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

   1 /*
   2  * Copyright (c) 2014 Cisco 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
   9 package org.opendaylight.controller.cluster.datastore;
  10
  11 import akka.actor.ActorPath;
  12 import akka.actor.ActorSelection;
  13 import akka.dispatch.OnComplete;
  14
  15 import com.google.common.annotations.VisibleForTesting;
  16 import com.google.common.base.FinalizablePhantomReference;
  17 import com.google.common.base.FinalizableReferenceQueue;
  18 import com.google.common.base.Optional;
  19 import com.google.common.base.Preconditions;
  20 import com.google.common.collect.Lists;
  21 import com.google.common.util.concurrent.CheckedFuture;
  22 import com.google.common.util.concurrent.Futures;
  23 import com.google.common.util.concurrent.SettableFuture;
  24
  25 import org.opendaylight.controller.cluster.datastore.identifiers.TransactionIdentifier;
  26 import org.opendaylight.controller.cluster.datastore.messages.CloseTransaction;
  27 import org.opendaylight.controller.cluster.datastore.messages.CreateTransaction;
  28 import org.opendaylight.controller.cluster.datastore.messages.CreateTransactionReply;
  29 import org.opendaylight.controller.cluster.datastore.messages.DataExists;
  30 import org.opendaylight.controller.cluster.datastore.messages.DataExistsReply;
  31 import org.opendaylight.controller.cluster.datastore.messages.DeleteData;
  32 import org.opendaylight.controller.cluster.datastore.messages.MergeData;
  33 import org.opendaylight.controller.cluster.datastore.messages.ReadData;
  34 import org.opendaylight.controller.cluster.datastore.messages.ReadDataReply;
  35 import org.opendaylight.controller.cluster.datastore.messages.ReadyTransaction;
  36 import org.opendaylight.controller.cluster.datastore.messages.ReadyTransactionReply;
  37 import org.opendaylight.controller.cluster.datastore.messages.WriteData;
  38 import org.opendaylight.controller.cluster.datastore.shardstrategy.ShardStrategyFactory;
  39 import org.opendaylight.controller.cluster.datastore.utils.ActorContext;
  40 import org.opendaylight.controller.md.sal.common.api.data.ReadFailedException;
  41 import org.opendaylight.controller.sal.core.spi.data.DOMStoreReadWriteTransaction;
  42 import org.opendaylight.controller.sal.core.spi.data.DOMStoreThreePhaseCommitCohort;
  43 import org.opendaylight.yangtools.util.concurrent.MappingCheckedFuture;
  44 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
  45 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
  46 import org.opendaylight.yangtools.yang.model.api.SchemaContext;
  47 import org.slf4j.Logger;
  48 import org.slf4j.LoggerFactory;
  49
  50 import scala.Function1;
  51 import scala.concurrent.Future;
  52 import scala.runtime.AbstractFunction1;
  53
  54 import java.util.HashMap;
  55 import java.util.List;
  56 import java.util.Map;
  57 import java.util.concurrent.ConcurrentHashMap;
  58 import java.util.concurrent.atomic.AtomicBoolean;
  59 import java.util.concurrent.atomic.AtomicLong;
  60
  61 /**
  62  * TransactionProxy acts as a proxy for one or more transactions that were created on a remote shard
  63  * <p>
  64  * Creating a transaction on the consumer side will create one instance of a transaction proxy. If during
  65  * the transaction reads and writes are done on data that belongs to different shards then a separate transaction will
  66  * be created on each of those shards by the TransactionProxy
  67  *</p>
  68  * <p>
  69  * The TransactionProxy does not make any guarantees about atomicity or order in which the transactions on the various
  70  * shards will be executed.
  71  * </p>
  72  */
  73 public class TransactionProxy implements DOMStoreReadWriteTransaction {
  74
  75     private final TransactionChainProxy transactionChainProxy;
  76
  77
  78
  79     public enum TransactionType {
  80         READ_ONLY,
  81         WRITE_ONLY,
  82         READ_WRITE
  83     }
  84
  85     static Function1<Throwable, Throwable> SAME_FAILURE_TRANSFORMER = new AbstractFunction1<
  86                                                                           Throwable, Throwable>() {
  87         @Override
  88         public Throwable apply(Throwable failure) {
  89             return failure;
  90         }
  91     };
  92
  93     private static final AtomicLong counter = new AtomicLong();
  94
  95     private static final Logger
  96         LOG = LoggerFactory.getLogger(TransactionProxy.class);
  97
  98
  99     /**
 100      * Used to enqueue the PhantomReferences for read-only TransactionProxy instances. The
 101      * FinalizableReferenceQueue is safe to use statically in an OSGi environment as it uses some
 102      * trickery to clean up its internal thread when the bundle is unloaded.
 103      */
 104     private static final FinalizableReferenceQueue phantomReferenceQueue =
 105                                                                   new FinalizableReferenceQueue();
 106
 107     /**
 108      * This stores the TransactionProxyCleanupPhantomReference instances statically, This is
 109      * necessary because PhantomReferences need a hard reference so they're not garbage collected.
 110      * Once finalized, the TransactionProxyCleanupPhantomReference removes itself from this map
 111      * and thus becomes eligible for garbage collection.
 112      */
 113     private static final Map<TransactionProxyCleanupPhantomReference,
 114                              TransactionProxyCleanupPhantomReference> phantomReferenceCache =
 115                                                                         new ConcurrentHashMap<>();
 116
 117     /**
 118      * A PhantomReference that closes remote transactions for a TransactionProxy when it's
 119      * garbage collected. This is used for read-only transactions as they're not explicitly closed
 120      * by clients. So the only way to detect that a transaction is no longer in use and it's safe
 121      * to clean up is when it's garbage collected. It's inexact as to when an instance will be GC'ed
 122      * but TransactionProxy instances should generally be short-lived enough to avoid being moved
 123      * to the old generation space and thus should be cleaned up in a timely manner as the GC
 124      * runs on the young generation (eden, swap1...) space much more frequently.
 125      */
 126     private static class TransactionProxyCleanupPhantomReference
 127                                            extends FinalizablePhantomReference<TransactionProxy> {
 128
 129         private final List<ActorSelection> remoteTransactionActors;
 130         private final AtomicBoolean remoteTransactionActorsMB;
 131         private final ActorContext actorContext;
 132         private final TransactionIdentifier identifier;
 133
 134         protected TransactionProxyCleanupPhantomReference(TransactionProxy referent) {
 135             super(referent, phantomReferenceQueue);
 136
 137             // Note we need to cache the relevant fields from the TransactionProxy as we can't
 138             // have a hard reference to the TransactionProxy instance itself.
 139
 140             remoteTransactionActors = referent.remoteTransactionActors;
 141             remoteTransactionActorsMB = referent.remoteTransactionActorsMB;
 142             actorContext = referent.actorContext;
 143             identifier = referent.identifier;
 144         }
 145
 146         @Override
 147         public void finalizeReferent() {
 148             LOG.trace("Cleaning up {} Tx actors for TransactionProxy {}",
 149                     remoteTransactionActors.size(), identifier);
 150
 151             phantomReferenceCache.remove(this);
 152
 153             // Access the memory barrier volatile to ensure all previous updates to the
 154             // remoteTransactionActors list are visible to this thread.
 155
 156             if(remoteTransactionActorsMB.get()) {
 157                 for(ActorSelection actor : remoteTransactionActors) {
 158                     LOG.trace("Sending CloseTransaction to {}", actor);
 159                     actorContext.sendRemoteOperationAsync(actor,
 160                             new CloseTransaction().toSerializable());
 161                 }
 162             }
 163         }
 164     }
 165
 166     /**
 167      * Stores the remote Tx actors for each requested data store path to be used by the
 168      * PhantomReference to close the remote Tx's. This is only used for read-only Tx's. The
 169      * remoteTransactionActorsMB volatile serves as a memory barrier to publish updates to the
 170      * remoteTransactionActors list so they will be visible to the thread accessing the
 171      * PhantomReference.
 172      */
 173     private List<ActorSelection> remoteTransactionActors;
 174     private AtomicBoolean remoteTransactionActorsMB;
 175
 176     private final Map<String, TransactionContext> remoteTransactionPaths = new HashMap<>();
 177
 178     private final TransactionType transactionType;
 179     private final ActorContext actorContext;
 180     private final TransactionIdentifier identifier;
 181     private final SchemaContext schemaContext;
 182     private boolean inReadyState;
 183
 184     public TransactionProxy(ActorContext actorContext, TransactionType transactionType) {
 185         this(actorContext, transactionType, null);
 186     }
 187
 188     @VisibleForTesting
 189     List<Future<Object>> getRecordedOperationFutures() {
 190         List<Future<Object>> recordedOperationFutures = Lists.newArrayList();
 191         for(TransactionContext transactionContext : remoteTransactionPaths.values()) {
 192             recordedOperationFutures.addAll(transactionContext.getRecordedOperationFutures());
 193         }
 194
 195         return recordedOperationFutures;
 196     }
 197
 198     public TransactionProxy(ActorContext actorContext, TransactionType transactionType, TransactionChainProxy transactionChainProxy) {
 199         this.actorContext = Preconditions.checkNotNull(actorContext,
 200             "actorContext should not be null");
 201         this.transactionType = Preconditions.checkNotNull(transactionType,
 202             "transactionType should not be null");
 203         this.schemaContext = Preconditions.checkNotNull(actorContext.getSchemaContext(),
 204             "schemaContext should not be null");
 205         this.transactionChainProxy = transactionChainProxy;
 206
 207         String memberName = actorContext.getCurrentMemberName();
 208         if(memberName == null){
 209             memberName = "UNKNOWN-MEMBER";
 210         }
 211
 212         this.identifier = TransactionIdentifier.builder().memberName(memberName).counter(
 213             counter.getAndIncrement()).build();
 214
 215         if(transactionType == TransactionType.READ_ONLY) {
 216             // Read-only Tx's aren't explicitly closed by the client so we create a PhantomReference
 217             // to close the remote Tx's when this instance is no longer in use and is garbage
 218             // collected.
 219
 220             remoteTransactionActors = Lists.newArrayList();
 221             remoteTransactionActorsMB = new AtomicBoolean();
 222
 223             TransactionProxyCleanupPhantomReference cleanup =
 224                 new TransactionProxyCleanupPhantomReference(this);
 225             phantomReferenceCache.put(cleanup, cleanup);
 226         }
 227
 228         LOG.debug("Created txn {} of type {}", identifier, transactionType);
 229     }
 230
 231     @Override
 232     public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> read(
 233             final YangInstanceIdentifier path) {
 234
 235         Preconditions.checkState(transactionType != TransactionType.WRITE_ONLY,
 236                 "Read operation on write-only transaction is not allowed");
 237
 238         LOG.debug("Tx {} read {}", identifier, path);
 239
 240         createTransactionIfMissing(actorContext, path);
 241
 242         return transactionContext(path).readData(path);
 243     }
 244
 245     @Override
 246     public CheckedFuture<Boolean, ReadFailedException> exists(YangInstanceIdentifier path) {
 247
 248         Preconditions.checkState(transactionType != TransactionType.WRITE_ONLY,
 249                 "Exists operation on write-only transaction is not allowed");
 250
 251         LOG.debug("Tx {} exists {}", identifier, path);
 252
 253         createTransactionIfMissing(actorContext, path);
 254
 255         return transactionContext(path).dataExists(path);
 256     }
 257
 258     private void checkModificationState() {
 259         Preconditions.checkState(transactionType != TransactionType.READ_ONLY,
 260                 "Modification operation on read-only transaction is not allowed");
 261         Preconditions.checkState(!inReadyState,
 262                 "Transaction is sealed - further modifications are not allowed");
 263     }
 264
 265     @Override
 266     public void write(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
 267
 268         checkModificationState();
 269
 270         LOG.debug("Tx {} write {}", identifier, path);
 271
 272         createTransactionIfMissing(actorContext, path);
 273
 274         transactionContext(path).writeData(path, data);
 275     }
 276
 277     @Override
 278     public void merge(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
 279
 280         checkModificationState();
 281
 282         LOG.debug("Tx {} merge {}", identifier, path);
 283
 284         createTransactionIfMissing(actorContext, path);
 285
 286         transactionContext(path).mergeData(path, data);
 287     }
 288
 289     @Override
 290     public void delete(YangInstanceIdentifier path) {
 291
 292         checkModificationState();
 293
 294         LOG.debug("Tx {} delete {}", identifier, path);
 295
 296         createTransactionIfMissing(actorContext, path);
 297
 298         transactionContext(path).deleteData(path);
 299     }
 300
 301     @Override
 302     public DOMStoreThreePhaseCommitCohort ready() {
 303
 304         checkModificationState();
 305
 306         inReadyState = true;
 307
 308         LOG.debug("Tx {} Trying to get {} transactions ready for commit", identifier,
 309                 remoteTransactionPaths.size());
 310
 311         List<Future<ActorPath>> cohortPathFutures = Lists.newArrayList();
 312
 313         for(TransactionContext transactionContext : remoteTransactionPaths.values()) {
 314
 315             LOG.debug("Tx {} Readying transaction for shard {}", identifier,
 316                     transactionContext.getShardName());
 317
 318             cohortPathFutures.add(transactionContext.readyTransaction());
 319         }
 320
 321         if(transactionChainProxy != null){
 322             transactionChainProxy.onTransactionReady(cohortPathFutures);
 323         }
 324
 325         return new ThreePhaseCommitCohortProxy(actorContext, cohortPathFutures,
 326                 identifier.toString());
 327     }
 328
 329     @Override
 330     public Object getIdentifier() {
 331         return this.identifier;
 332     }
 333
 334     @Override
 335     public void close() {
 336         for(TransactionContext transactionContext : remoteTransactionPaths.values()) {
 337             transactionContext.closeTransaction();
 338         }
 339
 340         remoteTransactionPaths.clear();
 341
 342         if(transactionType == TransactionType.READ_ONLY) {
 343             remoteTransactionActors.clear();
 344             remoteTransactionActorsMB.set(true);
 345         }
 346     }
 347
 348     private TransactionContext transactionContext(YangInstanceIdentifier path){
 349         String shardName = shardNameFromIdentifier(path);
 350         return remoteTransactionPaths.get(shardName);
 351     }
 352
 353     private String shardNameFromIdentifier(YangInstanceIdentifier path){
 354         return ShardStrategyFactory.getStrategy(path).findShard(path);
 355     }
 356
 357     private void createTransactionIfMissing(ActorContext actorContext,
 358         YangInstanceIdentifier path) {
 359
 360         if(transactionChainProxy != null){
 361             transactionChainProxy.waitTillCurrentTransactionReady();
 362         }
 363
 364         String shardName = ShardStrategyFactory.getStrategy(path).findShard(path);
 365
 366         TransactionContext transactionContext =
 367             remoteTransactionPaths.get(shardName);
 368
 369         if (transactionContext != null) {
 370             // A transaction already exists with that shard
 371             return;
 372         }
 373
 374         try {
 375             Object response = actorContext.executeShardOperation(shardName,
 376                 new CreateTransaction(identifier.toString(), this.transactionType.ordinal(),
 377                     getTransactionChainId()).toSerializable());
 378             if (response.getClass().equals(CreateTransactionReply.SERIALIZABLE_CLASS)) {
 379                 CreateTransactionReply reply =
 380                     CreateTransactionReply.fromSerializable(response);
 381
 382                 String transactionPath = reply.getTransactionPath();
 383
 384                 LOG.debug("Tx {} Received transaction path = {}", identifier, transactionPath);
 385
 386                 ActorSelection transactionActor = actorContext.actorSelection(transactionPath);
 387
 388                 if (transactionType == TransactionType.READ_ONLY) {
 389                     // Add the actor to the remoteTransactionActors list for access by the
 390                     // cleanup PhantonReference.
 391                     remoteTransactionActors.add(transactionActor);
 392
 393                     // Write to the memory barrier volatile to publish the above update to the
 394                     // remoteTransactionActors list for thread visibility.
 395                     remoteTransactionActorsMB.set(true);
 396                 }
 397
 398                 transactionContext = new TransactionContextImpl(shardName, transactionPath,
 399                     transactionActor, identifier, actorContext, schemaContext);
 400
 401                 remoteTransactionPaths.put(shardName, transactionContext);
 402             } else {
 403                 throw new IllegalArgumentException(String.format(
 404                     "Invalid reply type {} for CreateTransaction", response.getClass()));
 405             }
 406         } catch (Exception e) {
 407             LOG.debug("Tx {} Creating NoOpTransaction because of : {}", identifier, e.getMessage());
 408             remoteTransactionPaths
 409                 .put(shardName, new NoOpTransactionContext(shardName, e, identifier));
 410         }
 411     }
 412
 413     public String getTransactionChainId() {
 414         if(transactionChainProxy == null){
 415             return "";
 416         }
 417         return transactionChainProxy.getTransactionChainId();
 418     }
 419
 420
 421     private interface TransactionContext {
 422         String getShardName();
 423
 424         void closeTransaction();
 425
 426         Future<ActorPath> readyTransaction();
 427
 428         void writeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data);
 429
 430         void deleteData(YangInstanceIdentifier path);
 431
 432         void mergeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data);
 433
 434         CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> readData(
 435                 final YangInstanceIdentifier path);
 436
 437         CheckedFuture<Boolean, ReadFailedException> dataExists(YangInstanceIdentifier path);
 438
 439         List<Future<Object>> getRecordedOperationFutures();
 440     }
 441
 442     private static abstract class AbstractTransactionContext implements TransactionContext {
 443
 444         protected final TransactionIdentifier identifier;
 445         protected final String shardName;
 446         protected final List<Future<Object>> recordedOperationFutures = Lists.newArrayList();
 447
 448         AbstractTransactionContext(String shardName, TransactionIdentifier identifier) {
 449             this.shardName = shardName;
 450             this.identifier = identifier;
 451         }
 452
 453         @Override
 454         public String getShardName() {
 455             return shardName;
 456         }
 457
 458         @Override
 459         public List<Future<Object>> getRecordedOperationFutures() {
 460             return recordedOperationFutures;
 461         }
 462     }
 463
 464     private static class TransactionContextImpl extends AbstractTransactionContext {
 465         private final Logger LOG = LoggerFactory.getLogger(TransactionContextImpl.class);
 466
 467         private final ActorContext actorContext;
 468         private final SchemaContext schemaContext;
 469         private final String actorPath;
 470         private final ActorSelection actor;
 471
 472         private TransactionContextImpl(String shardName, String actorPath,
 473                 ActorSelection actor, TransactionIdentifier identifier, ActorContext actorContext,
 474                 SchemaContext schemaContext) {
 475             super(shardName, identifier);
 476             this.actorPath = actorPath;
 477             this.actor = actor;
 478             this.actorContext = actorContext;
 479             this.schemaContext = schemaContext;
 480         }
 481
 482         private ActorSelection getActor() {
 483             return actor;
 484         }
 485
 486         private String getResolvedCohortPath(String cohortPath) {
 487             return actorContext.resolvePath(actorPath, cohortPath);
 488         }
 489
 490         @Override
 491         public void closeTransaction() {
 492             LOG.debug("Tx {} closeTransaction called", identifier);
 493             actorContext.sendRemoteOperationAsync(getActor(), new CloseTransaction().toSerializable());
 494         }
 495
 496         @Override
 497         public Future<ActorPath> readyTransaction() {
 498             LOG.debug("Tx {} readyTransaction called with {} previous recorded operations pending",
 499                     identifier, recordedOperationFutures.size());
 500
 501             // Send the ReadyTransaction message to the Tx actor.
 502
 503             final Future<Object> replyFuture = actorContext.executeRemoteOperationAsync(getActor(),
 504                     new ReadyTransaction().toSerializable());
 505
 506             // Combine all the previously recorded put/merge/delete operation reply Futures and the
 507             // ReadyTransactionReply Future into one Future. If any one fails then the combined
 508             // Future will fail. We need all prior operations and the ready operation to succeed
 509             // in order to attempt commit.
 510
 511             List<Future<Object>> futureList =
 512                     Lists.newArrayListWithCapacity(recordedOperationFutures.size() + 1);
 513             futureList.addAll(recordedOperationFutures);
 514             futureList.add(replyFuture);
 515
 516             Future<Iterable<Object>> combinedFutures = akka.dispatch.Futures.sequence(futureList,
 517                     actorContext.getActorSystem().dispatcher());
 518
 519             // Transform the combined Future into a Future that returns the cohort actor path from
 520             // the ReadyTransactionReply. That's the end result of the ready operation.
 521
 522             return combinedFutures.transform(new AbstractFunction1<Iterable<Object>, ActorPath>() {
 523                 @Override
 524                 public ActorPath apply(Iterable<Object> notUsed) {
 525
 526                     LOG.debug("Tx {} readyTransaction: pending recorded operations succeeded",
 527                             identifier);
 528
 529                     // At this point all the Futures succeeded and we need to extract the cohort
 530                     // actor path from the ReadyTransactionReply. For the recorded operations, they
 531                     // don't return any data so we're only interested that they completed
 532                     // successfully. We could be paranoid and verify the correct reply types but
 533                     // that really should never happen so it's not worth the overhead of
 534                     // de-serializing each reply.
 535
 536                     // Note the Future get call here won't block as it's complete.
 537                     Object serializedReadyReply = replyFuture.value().get().get();
 538                     if(serializedReadyReply.getClass().equals(
 539                                                      ReadyTransactionReply.SERIALIZABLE_CLASS)) {
 540                         ReadyTransactionReply reply = ReadyTransactionReply.fromSerializable(
 541                                 actorContext.getActorSystem(), serializedReadyReply);
 542
 543                         String resolvedCohortPath = getResolvedCohortPath(
 544                                 reply.getCohortPath().toString());
 545
 546                         LOG.debug("Tx {} readyTransaction: resolved cohort path {}",
 547                                 identifier, resolvedCohortPath);
 548
 549                         return actorContext.actorFor(resolvedCohortPath);
 550                     } else {
 551                         // Throwing an exception here will fail the Future.
 552
 553                         throw new IllegalArgumentException(String.format("Invalid reply type {}",
 554                                 serializedReadyReply.getClass()));
 555                     }
 556                 }
 557             }, SAME_FAILURE_TRANSFORMER, actorContext.getActorSystem().dispatcher());
 558         }
 559
 560         @Override
 561         public void deleteData(YangInstanceIdentifier path) {
 562             LOG.debug("Tx {} deleteData called path = {}", identifier, path);
 563             recordedOperationFutures.add(actorContext.executeRemoteOperationAsync(getActor(),
 564                     new DeleteData(path).toSerializable() ));
 565         }
 566
 567         @Override
 568         public void mergeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
 569             LOG.debug("Tx {} mergeData called path = {}", identifier, path);
 570             recordedOperationFutures.add(actorContext.executeRemoteOperationAsync(getActor(),
 571                     new MergeData(path, data, schemaContext).toSerializable()));
 572         }
 573
 574         @Override
 575         public void writeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
 576             LOG.debug("Tx {} writeData called path = {}", identifier, path);
 577             recordedOperationFutures.add(actorContext.executeRemoteOperationAsync(getActor(),
 578                     new WriteData(path, data, schemaContext).toSerializable()));
 579         }
 580
 581         @Override
 582         public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> readData(
 583                 final YangInstanceIdentifier path) {
 584
 585             LOG.debug("Tx {} readData called path = {}", identifier, path);
 586
 587             final SettableFuture<Optional<NormalizedNode<?, ?>>> returnFuture = SettableFuture.create();
 588
 589             // If there were any previous recorded put/merge/delete operation reply Futures then we
 590             // must wait for them to successfully complete. This is necessary to honor the read
 591             // uncommitted semantics of the public API contract. If any one fails then fail the read.
 592
 593             if(recordedOperationFutures.isEmpty()) {
 594                 finishReadData(path, returnFuture);
 595             } else {
 596                 LOG.debug("Tx {} readData: verifying {} previous recorded operations",
 597                         identifier, recordedOperationFutures.size());
 598
 599                 // Note: we make a copy of recordedOperationFutures to be on the safe side in case
 600                 // Futures#sequence accesses the passed List on a different thread, as
 601                 // recordedOperationFutures is not synchronized.
 602
 603                 Future<Iterable<Object>> combinedFutures = akka.dispatch.Futures.sequence(
 604                         Lists.newArrayList(recordedOperationFutures),
 605                         actorContext.getActorSystem().dispatcher());
 606                 OnComplete<Iterable<Object>> onComplete = new OnComplete<Iterable<Object>>() {
 607                     @Override
 608                     public void onComplete(Throwable failure, Iterable<Object> notUsed)
 609                             throws Throwable {
 610                         if(failure != null) {
 611                             LOG.debug("Tx {} readData: a recorded operation failed: {}",
 612                                     identifier, failure);
 613
 614                             returnFuture.setException(new ReadFailedException(
 615                                     "The read could not be performed because a previous put, merge,"
 616                                     + "or delete operation failed", failure));
 617                         } else {
 618                             finishReadData(path, returnFuture);
 619                         }
 620                     }
 621                 };
 622
 623                 combinedFutures.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
 624             }
 625
 626             return MappingCheckedFuture.create(returnFuture, ReadFailedException.MAPPER);
 627         }
 628
 629         private void finishReadData(final YangInstanceIdentifier path,
 630                 final SettableFuture<Optional<NormalizedNode<?, ?>>> returnFuture) {
 631
 632             LOG.debug("Tx {} finishReadData called path = {}", identifier, path);
 633
 634             OnComplete<Object> onComplete = new OnComplete<Object>() {
 635                 @Override
 636                 public void onComplete(Throwable failure, Object readResponse) throws Throwable {
 637                     if(failure != null) {
 638                         LOG.debug("Tx {} read operation failed: {}", identifier, failure);
 639
 640                         returnFuture.setException(new ReadFailedException(
 641                                 "Error reading data for path " + path, failure));
 642
 643                     } else {
 644                         LOG.debug("Tx {} read operation succeeded", identifier, failure);
 645
 646                         if (readResponse.getClass().equals(ReadDataReply.SERIALIZABLE_CLASS)) {
 647                             ReadDataReply reply = ReadDataReply.fromSerializable(schemaContext,
 648                                     path, readResponse);
 649                             if (reply.getNormalizedNode() == null) {
 650                                 returnFuture.set(Optional.<NormalizedNode<?, ?>>absent());
 651                             } else {
 652                                 returnFuture.set(Optional.<NormalizedNode<?, ?>>of(
 653                                         reply.getNormalizedNode()));
 654                             }
 655                         } else {
 656                             returnFuture.setException(new ReadFailedException(
 657                                     "Invalid response reading data for path " + path));
 658                         }
 659                     }
 660                 }
 661             };
 662
 663             Future<Object> readFuture = actorContext.executeRemoteOperationAsync(getActor(),
 664                     new ReadData(path).toSerializable());
 665             readFuture.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
 666         }
 667
 668         @Override
 669         public CheckedFuture<Boolean, ReadFailedException> dataExists(
 670                 final YangInstanceIdentifier path) {
 671
 672             LOG.debug("Tx {} dataExists called path = {}", identifier, path);
 673
 674             final SettableFuture<Boolean> returnFuture = SettableFuture.create();
 675
 676             // If there were any previous recorded put/merge/delete operation reply Futures then we
 677             // must wait for them to successfully complete. This is necessary to honor the read
 678             // uncommitted semantics of the public API contract. If any one fails then fail this
 679             // request.
 680
 681             if(recordedOperationFutures.isEmpty()) {
 682                 finishDataExists(path, returnFuture);
 683             } else {
 684                 LOG.debug("Tx {} dataExists: verifying {} previous recorded operations",
 685                         identifier, recordedOperationFutures.size());
 686
 687                 // Note: we make a copy of recordedOperationFutures to be on the safe side in case
 688                 // Futures#sequence accesses the passed List on a different thread, as
 689                 // recordedOperationFutures is not synchronized.
 690
 691                 Future<Iterable<Object>> combinedFutures = akka.dispatch.Futures.sequence(
 692                         Lists.newArrayList(recordedOperationFutures),
 693                         actorContext.getActorSystem().dispatcher());
 694                 OnComplete<Iterable<Object>> onComplete = new OnComplete<Iterable<Object>>() {
 695                     @Override
 696                     public void onComplete(Throwable failure, Iterable<Object> notUsed)
 697                             throws Throwable {
 698                         if(failure != null) {
 699                             LOG.debug("Tx {} dataExists: a recorded operation failed: {}",
 700                                     identifier, failure);
 701
 702                             returnFuture.setException(new ReadFailedException(
 703                                     "The data exists could not be performed because a previous "
 704                                     + "put, merge, or delete operation failed", failure));
 705                         } else {
 706                             finishDataExists(path, returnFuture);
 707                         }
 708                     }
 709                 };
 710
 711                 combinedFutures.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
 712             }
 713
 714             return MappingCheckedFuture.create(returnFuture, ReadFailedException.MAPPER);
 715         }
 716
 717         private void finishDataExists(final YangInstanceIdentifier path,
 718                 final SettableFuture<Boolean> returnFuture) {
 719
 720             LOG.debug("Tx {} finishDataExists called path = {}", identifier, path);
 721
 722             OnComplete<Object> onComplete = new OnComplete<Object>() {
 723                 @Override
 724                 public void onComplete(Throwable failure, Object response) throws Throwable {
 725                     if(failure != null) {
 726                         LOG.debug("Tx {} dataExists operation failed: {}", identifier, failure);
 727
 728                         returnFuture.setException(new ReadFailedException(
 729                                 "Error checking data exists for path " + path, failure));
 730                     } else {
 731                         LOG.debug("Tx {} dataExists operation succeeded", identifier, failure);
 732
 733                         if (response.getClass().equals(DataExistsReply.SERIALIZABLE_CLASS)) {
 734                             returnFuture.set(Boolean.valueOf(DataExistsReply.
 735                                         fromSerializable(response).exists()));
 736                         } else {
 737                             returnFuture.setException(new ReadFailedException(
 738                                     "Invalid response checking exists for path " + path));
 739                         }
 740                     }
 741                 }
 742             };
 743
 744             Future<Object> future = actorContext.executeRemoteOperationAsync(getActor(),
 745                     new DataExists(path).toSerializable());
 746             future.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
 747         }
 748     }
 749
 750     private static class NoOpTransactionContext extends AbstractTransactionContext {
 751
 752         private final Logger LOG = LoggerFactory.getLogger(NoOpTransactionContext.class);
 753
 754         private final Exception failure;
 755
 756         public NoOpTransactionContext(String shardName, Exception failure,
 757                 TransactionIdentifier identifier){
 758             super(shardName, identifier);
 759             this.failure = failure;
 760         }
 761
 762         @Override
 763         public void closeTransaction() {
 764             LOG.debug("NoOpTransactionContext {} closeTransaction called", identifier);
 765         }
 766
 767         @Override
 768         public Future<ActorPath> readyTransaction() {
 769             LOG.debug("Tx {} readyTransaction called", identifier);
 770             return akka.dispatch.Futures.failed(failure);
 771         }
 772
 773         @Override
 774         public void deleteData(YangInstanceIdentifier path) {
 775             LOG.debug("Tx {} deleteData called path = {}", identifier, path);
 776         }
 777
 778         @Override
 779         public void mergeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
 780             LOG.debug("Tx {} mergeData called path = {}", identifier, path);
 781         }
 782
 783         @Override
 784         public void writeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
 785             LOG.debug("Tx {} writeData called path = {}", identifier, path);
 786         }
 787
 788         @Override
 789         public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> readData(
 790             YangInstanceIdentifier path) {
 791             LOG.debug("Tx {} readData called path = {}", identifier, path);
 792             return Futures.immediateFailedCheckedFuture(new ReadFailedException(
 793                     "Error reading data for path " + path, failure));
 794         }
 795
 796         @Override
 797         public CheckedFuture<Boolean, ReadFailedException> dataExists(
 798             YangInstanceIdentifier path) {
 799             LOG.debug("Tx {} dataExists called path = {}", identifier, path);
 800             return Futures.immediateFailedCheckedFuture(new ReadFailedException(
 801                     "Error checking exists for path " + path, failure));
 802         }
 803     }
 804 }