*/
package org.opendaylight.mdsal.dom.spi;
-import static com.google.common.base.Preconditions.checkState;
-import static com.google.common.base.Verify.verify;
-import static java.util.Objects.requireNonNull;
-
-import com.google.common.util.concurrent.FluentFuture;
-import com.google.common.util.concurrent.FutureCallback;
-import com.google.common.util.concurrent.MoreExecutors;
-import java.util.AbstractMap.SimpleImmutableEntry;
-import java.util.Map.Entry;
-import java.util.Optional;
-import java.util.concurrent.CancellationException;
-import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
-import java.util.function.Function;
-import org.checkerframework.checker.lock.qual.GuardedBy;
-import org.checkerframework.checker.lock.qual.Holding;
-import org.eclipse.jdt.annotation.NonNull;
-import org.opendaylight.mdsal.common.api.CommitInfo;
-import org.opendaylight.mdsal.common.api.LogicalDatastoreType;
-import org.opendaylight.mdsal.dom.api.DOMDataTreeReadTransaction;
-import org.opendaylight.mdsal.dom.api.DOMDataTreeReadWriteTransaction;
-import org.opendaylight.mdsal.dom.api.DOMDataTreeTransaction;
-import org.opendaylight.mdsal.dom.api.DOMDataTreeWriteTransaction;
import org.opendaylight.mdsal.dom.api.DOMTransactionChain;
-import org.opendaylight.mdsal.dom.api.DOMTransactionChainListener;
-import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
-import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
/**
* An implementation of {@link DOMTransactionChain}, which has a very specific behavior, which some users may find
* It furthermore means that the transactions returned by {@link #newReadOnlyTransaction()} counts as an outstanding
* transaction and the user may not allocate multiple read-only transactions at the same time.
*/
-public final class PingPongTransactionChain implements DOMTransactionChain {
- private static final Logger LOG = LoggerFactory.getLogger(PingPongTransactionChain.class);
-
- private final DOMTransactionChainListener listener;
- private final DOMTransactionChain delegate;
-
- @GuardedBy("this")
- private boolean failed;
- @GuardedBy("this")
- private PingPongTransaction shutdownTx;
- @GuardedBy("this")
- private Entry<PingPongTransaction, Throwable> deadTx;
-
- // This updater is used to manipulate the "ready" transaction. We perform only atomic get-and-set on it.
- private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> READY_UPDATER =
- AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class,
- "readyTx");
- private volatile PingPongTransaction readyTx;
-
- /*
- * This updater is used to manipulate the "locked" transaction. A locked transaction means we know that the user
- * still holds a transaction and should at some point call us. We perform on compare-and-swap to ensure we properly
- * detect when a user is attempting to allocated multiple transactions concurrently.
- */
- private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> LOCKED_UPDATER =
- 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;
-
- public PingPongTransactionChain(final Function<DOMTransactionChainListener, DOMTransactionChain> delegateFactory,
- final DOMTransactionChainListener listener) {
- this.listener = requireNonNull(listener);
- this.delegate = delegateFactory.apply(new DOMTransactionChainListener() {
- @Override
- public void onTransactionChainFailed(final DOMTransactionChain chain,
- final DOMDataTreeTransaction transaction, final Throwable cause) {
- LOG.debug("Transaction chain {} reported failure in {}", chain, transaction, cause);
- delegateFailed(chain, cause);
- }
-
- @Override
- public void onTransactionChainSuccessful(final DOMTransactionChain chain) {
- delegateSuccessful(chain);
- }
- });
- }
-
- void delegateSuccessful(final DOMTransactionChain chain) {
- final Entry<PingPongTransaction, Throwable> canceled;
- synchronized (this) {
- // This looks weird, but we need not hold the lock while invoking callbacks
- canceled = deadTx;
- }
-
- if (canceled == null) {
- listener.onTransactionChainSuccessful(this);
- return;
- }
-
- // Backend shutdown successful, but we have a batch of transactions we have to report as dead due to the
- // user calling cancel().
- final PingPongTransaction tx = canceled.getKey();
- final Throwable cause = canceled.getValue();
- LOG.debug("Transaction chain {} successful, failing cancelled transaction {}", chain, tx, cause);
-
- listener.onTransactionChainFailed(this, tx.getFrontendTransaction(), cause);
- tx.onFailure(cause);
- }
-
- void delegateFailed(final DOMTransactionChain chain, final Throwable cause) {
-
- final DOMDataTreeReadWriteTransaction frontend;
- final PingPongTransaction tx = inflightTx;
- if (tx == null) {
- LOG.warn("Transaction chain {} failed with no pending transactions", chain);
- frontend = null;
- } else {
- frontend = tx.getFrontendTransaction();
- }
-
- listener.onTransactionChainFailed(this, frontend, cause);
-
- synchronized (this) {
- failed = true;
-
- /*
- * If we do not have a locked transaction, we need to ensure that the backend transaction is cancelled.
- * Otherwise we can defer until the user calls us.
- */
- if (lockedTx == null) {
- processIfReady();
- }
- }
- }
-
- private synchronized @NonNull PingPongTransaction slowAllocateTransaction() {
- checkState(shutdownTx == null, "Transaction chain %s has been shut down", this);
-
- if (deadTx != null) {
- throw new IllegalStateException(String.format(
- "Transaction chain %s has failed due to transaction %s being canceled", this, deadTx.getKey()),
- deadTx.getValue());
- }
-
- final DOMDataTreeReadWriteTransaction delegateTx = delegate.newReadWriteTransaction();
- final PingPongTransaction newTx = new PingPongTransaction(delegateTx);
-
- if (!LOCKED_UPDATER.compareAndSet(this, null, newTx)) {
- delegateTx.cancel();
- throw new IllegalStateException(
- String.format("New transaction %s raced with transaction %s", newTx, lockedTx));
- }
-
- return newTx;
- }
-
- private @NonNull PingPongTransaction allocateTransaction() {
- // Step 1: acquire current state
- final PingPongTransaction oldTx = READY_UPDATER.getAndSet(this, null);
-
- // Slow path: allocate a delegate transaction
- if (oldTx == null) {
- return slowAllocateTransaction();
- }
-
- // Fast path: reuse current transaction. We will check failures and similar on commit().
- if (!LOCKED_UPDATER.compareAndSet(this, null, oldTx)) {
- // Ouch. Delegate chain has not detected a duplicate transaction allocation. This is the best we can do.
- oldTx.getTransaction().cancel();
- throw new IllegalStateException(String.format("Reusable transaction %s raced with transaction %s", oldTx,
- lockedTx));
- }
-
- return oldTx;
- }
-
- /**
- * 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.
- */
- @Holding("this")
- private void processIfReady() {
- if (inflightTx == null) {
- final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
- if (tx != null) {
- processTransaction(tx);
- }
- }
- }
-
- /**
- * Process a ready transaction. The caller needs to ensure that each transaction is seen only once by this method.
- *
- * @param tx Transaction which needs processing.
- */
- @Holding("this")
- private void processTransaction(final @NonNull PingPongTransaction tx) {
- if (failed) {
- LOG.debug("Cancelling transaction {}", tx);
- tx.getTransaction().cancel();
- return;
- }
-
- LOG.debug("Submitting transaction {}", tx);
- if (!INFLIGHT_UPDATER.compareAndSet(this, null, tx)) {
- LOG.warn("Submitting transaction {} while {} is still running", tx, inflightTx);
- }
-
- tx.getTransaction().commit().addCallback(new FutureCallback<CommitInfo>() {
- @Override
- public void onSuccess(final CommitInfo result) {
- transactionSuccessful(tx, result);
- }
-
- @Override
- public void onFailure(final Throwable throwable) {
- transactionFailed(tx, throwable);
- }
- }, MoreExecutors.directExecutor());
- }
-
- /*
- * 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);
- checkState(success, "Completed transaction %s while %s was submitted", tx, inflightTx);
-
- final PingPongTransaction nextTx = READY_UPDATER.getAndSet(this, null);
- if (nextTx != null) {
- processTransaction(nextTx);
- } else if (shutdownTx != null) {
- processTransaction(shutdownTx);
- delegate.close();
- shutdownTx = null;
- }
- }
-
- void transactionSuccessful(final PingPongTransaction tx, final CommitInfo result) {
- LOG.debug("Transaction {} completed successfully", tx);
-
- tx.onSuccess(result);
- processNextTransaction(tx);
- }
-
- void transactionFailed(final PingPongTransaction tx, final Throwable throwable) {
- LOG.debug("Transaction {} failed", tx, throwable);
-
- tx.onFailure(throwable);
- processNextTransaction(tx);
- }
-
- void readyTransaction(final @NonNull PingPongTransaction tx) {
- // First mark the transaction as not locked.
- final boolean lockedMatch = LOCKED_UPDATER.compareAndSet(this, tx, null);
- checkState(lockedMatch, "Attempted to submit transaction %s while we have %s", tx, lockedTx);
- LOG.debug("Transaction {} unlocked", 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);
- 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();
- }
- }
- }
-
- /**
- * Transaction cancellation is a heavyweight operation. We only support cancelation of a locked transaction
- * and return false for everything else. Cancelling such a transaction will result in all transactions in the
- * batch to be cancelled.
- *
- * @param tx Backend shared transaction
- * @param frontendTx transaction
- * @param isOpen indicator whether the transaction was already closed
- */
- synchronized void cancelTransaction(final PingPongTransaction tx,
- final DOMDataTreeReadWriteTransaction frontendTx) {
- // Attempt to unlock the operation.
- final boolean lockedMatch = LOCKED_UPDATER.compareAndSet(this, tx, null);
- verify(lockedMatch, "Cancelling transaction %s collided with locked transaction %s", tx, lockedTx);
-
- // Cancel the backend transaction, so we do not end up leaking it.
- final boolean backendCancelled = tx.getTransaction().cancel();
-
- if (failed) {
- // The transaction has failed, this is probably the user just clearing up the transaction they had. We have
- // already cancelled the transaction anyway,
- return;
- } else if (!backendCancelled) {
- LOG.warn("Backend transaction cannot be cancelled during cancellation of {}, attempting to continue", tx);
- }
-
- // We have dealt with canceling the backend transaction and have unlocked the transaction. Since we are still
- // inside the synchronized block, any allocations are blocking on the slow path. Now we have to decide the fate
- // of this transaction chain.
- //
- // If there are no other frontend transactions in this batch we are aligned with backend state and we can
- // continue processing.
- if (frontendTx.equals(tx.getFrontendTransaction())) {
- LOG.debug("Cancelled transaction {} was head of the batch, resuming processing", tx);
- return;
- }
-
- // There are multiple frontend transactions in this batch. We have to report them as failed, which dooms this
- // transaction chain, too. Since we just came off of a locked transaction, we do not have a ready transaction
- // at the moment, but there may be some transaction in-flight. So we proceed to shutdown the backend chain
- // and mark the fact that we should be turning its completion into a failure.
- deadTx = new SimpleImmutableEntry<>(tx, new CancellationException("Transaction " + frontendTx + " canceled")
- .fillInStackTrace());
- delegate.close();
- }
-
- @Override
- public synchronized void close() {
- final PingPongTransaction notLocked = lockedTx;
- checkState(notLocked == null, "Attempted to close chain with outstanding transaction %s", notLocked);
-
- // 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.
- checkState(shutdownTx == null, "Attempted to close an already-closed chain");
-
- // This may be a reaction to our failure callback, in that case the backend is already shutdown
- if (deadTx != null) {
- LOG.debug("Delegate {} is already closed due to failure {}", delegate, deadTx);
- return;
- }
-
- // 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();
- }
- }
-
- @Override
- public DOMDataTreeReadTransaction newReadOnlyTransaction() {
- final PingPongTransaction tx = allocateTransaction();
-
- return new DOMDataTreeReadTransaction() {
- @Override
- public FluentFuture<Optional<NormalizedNode>> read(
- final LogicalDatastoreType store, final YangInstanceIdentifier path) {
- return tx.getTransaction().read(store, path);
- }
-
- @Override
- public FluentFuture<Boolean> exists(final LogicalDatastoreType store, final YangInstanceIdentifier path) {
- return tx.getTransaction().exists(store, path);
- }
-
- @Override
- public Object getIdentifier() {
- return tx.getTransaction().getIdentifier();
- }
-
- @Override
- public void close() {
- readyTransaction(tx);
- }
- };
- }
-
- @Override
- public DOMDataTreeReadWriteTransaction newReadWriteTransaction() {
- final PingPongTransaction tx = allocateTransaction();
- final DOMDataTreeReadWriteTransaction ret = new ForwardingDOMDataReadWriteTransaction() {
- private boolean isOpen = true;
-
- @Override
- protected DOMDataTreeReadWriteTransaction delegate() {
- return tx.getTransaction();
- }
-
- @Override
- public FluentFuture<? extends CommitInfo> commit() {
- readyTransaction(tx);
- isOpen = false;
- return tx.getCommitFuture().transform(ignored -> CommitInfo.empty(), MoreExecutors.directExecutor());
- }
-
- @Override
- public boolean cancel() {
- if (isOpen) {
- cancelTransaction(tx, this);
- isOpen = false;
- return true;
- }
-
- return false;
- }
- };
-
- tx.recordFrontendTransaction(ret);
- return ret;
- }
-
- @Override
- public DOMDataTreeWriteTransaction newWriteOnlyTransaction() {
- return newReadWriteTransaction();
+public final class PingPongTransactionChain extends AbstractPingPongTransactionChain {
+ public PingPongTransactionChain(final DOMTransactionChain delegate) {
+ super(delegate);
}
}
Code Review / mdsal.git / blobdiff