- /**
- * This method is overridden to ensure the previous Tx's ready operations complete
- * before we create the next shard Tx in the chain to avoid creation failures if the
- * previous Tx's ready operations haven't completed yet.
- */
- @Override
- protected Future<Object> sendCreateTransaction(final ActorSelection shard,
- final Object serializedCreateMessage) {
-
- // Check if there are any previous ready Futures, otherwise let the super class handle it.
- // The second check is done to ensure the the previous ready Futures aren't for this
- // Tx instance as deadlock would occur if we tried to wait on our own Futures. This can
- // occur in this scenario:
- //
- // - the TransactionProxy is created and the client does a write.
- //
- // - the TransactionProxy then attempts to create the shard Tx. However it first
- // sends a FindPrimaryShard message to the shard manager to find the local shard
- // This call is done async.
- //
- // - the client submits the Tx and the TransactionProxy is readied and we cache
- // the ready Futures here.
- //
- // - then the FindPrimaryShard call completes and this method is called to create
- // the shard Tx. However the cached Futures were from the ready on this Tx. If we
- // tried to wait on them, it would cause a form of deadlock as the ready Future
- // would be waiting on the Tx create Future and vice versa.
- SimpleEntry<Object, List<Future<ActorSelection>>> readyFuturesEntry = state.getReadyFutures();
- List<Future<ActorSelection>> readyFutures = readyFuturesEntry.getValue();
- if(readyFutures.isEmpty() || getIdentifier().equals(readyFuturesEntry.getKey())) {
- return super.sendCreateTransaction(shard, serializedCreateMessage);
- }
-
- // Combine the ready Futures into 1.
- Future<Iterable<ActorSelection>> combinedFutures = akka.dispatch.Futures.sequence(
- readyFutures, actorContext.getActorSystem().dispatcher());
-
- // Add a callback for completion of the combined Futures.
- final Promise<Object> createTxPromise = akka.dispatch.Futures.promise();
- OnComplete<Iterable<ActorSelection>> onComplete = new OnComplete<Iterable<ActorSelection>>() {
- @Override
- public void onComplete(Throwable failure, Iterable<ActorSelection> notUsed) {
- if(failure != null) {
- // A Ready Future failed so fail the returned Promise.
- createTxPromise.failure(failure);
- } else {
- // Send the CreateTx message and use the resulting Future to complete the
- // returned Promise.
- createTxPromise.completeWith(actorContext.executeOperationAsync(shard,
- serializedCreateMessage));
- }
- }
- };
-
- combinedFutures.onComplete(onComplete, actorContext.getActorSystem().dispatcher());
-
- return createTxPromise.future();
- }