private static final Logger LOG = LoggerFactory.getLogger(PingPongTransactionChain.class);
private final DOMTransactionChain delegate;
- @GuardedBy("this")
- private PingPongTransaction inflightTransaction;
@GuardedBy("this")
private boolean failed;
*/
private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> READY_UPDATER =
AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class, "readyTx");
- @SuppressWarnings("unused") // Accessed via READY_UPDATER
private volatile PingPongTransaction readyTx;
/**
AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class, "lockedTx");
private volatile PingPongTransaction lockedTx;
+ /**
+ * This updater is used to manipulate the "inflight" transaction. There can be at most
+ * one of these at any given time. We perform only compare-and-swap on these.
+ */
+ private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> INFLIGHT_UPDATER =
+ AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class, "inflightTx");
+ private volatile PingPongTransaction inflightTx;
+
PingPongTransactionChain(final DOMDataBroker broker, final TransactionChainListener listener) {
this.delegate = broker.createTransactionChain(new TransactionChainListener() {
@Override
LOG.debug("Delegate chain {} reported failure in {}", chain, transaction, cause);
final DOMDataReadWriteTransaction frontend;
- if (inflightTransaction == null) {
+ final PingPongTransaction tx = inflightTx;
+ if (tx == null) {
LOG.warn("Transaction chain {} failed with no pending transactions", chain);
frontend = null;
} else {
- frontend = inflightTransaction.getFrontendTransaction();
+ frontend = tx.getFrontendTransaction();
}
- listener.onTransactionChainFailed(PingPongTransactionChain.this, frontend , cause);
+ listener.onTransactionChainFailed(PingPongTransactionChain.this, frontend, cause);
delegateFailed();
}
return oldTx;
}
- // This forces allocateTransaction() on a slow path
+ /*
+ * This forces allocateTransaction() on a slow path, which has to happen after
+ * this method has completed executing. Also inflightTx may be updated outside
+ * the lock, hence we need to re-check.
+ */
@GuardedBy("this")
private void processIfReady() {
- final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
- if (tx != null) {
- processTransaction(tx);
+ if (inflightTx == null) {
+ final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
+ if (tx != null) {
+ processTransaction(tx);
+ }
}
}
}
LOG.debug("Submitting transaction {}", tx);
- final CheckedFuture<Void, ?> f = tx.getTransaction().submit();
- inflightTransaction = tx;
+ if (!INFLIGHT_UPDATER.compareAndSet(this, null, tx)) {
+ LOG.warn("Submitting transaction {} while {} is still running", tx, inflightTx);
+ }
- Futures.addCallback(f, new FutureCallback<Void>() {
+ Futures.addCallback(tx.getTransaction().submit(), new FutureCallback<Void>() {
@Override
public void onSuccess(final Void result) {
transactionSuccessful(tx, result);
private void transactionSuccessful(final PingPongTransaction tx, final Void result) {
LOG.debug("Transaction {} completed successfully", tx);
- synchronized (this) {
- Preconditions.checkState(inflightTransaction == tx, "Successful transaction %s while %s was submitted", tx, inflightTransaction);
+ final boolean success = INFLIGHT_UPDATER.compareAndSet(this, tx, null);
+ Preconditions.checkState(success, "Successful transaction %s while %s was submitted", tx, inflightTx);
- inflightTransaction = null;
+ synchronized (this) {
processIfReady();
}
private void transactionFailed(final PingPongTransaction tx, final Throwable t) {
LOG.debug("Transaction {} failed", tx, t);
- synchronized (this) {
- Preconditions.checkState(inflightTransaction == tx, "Failed transaction %s while %s was submitted", tx, inflightTransaction);
- inflightTransaction = null;
- }
+ final boolean success = INFLIGHT_UPDATER.compareAndSet(this, tx, null);
+ Preconditions.checkState(success, "Failed transaction %s while %s was submitted", tx, inflightTx);
tx.onFailure(t);
}
private void readyTransaction(final @Nonnull PingPongTransaction tx) {
+ // First mark the transaction as not locked.
final boolean lockedMatch = LOCKED_UPDATER.compareAndSet(this, tx, null);
Preconditions.checkState(lockedMatch, "Attempted to submit transaction %s while we have %s", tx, lockedTx);
-
LOG.debug("Transaction {} unlocked", tx);
- synchronized (this) {
- if (inflightTransaction == null) {
- processTransaction(tx);
+ /*
+ * The transaction is ready. It will then be picked up by either next allocation,
+ * or a background transaction completion callback.
+ */
+ final boolean success = READY_UPDATER.compareAndSet(this, null, tx);
+ Preconditions.checkState(success, "Transaction %s collided on ready state", tx, readyTx);
+ LOG.debug("Transaction {} readied", tx);
+
+ /*
+ * We do not see a transaction being in-flight, so we need to take care of dispatching
+ * the transaction to the backend. We are in the ready case, we cannot short-cut
+ * the checking of readyTx, as an in-flight transaction may have completed between us
+ * setting the field above and us checking.
+ */
+ if (inflightTx == null) {
+ synchronized (this) {
+ processIfReady();
}
}
}
@Override
- public void close() {
+ public synchronized void close() {
final PingPongTransaction notLocked = lockedTx;
Preconditions.checkState(notLocked == null, "Attempted to close chain with outstanding transaction %s", notLocked);
- synchronized (this) {
- processIfReady();
- delegate.close();
+ // Force allocations on slow path. We will complete the rest
+ final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
+
+ // Make sure no transaction is outstanding. Otherwise sleep a bit and retry
+ while (inflightTx != null) {
+ LOG.debug("Busy-waiting for in-flight transaction {} to complete", inflightTx);
+ Thread.yield();
+ continue;
+ }
+
+ // If we have an outstanding transaction, send it down
+ if (tx != null) {
+ processTransaction(tx);
}
+
+ // All done, close the delegate. All new allocations should fail.
+ delegate.close();
}
@Override
Code Review / controller.git / blobdiff