@GuardedBy("this")
private boolean failed;
+ @GuardedBy("this")
+ private PingPongTransaction shutdownTx;
/**
* This updater is used to manipulate the "ready" transaction. We perform only atomic
}
private synchronized PingPongTransaction slowAllocateTransaction() {
+ Preconditions.checkState(shutdownTx == null, "Transaction chain %s has been shut down", this);
+
final DOMDataReadWriteTransaction delegateTx = delegate.newReadWriteTransaction();
final PingPongTransaction newTx = new PingPongTransaction(delegateTx);
/*
* This forces allocateTransaction() on a slow path, which has to happen after
- * this method has completed executing.
+ * 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);
+ }
}
}
* @param tx Transaction which needs processing.
*/
@GuardedBy("this")
- private void processTransaction(final @Nonnull PingPongTransaction tx) {
+ private void processTransaction(@Nonnull final PingPongTransaction tx) {
if (failed) {
LOG.debug("Cancelling transaction {}", tx);
tx.getTransaction().cancel();
});
}
- private void transactionSuccessful(final PingPongTransaction tx, final Void result) {
- LOG.debug("Transaction {} completed successfully", tx);
-
+ /*
+ * We got invoked from the data store thread. We need to do two things:
+ * 1) release the in-flight transaction
+ * 2) process the potential next transaction
+ *
+ * We have to perform 2) under lock. We could perform 1) without locking, but that means the CAS result may
+ * not be accurate, as a user thread may submit the ready transaction before we acquire the lock -- and checking
+ * for next transaction is not enough, as that may have also be allocated (as a result of a quick
+ * submit/allocate/submit between 1) and 2)). Hence we'd end up doing the following:
+ * 1) CAS of inflightTx
+ * 2) take lock
+ * 3) volatile read of inflightTx
+ *
+ * Rather than doing that, we keep this method synchronized, hence performing only:
+ * 1) take lock
+ * 2) CAS of inflightTx
+ *
+ * Since the user thread is barred from submitting the transaction (in processIfReady), we can then proceed with
+ * the knowledge that inflightTx is null -- processTransaction() will still do a CAS, but that is only for
+ * correctness.
+ */
+ private synchronized void processNextTransaction(final PingPongTransaction tx) {
final boolean success = INFLIGHT_UPDATER.compareAndSet(this, tx, null);
- Preconditions.checkState(success, "Successful transaction %s while %s was submitted", tx, inflightTx);
+ Preconditions.checkState(success, "Completed transaction %s while %s was submitted", tx, inflightTx);
- synchronized (this) {
- processIfReady();
+ final PingPongTransaction nextTx = READY_UPDATER.getAndSet(this, null);
+ if (nextTx != null) {
+ processTransaction(nextTx);
+ } else if (shutdownTx != null) {
+ processTransaction(shutdownTx);
+ delegate.close();
+ shutdownTx = null;
}
+ }
+
+ private void transactionSuccessful(final PingPongTransaction tx, final Void result) {
+ LOG.debug("Transaction {} completed successfully", tx);
- // Can run unsynchronized
tx.onSuccess(result);
+ processNextTransaction(tx);
}
private void transactionFailed(final PingPongTransaction tx, final Throwable t) {
LOG.debug("Transaction {} failed", tx, t);
- final boolean success = INFLIGHT_UPDATER.compareAndSet(this, tx, null);
- Preconditions.checkState(success, "Failed transaction %s while %s was submitted", tx, inflightTx);
-
tx.onFailure(t);
+ processNextTransaction(tx);
}
- private void readyTransaction(final @Nonnull PingPongTransaction tx) {
+ private void readyTransaction(@Nonnull final 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);
}
@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();
+ // This is not reliable, but if we observe it to be null and the process has already completed,
+ // the backend transaction chain will throw the appropriate error.
+ Preconditions.checkState(shutdownTx == null, "Attempted to close an already-closed chain");
+
+ // Force allocations on slow path, picking up a potentially-outstanding transaction
+ final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
+
+ if (tx != null) {
+ // We have one more transaction, which needs to be processed somewhere. If we do not
+ // a transaction in-flight, we need to push it down ourselves.
+ // If there is an in-flight transaction we will schedule this last one into a dedicated
+ // slot. Allocation slow path will check its presence and fail, the in-flight path will
+ // pick it up, submit and immediately close the chain.
+ if (inflightTx == null) {
+ processTransaction(tx);
+ delegate.close();
+ } else {
+ shutdownTx = tx;
+ }
+ } else {
+ // Nothing outstanding, we can safely shutdown
delegate.close();
}
}
Code Review / controller.git / blobdiff