Merge "Bug 1637: Change Rpc actor calls to async"
[controller.git] / opendaylight / md-sal / sal-distributed-datastore / src / main / java / org / opendaylight / controller / cluster / datastore / TransactionProxy.java
index e30076d09e05930f6441a9454b791a83cfd180d8..a8b20c030e1dd34f274ce2e02b56669739824af3 100644 (file)
@@ -10,11 +10,24 @@ package org.opendaylight.controller.cluster.datastore;
 
 import akka.actor.ActorPath;
 import akka.actor.ActorSelection;
+import akka.dispatch.OnComplete;
+
+import com.google.common.annotations.VisibleForTesting;
+import com.google.common.base.FinalizablePhantomReference;
+import com.google.common.base.FinalizableReferenceQueue;
 import com.google.common.base.Optional;
-import com.google.common.util.concurrent.ListenableFuture;
-import com.google.common.util.concurrent.ListenableFutureTask;
+import com.google.common.base.Preconditions;
+import com.google.common.collect.Lists;
+import com.google.common.util.concurrent.CheckedFuture;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.SettableFuture;
+
+import org.opendaylight.controller.cluster.datastore.identifiers.TransactionIdentifier;
 import org.opendaylight.controller.cluster.datastore.messages.CloseTransaction;
 import org.opendaylight.controller.cluster.datastore.messages.CreateTransaction;
+import org.opendaylight.controller.cluster.datastore.messages.CreateTransactionReply;
+import org.opendaylight.controller.cluster.datastore.messages.DataExists;
+import org.opendaylight.controller.cluster.datastore.messages.DataExistsReply;
 import org.opendaylight.controller.cluster.datastore.messages.DeleteData;
 import org.opendaylight.controller.cluster.datastore.messages.MergeData;
 import org.opendaylight.controller.cluster.datastore.messages.ReadData;
@@ -22,20 +35,27 @@ import org.opendaylight.controller.cluster.datastore.messages.ReadDataReply;
 import org.opendaylight.controller.cluster.datastore.messages.ReadyTransaction;
 import org.opendaylight.controller.cluster.datastore.messages.ReadyTransactionReply;
 import org.opendaylight.controller.cluster.datastore.messages.WriteData;
+import org.opendaylight.controller.cluster.datastore.shardstrategy.ShardStrategyFactory;
 import org.opendaylight.controller.cluster.datastore.utils.ActorContext;
-import org.opendaylight.controller.protobuff.messages.transaction.ShardTransactionMessages.CreateTransactionReply;
+import org.opendaylight.controller.md.sal.common.api.data.ReadFailedException;
 import org.opendaylight.controller.sal.core.spi.data.DOMStoreReadWriteTransaction;
 import org.opendaylight.controller.sal.core.spi.data.DOMStoreThreePhaseCommitCohort;
-import org.opendaylight.yangtools.yang.data.api.InstanceIdentifier;
+import org.opendaylight.yangtools.util.concurrent.MappingCheckedFuture;
+import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
 import org.opendaylight.yangtools.yang.model.api.SchemaContext;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import scala.Function1;
+import scala.concurrent.Future;
+import scala.runtime.AbstractFunction1;
 
-import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.concurrent.Callable;
-import java.util.concurrent.ExecutorService;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicLong;
 
 /**
@@ -57,101 +77,239 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
         READ_WRITE
     }
 
+    static Function1<Throwable, Throwable> SAME_FAILURE_TRANSFORMER = new AbstractFunction1<
+                                                                          Throwable, Throwable>() {
+        @Override
+        public Throwable apply(Throwable failure) {
+            return failure;
+        }
+    };
+
     private static final AtomicLong counter = new AtomicLong();
 
+    private static final Logger
+        LOG = LoggerFactory.getLogger(TransactionProxy.class);
+
+
+    /**
+     * Used to enqueue the PhantomReferences for read-only TransactionProxy instances. The
+     * FinalizableReferenceQueue is safe to use statically in an OSGi environment as it uses some
+     * trickery to clean up its internal thread when the bundle is unloaded.
+     */
+    private static final FinalizableReferenceQueue phantomReferenceQueue =
+                                                                  new FinalizableReferenceQueue();
+
+    /**
+     * This stores the TransactionProxyCleanupPhantomReference instances statically, This is
+     * necessary because PhantomReferences need a hard reference so they're not garbage collected.
+     * Once finalized, the TransactionProxyCleanupPhantomReference removes itself from this map
+     * and thus becomes eligible for garbage collection.
+     */
+    private static final Map<TransactionProxyCleanupPhantomReference,
+                             TransactionProxyCleanupPhantomReference> phantomReferenceCache =
+                                                                        new ConcurrentHashMap<>();
+
+    /**
+     * A PhantomReference that closes remote transactions for a TransactionProxy when it's
+     * garbage collected. This is used for read-only transactions as they're not explicitly closed
+     * by clients. So the only way to detect that a transaction is no longer in use and it's safe
+     * to clean up is when it's garbage collected. It's inexact as to when an instance will be GC'ed
+     * but TransactionProxy instances should generally be short-lived enough to avoid being moved
+     * to the old generation space and thus should be cleaned up in a timely manner as the GC
+     * runs on the young generation (eden, swap1...) space much more frequently.
+     */
+    private static class TransactionProxyCleanupPhantomReference
+                                           extends FinalizablePhantomReference<TransactionProxy> {
+
+        private final List<ActorSelection> remoteTransactionActors;
+        private final AtomicBoolean remoteTransactionActorsMB;
+        private final ActorContext actorContext;
+        private final TransactionIdentifier identifier;
+
+        protected TransactionProxyCleanupPhantomReference(TransactionProxy referent) {
+            super(referent, phantomReferenceQueue);
+
+            // Note we need to cache the relevant fields from the TransactionProxy as we can't
+            // have a hard reference to the TransactionProxy instance itself.
+
+            remoteTransactionActors = referent.remoteTransactionActors;
+            remoteTransactionActorsMB = referent.remoteTransactionActorsMB;
+            actorContext = referent.actorContext;
+            identifier = referent.identifier;
+        }
+
+        @Override
+        public void finalizeReferent() {
+            LOG.trace("Cleaning up {} Tx actors for TransactionProxy {}",
+                    remoteTransactionActors.size(), identifier);
+
+            phantomReferenceCache.remove(this);
+
+            // Access the memory barrier volatile to ensure all previous updates to the
+            // remoteTransactionActors list are visible to this thread.
+
+            if(remoteTransactionActorsMB.get()) {
+                for(ActorSelection actor : remoteTransactionActors) {
+                    LOG.trace("Sending CloseTransaction to {}", actor);
+                    actorContext.sendRemoteOperationAsync(actor,
+                            new CloseTransaction().toSerializable());
+                }
+            }
+        }
+    }
+
+    /**
+     * Stores the remote Tx actors for each requested data store path to be used by the
+     * PhantomReference to close the remote Tx's. This is only used for read-only Tx's. The
+     * remoteTransactionActorsMB volatile serves as a memory barrier to publish updates to the
+     * remoteTransactionActors list so they will be visible to the thread accessing the
+     * PhantomReference.
+     */
+    private List<ActorSelection> remoteTransactionActors;
+    private AtomicBoolean remoteTransactionActorsMB;
+
+    private final Map<String, TransactionContext> remoteTransactionPaths = new HashMap<>();
+
     private final TransactionType transactionType;
     private final ActorContext actorContext;
-    private final Map<String, ActorSelection> remoteTransactionPaths = new HashMap<>();
-    private final String identifier;
-    private final ExecutorService executor;
+    private final TransactionIdentifier identifier;
     private final SchemaContext schemaContext;
+    private boolean inReadyState;
 
-    public TransactionProxy(
-        ActorContext actorContext,
-        TransactionType transactionType,
-        ExecutorService executor,
-        SchemaContext schemaContext
-        ) {
+    public TransactionProxy(ActorContext actorContext, TransactionType transactionType) {
+        this.actorContext = Preconditions.checkNotNull(actorContext,
+                "actorContext should not be null");
+        this.transactionType = Preconditions.checkNotNull(transactionType,
+                "transactionType should not be null");
+        this.schemaContext = Preconditions.checkNotNull(actorContext.getSchemaContext(),
+                "schemaContext should not be null");
 
-        this.identifier = "txn-" + counter.getAndIncrement();
-        this.transactionType = transactionType;
-        this.actorContext = actorContext;
-        this.executor = executor;
-        this.schemaContext = schemaContext;
+        String memberName = actorContext.getCurrentMemberName();
+        if(memberName == null){
+            memberName = "UNKNOWN-MEMBER";
+        }
 
-        Object response = actorContext.executeShardOperation(Shard.DEFAULT_NAME, new CreateTransaction(identifier), ActorContext.ASK_DURATION);
-        if(response instanceof CreateTransactionReply){
-            CreateTransactionReply reply = (CreateTransactionReply) response;
-            remoteTransactionPaths.put(Shard.DEFAULT_NAME, actorContext.actorSelection(reply.getTransactionActorPath()));
+        this.identifier = TransactionIdentifier.builder().memberName(memberName).counter(
+                counter.getAndIncrement()).build();
+
+        if(transactionType == TransactionType.READ_ONLY) {
+            // Read-only Tx's aren't explicitly closed by the client so we create a PhantomReference
+            // to close the remote Tx's when this instance is no longer in use and is garbage
+            // collected.
+
+            remoteTransactionActors = Lists.newArrayList();
+            remoteTransactionActorsMB = new AtomicBoolean();
+
+            TransactionProxyCleanupPhantomReference cleanup =
+                                              new TransactionProxyCleanupPhantomReference(this);
+            phantomReferenceCache.put(cleanup, cleanup);
         }
+
+        LOG.debug("Created txn {} of type {}", identifier, transactionType);
+    }
+
+    @VisibleForTesting
+    List<Future<Object>> getRecordedOperationFutures() {
+        List<Future<Object>> recordedOperationFutures = Lists.newArrayList();
+        for(TransactionContext transactionContext : remoteTransactionPaths.values()) {
+            recordedOperationFutures.addAll(transactionContext.getRecordedOperationFutures());
+        }
+
+        return recordedOperationFutures;
     }
 
     @Override
-    public ListenableFuture<Optional<NormalizedNode<?, ?>>> read(final InstanceIdentifier path) {
-        final ActorSelection remoteTransaction = remoteTransactionFromIdentifier(path);
-
-        Callable<Optional<NormalizedNode<?,?>>> call = new Callable() {
-
-            @Override public Optional<NormalizedNode<?,?>> call() throws Exception {
-                Object response = actorContext
-                    .executeRemoteOperation(remoteTransaction, new ReadData(path).toSerializable(),
-                        ActorContext.ASK_DURATION);
-                if(response.getClass().equals(ReadDataReply.SERIALIZABLE_CLASS)){
-                    ReadDataReply reply = ReadDataReply.fromSerializable(schemaContext,path, response);
-                    if(reply.getNormalizedNode() == null){
-                        return Optional.absent();
-                    }
-                    //FIXME : A cast should not be required here ???
-                    return (Optional<NormalizedNode<?, ?>>) Optional.of(reply.getNormalizedNode());
-                }
+    public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> read(
+            final YangInstanceIdentifier path) {
 
-                return Optional.absent();
-            }
-        };
+        Preconditions.checkState(transactionType != TransactionType.WRITE_ONLY,
+                "Read operation on write-only transaction is not allowed");
 
-        ListenableFutureTask<Optional<NormalizedNode<?, ?>>>
-            future = ListenableFutureTask.create(call);
+        LOG.debug("Tx {} read {}", identifier, path);
 
-        executor.submit(future);
+        createTransactionIfMissing(actorContext, path);
 
-        return future;
+        return transactionContext(path).readData(path);
     }
 
     @Override
-    public void write(InstanceIdentifier path, NormalizedNode<?, ?> data) {
-        final ActorSelection remoteTransaction = remoteTransactionFromIdentifier(path);
-        remoteTransaction.tell(new WriteData(path, data, schemaContext).toSerializable(), null);
+    public CheckedFuture<Boolean, ReadFailedException> exists(YangInstanceIdentifier path) {
+
+        Preconditions.checkState(transactionType != TransactionType.WRITE_ONLY,
+                "Exists operation on write-only transaction is not allowed");
+
+        LOG.debug("Tx {} exists {}", identifier, path);
+
+        createTransactionIfMissing(actorContext, path);
+
+        return transactionContext(path).dataExists(path);
+    }
+
+    private void checkModificationState() {
+        Preconditions.checkState(transactionType != TransactionType.READ_ONLY,
+                "Modification operation on read-only transaction is not allowed");
+        Preconditions.checkState(!inReadyState,
+                "Transaction is sealed - further modifications are not allowed");
     }
 
     @Override
-    public void merge(InstanceIdentifier path, NormalizedNode<?, ?> data) {
-        final ActorSelection remoteTransaction = remoteTransactionFromIdentifier(path);
-        remoteTransaction.tell(new MergeData(path, data, schemaContext).toSerializable(), null);
+    public void write(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
+
+        checkModificationState();
+
+        LOG.debug("Tx {} write {}", identifier, path);
+
+        createTransactionIfMissing(actorContext, path);
+
+        transactionContext(path).writeData(path, data);
     }
 
     @Override
-    public void delete(InstanceIdentifier path) {
-        final ActorSelection remoteTransaction = remoteTransactionFromIdentifier(path);
-        remoteTransaction.tell(new DeleteData(path).toSerializable(), null);
+    public void merge(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
+
+        checkModificationState();
+
+        LOG.debug("Tx {} merge {}", identifier, path);
+
+        createTransactionIfMissing(actorContext, path);
+
+        transactionContext(path).mergeData(path, data);
+    }
+
+    @Override
+    public void delete(YangInstanceIdentifier path) {
+
+        checkModificationState();
+
+        LOG.debug("Tx {} delete {}", identifier, path);
+
+        createTransactionIfMissing(actorContext, path);
+
+        transactionContext(path).deleteData(path);
     }
 
     @Override
     public DOMStoreThreePhaseCommitCohort ready() {
-        List<ActorPath> cohortPaths = new ArrayList<>();
 
-        for(ActorSelection remoteTransaction : remoteTransactionPaths.values()) {
-            Object result = actorContext.executeRemoteOperation(remoteTransaction,
-                new ReadyTransaction(),
-                ActorContext.ASK_DURATION
-            );
+        checkModificationState();
 
-            if(result instanceof ReadyTransactionReply){
-                ReadyTransactionReply reply = (ReadyTransactionReply) result;
-                cohortPaths.add(reply.getCohortPath());
-            }
+        inReadyState = true;
+
+        LOG.debug("Tx {} Trying to get {} transactions ready for commit", identifier,
+                remoteTransactionPaths.size());
+
+        List<Future<ActorPath>> cohortPathFutures = Lists.newArrayList();
+
+        for(TransactionContext transactionContext : remoteTransactionPaths.values()) {
+
+            LOG.debug("Tx {} Readying transaction for shard {}", identifier,
+                    transactionContext.getShardName());
+
+            cohortPathFutures.add(transactionContext.readyTransaction());
         }
 
-        return new ThreePhaseCommitCohortProxy(actorContext, cohortPaths, identifier, executor);
+        return new ThreePhaseCommitCohortProxy(actorContext, cohortPathFutures,
+                identifier.toString());
     }
 
     @Override
@@ -161,17 +319,456 @@ public class TransactionProxy implements DOMStoreReadWriteTransaction {
 
     @Override
     public void close() {
-        for(ActorSelection remoteTransaction : remoteTransactionPaths.values()) {
-            remoteTransaction.tell(new CloseTransaction(), null);
+        for(TransactionContext transactionContext : remoteTransactionPaths.values()) {
+            transactionContext.closeTransaction();
+        }
+
+        remoteTransactionPaths.clear();
+
+        if(transactionType == TransactionType.READ_ONLY) {
+            remoteTransactionActors.clear();
+            remoteTransactionActorsMB.set(true);
         }
     }
 
-    private ActorSelection remoteTransactionFromIdentifier(InstanceIdentifier path){
+    private TransactionContext transactionContext(YangInstanceIdentifier path){
         String shardName = shardNameFromIdentifier(path);
         return remoteTransactionPaths.get(shardName);
     }
 
-    private String shardNameFromIdentifier(InstanceIdentifier path){
-        return Shard.DEFAULT_NAME;
+    private String shardNameFromIdentifier(YangInstanceIdentifier path){
+        return ShardStrategyFactory.getStrategy(path).findShard(path);
+    }
+
+    private void createTransactionIfMissing(ActorContext actorContext, YangInstanceIdentifier path) {
+        String shardName = ShardStrategyFactory.getStrategy(path).findShard(path);
+
+        TransactionContext transactionContext =
+            remoteTransactionPaths.get(shardName);
+
+        if(transactionContext != null){
+            // A transaction already exists with that shard
+            return;
+        }
+
+        try {
+            Object response = actorContext.executeShardOperation(shardName,
+                new CreateTransaction(identifier.toString(),this.transactionType.ordinal() ).toSerializable());
+            if (response.getClass().equals(CreateTransactionReply.SERIALIZABLE_CLASS)) {
+                CreateTransactionReply reply =
+                    CreateTransactionReply.fromSerializable(response);
+
+                String transactionPath = reply.getTransactionPath();
+
+                LOG.debug("Tx {} Received transaction path = {}", identifier, transactionPath);
+
+                ActorSelection transactionActor = actorContext.actorSelection(transactionPath);
+
+                if(transactionType == TransactionType.READ_ONLY) {
+                    // Add the actor to the remoteTransactionActors list for access by the
+                    // cleanup PhantonReference.
+                    remoteTransactionActors.add(transactionActor);
+
+                    // Write to the memory barrier volatile to publish the above update to the
+                    // remoteTransactionActors list for thread visibility.
+                    remoteTransactionActorsMB.set(true);
+                }
+
+                transactionContext = new TransactionContextImpl(shardName, transactionPath,
+                        transactionActor, identifier, actorContext, schemaContext);
+
+                remoteTransactionPaths.put(shardName, transactionContext);
+            } else {
+                throw new IllegalArgumentException(String.format(
+                        "Invalid reply type {} for CreateTransaction", response.getClass()));
+            }
+        } catch(Exception e){
+            LOG.debug("Tx {} Creating NoOpTransaction because of : {}", identifier, e.getMessage());
+            remoteTransactionPaths.put(shardName, new NoOpTransactionContext(shardName, e, identifier));
+        }
+    }
+
+    private interface TransactionContext {
+        String getShardName();
+
+        void closeTransaction();
+
+        Future<ActorPath> readyTransaction();
+
+        void writeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data);
+
+        void deleteData(YangInstanceIdentifier path);
+
+        void mergeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data);
+
+        CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> readData(
+                final YangInstanceIdentifier path);
+
+        CheckedFuture<Boolean, ReadFailedException> dataExists(YangInstanceIdentifier path);
+
+        List<Future<Object>> getRecordedOperationFutures();
+    }
+
+    private static abstract class AbstractTransactionContext implements TransactionContext {
+
+        protected final TransactionIdentifier identifier;
+        protected final String shardName;
+        protected final List<Future<Object>> recordedOperationFutures = Lists.newArrayList();
+
+        AbstractTransactionContext(String shardName, TransactionIdentifier identifier) {
+            this.shardName = shardName;
+            this.identifier = identifier;
+        }
+
+        @Override
+        public String getShardName() {
+            return shardName;
+        }
+
+        @Override
+        public List<Future<Object>> getRecordedOperationFutures() {
+            return recordedOperationFutures;
+        }
+    }
+
+    private static class TransactionContextImpl extends AbstractTransactionContext {
+        private final Logger LOG = LoggerFactory.getLogger(TransactionContextImpl.class);
+
+        private final ActorContext actorContext;
+        private final SchemaContext schemaContext;
+        private final String actorPath;
+        private final ActorSelection actor;
+
+        private TransactionContextImpl(String shardName, String actorPath,
+                ActorSelection actor, TransactionIdentifier identifier, ActorContext actorContext,
+                SchemaContext schemaContext) {
+            super(shardName, identifier);
+            this.actorPath = actorPath;
+            this.actor = actor;
+            this.actorContext = actorContext;
+            this.schemaContext = schemaContext;
+        }
+
+        private ActorSelection getActor() {
+            return actor;
+        }
+
+        private String getResolvedCohortPath(String cohortPath) {
+            return actorContext.resolvePath(actorPath, cohortPath);
+        }
+
+        @Override
+        public void closeTransaction() {
+            LOG.debug("Tx {} closeTransaction called", identifier);
+            actorContext.sendRemoteOperationAsync(getActor(), new CloseTransaction().toSerializable());
+        }
+
+        @Override
+        public Future<ActorPath> readyTransaction() {
+            LOG.debug("Tx {} readyTransaction called with {} previous recorded operations pending",
+                    identifier, recordedOperationFutures.size());
+
+            // Send the ReadyTransaction message to the Tx actor.
+
+            final Future<Object> replyFuture = actorContext.executeRemoteOperationAsync(getActor(),
+                    new ReadyTransaction().toSerializable());
+
+            // Combine all the previously recorded put/merge/delete operation reply Futures and the
+            // ReadyTransactionReply Future into one Future. If any one fails then the combined
+            // Future will fail. We need all prior operations and the ready operation to succeed
+            // in order to attempt commit.
+
+            List<Future<Object>> futureList =
+                    Lists.newArrayListWithCapacity(recordedOperationFutures.size() + 1);
+            futureList.addAll(recordedOperationFutures);
+            futureList.add(replyFuture);
+
+            Future<Iterable<Object>> combinedFutures = akka.dispatch.Futures.sequence(futureList,
+                    actorContext.getActorSystem().dispatcher());
+
+            // Transform the combined Future into a Future that returns the cohort actor path from
+            // the ReadyTransactionReply. That's the end result of the ready operation.
+
+            return combinedFutures.transform(new AbstractFunction1<Iterable<Object>, ActorPath>() {
+                @Override
+                public ActorPath apply(Iterable<Object> notUsed) {
+
+                    LOG.debug("Tx {} readyTransaction: pending recorded operations succeeded",
+                            identifier);
+
+                    // At this point all the Futures succeeded and we need to extract the cohort
+                    // actor path from the ReadyTransactionReply. For the recorded operations, they
+                    // don't return any data so we're only interested that they completed
+                    // successfully. We could be paranoid and verify the correct reply types but
+                    // that really should never happen so it's not worth the overhead of
+                    // de-serializing each reply.
+
+                    // Note the Future get call here won't block as it's complete.
+                    Object serializedReadyReply = replyFuture.value().get().get();
+                    if(serializedReadyReply.getClass().equals(
+                                                     ReadyTransactionReply.SERIALIZABLE_CLASS)) {
+                        ReadyTransactionReply reply = ReadyTransactionReply.fromSerializable(
+                                actorContext.getActorSystem(), serializedReadyReply);
+
+                        String resolvedCohortPath = getResolvedCohortPath(
+                                reply.getCohortPath().toString());
+
+                        LOG.debug("Tx {} readyTransaction: resolved cohort path {}",
+                                identifier, resolvedCohortPath);
+
+                        return actorContext.actorFor(resolvedCohortPath);
+                    } else {
+                        // Throwing an exception here will fail the Future.
+
+                        throw new IllegalArgumentException(String.format("Invalid reply type {}",
+                                serializedReadyReply.getClass()));
+                    }
+                }
+            }, SAME_FAILURE_TRANSFORMER, actorContext.getActorSystem().dispatcher());
+        }
+
+        @Override
+        public void deleteData(YangInstanceIdentifier path) {
+            LOG.debug("Tx {} deleteData called path = {}", identifier, path);
+            recordedOperationFutures.add(actorContext.executeRemoteOperationAsync(getActor(),
+                    new DeleteData(path).toSerializable() ));
+        }
+
+        @Override
+        public void mergeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
+            LOG.debug("Tx {} mergeData called path = {}", identifier, path);
+            recordedOperationFutures.add(actorContext.executeRemoteOperationAsync(getActor(),
+                    new MergeData(path, data, schemaContext).toSerializable()));
+        }
+
+        @Override
+        public void writeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
+            LOG.debug("Tx {} writeData called path = {}", identifier, path);
+            recordedOperationFutures.add(actorContext.executeRemoteOperationAsync(getActor(),
+                    new WriteData(path, data, schemaContext).toSerializable()));
+        }
+
+        @Override
+        public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> readData(
+                final YangInstanceIdentifier path) {
+
+            LOG.debug("Tx {} readData called path = {}", identifier, path);
+
+            final SettableFuture<Optional<NormalizedNode<?, ?>>> returnFuture = SettableFuture.create();
+
+            // If there were any previous recorded put/merge/delete operation reply Futures then we
+            // must wait for them to successfully complete. This is necessary to honor the read
+            // uncommitted semantics of the public API contract. If any one fails then fail the read.
+
+            if(recordedOperationFutures.isEmpty()) {
+                finishReadData(path, returnFuture);
+            } else {
+                LOG.debug("Tx {} readData: verifying {} previous recorded operations",
+                        identifier, recordedOperationFutures.size());
+
+                // Note: we make a copy of recordedOperationFutures to be on the safe side in case
+                // Futures#sequence accesses the passed List on a different thread, as
+                // recordedOperationFutures is not synchronized.
+
+                Future<Iterable<Object>> combinedFutures = akka.dispatch.Futures.sequence(
+                        Lists.newArrayList(recordedOperationFutures),
+                        actorContext.getActorSystem().dispatcher());
+                OnComplete<Iterable<Object>> onComplete = new OnComplete<Iterable<Object>>() {
+                    @Override
+                    public void onComplete(Throwable failure, Iterable<Object> notUsed)
+                            throws Throwable {
+                        if(failure != null) {
+                            LOG.debug("Tx {} readData: a recorded operation failed: {}",
+                                    identifier, failure);
+
+                            returnFuture.setException(new ReadFailedException(
+                                    "The read could not be performed because a previous put, merge,"
+                                    + "or delete operation failed", failure));
+                        } else {
+                            finishReadData(path, returnFuture);
+                        }
+                    }
+                };
+
+                combinedFutures.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
+            }
+
+            return MappingCheckedFuture.create(returnFuture, ReadFailedException.MAPPER);
+        }
+
+        private void finishReadData(final YangInstanceIdentifier path,
+                final SettableFuture<Optional<NormalizedNode<?, ?>>> returnFuture) {
+
+            LOG.debug("Tx {} finishReadData called path = {}", identifier, path);
+
+            OnComplete<Object> onComplete = new OnComplete<Object>() {
+                @Override
+                public void onComplete(Throwable failure, Object readResponse) throws Throwable {
+                    if(failure != null) {
+                        LOG.debug("Tx {} read operation failed: {}", identifier, failure);
+
+                        returnFuture.setException(new ReadFailedException(
+                                "Error reading data for path " + path, failure));
+
+                    } else {
+                        LOG.debug("Tx {} read operation succeeded", identifier, failure);
+
+                        if (readResponse.getClass().equals(ReadDataReply.SERIALIZABLE_CLASS)) {
+                            ReadDataReply reply = ReadDataReply.fromSerializable(schemaContext,
+                                    path, readResponse);
+                            if (reply.getNormalizedNode() == null) {
+                                returnFuture.set(Optional.<NormalizedNode<?, ?>>absent());
+                            } else {
+                                returnFuture.set(Optional.<NormalizedNode<?, ?>>of(
+                                        reply.getNormalizedNode()));
+                            }
+                        } else {
+                            returnFuture.setException(new ReadFailedException(
+                                    "Invalid response reading data for path " + path));
+                        }
+                    }
+                }
+            };
+
+            Future<Object> readFuture = actorContext.executeRemoteOperationAsync(getActor(),
+                    new ReadData(path).toSerializable());
+            readFuture.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
+        }
+
+        @Override
+        public CheckedFuture<Boolean, ReadFailedException> dataExists(
+                final YangInstanceIdentifier path) {
+
+            LOG.debug("Tx {} dataExists called path = {}", identifier, path);
+
+            final SettableFuture<Boolean> returnFuture = SettableFuture.create();
+
+            // If there were any previous recorded put/merge/delete operation reply Futures then we
+            // must wait for them to successfully complete. This is necessary to honor the read
+            // uncommitted semantics of the public API contract. If any one fails then fail this
+            // request.
+
+            if(recordedOperationFutures.isEmpty()) {
+                finishDataExists(path, returnFuture);
+            } else {
+                LOG.debug("Tx {} dataExists: verifying {} previous recorded operations",
+                        identifier, recordedOperationFutures.size());
+
+                // Note: we make a copy of recordedOperationFutures to be on the safe side in case
+                // Futures#sequence accesses the passed List on a different thread, as
+                // recordedOperationFutures is not synchronized.
+
+                Future<Iterable<Object>> combinedFutures = akka.dispatch.Futures.sequence(
+                        Lists.newArrayList(recordedOperationFutures),
+                        actorContext.getActorSystem().dispatcher());
+                OnComplete<Iterable<Object>> onComplete = new OnComplete<Iterable<Object>>() {
+                    @Override
+                    public void onComplete(Throwable failure, Iterable<Object> notUsed)
+                            throws Throwable {
+                        if(failure != null) {
+                            LOG.debug("Tx {} dataExists: a recorded operation failed: {}",
+                                    identifier, failure);
+
+                            returnFuture.setException(new ReadFailedException(
+                                    "The data exists could not be performed because a previous "
+                                    + "put, merge, or delete operation failed", failure));
+                        } else {
+                            finishDataExists(path, returnFuture);
+                        }
+                    }
+                };
+
+                combinedFutures.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
+            }
+
+            return MappingCheckedFuture.create(returnFuture, ReadFailedException.MAPPER);
+        }
+
+        private void finishDataExists(final YangInstanceIdentifier path,
+                final SettableFuture<Boolean> returnFuture) {
+
+            LOG.debug("Tx {} finishDataExists called path = {}", identifier, path);
+
+            OnComplete<Object> onComplete = new OnComplete<Object>() {
+                @Override
+                public void onComplete(Throwable failure, Object response) throws Throwable {
+                    if(failure != null) {
+                        LOG.debug("Tx {} dataExists operation failed: {}", identifier, failure);
+
+                        returnFuture.setException(new ReadFailedException(
+                                "Error checking data exists for path " + path, failure));
+                    } else {
+                        LOG.debug("Tx {} dataExists operation succeeded", identifier, failure);
+
+                        if (response.getClass().equals(DataExistsReply.SERIALIZABLE_CLASS)) {
+                            returnFuture.set(Boolean.valueOf(DataExistsReply.
+                                        fromSerializable(response).exists()));
+                        } else {
+                            returnFuture.setException(new ReadFailedException(
+                                    "Invalid response checking exists for path " + path));
+                        }
+                    }
+                }
+            };
+
+            Future<Object> future = actorContext.executeRemoteOperationAsync(getActor(),
+                    new DataExists(path).toSerializable());
+            future.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
+        }
+    }
+
+    private static class NoOpTransactionContext extends AbstractTransactionContext {
+
+        private final Logger LOG = LoggerFactory.getLogger(NoOpTransactionContext.class);
+
+        private final Exception failure;
+
+        public NoOpTransactionContext(String shardName, Exception failure,
+                TransactionIdentifier identifier){
+            super(shardName, identifier);
+            this.failure = failure;
+        }
+
+        @Override
+        public void closeTransaction() {
+            LOG.debug("NoOpTransactionContext {} closeTransaction called", identifier);
+        }
+
+        @Override
+        public Future<ActorPath> readyTransaction() {
+            LOG.debug("Tx {} readyTransaction called", identifier);
+            return akka.dispatch.Futures.failed(failure);
+        }
+
+        @Override
+        public void deleteData(YangInstanceIdentifier path) {
+            LOG.debug("Tx {} deleteData called path = {}", identifier, path);
+        }
+
+        @Override
+        public void mergeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
+            LOG.debug("Tx {} mergeData called path = {}", identifier, path);
+        }
+
+        @Override
+        public void writeData(YangInstanceIdentifier path, NormalizedNode<?, ?> data) {
+            LOG.debug("Tx {} writeData called path = {}", identifier, path);
+        }
+
+        @Override
+        public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> readData(
+            YangInstanceIdentifier path) {
+            LOG.debug("Tx {} readData called path = {}", identifier, path);
+            return Futures.immediateFailedCheckedFuture(new ReadFailedException(
+                    "Error reading data for path " + path, failure));
+        }
+
+        @Override
+        public CheckedFuture<Boolean, ReadFailedException> dataExists(
+            YangInstanceIdentifier path) {
+            LOG.debug("Tx {} dataExists called path = {}", identifier, path);
+            return Futures.immediateFailedCheckedFuture(new ReadFailedException(
+                    "Error checking exists for path " + path, failure));
+        }
     }
 }