout) {
     if (hc == null) {
       throw new IllegalArgumentException("HConnection cannot be null.");
     }
 
     this.connection = hc;
     this.pool = pool;
     this.globalErrors = useGlobalErrors ? new BatchErrors() : null;
 
     this.id = COUNTER.incrementAndGet();
 
     this.pause = conf.getLong(HConstants.HBASE_CLIENT_PAUSE,
         HConstants.DEFAULT_HBASE_CLIENT_PAUSE);
     this.numTries = conf.getInt(HConstants.HBASE_CLIENT_RETRIES_NUMBER,
         HConstants.DEFAULT_HBASE_CLIENT_RETRIES_NUMBER);
     this.rpcTimeout = rpcTimeout;
     this.operationTimeout = conf.getInt(HConstants.HBASE_CLIENT_OPERATION_TIMEOUT,
         HConstants.DEFAULT_HBASE_CLIENT_OPERATION_TIMEOUT);
     this.primaryCallTimeoutMicroseconds = conf.getInt(PRIMARY_CALL_TIMEOUT_KEY, 10000);
 
     this.maxTotalConcurrentTasks = conf.getInt(HConstants.HBASE_CLIENT_MAX_TOTAL_TASKS,
       HConstants.DEFAULT_HBASE_CLIENT_MAX_TOTAL_TASKS);
     this.maxConcurrentTasksPerServer = conf.getInt(HConstants.HBASE_CLIENT_MAX_PERSERVER_TASKS,
           HConstants.DEFAULT_HBASE_CLIENT_MAX_PERSERVER_TASKS);
     this.maxConcurrentTasksPerRegion = conf.getInt(HConstants.HBASE_CLIENT_MAX_PERREGION_TASKS,
           HConstants.DEFAULT_HBASE_CLIENT_MAX_PERREGION_TASKS);
 
     this.startLogErrorsCnt =
         conf.getInt(START_LOG_ERRORS_AFTER_COUNT_KEY, DEFAULT_START_LOG_ERRORS_AFTER_COUNT);
 
     if (this.maxTotalConcurrentTasks <= 0) {
       throw new IllegalArgumentException("maxTotalConcurrentTasks=" + maxTotalConcurrentTasks);
     }
     if (this.maxConcurrentTasksPerServer <= 0) {
       throw new IllegalArgumentException("maxConcurrentTasksPerServer=" +
           maxConcurrentTasksPerServer);
     }
     if (this.maxConcurrentTasksPerRegion <= 0) {
       throw new IllegalArgumentException("maxConcurrentTasksPerRegion=" +
           maxConcurrentTasksPerRegion);
     }
 
     // Server tracker allows us to do faster, and yet useful (hopefully), retries.
     // However, if we are too useful, we might fail very quickly due to retry count limit.
     // To avoid this, we are going to cheat for now (see HBASE-7659), and calculate maximum
     // retry time if normal retries were used. Then we will retry until this time runs out.
     // If we keep hitting one server, the net effect will be the incremental backoff, and
     // essentially the same number of retries as planned. If we have to do faster retries,
     // we will do more retries in aggregate, but the user will be none the wiser.
     this.serverTrackerTimeout = 0;
     for (int i = 0; i < this.numTries; ++i) {
       serverTrackerTimeout += ConnectionUtils.getPauseTime(this.pause, i);
     }
 
     this.rpcCallerFactory = rpcCaller;
     this.rpcFactory = rpcFactory;
 
     this.thresholdToLogUndoneTaskDetails =
         conf.getInt(THRESHOLD_TO_LOG_UNDONE_TASK_DETAILS,
           DEFAULT_THRESHOLD_TO_LOG_UNDONE_TASK_DETAILS);
   }
 
   public void setRpcTimeout(int rpcTimeout) {
     this.rpcTimeout = rpcTimeout;
   }
 
   public void setOperationTimeout(int operationTimeout) {
     this.operationTimeout = operationTimeout;
   }
 
   /**
    * @return pool if non null, otherwise returns this.pool if non null, otherwise throws
    *         RuntimeException
    */
   private ExecutorService getPool(ExecutorService pool) {
     if (pool != null) {
       return pool;
     }
     if (this.pool != null) {
       return this.pool;
     }
     throw new RuntimeException("Neither AsyncProcess nor request have ExecutorService");
   }
 
   /**
    * See {@link #submit(ExecutorService, TableName, List, boolean, org.apache.hadoop.hbase.client.coprocessor.Batch.Callback, boolean)}.
    * Uses default ExecutorService for this AP (must have been created with one).
    */
   public <CResult> AsyncRequestFuture submit(TableName tableName, List<? extends Row> rows,
       boolean atLeastOne, Batch.Callback<CResult> callback, boolean needResults)
       throws InterruptedIOException {
     return submit(null, tableName, rows, atLeastOne, callback, needResults);
   }
 
   /**
    * Extract from the rows list what we can submit. The rows we can not submit are kept in the
    * list. Does not send requests to replicas (not currently used for anything other
    * than streaming puts anyway).
    *
    * @param pool ExecutorService to use.
    * @param tableName The table for which this request is needed.
    * @param callback Batch callback. Only called on success (94 behavior).
    * @param needResults Whether results are needed, or can be discarded.
    * @param rows - the submitted row. Modified by the method: we remove the rows we took.
    * @param atLeastOne true if we should submit at least a subset.
    */
   public <CResult> AsyncRequestFuture submit(ExecutorService pool, TableName tableName,
       List<? extends Row> rows, boolean atLeastOne, Batch.Callback<CResult> callback,
       boolean needResults) throws InterruptedIOException {
     if (rows.isEmpty()) {
       return NO_REQS_RESULT;
     }
 
     Map<ServerName, MultiAction<Row>> actionsByServer =
         new HashMap<ServerName, MultiAction<Row>>();
     List<Action<Row>> retainedActions = new ArrayList<Action<Row>>(rows.size());
 
     NonceGenerator ng = this.connection.getNonceGenerator();
     long nonceGroup = ng.getNonceGroup(); // Currently, nonce group is per entire client.
 
     // Location errors that happen before we decide what requests to take.
     List<Exception> locationErrors = null;
     List<Integer> locationErrorRows = null;
     do {
       // Wait until there is at least one slot for a new task.
       waitForMaximumCurrentTasks(maxTotalConcurrentTasks - 1, tableName.getNameAsString());
 
       // Remember the previous decisions about regions or region servers we put in the
       //  final multi.
       Map<HRegionInfo, Boolean> regionIncluded = new HashMap<HRegionInfo, Boolean>();
       Map<ServerName, Boolean> serverIncluded = new HashMap<ServerName, Boolean>();
 
       int posInList = -1;
       Iterator<? extends Row> it = rows.iterator();
       while (it.hasNext()) {
         Row r = it.next();
         HRegionLocation loc;
         try {
           if (r == null) {
             throw new IllegalArgumentException("#" + id + ", row cannot be null");
           }
           // Make sure we get 0-s replica.
           RegionLocations locs = connection.locateRegion(
               tableName, r.getRow(), true, true, RegionReplicaUtil.DEFAULT_REPLICA_ID);
           if (locs == null || locs.isEmpty() || locs.getDefaultRegionLocation() == null) {
             throw new IOException("#" + id + ", no location found, aborting submit for"
                 + " tableName=" + tableName + " rowkey=" + Bytes.toStringBinary(r.getRow()));
           }
           loc = locs.getDefaultRegionLocation();
         } catch (IOException ex) {
           locationErrors = new ArrayList<Exception>();
           locationErrorRows = new ArrayList<Integer>();
           LOG.error("Failed to get region location ", ex);
           // This action failed before creating ars. Retain it, but do not add to submit list.
           // We will then add it to ars in an already-failed state.
           retainedActions.add(new Action<Row>(r, ++posInList));
           locationErrors.add(ex);
           locationErrorRows.add(posInList);
           it.remove();
           break; // Backward compat: we stop considering actions on location error.
         }
 
         if (canTakeOperation(loc, regionIncluded, serverIncluded)) {
           Action<Row> action = new Action<Row>(r, ++posInList);
           setNonce(ng, r, action);
           retainedActions.add(action);
           // TODO: replica-get is not supported on this path
           byte[] regionName = loc.getRegionInfo().getRegionName();
           addAction(loc.getServerName(), regionName, action, actionsByServer, nonceGroup);
           it.remove();
         }
       }
     } while (retainedActions.isEmpty() && atLeastOne && (locationErrors == null));
 
     if (retainedActions.isEmpty()) return NO_REQS_RESULT;
 
     return submitMultiActions(tableName, retainedActions, nonceGroup, callback, null, needResults,
         locationErrors, locationErrorRows, actionsByServer, pool);
   }
 
   <CResult> AsyncRequestFuture submitMultiActions(TableName tableName,
       List<Action<Row>> retainedActions, long nonceGroup, Batch.Callback<CResult> callback,
       Object[] results, boolean needResults, List<Exception> locationErrors,
       List<Integer> locationErrorRows, Map<ServerName, MultiAction<Row>> actionsByServer,
       ExecutorService pool) {
     AsyncRequestFutureImpl<CResult> ars = createAsyncRequestFuture(
       tableName, retainedActions, nonceGroup, pool, callback, results, needResults);
     // Add location errors if any
     if (locationErrors != null) {
       for (int i = 0; i < locationErrors.size(); ++i) {
         int originalIndex = locationErrorRows.get(i);
         Row row = retainedActions.get(originalIndex).getAction();
         ars.manageError(originalIndex, row,
             Retry.NO_LOCATION_PROBLEM, locationErrors.get(i), null);
       }
     }
     ars.sendMultiAction(actionsByServer, 1, null, false);
     return ars;
   }
 
   /**
    * Helper that is used when grouping the actions per region server.
    *
    * @param loc - the destination. Must not be null.
    * @param action - the action to add to the multiaction
    * @param actionsByServer the multiaction per server
    * @param nonceGroup Nonce group.
    */
   private static void addAction(ServerName server, byte[] regionName, Action<Row> action,
       Map<ServerName, MultiAction<Row>> actionsByServer, long nonceGroup) {
     MultiAction<Row> multiAction = actionsByServer.get(server);
     if (multiAction == null) {
       multiAction = new MultiAction<Row>();
       actionsByServer.put(server, multiAction);
     }
     if (action.hasNonce() && !multiAction.hasNonceGroup()) {
       multiAction.setNonceGroup(nonceGroup);
     }
 
     multiAction.add(regionName, action);
   }
 
   /**
    * Check if we should send new operations to this region or region server.
    * We're taking into account the past decision; if we have already accepted
    * operation on a given region, we accept all operations for this region.
    *
    * @param loc; the region and the server name we want to use.
    * @return true if this region is considered as busy.
    */
   protected boolean canTakeOperation(HRegionLocation loc,
                                      Map<HRegionInfo, Boolean> regionsIncluded,
                                      Map<ServerName, Boolean> serversIncluded) {
     HRegionInfo regionInfo = loc.getRegionInfo();
     Boolean regionPrevious = regionsIncluded.get(regionInfo);
 
     if (regionPrevious != null) {
       // We already know what to do with this region.
       return regionPrevious;
     }
 
     Boolean serverPrevious = serversIncluded.get(loc.getServerName());
     if (Boolean.FALSE.equals(serverPrevious)) {
       // It's a new region, on a region server that we have already excluded.
       regionsIncluded.put(regionInfo, Boolean.FALSE);
       return false;
     }
 
     AtomicInteger regionCnt = taskCounterPerRegion.get(loc.getRegionInfo().getRegionName());
     if (regionCnt != null && regionCnt.get() >= maxConcurrentTasksPerRegion) {
       // Too many tasks on this region already.
       regionsIncluded.put(regionInfo, Boolean.FALSE);
       return false;
     }
 
     if (serverPrevious == null) {
       // The region is ok, but we need to decide for this region server.
       int newServers = 0; // number of servers we're going to contact so far
       for (Map.Entry<ServerName, Boolean> kv : serversIncluded.entrySet()) {
         if (kv.getValue()) {
           newServers++;
         }
       }
 
       // Do we have too many total tasks already?
       boolean ok = (newServers + tasksInProgress.get()) < maxTotalConcurrentTasks;
 
       if (ok) {
         // If the total is fine, is it ok for this individual server?
         AtomicInteger serverCnt = taskCounterPerServer.get(loc.getServerName());
         ok = (serverCnt == null || serverCnt.get() < maxConcurrentTasksPerServer);
       }
 
       if (!ok) {
         regionsIncluded.put(regionInfo, Boolean.FALSE);
         serversIncluded.put(loc.getServerName(), Boolean.FALSE);
         return false;
       }
 
       serversIncluded.put(loc.getServerName(), Boolean.TRUE);
     } else {
       assert serverPrevious.equals(Boolean.TRUE);
     }
 
     regionsIncluded.put(regionInfo, Boolean.TRUE);
 
     return true;
   }
 
   /**
    * See {@link #submitAll(ExecutorService, TableName, List, org.apache.hadoop.hbase.client.coprocessor.Batch.Callback, Object[])}.
    * Uses default ExecutorService for this AP (must have been created with one).
    */
   public <CResult> AsyncRequestFuture submitAll(TableName tableName,
       List<? extends Row> rows, Batch.Callback<CResult> callback, Object[] results) {
     return submitAll(null, tableName, rows, callback, results, null, operationTimeout, rpcTimeout);
   }
 
   public <CResult> AsyncRequestFuture submitAll(ExecutorService pool, TableName tableName,
       List<? extends Row> rows, Batch.Callback<CResult> callback, Object[] results) {
     return submitAll(pool, tableName, rows, callback, results, null, operationTimeout, rpcTimeout);
   }
   /**
    * Submit immediately the list of rows, whatever the server status. Kept for backward
    * compatibility: it allows to be used with the batch interface that return an array of objects.
    *
    * @param pool ExecutorService to use.
    * @param tableName name of the table for which the submission is made.
    * @param rows the list of rows.
    * @param callback the callback.
    * @param results Optional array to return the results thru; backward compat.
    */
   public <CResult> AsyncRequestFuture submitAll(ExecutorService pool, TableName tableName,
       List<? extends Row> rows, Batch.Callback<CResult> callback, Object[] results,
       PayloadCarryingServerCallable callable, int operationTimeout, int rpcTimeout) {
     List<Action<Row>> actions = new ArrayList<Action<Row>>(rows.size());
 
     // The position will be used by the processBatch to match the object array returned.
     int posInList = -1;
     NonceGenerator ng = this.connection.getNonceGenerator();
     for (Row r : rows) {
       posInList++;
       if (r instanceof Put) {
         Put put = (Put) r;
         if (put.isEmpty()) {
           throw new IllegalArgumentException("No columns to insert for #" + (posInList+1)+ " item");
         }
       }
       Action<Row> action = new Action<Row>(r, posInList);
       setNonce(ng, r, action);
       actions.add(action);
     }
     AsyncRequestFutureImpl<CResult> ars = createAsyncRequestFuture(
         tableName, actions, ng.getNonceGroup(), getPool(pool), callback, results, results != null,
         callable, operationTimeout, rpcTimeout);
     ars.groupAndSendMultiAction(actions, 1);
     return ars;
   }
 
   private static void setNonce(NonceGenerator ng, Row r, Action<Row> action) {
     if (!(r instanceof Append) && !(r instanceof Increment)) return;
     action.setNonce(ng.newNonce()); // Action handles NO_NONCE, so it's ok if ng is disabled.
   }
 
   /**
    * The context, and return value, for a single submit/submitAll call.
    * Note on how this class (one AP submit) works. Initially, all requests are split into groups
    * by server; request is sent to each server in parallel; the RPC calls are not async so a
    * thread per server is used. Every time some actions fail, regions/locations might have
    * changed, so we re-group them by server and region again and send these groups in parallel
    * too. The result, in case of retries, is a "tree" of threads, with parent exiting after
    * scheduling children. This is why lots of code doesn't require any synchronization.
    */
   protected class AsyncRequestFutureImpl<CResult> implements AsyncRequestFuture {
 
     /**
      * Runnable (that can be submitted to thread pool) that waits for when it's time
      * to issue replica calls, finds region replicas, groups the requests by replica and
      * issues the calls (on separate threads, via sendMultiAction).
      * This is done on a separate thread because we don't want to wait on user thread for
      * our asynchronous call, and usually we have to wait before making replica calls.
      */
     private final class ReplicaCallIssuingRunnable implements Runnable {
       private final long startTime;
       private final List<Action<Row>> initialActions;
 
       public ReplicaCallIssuingRunnable(List<Action<Row>> initialActions, long startTime) {
         this.initialActions = initialActions;
         this.startTime = startTime;
       }
 
       @Override
       public void run() {
         boolean done = false;
         if (primaryCallTimeoutMicroseconds > 0) {
           try {
             done = waitUntilDone(startTime * 1000L + primaryCallTimeoutMicroseconds);
           } catch (InterruptedException ex) {
             LOG.error("Replica thread was interrupted - no replica calls: " + ex.getMessage());
             return;
           }
         }
         if (done) return; // Done within primary timeout
         Map<ServerName, MultiAction<Row>> actionsByServer =
             new HashMap<ServerName, MultiAction<Row>>();
         List<Action<Row>> unknownLocActions = new ArrayList<Action<Row>>();
         if (replicaGetIndices == null) {
           for (int i = 0; i < results.length; ++i) {
             addReplicaActions(i, actionsByServer, unknownLocActions);
           }
         } else {
           for (int replicaGetIndice : replicaGetIndices) {
             addReplicaActions(replicaGetIndice, actionsByServer, unknownLocActions);
           }
         }
         if (!actionsByServer.isEmpty()) {
           sendMultiAction(actionsByServer, 1, null, unknownLocActions.isEmpty());
         }
         if (!unknownLocActions.isEmpty()) {
           actionsByServer = new HashMap<ServerName, MultiAction<Row>>();
           for (Action<Row> action : unknownLocActions) {
             addReplicaActionsAgain(action, actionsByServer);
           }
           // Some actions may have completely failed, they are handled inside addAgain.
           if (!actionsByServer.isEmpty()) {
             sendMultiAction(actionsByServer, 1, null, true);
           }
         }
       }
 
       /**
        * Add replica actions to action map by server.
        * @param index Index of the original action.
        * @param actionsByServer The map by server to add it to.
        */
       private void addReplicaActions(int index, Map<ServerName, MultiAction<Row>> actionsByServer,
           List<Action<Row>> unknownReplicaActions) {
         if (results[index] != null) return; // opportunistic. Never goes from non-null to null.
         Action<Row> action = initialActions.get(index);
         RegionLocations loc = findAllLocationsOrFail(action, true);
         if (loc == null) return;
         HRegionLocation[] locs = loc.getRegionLocations();
         if (locs.length == 1) {
           LOG.warn("No replicas found for " + action.getAction());
           return;
         }
         synchronized (replicaResultLock) {
           // Don't run replica calls if the original has finished. We could do it e.g. if
           // original has already failed before first replica call (unlikely given retries),
           // but that would require additional synchronization w.r.t. returning to caller.
           if (results[index] != null) return;
           // We set the number of calls here. After that any path must call setResult/setError.
           // True even for replicas that are not found - if we refuse to send we MUST set error.
           results[index] = new ReplicaResultState(locs.length);
         }
         for (int i = 1; i < locs.length; ++i) {
           Action<Row> replicaAction = new Action<Row>(action, i);
           if (locs[i] != null) {
             addAction(locs[i].getServerName(), locs[i].getRegionInfo().getRegionName(),
                 replicaAction, actionsByServer, nonceGroup);
           } else {
             unknownReplicaActions.add(replicaAction);
           }
         }
       }
 
       private void addReplicaActionsAgain(
           Action<Row> action, Map<ServerName, MultiAction<Row>> actionsByServer) {
         if (action.getReplicaId() == RegionReplicaUtil.DEFAULT_REPLICA_ID) {
           throw new AssertionError("Cannot have default replica here");
         }
         HRegionLocation loc = getReplicaLocationOrFail(action);
         if (loc == null) return;
         addAction(loc.getServerName(), loc.getRegionInfo().getRegionName(),
             action, actionsByServer, nonceGroup);
       }
     }
 
     /**
      * Runnable (that can be submitted to thread pool) that submits MultiAction to a
      * single server. The server call is synchronous, therefore we do it on a thread pool.
      */
     private final class SingleServerRequestRunnable implements Runnable {
       private final MultiAction<Row> multiAction;
       private final int numAttempt;
       private final ServerName server;
       private final Set<PayloadCarryingServerCallable> callsInProgress;
 
       private SingleServerRequestRunnable(
           MultiAction<Row> multiAction, int numAttempt, ServerName server,
           Set<PayloadCarryingServerCallable> callsInProgress) {
         this.multiAction = multiAction;
         this.numAttempt = numAttempt;
         this.server = server;
         this.callsInProgress = callsInProgress;
       }
 
       @Override
       public void run() {
         MultiResponse res;
         PayloadCarryingServerCallable callable = currentCallable;
         try {
           // setup the callable based on the actions, if we don't have one already from the request
           if (callable == null) {
             callable = createCallable(server, tableName, multiAction);
           }
           RpcRetryingCaller<MultiResponse> caller = createCaller(callable, rpcTimeout);
           try {
             if (callsInProgress != null) {
               callsInProgress.add(callable);
             }
             res = caller.callWithoutRetries(callable, operationTimeout);
             if (res == null) {
               // Cancelled
               return;
             }
           } catch (IOException e) {
             // The service itself failed . It may be an error coming from the communication
             //   layer, but, as well, a functional error raised by the server.
             receiveGlobalFailure(multiAction, server, numAttempt, e);
             return;
           } catch (Throwable t) {
             // This should not happen. Let's log & retry anyway.
             LOG.error("#" + id + ", Caught throwable while calling. This is unexpected." +
                 " Retrying. Server is " + server + ", tableName=" + tableName, t);
             receiveGlobalFailure(multiAction, server, numAttempt, t);
             return;
           }
 
           // Normal case: we received an answer from the server, and it's not an exception.
           receiveMultiAction(multiAction, server, res, numAttempt);
         } catch (Throwable t) {
           // Something really bad happened. We are on the send thread that will now die.
           LOG.error("Internal AsyncProcess #" + id + " error for "
               + tableName + " processing for " + server, t);
           throw new RuntimeException(t);
         } finally {
           decTaskCounters(multiAction.getRegions(), server);
           if (callsInProgress != null && callable != null) {
             callsInProgress.remove(callable);
           }
         }
       }
     }
 
     private final Batch.Callback<CResult> callback;
     private final BatchErrors errors;
     private final ConnectionManager.ServerErrorTracker errorsByServer;
     private final ExecutorService pool;
     private final Set<PayloadCarryingServerCallable> callsInProgress;
 
 
     private final TableName tableName;
     private final AtomicLong actionsInProgress = new AtomicLong(-1);
     /**
      * The lock controls access to results. It is only held when populating results where
      * there might be several callers (eventual consistency gets). For other requests,
      * there's one unique call going on per result index.
      */
     private final Object replicaResultLock = new Object();
     /**
      * Result array.  Null if results are not needed. Otherwise, each index corresponds to
      * the action index in initial actions submitted. For most request types, has null-s for
      * requests that are not done, and result/exception for those that are done.
      * For eventual-consistency gets, initially the same applies; at some point, replica calls
      * might be started, and ReplicaResultState is put at the corresponding indices. The
      * returning calls check the type to detect when this is the case. After all calls are done,
      * ReplicaResultState-s are replaced with results for the user.
      */
     private final Object[] results;
     /**
      * Indices of replica gets in results. If null, all or no actions are replica-gets.
      */
     private final int[] replicaGetIndices;
     private final boolean hasAnyReplicaGets;
     private final long nonceGroup;
     private PayloadCarryingServerCallable currentCallable;
     private int operationTimeout;
     private int rpcTimeout;
     private RetryingTimeTracker tracker;
 
     public AsyncRequestFutureImpl(TableName tableName, List<Action<Row>> actions, long nonceGroup,
         ExecutorService pool, boolean needResults, Object[] results,
         Batch.Callback<CResult> callback, PayloadCarryingServerCallable callable,
         int operationTimeout, int rpcTimeout) {
       this.pool = pool;
       this.callback = callback;
       this.nonceGroup = nonceGroup;
       this.tableName = tableName;
       this.actionsInProgress.set(actions.size());
       if (results != null) {
         assert needResults;
         if (results.length != actions.size()) {
           throw new AssertionError("results.length");
         }
         this.results = results;
         for (int i = 0; i != this.results.length; ++i) {
           results[i] = null;
         }
       } else {
         this.results = needResults ? new Object[actions.size()] : null;
       }
       List<Integer> replicaGetIndices = null;
       boolean hasAnyReplicaGets = false;
       if (needResults) {
         // Check to see if any requests might require replica calls.
         // We expect that many requests will consist of all or no multi-replica gets; in such
         // cases we would just use a boolean (hasAnyReplicaGets). If there's a mix, we will
         // store the list of action indexes for which replica gets are possible, and set
         // hasAnyReplicaGets to true.
         boolean hasAnyNonReplicaReqs = false;
         int posInList = 0;
         for (Action<Row> action : actions) {
           boolean isReplicaGet = isReplicaGet(action.getAction());
           if (isReplicaGet) {
             hasAnyReplicaGets = true;
             if (hasAnyNonReplicaReqs) { // Mixed case
               if (replicaGetIndices == null) {
                 replicaGetIndices = new ArrayList<Integer>(actions.size() - 1);
               }
               replicaGetIndices.add(posInList);
             }
           } else if (!hasAnyNonReplicaReqs) {
             // The first non-multi-replica request in the action list.
             hasAnyNonReplicaReqs = true;
             if (posInList > 0) {
               // Add all the previous requests to the index lists. We know they are all
               // replica-gets because this is the first non-multi-replica request in the list.
               replicaGetIndices = new ArrayList<Integer>(actions.size() - 1);
               for (int i = 0; i < posInList; ++i) {
                 replicaGetIndices.add(i);
               }
             }
           }
           ++posInList;
         }
       }
       this.hasAnyReplicaGets = hasAnyReplicaGets;
       if (replicaGetIndices != null) {
         this.replicaGetIndices = new int[replicaGetIndices.size()];
         int i = 0;
         for (Integer el : replicaGetIndices) {
           this.replicaGetIndices[i++] = el;
         }
       } else {
         this.replicaGetIndices = null;
       }
       this.callsInProgress = !hasAnyReplicaGets ? null :
           Collections.newSetFromMap(
               new ConcurrentHashMap<PayloadCarryingServerCallable, Boolean>());
 
       this.errorsByServer = createServerErrorTracker();
       this.errors = (globalErrors != null) ? globalErrors : new BatchErrors();
       this.currentCallable = callable;
       this.operationTimeout = operationTimeout;
       this.rpcTimeout = rpcTimeout;
       if (callable == null) {
         this.tracker = new RetryingTimeTracker().start();
       }
     }
 
     public Set<PayloadCarryingServerCallable> getCallsInProgress() {
       return callsInProgress;
     }
 
     /**
      * Group a list of actions per region servers, and send them.
      *
      * @param currentActions - the list of row to submit
      * @param numAttempt - the current numAttempt (first attempt is 1)
      */
     private void groupAndSendMultiAction(List<Action<Row>> currentActions, int numAttempt) {
       Map<ServerName, MultiAction<Row>> actionsByServer =
           new HashMap<ServerName, MultiAction<Row>>();
 
       boolean isReplica = false;
       List<Action<Row>> unknownReplicaActions = null;
       for (Action<Row> action : currentActions) {
         RegionLocations locs = findAllLocationsOrFail(action, true);
         if (locs == null) continue;
         boolean isReplicaAction = !RegionReplicaUtil.isDefaultReplica(action.getReplicaId());
         if (isReplica && !isReplicaAction) {
           // This is the property of the current implementation, not a requirement.
           throw new AssertionError("Replica and non-replica actions in the same retry");
         }
         isReplica = isReplicaAction;
         HRegionLocation loc = locs.getRegionLocation(action.getReplicaId());
         if (loc == null || loc.getServerName() == null) {
           if (isReplica) {
             if (unknownReplicaActions == null) {
               unknownReplicaActions = new ArrayList<Action<Row>>();
             }
             unknownReplicaActions.add(action);
           } else {
             // TODO: relies on primary location always being fetched
             manageLocationError(action, null);
           }
         } else {
           byte[] regionName = loc.getRegionInfo().getRegionName();
           addAction(loc.getServerName(), regionName, action, actionsByServer, nonceGroup);
         }
       }
       boolean doStartReplica = (numAttempt == 1 && !isReplica && hasAnyReplicaGets);
       boolean hasUnknown = unknownReplicaActions != null && !unknownReplicaActions.isEmpty();
 
       if (!actionsByServer.isEmpty()) {
         // If this is a first attempt to group and send, no replicas, we need replica thread.
         sendMultiAction(actionsByServer, numAttempt, (doStartReplica && !hasUnknown)
             ? currentActions : null, numAttempt > 1 && !hasUnknown);
       }
 
       if (hasUnknown) {
         actionsByServer = new HashMap<ServerName, MultiAction<Row>>();
         for (Action<Row> action : unknownReplicaActions) {
           HRegionLocation loc = getReplicaLocationOrFail(action);
           if (loc == null) continue;
           byte[] regionName = loc.getRegionInfo().getRegionName();
           addAction(loc.getServerName(), regionName, action, actionsByServer, nonceGroup);
         }
         if (!actionsByServer.isEmpty()) {
           sendMultiAction(
               actionsByServer, numAttempt, doStartReplica ? currentActions : null, true);
         }
       }
     }
 
     private HRegionLocation getReplicaLocationOrFail(Action<Row> action) {
       // We are going to try get location once again. For each action, we'll do it once
       // from cache, because the previous calls in the loop might populate it.
       int replicaId = action.getReplicaId();
       RegionLocations locs = findAllLocationsOrFail(action, true);
       if (locs == null) return null; // manageError already called
       HRegionLocation loc = locs.getRegionLocation(replicaId);
       if (loc == null || loc.getServerName() == null) {
         locs = findAllLocationsOrFail(action, false);
         if (locs == null) return null; // manageError already called
         loc = locs.getRegionLocation(replicaId);
       }
       if (loc == null || loc.getServerName() == null) {
         manageLocationError(action, null);
         return null;
       }
       return loc;
     }
 
     private void manageLocationError(Action<Row> action, Exception ex) {
       String msg = "Cannot get replica " + action.getReplicaId()
           + " location for " + action.getAction();
       LOG.error(msg);
       if (ex == null) {
         ex = new IOException(msg);
       }
       manageError(action.getOriginalIndex(), action.getAction(),
           Retry.NO_LOCATION_PROBLEM, ex, null);
     }
 
     private RegionLocations findAllLocationsOrFail(Action<Row> action, boolean useCache) {
       if (action.getAction() == null) throw new IllegalArgumentException("#" + id +
           ", row cannot be null");
       RegionLocations loc = null;
       try {
         loc = connection.locateRegion(
             tableName, action.getAction().getRow(), useCache, true, action.getReplicaId());
       } catch (IOException ex) {
         manageLocationError(action, ex);
       }
       return loc;
     }
 
     /**
      * Send a multi action structure to the servers, after a delay depending on the attempt
      * number. Asynchronous.
      *
      * @param actionsByServer the actions structured by regions
      * @param numAttempt the attempt number.
      * @param actionsForReplicaThread original actions for replica thread; null on non-first call.
      */
     private void sendMultiAction(Map<ServerName, MultiAction<Row>> actionsByServer,
         int numAttempt, List<Action<Row>> actionsForReplicaThread, boolean reuseThread) {
       // Run the last item on the same thread if we are already on a send thread.
       // We hope most of the time it will be the only item, so we can cut down on threads.
       int actionsRemaining = actionsByServer.size();
       // This iteration is by server (the HRegionLocation comparator is by server portion only).
       for (Map.Entry<ServerName, MultiAction<Row>> e : actionsByServer.entrySet()) {
         ServerName server = e.getKey();
         MultiAction<Row> multiAction = e.getValue();
         incTaskCounters(multiAction.getRegions(), server);
         Collection<? extends Runnable> runnables = getNewMultiActionRunnable(server, multiAction,
             numAttempt);
         // make sure we correctly count the number of runnables before we try to reuse the send
         // thread, in case we had to split the request into different runnables because of backoff
         if (runnables.size() > actionsRemaining) {
           actionsRemaining = runnables.size();
         }
 
         // run all the runnables
         // HBASE-17475: Do not reuse the thread after stack reach a certain depth to prevent stack overflow
         // for now, we use HConstants.DEFAULT_HBASE_CLIENT_RETRIES_NUMBER to control the depth
         for (Runnable runnable : runnables) {
           if ((--actionsRemaining == 0) && reuseThread
               && numAttempt % HConstants.DEFAULT_HBASE_CLIENT_RETRIES_NUMBER != 0) {
             runnable.run();
           } else {
             try {
               pool.submit(runnable);
             } catch (Throwable t) {
               if (t instanceof RejectedExecutionException) {
                 // This should never happen. But as the pool is provided by the end user,
                // let's secure this a little.
                LOG.warn("#" + id + ", the task was rejected by the pool. This is unexpected." +
                   " Server is " + server.getServerName(), t);
               } else {
                 // see #HBASE-14359 for more details
                 LOG.warn("Caught unexpected exception/error: ", t);
               }
               decTaskCounters(multiAction.getRegions(), server);
               // We're likely to fail again, but this will increment the attempt counter,
              // so it will finish.
               receiveGlobalFailure(multiAction, server, numAttempt, t);
             }
           }
         }
       }
 
       if (actionsForReplicaThread != null) {
         startWaitingForReplicaCalls(actionsForReplicaThread);
       }
     }
 
     private Collection<? extends Runnable> getNewMultiActionRunnable(ServerName server,
         MultiAction<Row> multiAction,
         int numAttempt) {
       // no stats to manage, just do the standard action
       if (AsyncProcess.this.connection.getStatisticsTracker() == null) {
         if (connection.getConnectionMetrics() != null) {
           connection.getConnectionMetrics().incrNormalRunners();
         }
         return Collections.singletonList(Trace.wrap("AsyncProcess.sendMultiAction",
             new SingleServerRequestRunnable(multiAction, numAttempt, server, callsInProgress)));
       }
 
       // group the actions by the amount of delay
       Map<Long, DelayingRunner> actions = new HashMap<Long, DelayingRunner>(multiAction
           .size());
 
       // split up the actions
       for (Map.Entry<byte[], List<Action<Row>>> e : multiAction.actions.entrySet()) {
         Long backoff = getBackoff(server, e.getKey());
         DelayingRunner runner = actions.get(backoff);
         if (runner == null) {
           actions.put(backoff, new DelayingRunner(backoff, e));
         } else {
           runner.add(e);
         }
       }
 
       List<Runnable> toReturn = new ArrayList<Runnable>(actions.size());
       for (DelayingRunner runner : actions.values()) {
         String traceText = "AsyncProcess.sendMultiAction";
         Runnable runnable =
             new SingleServerRequestRunnable(runner.getActions(), numAttempt, server,
                 callsInProgress);
         // use a delay runner only if we need to sleep for some time
         if (runner.getSleepTime() > 0) {
           runner.setRunner(runnable);
           traceText = "AsyncProcess.clientBackoff.sendMultiAction";
           runnable = runner;
           if (connection.getConnectionMetrics() != null) {
             connection.getConnectionMetrics().incrDelayRunners();
             connection.getConnectionMetrics().updateDelayInterval(runner.getSleepTime());
           }
         } else {
           if (connection.getConnectionMetrics() != null) {
             connection.getConnectionMetrics().incrNormalRunners();
           }
         }
         runnable = Trace.wrap(traceText, runnable);
         toReturn.add(runnable);
 
       }
       return toReturn;
     }
 
     /**
      * @param server server location where the target region is hosted
      * @param regionName name of the region which we are going to write some data
      * @return the amount of time the client should wait until it submit a request to the
      * specified server and region
      */
     private Long getBackoff(ServerName server, byte[] regionName) {
       ServerStatisticTracker tracker = AsyncProcess.this.connection.getStatisticsTracker();
       ServerStatistics stats = tracker.getStats(server);
       return AsyncProcess.this.connection.getBackoffPolicy()
           .getBackoffTime(server, regionName, stats);
     }
 
     /**
      * Starts waiting to issue replica calls on a different thread; or issues them immediately.
      */
     private void startWaitingForReplicaCalls(List<Action<Row>> actionsForReplicaThread) {
       long startTime = EnvironmentEdgeManager.currentTime();
       ReplicaCallIssuingRunnable replicaRunnable = new ReplicaCallIssuingRunnable(
           actionsForReplicaThread, startTime);
       if (primaryCallTimeoutMicroseconds == 0) {
         // Start replica calls immediately.
         replicaRunnable.run();
       } else {
         // Start the thread that may kick off replica gets.
         // TODO: we could do it on the same thread, but it's a user thread, might be a bad idea.
         try {
           pool.submit(replicaRunnable);
         } catch (RejectedExecutionException ree) {
           LOG.warn("#" + id + ", replica task was rejected by the pool - no replica calls", ree);
         }
       }
     }
 
     /**
      * Check that we can retry acts accordingly: logs, set the error status.
      *
      * @param originalIndex the position in the list sent
      * @param row           the row
      * @param canRetry      if false, we won't retry whatever the settings.
      * @param throwable     the throwable, if any (can be null)
      * @param server        the location, if any (can be null)
      * @return true if the action can be retried, false otherwise.
      */
     public Retry manageError(int originalIndex, Row row, Retry canRetry,
                                 Throwable throwable, ServerName server) {
       if (canRetry == Retry.YES
           && throwable != null && (throwable instanceof DoNotRetryIOException ||
           throwable instanceof NeedUnmanagedConnectionException)) {
         canRetry = Retry.NO_NOT_RETRIABLE;
       }
 
       if (canRetry != Retry.YES) {
         // Batch.Callback<Res> was not called on failure in 0.94. We keep this.
         setError(originalIndex, row, throwable, server);
       } else if (isActionComplete(originalIndex, row)) {
         canRetry = Retry.NO_OTHER_SUCCEEDED;
       }
       return canRetry;
     }
 
     /**
      * Resubmit all the actions from this multiaction after a failure.
      *
      * @param rsActions  the actions still to do from the initial list
      * @param server   the destination
      * @param numAttempt the number of attempts so far
      * @param t the throwable (if any) that caused the resubmit
      */
     private void receiveGlobalFailure(
         MultiAction<Row> rsActions, ServerName server, int numAttempt, Throwable t) {
       errorsByServer.reportServerError(server);
       Retry canRetry = errorsByServer.canRetryMore(numAttempt)
           ? Retry.YES : Retry.NO_RETRIES_EXHAUSTED;
 
       if (tableName == null && ClientExceptionsUtil.isMetaClearingException(t)) {
         // tableName is null when we made a cross-table RPC call.
         connection.clearCaches(server);
       }
       int failed = 0, stopped = 0;
       List<Action<Row>> toReplay = new ArrayList<Action<Row>>();
       for (Map.Entry<byte[], List<Action<Row>>> e : rsActions.actions.entrySet()) {
         byte[] regionName = e.getKey();
         byte[] row = e.getValue().iterator().next().getAction().getRow();
         // Do not use the exception for updating cache because it might be coming from
         // any of the regions in the MultiAction.
         try {
           if (tableName != null) {
             connection.updateCachedLocations(tableName, regionName, row,
               ClientExceptionsUtil.isMetaClearingException(t) ? null : t, server);
           }
         } catch (Throwable ex) {
           // That should never happen, but if it did, we want to make sure
           // we still process errors
           LOG.error("Couldn't update cached region locations: " + ex);
         }
         for (Action<Row> action : e.getValue()) {
           Retry retry = manageError(
               action.getOriginalIndex(), action.getAction(), canRetry, t, server);
           if (retry == Retry.YES) {
             toReplay.add(action);
           } else if (retry == Retry.NO_OTHER_SUCCEEDED) {
             ++stopped;
           } else {
             ++failed;
           }
         }
       }
 
       if (toReplay.isEmpty()) {
         logNoResubmit(server, numAttempt, rsActions.size(), t, failed, stopped);
       } else {
         resubmit(server, toReplay, numAttempt, rsActions.size(), t);
       }
     }
 
     /**
      * Log as much info as possible, and, if there is something to replay,
      * submit it again after a back off sleep.
      */
     private void resubmit(ServerName oldServer, List<Action<Row>> toReplay,
         int numAttempt, int failureCount, Throwable throwable) {
       // We have something to replay. We're going to sleep a little before.
 
       // We have two contradicting needs here:
       //  1) We want to get the new location after having slept, as it may change.
       //  2) We want to take into account the location when calculating the sleep time.
       //  3) If all this is just because the response needed to be chunked try again FAST.
       // It should be possible to have some heuristics to take the right decision. Short term,
       //  we go for one.
       boolean retryImmediately = throwable instanceof RetryImmediatelyException;
       int nextAttemptNumber = retryImmediately ? numAttempt : numAttempt + 1;
       long backOffTime = retryImmediately ? 0 :
           errorsByServer.calculateBackoffTime(oldServer, pause);
       if (numAttempt > startLogErrorsCnt) {
         // We use this value to have some logs when we have multiple failures, but not too many
         //  logs, as errors are to be expected when a region moves, splits and so on
         LOG.info(createLog(numAttempt, failureCount, toReplay.size(),
             oldServer, throwable, backOffTime, true, null, -1, -1));
       }
 
       try {
         if (backOffTime > 0) {
           Thread.sleep(backOffTime);
         }
       } catch (InterruptedException e) {
         LOG.warn("#" + id + ", not sent: " + toReplay.size() + " operations, " + oldServer, e);
         Thread.currentThread().interrupt();
         return;
       }
 
       groupAndSendMultiAction(toReplay, nextAttemptNumber);
     }
 
     private void logNoResubmit(ServerName oldServer, int numAttempt,
         int failureCount, Throwable throwable, int failed, int stopped) {
       if (failureCount != 0 || numAttempt > startLogErrorsCnt + 1) {
         String timeStr = new Date(errorsByServer.getStartTrackingTime()).toString();
         String logMessage = createLog(numAttempt, failureCount, 0, oldServer,
             throwable, -1, false, timeStr, failed, stopped);
         if (failed != 0) {
           // Only log final failures as warning
           LOG.warn(logMessage);
         } else {
           LOG.info(logMessage);
         }
       }
     }
 
     /**
      * Called when we receive the result of a server query.
      *
      * @param multiAction    - the multiAction we sent
      * @param server       - the location. It's used as a server name.
      * @param responses      - the response, if any
      * @param numAttempt     - the attempt
      */
     private void receiveMultiAction(MultiAction<Row> multiAction,
         ServerName server, MultiResponse responses, int numAttempt) {
        assert responses != null;
 
       // Success or partial success
       // Analyze detailed results. We can still have individual failures to be redo.
       // two specific throwables are managed:
       //  - DoNotRetryIOException: we continue to retry for other actions
       //  - RegionMovedException: we update the cache with the new region location
 
       List<Action<Row>> toReplay = new ArrayList<Action<Row>>();
       Throwable throwable = null;
       int failureCount = 0;
       boolean canRetry = true;
 
       Map<byte[], MultiResponse.RegionResult> results = responses.getResults();
       updateStats(server, results);
 
       int failed = 0, stopped = 0;
       // Go by original action.
       for (Map.Entry<byte[], List<Action<Row>>> regionEntry : multiAction.actions.entrySet()) {
         byte[] regionName = regionEntry.getKey();
         Map<Integer, Object> regionResults = results.get(regionName) == null
             ?  null : results.get(regionName).result;
         if (regionResults == null) {
           if (!responses.getExceptions().containsKey(regionName)) {
             LOG.error("Server sent us neither results nor exceptions for "
                 + Bytes.toStringBinary(regionName));
             responses.getExceptions().put(regionName, new RuntimeException("Invalid response"));
           }
           continue;
         }
         boolean regionFailureRegistered = false;
         for (Action<Row> sentAction : regionEntry.getValue()) {
           Object result = regionResults.get(sentAction.getOriginalIndex());
           // Failure: retry if it's make sense else update the errors lists
           if (result == null || result instanceof Throwable) {
             Row row = sentAction.getAction();
             throwable = ClientExceptionsUtil.findException(result);
             // Register corresponding failures once per server/once per region.
             if (!regionFailureRegistered) {
               regionFailureRegistered = true;
               try {
                 connection.updateCachedLocations(
                   tableName, regionName, row.getRow(), result, server);
               } catch (Throwable ex) {
                 // That should never happen, but if it did, we want to make sure
                 // we still process errors
                 LOG.error("Couldn't update cached region locations: " + ex);
               }
             }
             if (failureCount == 0) {
               errorsByServer.reportServerError(server);
               // We determine canRetry only once for all calls, after reporting server failure.
               canRetry = errorsByServer.canRetryMore(numAttempt);
             }
             ++failureCount;
             Retry retry = manageError(sentAction.getOriginalIndex(), row,
                 canRetry ? Retry.YES : Retry.NO_RETRIES_EXHAUSTED, (Throwable) result, server);
             if (retry == Retry.YES) {
               toReplay.add(sentAction);
             } else if (retry == Retry.NO_OTHER_SUCCEEDED) {
               ++stopped;
             } else {
               ++failed;
             }
           } else {
             if (callback != null) {
               try {
                 //noinspection unchecked
                 // TODO: would callback expect a replica region name if it gets one?
                 this.callback.update(regionName, sentAction.getAction().getRow(), (CResult) result);
               } catch (Throwable t) {
                 LOG.error("User callback threw an exception for "
                     + Bytes.toStringBinary(regionName) + ", ignoring", t);
               }
             }
             setResult(sentAction, result);
           }
         }
       }
 
       // The failures global to a region. We will use for multiAction we sent previously to find the
       //   actions to replay.
       for (Map.Entry<byte[], Throwable> throwableEntry : responses.getExceptions().entrySet()) {
         throwable = throwableEntry.getValue();
         byte[] region = throwableEntry.getKey();
         List<Action<Row>> actions = multiAction.actions.get(region);
         if (actions == null || actions.isEmpty()) {
           throw new IllegalStateException("Wrong response for the region: " +
               HRegionInfo.encodeRegionName(region));
         }
 
         if (failureCount == 0) {
           errorsByServer.reportServerError(server);
           canRetry = errorsByServer.canRetryMore(numAttempt);
         }
         if (null == tableName && ClientExceptionsUtil.isMetaClearingException(throwable)) {
           // For multi-actions, we don't have a table name, but we want to make sure to clear the
           // cache in case there were location-related exceptions. We don't to clear the cache
           // for every possible exception that comes through, however.
           connection.clearCaches(server);
         } else {
           try {
             connection.updateCachedLocations(
               tableName, region, actions.get(0).getAction().getRow(), throwable, server);
           } catch (Throwable ex) {
             // That should never happen, but if it did, we want to make sure
             // we still process errors
             LOG.error("Couldn't update cached region locations: " + ex);
           }
         }
         failureCount += actions.size();
 
         for (Action<Row> action : actions) {
           Row row = action.getAction();
           Retry retry = manageError(action.getOriginalIndex(), row,
               canRetry ? Retry.YES : Retry.NO_RETRIES_EXHAUSTED, throwable, server);
           if (retry == Retry.YES) {
             toReplay.add(action);
           } else if (retry == Retry.NO_OTHER_SUCCEEDED) {
             ++stopped;
           } else {
             ++failed;
           }
         }
       }
       if (toReplay.isEmpty()) {
         logNoResubmit(server, numAttempt, failureCount, throwable, failed, stopped);
       } else {
         resubmit(server, toReplay, numAttempt, failureCount, throwable);
       }
     }
 
     private String createLog(int numAttempt, int failureCount, int replaySize, ServerName sn,
         Throwable error, long backOffTime, boolean willRetry, String startTime,
         int failed, int stopped) {
       StringBuilder sb = new StringBuilder();
       sb.append("#").append(id).append(", table=").append(tableName).append(", ")
         .append("attempt=").append(numAttempt)
         .append("/").append(numTries).append(" ");
 
       if (failureCount > 0 || error != null){
         sb.append("failed=").append(failureCount).append("ops").append(", last exception: ").
             append(error == null ? "null" : error);
       } else {
         sb.append("succeeded");
       }
 
       sb.append(" on ").append(sn).append(", tracking started ").append(startTime);
 
       if (willRetry) {
         sb.append(", retrying after=").append(backOffTime).append("ms").
             append(", replay=").append(replaySize).append("ops");
       } else if (failureCount > 0) {
         if (stopped > 0) {
           sb.append("; not retrying ").append(stopped).append(" due to success from other replica");
         }
         if (failed > 0) {
           sb.append("; not retrying ").append(failed).append(" - final failure");
         }
 
       }
 
       return sb.toString();
     }
 
     /**
      * Sets the non-error result from a particular action.
      * @param action Action (request) that the server responded to.
      * @param result The result.
      */
     private void setResult(Action<Row> action, Object result) {
       if (result == null) {
         throw new RuntimeException("Result cannot be null");
       }
       ReplicaResultState state = null;
       boolean isStale = !RegionReplicaUtil.isDefaultReplica(action.getReplicaId());
       int index = action.getOriginalIndex();
       if (results == null) {
          decActionCounter(index);
          return; // Simple case, no replica requests.
       } else if ((state = trySetResultSimple(
           index, action.getAction(), false, result, null, isStale)) == null) {
         return; // Simple case, no replica requests.
       }
       assert state != null;
       // At this point we know that state is set to replica tracking class.
       // It could be that someone else is also looking at it; however, we know there can
       // only be one state object, and only one thread can set callCount to 0. Other threads
       // will either see state with callCount 0 after locking it; or will not see state at all
       // we will replace it with the result.
       synchronized (state) {
         if (state.callCount == 0) {
           return; // someone already set the result
         }
         state.callCount = 0;
       }
       synchronized (replicaResultLock) {
         if (results[index] != state) {
           throw new AssertionError("We set the callCount but someone else replaced the result");
         }
         results[index] = result;
       }
 
       decActionCounter(index);
     }
 
     /**
      * Sets the error from a particular action.
      * @param index Original action index.
      * @param row Original request.
      * @param throwable The resulting error.
      * @param server The source server.
      */
     private void setError(int index, Row row, Throwable throwable, ServerName server) {
       ReplicaResultState state = null;
       if (results == null) {
         // Note that we currently cannot have replica requests with null results. So it shouldn't
         // happen that multiple replica calls will call dAC for same actions with results == null.
         // Only one call per action should be present in this case.
         errors.add(throwable, row, server);
         decActionCounter(index);
         return; // Simple case, no replica requests.
       } else if ((state = trySetResultSimple(
           index, row, true, throwable, server, false)) == null) {
         return; // Simple case, no replica requests.
       }
       assert state != null;
       BatchErrors target = null; // Error will be added to final errors, or temp replica errors.
       boolean isActionDone = false;
       synchronized (state) {
         switch (state.callCount) {
           case 0: return; // someone already set the result
           case 1: { // All calls failed, we are the last error.
             target = errors;
             isActionDone = true;
             break;
           }
           default: {
             assert state.callCount > 1;
             if (state.replicaErrors == null) {
               state.replicaErrors = new BatchErrors();
             }
             target = state.replicaErrors;
             break;
           }
         }
         --state.callCount;
       }
       target.add(throwable, row, server);
       if (isActionDone) {
         if (state.replicaErrors != null) { // last call, no need to lock
           errors.merge(state.replicaErrors);
         }
         // See setResult for explanations.
         synchronized (replicaResultLock) {
           if (results[index] != state) {
             throw new AssertionError("We set the callCount but someone else replaced the result");
           }
           results[index] = throwable;
         }
         decActionCounter(index);
       }
     }
 
     /**
      * Checks if the action is complete; used on error to prevent needless retries.
      * Does not synchronize, assuming element index/field accesses are atomic.
      * This is an opportunistic optimization check, doesn't have to be strict.
      * @param index Original action index.
      * @param row Original request.
      */
     private boolean isActionComplete(int index, Row row) {
       if (!isReplicaGet(row)) return false;
       Object resObj = results[index];
       return (resObj != null) && (!(resObj instanceof ReplicaResultState)
           || ((ReplicaResultState)resObj).callCount == 0);
     }
 
     /**
      * Tries to set the result or error for a particular action as if there were no replica calls.
      * @return null if successful; replica state if there were in fact replica calls.
      */
     private ReplicaResultState trySetResultSimple(int index, Row row, boolean isError,
         Object result, ServerName server, boolean isFromReplica) {
       Object resObj = null;
       if (!isReplicaGet(row)) {
         if (isFromReplica) {
           throw new AssertionError("Unexpected stale result for " + row);
         }
         results[index] = result;
       } else {
         synchronized (replicaResultLock) {
           if ((resObj = results[index]) == null) {
             if (isFromReplica) {
               throw new AssertionError("Unexpected stale result for " + row);
             }
             results[index] = result;
           }
         }
       }
 
       ReplicaResultState rrs =
           (resObj instanceof ReplicaResultState) ? (ReplicaResultState)resObj : null;
       if (rrs == null && isError) {
         // The resObj is not replica state (null or already set).
         errors.add((Throwable)result, row, server);
       }
 
       if (resObj == null) {
         // resObj is null - no replica calls were made.
         decActionCounter(index);
         return null;
       }
       return rrs;
     }
 
     private void decActionCounter(int index) {
       long actionsRemaining = actionsInProgress.decrementAndGet();
       if (actionsRemaining < 0) {
         String error = buildDetailedErrorMsg("Incorrect actions in progress", index);
         throw new AssertionError(error);
       } else if (actionsRemaining == 0) {
         synchronized (actionsInProgress) {
           actionsInProgress.notifyAll();
         }
       }
     }
 
     private String buildDetailedErrorMsg(String string, int index) {
       StringBuilder error = new StringBuilder(string);
       error.append("; called for ").
         append(index).
         append(", actionsInProgress ").
         append(actionsInProgress.get()).
         append("; replica gets: ");
       if (replicaGetIndices != null) {
         for (int i = 0; i < replicaGetIndices.length; ++i) {
           error.append(replicaGetIndices[i]).append(", ");
         }
       } else {
         error.append(hasAnyReplicaGets ? "all" : "none");
       }
       error.append("; results ");
       if (results != null) {
         for (int i = 0; i < results.length; ++i) {
           Object o = results[i];
           error.append(((o == null) ? "null" : o.toString())).append(", ");
         }
       }
       return error.toString();
     }
 
     @Override
     public void waitUntilDone() throws InterruptedIOException {
       try {
         waitUntilDone(Long.MAX_VALUE);
       } catch (InterruptedException iex) {
         throw new InterruptedIOException(iex.getMessage());
       } finally {
         if (callsInProgress != null) {
           for (PayloadCarryingServerCallable clb : callsInProgress) {
             clb.cancel();
           }
         }
       }
     }
 
     private boolean waitUntilDone(long cutoff) throws InterruptedException {
       boolean hasWait = cutoff != Long.MAX_VALUE;
       long lastLog = EnvironmentEdgeManager.currentTime();
       long currentInProgress;
       while (0 != (currentInProgress = actionsInProgress.get())) {
         long now = EnvironmentEdgeManager.currentTime();
         if (hasWait && (now * 1000L) > cutoff) {
           return false;
         }
         if (!hasWait) { // Only log if wait is infinite.
           if (now > lastLog + 10000) {
             lastLog = now;
             LOG.info("#" + id + ", waiting for " + currentInProgress
                 + "  actions to finish on table: " + tableName);
             if (currentInProgress <= thresholdToLogUndoneTaskDetails) {
               logDetailsOfUndoneTasks(currentInProgress);
             }
           }
         }
         synchronized (actionsInProgress) {
           if (actionsInProgress.get() == 0) break;
           if (!hasWait) {
             actionsInProgress.wait(10);
           } else {
             long waitMicroSecond = Math.min(100000L, (cutoff - now * 1000L));
             TimeUnit.MICROSECONDS.timedWait(actionsInProgress, waitMicroSecond);
           }
         }
       }
       return true;
     }
 
     @Override
     public boolean hasError() {
       return errors.hasErrors();
     }
 
     @Override
     public List<? extends Row> getFailedOperations() {
       return errors.actions;
     }
 
     @Override
     public RetriesExhaustedWithDetailsException getErrors() {
       return errors.makeException();
     }
 
     @Override
     public Object[] getResults() throws InterruptedIOException {
       waitUntilDone();
       return results;
     }
 
     /**
      * Create a callable. Isolated to be easily overridden in the tests.
      */
     @VisibleForTesting
     protected MultiServerCallable<Row> createCallable(final ServerName server,
         TableName tableName, final MultiAction<Row> multi) {
       return new MultiServerCallable<Row>(connection, tableName, server,
           AsyncProcess.this.rpcFactory, multi, rpcTimeout, tracker);
     }
   }
 
   private void updateStats(ServerName server, Map<byte[], MultiResponse.RegionResult> results) {
     boolean metrics = AsyncProcess.this.connection.getConnectionMetrics() != null;
     boolean stats = AsyncProcess.this.connection.getStatisticsTracker() != null;
     if (!stats && !metrics) {
       return;
     }
     for (Map.Entry<byte[], MultiResponse.RegionResult> regionStats : results.entrySet()) {
       byte[] regionName = regionStats.getKey();
       ClientProtos.RegionLoadStats stat = regionStats.getValue().getStat();
       ResultStatsUtil.updateStats(AsyncProcess.this.connection.getStatisticsTracker(), server,
           regionName, stat);
       ResultStatsUtil.updateStats(AsyncProcess.this.connection.getConnectionMetrics(),
           server, regionName, stat);
     }
   }
 
   protected <CResult> AsyncRequestFutureImpl<CResult> createAsyncRequestFuture(
       TableName tableName, List<Action<Row>> actions, long nonceGroup, ExecutorService pool,
       Batch.Callback<CResult> callback, Object[] results, boolean needResults,
       PayloadCarryingServerCallable callable, int operationTimeout, int rpcTimeout) {
     return new AsyncRequestFutureImpl<CResult>(
         tableName, actions, nonceGroup, getPool(pool), needResults,
         results, callback, callable, operationTimeout, rpcTimeout);
   }
 
   @VisibleForTesting
   /** Create AsyncRequestFuture. Isolated to be easily overridden in the tests. */
   protected <CResult> AsyncRequestFutureImpl<CResult> createAsyncRequestFuture(
       TableName tableName, List<Action<Row>> actions, long nonceGroup, ExecutorService pool,
       Batch.Callback<CResult> callback, Object[] results, boolean needResults) {
     return createAsyncRequestFuture(
         tableName, actions, nonceGroup, pool, callback, results, needResults, null,
         operationTimeout, rpcTimeout);
   }
 
   /**
    * Create a caller. Isolated to be easily overridden in the tests.
    */
   @VisibleForTesting
   protected RpcRetryingCaller<MultiResponse> createCaller(PayloadCarryingServerCallable callable,
       int rpcTimeout) {
     return rpcCallerFactory.<MultiResponse> newCaller(rpcTimeout);
   }
 
   @VisibleForTesting
   /** Waits until all outstanding tasks are done. Used in tests. */
   void waitUntilDone() throws InterruptedIOException {
     waitForMaximumCurrentTasks(0, null);
   }
 
   /** Wait until the async does not have more than max tasks in progress. */
   private void waitForMaximumCurrentTasks(int max, String tableName)
       throws InterruptedIOException {
     waitForMaximumCurrentTasks(max, tasksInProgress, id, tableName);
   }
 
   // Break out this method so testable
   @VisibleForTesting
   void waitForMaximumCurrentTasks(int max, final AtomicLong tasksInProgress, final long id,
       String tableName) throws InterruptedIOException {
     long lastLog = EnvironmentEdgeManager.currentTime();
     long currentInProgress, oldInProgress = Long.MAX_VALUE;
     while ((currentInProgress = tasksInProgress.get()) > max) {
       if (oldInProgress != currentInProgress) { // Wait for in progress to change.
         long now = EnvironmentEdgeManager.currentTime();
         if (now > lastLog + 10000) {
           lastLog = now;
           LOG.info("#" + id + ", waiting for some tasks to finish. Expected max="
               + max + ", tasksInProgress=" + currentInProgress +
               " hasError=" + hasError() + tableName == null ? "" : ", tableName=" + tableName);
           if (currentInProgress <= thresholdToLogUndoneTaskDetails) {
             logDetailsOfUndoneTasks(currentInProgress);
           }
         }
       }
       oldInProgress = currentInProgress;
       try {
         synchronized (tasksInProgress) {
           if (tasksInProgress.get() == oldInProgress) {
             tasksInProgress.wait(10);
           }
         }
       } catch (InterruptedException e) {
         throw new InterruptedIOException("#" + id + ", interrupted." +
             " currentNumberOfTask=" + currentInProgress);
       }
     }
   }
 
   private void logDetailsOfUndoneTasks(long taskInProgress) {
     ArrayList<ServerName> servers = new ArrayList<ServerName>();
     for (Map.Entry<ServerName, AtomicInteger> entry : taskCounterPerServer.entrySet()) {
       if (entry.getValue().get() > 0) {
         servers.add(entry.getKey());
       }
     }
     LOG.info("Left over " + taskInProgress + " task(s) are processed on server(s): " + servers);
     if (taskInProgress <= THRESHOLD_TO_LOG_REGION_DETAILS) {
       ArrayList<String> regions = new ArrayList<String>();
       for (Map.Entry<byte[], AtomicInteger> entry : taskCounterPerRegion.entrySet()) {
         if (entry.getValue().get() > 0) {
           regions.add(Bytes.toString(entry.getKey()));
         }
       }
       LOG.info("Regions against which left over task(s) are processed: " + regions);
     }
   }
 
   /**
    * Only used w/useGlobalErrors ctor argument, for HTable backward compat.
    * @return Whether there were any errors in any request since the last time
    *          {@link #waitForAllPreviousOpsAndReset(List)} was called, or AP was created.
    */
   public boolean hasError() {
     return globalErrors.hasErrors();
   }
 
   /**
    * Only used w/useGlobalErrors ctor argument, for HTable backward compat.
    * Waits for all previous operations to finish, and returns errors and (optionally)
    * failed operations themselves.
    * @param failedRows an optional list into which the rows that failed since the last time
    *        {@link #waitForAllPreviousOpsAndReset(List)} was called, or AP was created, are saved.
    * @param tableName name of the table
    * @return all the errors since the last time {@link #waitForAllPreviousOpsAndReset(List)}
    *          was called, or AP was created.
    */
   public RetriesExhaustedWithDetailsException waitForAllPreviousOpsAndReset(
       List<Row> failedRows, String tableName) throws InterruptedIOException {
     waitForMaximumCurrentTasks(0, tableName);
     if (!globalErrors.hasErrors()) {
       return null;
     }
     if (failedRows != null) {
       failedRows.addAll(globalErrors.actions);
     }
     RetriesExhaustedWithDetailsException result = globalErrors.makeException();
     globalErrors.clear();
     return result;
   }
 
   /**
    * increment the tasks counters for a given set of regions. MT safe.
    */
   protected void incTaskCounters(Collection<byte[]> regions, ServerName sn) {
     tasksInProgress.incrementAndGet();
 
     AtomicInteger serverCnt = taskCounterPerServer.get(sn);
     if (serverCnt == null) {
       taskCounterPerServer.putIfAbsent(sn, new AtomicInteger());
       serverCnt = taskCounterPerServer.get(sn);
     }
     serverCnt.incrementAndGet();
 
     for (byte[] regBytes : regions) {
       AtomicInteger regionCnt = taskCounterPerRegion.get(regBytes);
       if (regionCnt == null) {
         regionCnt = new AtomicInteger();
         AtomicInteger oldCnt = taskCounterPerRegion.putIfAbsent(regBytes, regionCnt);
         if (oldCnt != null) {
           regionCnt = oldCnt;
         }
       }
       regionCnt.incrementAndGet();
     }
   }
 
   /**
    * Decrements the counters for a given region and the region server. MT Safe.
    */
   protected void decTaskCounters(Collection<byte[]> regions, ServerName sn) {
     for (byte[] regBytes : regions) {
       AtomicInteger regionCnt = taskCounterPerRegion.get(regBytes);
       regionCnt.decrementAndGet();
     }
 
     taskCounterPerServer.get(sn).decrementAndGet();
     tasksInProgress.decrementAndGet();
     synchronized (tasksInProgress) {
       tasksInProgress.notifyAll();
     }
   }
 
   /**
    * Creates the server error tracker to use inside process.
    * Currently, to preserve the main assumption about current retries, and to work well with
    * the retry-limit-based calculation, the calculation is local per Process object.
    * We may benefit from connection-wide tracking of server errors.
    * @return ServerErrorTracker to use, null if there is no ServerErrorTracker on this connection
    */
   protected ConnectionManager.ServerErrorTracker createServerErrorTracker() {
     return new ConnectionManager.ServerErrorTracker(
         this.serverTrackerTimeout, this.numTries);
   }
 
   private static boolean isReplicaGet(Row row) {
     return (row instanceof Get) && (((Get)row).getConsistency() == Consistency.TIMELINE);
   }
 
   /**
    * For manageError. Only used to make logging more clear, we don't actually care why we don't retry.
    */
   private enum Retry {
     YES,
     NO_LOCATION_PROBLEM,
     NO_NOT_RETRIABLE,
     NO_RETRIES_EXHAUSTED,
     NO_OTHER_SUCCEEDED
   }
 }