org.opendaylight.mdsal.dom.spi.AbstractPingPongTransactionChain Maven / Gradle / Ivy
/*
* Copyright (c) 2014 Cisco Systems, Inc. and others. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v1.0 which accompanies this distribution,
* and is available at http://www.eclipse.org/legal/epl-v10.html
*/
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.ListenableFuture;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.common.util.concurrent.SettableFuture;
import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Optional;
import java.util.concurrent.CancellationException;
import org.checkerframework.checker.lock.qual.GuardedBy;
import org.checkerframework.checker.lock.qual.Holding;
import org.eclipse.jdt.annotation.NonNull;
import org.eclipse.jdt.annotation.Nullable;
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.DOMDataTreeWriteTransaction;
import org.opendaylight.mdsal.dom.api.DOMTransactionChain;
import org.opendaylight.yangtools.yang.common.Empty;
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;
/**
* The actual implementation of {@link PingPongTransactionChain}. Split out to allow deeper testing while keeping the
* externally-visible implementation final.
*/
abstract class AbstractPingPongTransactionChain implements DOMTransactionChain {
private static final Logger LOG = LoggerFactory.getLogger(AbstractPingPongTransactionChain.class);
private final @NonNull SettableFuture future = SettableFuture.create();
private final @NonNull DOMTransactionChain delegate;
@GuardedBy("this")
private boolean closed;
@GuardedBy("this")
private boolean failed;
@GuardedBy("this")
private PingPongTransaction shutdownTx;
@GuardedBy("this")
private Entry deadTx;
// This VarHandle is used to manipulate the "ready" transaction. We perform only atomic get-and-set on it.
private static final VarHandle READY_TX;
@SuppressWarnings("unused")
@SuppressFBWarnings(value = "UUF_UNUSED_FIELD", justification = "https://github.com/spotbugs/spotbugs/issues/2749")
private volatile PingPongTransaction readyTx;
/*
* This VarHandle 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 VarHandle LOCKED_TX;
@SuppressFBWarnings(value = "UWF_UNWRITTEN_FIELD",
justification = "https://github.com/spotbugs/spotbugs/issues/2749")
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 VarHandle INFLIGHT_TX;
@SuppressFBWarnings(value = "UWF_UNWRITTEN_FIELD",
justification = "https://github.com/spotbugs/spotbugs/issues/2749")
private volatile PingPongTransaction inflightTx;
static {
final var lookup = MethodHandles.lookup();
try {
INFLIGHT_TX = lookup.findVarHandle(AbstractPingPongTransactionChain.class, "inflightTx",
PingPongTransaction.class);
LOCKED_TX = lookup.findVarHandle(AbstractPingPongTransactionChain.class, "lockedTx",
PingPongTransaction.class);
READY_TX = lookup.findVarHandle(AbstractPingPongTransactionChain.class, "readyTx",
PingPongTransaction.class);
} catch (NoSuchFieldException | IllegalAccessException e) {
throw new ExceptionInInitializerError(e);
}
}
AbstractPingPongTransactionChain(final DOMTransactionChain delegate) {
this.delegate = requireNonNull(delegate);
delegate.addCallback(new FutureCallback<>() {
@Override
public void onSuccess(final Empty result) {
delegateSuccessful();
}
@Override
public void onFailure(final Throwable cause) {
delegateFailed(cause);
}
});
}
@Override
public final ListenableFuture future() {
return future;
}
private void delegateSuccessful() {
final Entry canceled;
synchronized (this) {
// This looks weird, but we need not hold the lock while invoking callbacks
canceled = deadTx;
}
if (canceled == null) {
future.set(Empty.value());
return;
}
// Backend shutdown successful, but we have a batch of transactions we have to report as dead due to the
// user calling cancel().
final var tx = canceled.getKey();
final var cause = canceled.getValue();
LOG.debug("Transaction chain {} successful, failing cancelled transaction {}", delegate, tx, cause);
future.setException(cause);
tx.onFailure(cause);
}
private void delegateFailed(final Throwable cause) {
LOG.debug("Transaction chain {} reported failure", delegate, cause);
final var tx = inflightTx;
if (tx == null) {
LOG.warn("Transaction chain {} failed with no pending transactions", delegate);
}
future.setException(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);
final Object witness = LOCKED_TX.compareAndExchange(this, null, newTx);
if (witness != null) {
delegateTx.cancel();
throw new IllegalStateException(
String.format("New transaction %s raced with transaction %s", newTx, witness));
}
return newTx;
}
private @Nullable PingPongTransaction acquireReadyTx() {
return (PingPongTransaction) READY_TX.getAndSet(this, null);
}
private @NonNull PingPongTransaction allocateTransaction() {
// Step 1: acquire current state
final PingPongTransaction oldTx = acquireReadyTx();
// Slow path: allocate a delegate transaction
if (oldTx == null) {
return slowAllocateTransaction();
}
// Fast path: reuse current transaction. We will check failures and similar on commit().
final Object witness = LOCKED_TX.compareAndExchange(this, null, oldTx);
if (witness != null) {
// 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,
witness));
}
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 = acquireReadyTx();
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);
final Object witness = INFLIGHT_TX.compareAndExchange(this, null, tx);
if (witness != null) {
LOG.warn("Submitting transaction {} while {} is still running", tx, witness);
}
tx.getTransaction().commit().addCallback(new FutureCallback() {
@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 Object witness = INFLIGHT_TX.compareAndExchange(this, tx, null);
checkState(witness == tx, "Completed transaction %s while %s was submitted", tx, witness);
final PingPongTransaction nextTx = acquireReadyTx();
if (nextTx == null) {
final PingPongTransaction local = shutdownTx;
if (local != null) {
shutdownTx = null;
processTransaction(local);
delegate.close();
}
} else {
processTransaction(nextTx);
}
}
private void transactionSuccessful(final PingPongTransaction tx, final CommitInfo result) {
LOG.debug("Transaction {} completed successfully", tx);
tx.onSuccess(result);
processNextTransaction(tx);
}
private void transactionFailed(final PingPongTransaction tx, final Throwable throwable) {
LOG.debug("Transaction {} failed", tx, throwable);
tx.onFailure(throwable);
processNextTransaction(tx);
}
private void readyTransaction(final @NonNull PingPongTransaction tx) {
// First mark the transaction as not locked.
final Object lockedWitness = LOCKED_TX.compareAndExchange(this, tx, null);
checkState(lockedWitness == tx, "Attempted to submit transaction %s while we have %s", tx, lockedWitness);
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 Object readyWitness = READY_TX.compareAndExchange(this, null, tx);
checkState(readyWitness == null, "Transaction %s collided on ready state with %s", tx, readyWitness);
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
* @return {@code true} if the transaction was cancelled successfully
*/
private synchronized boolean cancelTransaction(final PingPongTransaction tx,
final DOMDataTreeReadWriteTransaction frontendTx) {
// Attempt to unlock the operation.
final Object witness = LOCKED_TX.compareAndExchange(this, tx, null);
verify(witness == tx, "Cancelling transaction %s collided with locked transaction %s", tx, witness);
// 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 true;
}
// We have dealt with cancelling 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())) {
if (backendCancelled) {
LOG.debug("Cancelled transaction {} was head of the batch, resuming processing", tx);
return true;
}
// Backend refused to cancel the transaction. Reinstate it to locked state.
final Object reinstateWitness = LOCKED_TX.compareAndExchange(this, null, tx);
verify(reinstateWitness == null, "Reinstating transaction %s collided with locked transaction %s", tx,
reinstateWitness);
return false;
}
if (!backendCancelled) {
LOG.warn("Backend transaction cannot be cancelled during cancellation of {}, attempting to continue", tx);
}
// 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 = Map.entry(tx, new CancellationException("Transaction " + frontendTx + " canceled").fillInStackTrace());
delegate.close();
return true;
}
@Override
public final synchronized void close() {
if (closed) {
LOG.debug("Attempted to close an already-closed chain");
return;
}
// Note: we do not derive from AbstractRegistration due to ordering of this check
final var notLocked = lockedTx;
if (notLocked != null) {
throw new IllegalStateException("Attempted to close chain with outstanding transaction " + notLocked);
}
closed = true;
// 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 var tx = acquireReadyTx();
if (tx != null) {
// We have one more transaction, which needs to be processed somewhere. If we do not have
// 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 final DOMDataTreeReadTransaction newReadOnlyTransaction() {
return new PingPongReadTransaction(allocateTransaction());
}
@Override
public final DOMDataTreeReadWriteTransaction newReadWriteTransaction() {
final PingPongTransaction tx = allocateTransaction();
final DOMDataTreeReadWriteTransaction ret = new PingPongReadWriteTransaction(tx);
tx.recordFrontendTransaction(ret);
return ret;
}
@Override
public final DOMDataTreeWriteTransaction newWriteOnlyTransaction() {
return newReadWriteTransaction();
}
private final class PingPongReadTransaction implements DOMDataTreeReadTransaction {
private final @NonNull PingPongTransaction tx;
PingPongReadTransaction(final PingPongTransaction tx) {
this.tx = requireNonNull(tx);
}
@Override
public FluentFuture> read(final LogicalDatastoreType store,
final YangInstanceIdentifier path) {
return tx.getTransaction().read(store, path);
}
@Override
public FluentFuture 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);
}
}
private final class PingPongReadWriteTransaction extends ForwardingDOMDataReadWriteTransaction {
private final @NonNull PingPongTransaction tx;
private boolean isOpen = true;
PingPongReadWriteTransaction(final PingPongTransaction tx) {
this.tx = requireNonNull(tx);
}
@Override
public FluentFuture commit() {
readyTransaction(tx);
isOpen = false;
return tx.completionFuture();
}
@Override
public boolean cancel() {
if (isOpen && cancelTransaction(tx, this)) {
isOpen = false;
return true;
}
return false;
}
@Override
protected DOMDataTreeReadWriteTransaction delegate() {
return tx.getTransaction();
}
}
}
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