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