opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/datastore/ShardCommitCoordinator.java

   1 /*
   2  * Copyright (c) 2014 Brocade Communications Systems, Inc. and others.  All rights reserved.
   3  *
   4  * This program and the accompanying materials are made available under the
   5  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
   6  * and is available at http://www.eclipse.org/legal/epl-v10.html
   7  */
   8 package org.opendaylight.controller.cluster.datastore;
   9
  10 import akka.actor.ActorRef;
  11 import akka.actor.Status.Failure;
  12 import akka.serialization.Serialization;
  13 import com.google.common.annotations.VisibleForTesting;
  14 import com.google.common.base.Preconditions;
  15 import com.google.common.base.Stopwatch;
  16 import java.util.ArrayList;
  17 import java.util.HashMap;
  18 import java.util.Iterator;
  19 import java.util.LinkedList;
  20 import java.util.List;
  21 import java.util.Map;
  22 import java.util.Queue;
  23 import java.util.concurrent.ExecutionException;
  24 import java.util.concurrent.TimeUnit;
  25 import org.opendaylight.controller.cluster.datastore.messages.AbortTransactionReply;
  26 import org.opendaylight.controller.cluster.datastore.messages.BatchedModifications;
  27 import org.opendaylight.controller.cluster.datastore.messages.BatchedModificationsReply;
  28 import org.opendaylight.controller.cluster.datastore.messages.CanCommitTransactionReply;
  29 import org.opendaylight.controller.cluster.datastore.messages.ForwardedReadyTransaction;
  30 import org.opendaylight.controller.cluster.datastore.messages.ReadyLocalTransaction;
  31 import org.opendaylight.controller.cluster.datastore.messages.ReadyTransactionReply;
  32 import org.opendaylight.controller.cluster.datastore.modification.Modification;
  33 import org.opendaylight.controller.md.sal.common.api.data.TransactionCommitFailedException;
  34 import org.opendaylight.yangtools.yang.data.api.schema.tree.DataTreeCandidate;
  35 import org.slf4j.Logger;
  36
  37 /**
  38  * Coordinates commits for a shard ensuring only one concurrent 3-phase commit.
  39  *
  40  * @author Thomas Pantelis
  41  */
  42 class ShardCommitCoordinator {
  43
  44     // Interface hook for unit tests to replace or decorate the DOMStoreThreePhaseCommitCohorts.
  45     public interface CohortDecorator {
  46         ShardDataTreeCohort decorate(String transactionID, ShardDataTreeCohort actual);
  47     }
  48
  49     private final Map<String, CohortEntry> cohortCache = new HashMap<>();
  50
  51     private CohortEntry currentCohortEntry;
  52
  53     private final ShardDataTree dataTree;
  54
  55     // We use a LinkedList here to avoid synchronization overhead with concurrent queue impls
  56     // since this should only be accessed on the shard's dispatcher.
  57     private final Queue<CohortEntry> queuedCohortEntries = new LinkedList<>();
  58
  59     private int queueCapacity;
  60
  61     private final Logger log;
  62
  63     private final String name;
  64
  65     private final long cacheExpiryTimeoutInMillis;
  66
  67     // This is a hook for unit tests to replace or decorate the DOMStoreThreePhaseCommitCohorts.
  68     private CohortDecorator cohortDecorator;
  69
  70     private ReadyTransactionReply readyTransactionReply;
  71
  72     private Runnable runOnPendingTransactionsComplete;
  73
  74     ShardCommitCoordinator(ShardDataTree dataTree,
  75             long cacheExpiryTimeoutInMillis, int queueCapacity, Logger log, String name) {
  76
  77         this.queueCapacity = queueCapacity;
  78         this.log = log;
  79         this.name = name;
  80         this.dataTree = Preconditions.checkNotNull(dataTree);
  81         this.cacheExpiryTimeoutInMillis = cacheExpiryTimeoutInMillis;
  82     }
  83
  84     int getQueueSize() {
  85         return queuedCohortEntries.size();
  86     }
  87
  88     int getCohortCacheSize() {
  89         return cohortCache.size();
  90     }
  91
  92     void setQueueCapacity(int queueCapacity) {
  93         this.queueCapacity = queueCapacity;
  94     }
  95
  96     private ReadyTransactionReply readyTransactionReply(Shard shard) {
  97         if(readyTransactionReply == null) {
  98             readyTransactionReply = new ReadyTransactionReply(Serialization.serializedActorPath(shard.self()));
  99         }
 100
 101         return readyTransactionReply;
 102     }
 103
 104     private boolean queueCohortEntry(CohortEntry cohortEntry, ActorRef sender, Shard shard) {
 105         if(queuedCohortEntries.size() < queueCapacity) {
 106             queuedCohortEntries.offer(cohortEntry);
 107
 108             log.debug("{}: Enqueued transaction {}, queue size {}", name, cohortEntry.getTransactionID(),
 109                     queuedCohortEntries.size());
 110
 111             return true;
 112         } else {
 113             cohortCache.remove(cohortEntry.getTransactionID());
 114
 115             RuntimeException ex = new RuntimeException(
 116                     String.format("%s: Could not enqueue transaction %s - the maximum commit queue"+
 117                                   " capacity %d has been reached.",
 118                                   name, cohortEntry.getTransactionID(), queueCapacity));
 119             log.error(ex.getMessage());
 120             sender.tell(new Failure(ex), shard.self());
 121             return false;
 122         }
 123     }
 124
 125     /**
 126      * This method is called to ready a transaction that was prepared by ShardTransaction actor. It caches
 127      * the prepared cohort entry for the given transactions ID in preparation for the subsequent 3-phase commit.
 128      *
 129      * @param ready the ForwardedReadyTransaction message to process
 130      * @param sender the sender of the message
 131      * @param shard the transaction's shard actor
 132      */
 133     void handleForwardedReadyTransaction(ForwardedReadyTransaction ready, ActorRef sender, Shard shard) {
 134         log.debug("{}: Readying transaction {}, client version {}", name,
 135                 ready.getTransactionID(), ready.getTxnClientVersion());
 136
 137         ShardDataTreeCohort cohort = ready.getTransaction().ready();
 138         CohortEntry cohortEntry = new CohortEntry(ready.getTransactionID(), cohort);
 139         cohortCache.put(ready.getTransactionID(), cohortEntry);
 140
 141         if(!queueCohortEntry(cohortEntry, sender, shard)) {
 142             return;
 143         }
 144
 145         if(ready.isDoImmediateCommit()) {
 146             cohortEntry.setDoImmediateCommit(true);
 147             cohortEntry.setReplySender(sender);
 148             cohortEntry.setShard(shard);
 149             handleCanCommit(cohortEntry);
 150         } else {
 151             // The caller does not want immediate commit - the 3-phase commit will be coordinated by the
 152             // front-end so send back a ReadyTransactionReply with our actor path.
 153             sender.tell(readyTransactionReply(shard), shard.self());
 154         }
 155     }
 156
 157     /**
 158      * This method handles a BatchedModifications message for a transaction being prepared directly on the
 159      * Shard actor instead of via a ShardTransaction actor. If there's no currently cached
 160      * DOMStoreWriteTransaction, one is created. The batched modifications are applied to the write Tx. If
 161      * the BatchedModifications is ready to commit then a DOMStoreThreePhaseCommitCohort is created.
 162      *
 163      * @param batched the BatchedModifications message to process
 164      * @param sender the sender of the message
 165      * @param shard the transaction's shard actor
 166      */
 167     void handleBatchedModifications(BatchedModifications batched, ActorRef sender, Shard shard) {
 168         CohortEntry cohortEntry = cohortCache.get(batched.getTransactionID());
 169         if(cohortEntry == null) {
 170             cohortEntry = new CohortEntry(batched.getTransactionID(),
 171                     dataTree.newReadWriteTransaction(batched.getTransactionID(),
 172                         batched.getTransactionChainID()));
 173             cohortCache.put(batched.getTransactionID(), cohortEntry);
 174         }
 175
 176         if(log.isDebugEnabled()) {
 177             log.debug("{}: Applying {} batched modifications for Tx {}", name,
 178                     batched.getModifications().size(), batched.getTransactionID());
 179         }
 180
 181         cohortEntry.applyModifications(batched.getModifications());
 182
 183         if(batched.isReady()) {
 184             if(cohortEntry.getLastBatchedModificationsException() != null) {
 185                 cohortCache.remove(cohortEntry.getTransactionID());
 186                 throw cohortEntry.getLastBatchedModificationsException();
 187             }
 188
 189             if(cohortEntry.getTotalBatchedModificationsReceived() != batched.getTotalMessagesSent()) {
 190                 cohortCache.remove(cohortEntry.getTransactionID());
 191                 throw new IllegalStateException(String.format(
 192                         "The total number of batched messages received %d does not match the number sent %d",
 193                         cohortEntry.getTotalBatchedModificationsReceived(), batched.getTotalMessagesSent()));
 194             }
 195
 196             if(!queueCohortEntry(cohortEntry, sender, shard)) {
 197                 return;
 198             }
 199
 200             if(log.isDebugEnabled()) {
 201                 log.debug("{}: Readying Tx {}, client version {}", name,
 202                         batched.getTransactionID(), batched.getVersion());
 203             }
 204
 205             cohortEntry.ready(cohortDecorator, batched.isDoCommitOnReady());
 206
 207             if(batched.isDoCommitOnReady()) {
 208                 cohortEntry.setReplySender(sender);
 209                 cohortEntry.setShard(shard);
 210                 handleCanCommit(cohortEntry);
 211             } else {
 212                 sender.tell(readyTransactionReply(shard), shard.self());
 213             }
 214         } else {
 215             sender.tell(new BatchedModificationsReply(batched.getModifications().size()), shard.self());
 216         }
 217     }
 218
 219     /**
 220      * This method handles {@link ReadyLocalTransaction} message. All transaction modifications have
 221      * been prepared beforehand by the sender and we just need to drive them through into the dataTree.
 222      *
 223      * @param message the ReadyLocalTransaction message to process
 224      * @param sender the sender of the message
 225      * @param shard the transaction's shard actor
 226      */
 227     void handleReadyLocalTransaction(ReadyLocalTransaction message, ActorRef sender, Shard shard) {
 228         final ShardDataTreeCohort cohort = new SimpleShardDataTreeCohort(dataTree, message.getModification(),
 229                 message.getTransactionID());
 230         final CohortEntry cohortEntry = new CohortEntry(message.getTransactionID(), cohort);
 231         cohortCache.put(message.getTransactionID(), cohortEntry);
 232         cohortEntry.setDoImmediateCommit(message.isDoCommitOnReady());
 233
 234         if(!queueCohortEntry(cohortEntry, sender, shard)) {
 235             return;
 236         }
 237
 238         log.debug("{}: Applying local modifications for Tx {}", name, message.getTransactionID());
 239
 240         if (message.isDoCommitOnReady()) {
 241             cohortEntry.setReplySender(sender);
 242             cohortEntry.setShard(shard);
 243             handleCanCommit(cohortEntry);
 244         } else {
 245             sender.tell(readyTransactionReply(shard), shard.self());
 246         }
 247     }
 248
 249     private void handleCanCommit(CohortEntry cohortEntry) {
 250         String transactionID = cohortEntry.getTransactionID();
 251
 252         cohortEntry.updateLastAccessTime();
 253
 254         if(currentCohortEntry != null) {
 255             // There's already a Tx commit in progress so we can't process this entry yet - but it's in the
 256             // queue and will get processed after all prior entries complete.
 257
 258             if(log.isDebugEnabled()) {
 259                 log.debug("{}: Commit for Tx {} already in progress - skipping canCommit for {} for now",
 260                         name, currentCohortEntry.getTransactionID(), transactionID);
 261             }
 262
 263             return;
 264         }
 265
 266         // No Tx commit currently in progress - check if this entry is the next one in the queue, If so make
 267         // it the current entry and proceed with canCommit.
 268         // Purposely checking reference equality here.
 269         if(queuedCohortEntries.peek() == cohortEntry) {
 270             currentCohortEntry = queuedCohortEntries.poll();
 271             doCanCommit(currentCohortEntry);
 272         } else {
 273             if(log.isDebugEnabled()) {
 274                 log.debug("{}: Tx {} is the next pending canCommit - skipping {} for now",
 275                         name, queuedCohortEntries.peek().getTransactionID(), transactionID);
 276             }
 277         }
 278     }
 279
 280     /**
 281      * This method handles the canCommit phase for a transaction.
 282      *
 283      * @param transactionID the ID of the transaction to canCommit
 284      * @param sender the actor to which to send the response
 285      * @param shard the transaction's shard actor
 286      */
 287     void handleCanCommit(String transactionID, final ActorRef sender, final Shard shard) {
 288         // Lookup the cohort entry that was cached previously (or should have been) by
 289         // transactionReady (via the ForwardedReadyTransaction message).
 290         final CohortEntry cohortEntry = cohortCache.get(transactionID);
 291         if(cohortEntry == null) {
 292             // Either canCommit was invoked before ready(shouldn't happen)  or a long time passed
 293             // between canCommit and ready and the entry was expired from the cache.
 294             IllegalStateException ex = new IllegalStateException(
 295                     String.format("%s: No cohort entry found for transaction %s", name, transactionID));
 296             log.error(ex.getMessage());
 297             sender.tell(new Failure(ex), shard.self());
 298             return;
 299         }
 300
 301         cohortEntry.setReplySender(sender);
 302         cohortEntry.setShard(shard);
 303
 304         handleCanCommit(cohortEntry);
 305     }
 306
 307     private void doCanCommit(final CohortEntry cohortEntry) {
 308         boolean canCommit = false;
 309         try {
 310             canCommit = cohortEntry.canCommit();
 311
 312             log.debug("{}: canCommit for {}: {}", name, cohortEntry.getTransactionID(), canCommit);
 313
 314             if(cohortEntry.isDoImmediateCommit()) {
 315                 if(canCommit) {
 316                     doCommit(cohortEntry);
 317                 } else {
 318                     cohortEntry.getReplySender().tell(new Failure(new TransactionCommitFailedException(
 319                                 "Can Commit failed, no detailed cause available.")), cohortEntry.getShard().self());
 320                 }
 321             } else {
 322                 cohortEntry.getReplySender().tell(
 323                         canCommit ? CanCommitTransactionReply.YES.toSerializable() :
 324                             CanCommitTransactionReply.NO.toSerializable(), cohortEntry.getShard().self());
 325             }
 326         } catch (Exception e) {
 327             log.debug("{}: An exception occurred during canCommit", name, e);
 328
 329             Throwable failure = e;
 330             if(e instanceof ExecutionException) {
 331                 failure = e.getCause();
 332             }
 333
 334             cohortEntry.getReplySender().tell(new Failure(failure), cohortEntry.getShard().self());
 335         } finally {
 336             if(!canCommit) {
 337                 // Remove the entry from the cache now.
 338                 currentTransactionComplete(cohortEntry.getTransactionID(), true);
 339             }
 340         }
 341     }
 342
 343     private boolean doCommit(CohortEntry cohortEntry) {
 344         log.debug("{}: Committing transaction {}", name, cohortEntry.getTransactionID());
 345
 346         boolean success = false;
 347
 348         // We perform the preCommit phase here atomically with the commit phase. This is an
 349         // optimization to eliminate the overhead of an extra preCommit message. We lose front-end
 350         // coordination of preCommit across shards in case of failure but preCommit should not
 351         // normally fail since we ensure only one concurrent 3-phase commit.
 352
 353         try {
 354             cohortEntry.preCommit();
 355
 356             cohortEntry.getShard().continueCommit(cohortEntry);
 357
 358             cohortEntry.updateLastAccessTime();
 359
 360             success = true;
 361         } catch (Exception e) {
 362             log.error("{} An exception occurred while preCommitting transaction {}",
 363                     name, cohortEntry.getTransactionID(), e);
 364             cohortEntry.getReplySender().tell(new Failure(e), cohortEntry.getShard().self());
 365
 366             currentTransactionComplete(cohortEntry.getTransactionID(), true);
 367         }
 368
 369         return success;
 370     }
 371
 372     /**
 373      * This method handles the preCommit and commit phases for a transaction.
 374      *
 375      * @param transactionID the ID of the transaction to commit
 376      * @param sender the actor to which to send the response
 377      * @param shard the transaction's shard actor
 378      * @return true if the transaction was successfully prepared, false otherwise.
 379      */
 380     boolean handleCommit(final String transactionID, final ActorRef sender, final Shard shard) {
 381         // Get the current in-progress cohort entry in the commitCoordinator if it corresponds to
 382         // this transaction.
 383         final CohortEntry cohortEntry = getCohortEntryIfCurrent(transactionID);
 384         if(cohortEntry == null) {
 385             // We're not the current Tx - the Tx was likely expired b/c it took too long in
 386             // between the canCommit and commit messages.
 387             IllegalStateException ex = new IllegalStateException(
 388                     String.format("%s: Cannot commit transaction %s - it is not the current transaction",
 389                             name, transactionID));
 390             log.error(ex.getMessage());
 391             sender.tell(new Failure(ex), shard.self());
 392             return false;
 393         }
 394
 395         cohortEntry.setReplySender(sender);
 396         return doCommit(cohortEntry);
 397     }
 398
 399     void handleAbort(final String transactionID, final ActorRef sender, final Shard shard) {
 400         CohortEntry cohortEntry = getCohortEntryIfCurrent(transactionID);
 401         if(cohortEntry != null) {
 402             // We don't remove the cached cohort entry here (ie pass false) in case the Tx was
 403             // aborted during replication in which case we may still commit locally if replication
 404             // succeeds.
 405             currentTransactionComplete(transactionID, false);
 406         } else {
 407             cohortEntry = getAndRemoveCohortEntry(transactionID);
 408         }
 409
 410         if(cohortEntry == null) {
 411             return;
 412         }
 413
 414         log.debug("{}: Aborting transaction {}", name, transactionID);
 415
 416         final ActorRef self = shard.getSelf();
 417         try {
 418             cohortEntry.abort();
 419
 420             shard.getShardMBean().incrementAbortTransactionsCount();
 421
 422             if(sender != null) {
 423                 sender.tell(new AbortTransactionReply().toSerializable(), self);
 424             }
 425         } catch (Exception e) {
 426             log.error("{}: An exception happened during abort", name, e);
 427
 428             if(sender != null) {
 429                 sender.tell(new Failure(e), self);
 430             }
 431         }
 432     }
 433
 434     void checkForExpiredTransactions(final long timeout, final Shard shard) {
 435         CohortEntry cohortEntry = getCurrentCohortEntry();
 436         if(cohortEntry != null) {
 437             if(cohortEntry.isExpired(timeout)) {
 438                 log.warn("{}: Current transaction {} has timed out after {} ms - aborting",
 439                         name, cohortEntry.getTransactionID(), timeout);
 440
 441                 handleAbort(cohortEntry.getTransactionID(), null, shard);
 442             }
 443         }
 444
 445         cleanupExpiredCohortEntries();
 446     }
 447
 448     void abortPendingTransactions(final String reason, final Shard shard) {
 449         if(currentCohortEntry == null && queuedCohortEntries.isEmpty()) {
 450             return;
 451         }
 452
 453         List<CohortEntry> cohortEntries = new ArrayList<>();
 454
 455         if(currentCohortEntry != null) {
 456             cohortEntries.add(currentCohortEntry);
 457             currentCohortEntry = null;
 458         }
 459
 460         cohortEntries.addAll(queuedCohortEntries);
 461         queuedCohortEntries.clear();
 462
 463         for(CohortEntry cohortEntry: cohortEntries) {
 464             if(cohortEntry.getReplySender() != null) {
 465                 cohortEntry.getReplySender().tell(new Failure(new RuntimeException(reason)), shard.self());
 466             }
 467         }
 468     }
 469
 470     /**
 471      * Returns the cohort entry for the Tx commit currently in progress if the given transaction ID
 472      * matches the current entry.
 473      *
 474      * @param transactionID the ID of the transaction
 475      * @return the current CohortEntry or null if the given transaction ID does not match the
 476      *         current entry.
 477      */
 478     CohortEntry getCohortEntryIfCurrent(String transactionID) {
 479         if(isCurrentTransaction(transactionID)) {
 480             return currentCohortEntry;
 481         }
 482
 483         return null;
 484     }
 485
 486     CohortEntry getCurrentCohortEntry() {
 487         return currentCohortEntry;
 488     }
 489
 490     CohortEntry getAndRemoveCohortEntry(String transactionID) {
 491         return cohortCache.remove(transactionID);
 492     }
 493
 494     boolean isCurrentTransaction(String transactionID) {
 495         return currentCohortEntry != null &&
 496                 currentCohortEntry.getTransactionID().equals(transactionID);
 497     }
 498
 499     /**
 500      * This method is called when a transaction is complete, successful or not. If the given
 501      * given transaction ID matches the current in-progress transaction, the next cohort entry,
 502      * if any, is dequeued and processed.
 503      *
 504      * @param transactionID the ID of the completed transaction
 505      * @param removeCohortEntry if true the CohortEntry for the transaction is also removed from
 506      *        the cache.
 507      */
 508     void currentTransactionComplete(String transactionID, boolean removeCohortEntry) {
 509         if(removeCohortEntry) {
 510             cohortCache.remove(transactionID);
 511         }
 512
 513         if(isCurrentTransaction(transactionID)) {
 514             currentCohortEntry = null;
 515
 516             log.debug("{}: currentTransactionComplete: {}", name, transactionID);
 517
 518             maybeProcessNextCohortEntry();
 519         }
 520     }
 521
 522     private void maybeProcessNextCohortEntry() {
 523         // Check if there's a next cohort entry waiting in the queue and if it is ready to commit. Also
 524         // clean out expired entries.
 525         Iterator<CohortEntry> iter = queuedCohortEntries.iterator();
 526         while(iter.hasNext()) {
 527             CohortEntry next = iter.next();
 528             if(next.isReadyToCommit()) {
 529                 if(currentCohortEntry == null) {
 530                     if(log.isDebugEnabled()) {
 531                         log.debug("{}: Next entry to canCommit {}", name, next);
 532                     }
 533
 534                     iter.remove();
 535                     currentCohortEntry = next;
 536                     currentCohortEntry.updateLastAccessTime();
 537                     doCanCommit(currentCohortEntry);
 538                 }
 539
 540                 break;
 541             } else if(next.isExpired(cacheExpiryTimeoutInMillis)) {
 542                 log.warn("{}: canCommit for transaction {} was not received within {} ms - entry removed from cache",
 543                         name, next.getTransactionID(), cacheExpiryTimeoutInMillis);
 544             } else if(!next.isAborted()) {
 545                 break;
 546             }
 547
 548             iter.remove();
 549             cohortCache.remove(next.getTransactionID());
 550         }
 551
 552         maybeRunOperationOnPendingTransactionsComplete();
 553     }
 554
 555     void cleanupExpiredCohortEntries() {
 556         maybeProcessNextCohortEntry();
 557     }
 558
 559     void setRunOnPendingTransactionsComplete(Runnable operation) {
 560         runOnPendingTransactionsComplete = operation;
 561         maybeRunOperationOnPendingTransactionsComplete();
 562     }
 563
 564     private void maybeRunOperationOnPendingTransactionsComplete() {
 565         if(runOnPendingTransactionsComplete != null && currentCohortEntry == null && queuedCohortEntries.isEmpty()) {
 566             log.debug("{}: Pending transactions complete - running operation {}", name, runOnPendingTransactionsComplete);
 567
 568             runOnPendingTransactionsComplete.run();
 569             runOnPendingTransactionsComplete = null;
 570         }
 571     }
 572
 573     @VisibleForTesting
 574     void setCohortDecorator(CohortDecorator cohortDecorator) {
 575         this.cohortDecorator = cohortDecorator;
 576     }
 577
 578     static class CohortEntry {
 579         private final String transactionID;
 580         private ShardDataTreeCohort cohort;
 581         private final ReadWriteShardDataTreeTransaction transaction;
 582         private RuntimeException lastBatchedModificationsException;
 583         private ActorRef replySender;
 584         private Shard shard;
 585         private boolean doImmediateCommit;
 586         private final Stopwatch lastAccessTimer = Stopwatch.createStarted();
 587         private int totalBatchedModificationsReceived;
 588         private boolean aborted;
 589
 590         CohortEntry(String transactionID, ReadWriteShardDataTreeTransaction transaction) {
 591             this.transaction = Preconditions.checkNotNull(transaction);
 592             this.transactionID = transactionID;
 593         }
 594
 595         CohortEntry(String transactionID, ShardDataTreeCohort cohort) {
 596             this.transactionID = transactionID;
 597             this.cohort = cohort;
 598             this.transaction = null;
 599         }
 600
 601         void updateLastAccessTime() {
 602             lastAccessTimer.reset();
 603             lastAccessTimer.start();
 604         }
 605
 606         String getTransactionID() {
 607             return transactionID;
 608         }
 609
 610         DataTreeCandidate getCandidate() {
 611             return cohort.getCandidate();
 612         }
 613
 614         int getTotalBatchedModificationsReceived() {
 615             return totalBatchedModificationsReceived;
 616         }
 617
 618         RuntimeException getLastBatchedModificationsException() {
 619             return lastBatchedModificationsException;
 620         }
 621
 622         void applyModifications(Iterable<Modification> modifications) {
 623             totalBatchedModificationsReceived++;
 624             if(lastBatchedModificationsException == null) {
 625                 for (Modification modification : modifications) {
 626                         try {
 627                             modification.apply(transaction.getSnapshot());
 628                         } catch (RuntimeException e) {
 629                             lastBatchedModificationsException = e;
 630                             throw e;
 631                         }
 632                 }
 633             }
 634         }
 635
 636         boolean canCommit() throws InterruptedException, ExecutionException {
 637             // We block on the future here (and also preCommit(), commit(), abort()) so we don't have to worry
 638             // about possibly accessing our state on a different thread outside of our dispatcher.
 639             // TODO: the ShardDataTreeCohort returns immediate Futures anyway which begs the question - why
 640             // bother even returning Futures from ShardDataTreeCohort if we have to treat them synchronously
 641             // anyway?. The Futures are really a remnant from when we were using the InMemoryDataBroker.
 642             return cohort.canCommit().get();
 643         }
 644
 645         void preCommit() throws InterruptedException, ExecutionException {
 646             cohort.preCommit().get();
 647         }
 648
 649         void commit() throws InterruptedException, ExecutionException {
 650             cohort.commit().get();
 651         }
 652
 653         void abort() throws InterruptedException, ExecutionException {
 654             aborted = true;
 655             cohort.abort().get();
 656         }
 657
 658         void ready(CohortDecorator cohortDecorator, boolean doImmediateCommit) {
 659             Preconditions.checkState(cohort == null, "cohort was already set");
 660
 661             setDoImmediateCommit(doImmediateCommit);
 662
 663             cohort = transaction.ready();
 664
 665             if(cohortDecorator != null) {
 666                 // Call the hook for unit tests.
 667                 cohort = cohortDecorator.decorate(transactionID, cohort);
 668             }
 669         }
 670
 671         boolean isReadyToCommit() {
 672             return replySender != null;
 673         }
 674
 675         boolean isExpired(long expireTimeInMillis) {
 676             return lastAccessTimer.elapsed(TimeUnit.MILLISECONDS) >= expireTimeInMillis;
 677         }
 678
 679         boolean isDoImmediateCommit() {
 680             return doImmediateCommit;
 681         }
 682
 683         void setDoImmediateCommit(boolean doImmediateCommit) {
 684             this.doImmediateCommit = doImmediateCommit;
 685         }
 686
 687         ActorRef getReplySender() {
 688             return replySender;
 689         }
 690
 691         void setReplySender(ActorRef replySender) {
 692             this.replySender = replySender;
 693         }
 694
 695         Shard getShard() {
 696             return shard;
 697         }
 698
 699         void setShard(Shard shard) {
 700             this.shard = shard;
 701         }
 702
 703
 704         boolean isAborted() {
 705             return aborted;
 706         }
 707
 708         @Override
 709         public String toString() {
 710             StringBuilder builder = new StringBuilder();
 711             builder.append("CohortEntry [transactionID=").append(transactionID).append(", doImmediateCommit=")
 712                     .append(doImmediateCommit).append("]");
 713             return builder.toString();
 714         }
 715     }
 716 }