2 * Copyright (c) 2014 Cisco Systems, Inc. and others. All rights reserved.
4 * This program and the accompanying materials are made available under the
5 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
6 * and is available at http://www.eclipse.org/legal/epl-v10.html
8 package org.opendaylight.mdsal.dom.spi;
10 import static com.google.common.base.Preconditions.checkState;
11 import static com.google.common.base.Verify.verify;
12 import static java.util.Objects.requireNonNull;
14 import com.google.common.util.concurrent.FluentFuture;
15 import com.google.common.util.concurrent.FutureCallback;
16 import com.google.common.util.concurrent.MoreExecutors;
17 import java.util.AbstractMap.SimpleImmutableEntry;
18 import java.util.Map.Entry;
19 import java.util.Optional;
20 import java.util.concurrent.CancellationException;
21 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
22 import java.util.function.Function;
23 import javax.annotation.concurrent.GuardedBy;
24 import org.eclipse.jdt.annotation.NonNull;
25 import org.opendaylight.mdsal.common.api.CommitInfo;
26 import org.opendaylight.mdsal.common.api.LogicalDatastoreType;
27 import org.opendaylight.mdsal.dom.api.DOMDataTreeReadTransaction;
28 import org.opendaylight.mdsal.dom.api.DOMDataTreeReadWriteTransaction;
29 import org.opendaylight.mdsal.dom.api.DOMDataTreeTransaction;
30 import org.opendaylight.mdsal.dom.api.DOMDataTreeWriteTransaction;
31 import org.opendaylight.mdsal.dom.api.DOMTransactionChain;
32 import org.opendaylight.mdsal.dom.api.DOMTransactionChainListener;
33 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
34 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
35 import org.slf4j.Logger;
36 import org.slf4j.LoggerFactory;
39 * An implementation of {@link DOMTransactionChain}, which has a very specific behavior, which some users may find
40 * surprising. If keeps the general intent of the contract, but it makes sure there are never more than two transactions
41 * allocated at any given time: one of them is being committed, and while that is happening, the other one acts as
42 * a scratch pad. Once the committing transaction completes successfully, the scratch transaction is enqueued as soon as
46 * This mode of operation means that there is no inherent isolation between the front-end transactions and transactions
47 * cannot be reasonably cancelled.
50 * It furthermore means that the transactions returned by {@link #newReadOnlyTransaction()} counts as an outstanding
51 * transaction and the user may not allocate multiple read-only transactions at the same time.
53 public final class PingPongTransactionChain implements DOMTransactionChain {
54 private static final Logger LOG = LoggerFactory.getLogger(PingPongTransactionChain.class);
56 private final DOMTransactionChainListener listener;
57 private final DOMTransactionChain delegate;
60 private boolean failed;
62 private PingPongTransaction shutdownTx;
64 private Entry<PingPongTransaction, Throwable> deadTx;
66 // This updater is used to manipulate the "ready" transaction. We perform only atomic get-and-set on it.
67 private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> READY_UPDATER =
68 AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class,
70 private volatile PingPongTransaction readyTx;
73 * This updater is used to manipulate the "locked" transaction. A locked transaction means we know that the user
74 * still holds a transaction and should at some point call us. We perform on compare-and-swap to ensure we properly
75 * detect when a user is attempting to allocated multiple transactions concurrently.
77 private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> LOCKED_UPDATER =
78 AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class,
80 private volatile PingPongTransaction lockedTx;
83 * This updater is used to manipulate the "inflight" transaction. There can be at most one of these at any given
84 * time. We perform only compare-and-swap on these.
86 private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> INFLIGHT_UPDATER =
87 AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class,
89 private volatile PingPongTransaction inflightTx;
91 public PingPongTransactionChain(final Function<DOMTransactionChainListener, DOMTransactionChain> delegateFactory,
92 final DOMTransactionChainListener listener) {
93 this.listener = requireNonNull(listener);
94 this.delegate = delegateFactory.apply(new DOMTransactionChainListener() {
96 public void onTransactionChainFailed(final DOMTransactionChain chain,
97 final DOMDataTreeTransaction transaction, final Throwable cause) {
98 LOG.debug("Transaction chain {} reported failure in {}", chain, transaction, cause);
99 delegateFailed(chain, cause);
103 public void onTransactionChainSuccessful(final DOMTransactionChain chain) {
104 delegateSuccessful(chain);
109 void delegateSuccessful(final DOMTransactionChain chain) {
110 final Entry<PingPongTransaction, Throwable> canceled;
111 synchronized (this) {
112 // This looks weird, but we need not hold the lock while invoking callbacks
116 if (canceled == null) {
117 listener.onTransactionChainSuccessful(this);
121 // Backend shutdown successful, but we have a batch of transactions we have to report as dead due to the
122 // user calling cancel().
123 final PingPongTransaction tx = canceled.getKey();
124 final Throwable cause = canceled.getValue();
125 LOG.debug("Transaction chain {} successful, failing cancelled transaction {}", chain, tx, cause);
127 listener.onTransactionChainFailed(this, tx.getFrontendTransaction(), cause);
131 void delegateFailed(final DOMTransactionChain chain, final Throwable cause) {
133 final DOMDataTreeReadWriteTransaction frontend;
134 final PingPongTransaction tx = inflightTx;
136 LOG.warn("Transaction chain {} failed with no pending transactions", chain);
139 frontend = tx.getFrontendTransaction();
142 listener.onTransactionChainFailed(this, frontend, cause);
144 synchronized (this) {
148 * If we do not have a locked transaction, we need to ensure that the backend transaction is cancelled.
149 * Otherwise we can defer until the user calls us.
151 if (lockedTx == null) {
157 private synchronized @NonNull PingPongTransaction slowAllocateTransaction() {
158 checkState(shutdownTx == null, "Transaction chain %s has been shut down", this);
160 if (deadTx != null) {
161 throw new IllegalStateException(String.format(
162 "Transaction chain %s has failed due to transaction %s being canceled", this, deadTx.getKey()),
166 final DOMDataTreeReadWriteTransaction delegateTx = delegate.newReadWriteTransaction();
167 final PingPongTransaction newTx = new PingPongTransaction(delegateTx);
169 if (!LOCKED_UPDATER.compareAndSet(this, null, newTx)) {
171 throw new IllegalStateException(
172 String.format("New transaction %s raced with transaction %s", newTx, lockedTx));
178 private @NonNull PingPongTransaction allocateTransaction() {
179 // Step 1: acquire current state
180 final PingPongTransaction oldTx = READY_UPDATER.getAndSet(this, null);
182 // Slow path: allocate a delegate transaction
184 return slowAllocateTransaction();
187 // Fast path: reuse current transaction. We will check failures and similar on commit().
188 if (!LOCKED_UPDATER.compareAndSet(this, null, oldTx)) {
189 // Ouch. Delegate chain has not detected a duplicate transaction allocation. This is the best we can do.
190 oldTx.getTransaction().cancel();
191 throw new IllegalStateException(String.format("Reusable transaction %s raced with transaction %s", oldTx,
199 * This forces allocateTransaction() on a slow path, which has to happen after this method has completed executing.
200 * Also inflightTx may be updated outside the lock, hence we need to re-check.
203 private void processIfReady() {
204 if (inflightTx == null) {
205 final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
207 processTransaction(tx);
213 * Process a ready transaction. The caller needs to ensure that each transaction is seen only once by this method.
215 * @param tx Transaction which needs processing.
218 private void processTransaction(final @NonNull PingPongTransaction tx) {
220 LOG.debug("Cancelling transaction {}", tx);
221 tx.getTransaction().cancel();
225 LOG.debug("Submitting transaction {}", tx);
226 if (!INFLIGHT_UPDATER.compareAndSet(this, null, tx)) {
227 LOG.warn("Submitting transaction {} while {} is still running", tx, inflightTx);
230 tx.getTransaction().commit().addCallback(new FutureCallback<CommitInfo>() {
232 public void onSuccess(final CommitInfo result) {
233 transactionSuccessful(tx, result);
237 public void onFailure(final Throwable throwable) {
238 transactionFailed(tx, throwable);
240 }, MoreExecutors.directExecutor());
244 * We got invoked from the data store thread. We need to do two things:
245 * 1) release the in-flight transaction
246 * 2) process the potential next transaction
248 * We have to perform 2) under lock. We could perform 1) without locking, but that means the CAS result may
249 * not be accurate, as a user thread may submit the ready transaction before we acquire the lock -- and checking
250 * for next transaction is not enough, as that may have also be allocated (as a result of a quick
251 * submit/allocate/submit between 1) and 2)). Hence we'd end up doing the following:
252 * 1) CAS of inflightTx
254 * 3) volatile read of inflightTx
256 * Rather than doing that, we keep this method synchronized, hence performing only:
258 * 2) CAS of inflightTx
260 * Since the user thread is barred from submitting the transaction (in processIfReady), we can then proceed with
261 * the knowledge that inflightTx is null -- processTransaction() will still do a CAS, but that is only for
264 private synchronized void processNextTransaction(final PingPongTransaction tx) {
265 final boolean success = INFLIGHT_UPDATER.compareAndSet(this, tx, null);
266 checkState(success, "Completed transaction %s while %s was submitted", tx, inflightTx);
268 final PingPongTransaction nextTx = READY_UPDATER.getAndSet(this, null);
269 if (nextTx != null) {
270 processTransaction(nextTx);
271 } else if (shutdownTx != null) {
272 processTransaction(shutdownTx);
278 void transactionSuccessful(final PingPongTransaction tx, final CommitInfo result) {
279 LOG.debug("Transaction {} completed successfully", tx);
281 tx.onSuccess(result);
282 processNextTransaction(tx);
285 void transactionFailed(final PingPongTransaction tx, final Throwable throwable) {
286 LOG.debug("Transaction {} failed", tx, throwable);
288 tx.onFailure(throwable);
289 processNextTransaction(tx);
292 void readyTransaction(final @NonNull PingPongTransaction tx) {
293 // First mark the transaction as not locked.
294 final boolean lockedMatch = LOCKED_UPDATER.compareAndSet(this, tx, null);
295 checkState(lockedMatch, "Attempted to submit transaction %s while we have %s", tx, lockedTx);
296 LOG.debug("Transaction {} unlocked", tx);
299 * The transaction is ready. It will then be picked up by either next allocation,
300 * or a background transaction completion callback.
302 final boolean success = READY_UPDATER.compareAndSet(this, null, tx);
303 checkState(success, "Transaction %s collided on ready state", tx, readyTx);
304 LOG.debug("Transaction {} readied", tx);
307 * We do not see a transaction being in-flight, so we need to take care of dispatching
308 * the transaction to the backend. We are in the ready case, we cannot short-cut
309 * the checking of readyTx, as an in-flight transaction may have completed between us
310 * setting the field above and us checking.
312 if (inflightTx == null) {
313 synchronized (this) {
320 * Transaction cancellation is a heavyweight operation. We only support cancelation of a locked transaction
321 * and return false for everything else. Cancelling such a transaction will result in all transactions in the
322 * batch to be cancelled.
324 * @param tx Backend shared transaction
325 * @param frontendTx transaction
326 * @param isOpen indicator whether the transaction was already closed
328 synchronized void cancelTransaction(final PingPongTransaction tx,
329 final DOMDataTreeReadWriteTransaction frontendTx) {
330 // Attempt to unlock the operation.
331 final boolean lockedMatch = LOCKED_UPDATER.compareAndSet(this, tx, null);
332 verify(lockedMatch, "Cancelling transaction %s collided with locked transaction %s", tx, lockedTx);
334 // Cancel the backend transaction, so we do not end up leaking it.
335 final boolean backendCancelled = tx.getTransaction().cancel();
338 // The transaction has failed, this is probably the user just clearing up the transaction they had. We have
339 // already cancelled the transaction anyway,
341 } else if (!backendCancelled) {
342 LOG.warn("Backend transaction cannot be cancelled during cancellation of {}, attempting to continue", tx);
345 // We have dealt with canceling the backend transaction and have unlocked the transaction. Since we are still
346 // inside the synchronized block, any allocations are blocking on the slow path. Now we have to decide the fate
347 // of this transaction chain.
349 // If there are no other frontend transactions in this batch we are aligned with backend state and we can
350 // continue processing.
351 if (frontendTx.equals(tx.getFrontendTransaction())) {
352 LOG.debug("Cancelled transaction {} was head of the batch, resuming processing", tx);
356 // There are multiple frontend transactions in this batch. We have to report them as failed, which dooms this
357 // transaction chain, too. Since we just came off of a locked transaction, we do not have a ready transaction
358 // at the moment, but there may be some transaction in-flight. So we proceed to shutdown the backend chain
359 // and mark the fact that we should be turning its completion into a failure.
360 deadTx = new SimpleImmutableEntry<>(tx, new CancellationException("Transaction " + frontendTx + " canceled")
361 .fillInStackTrace());
366 public synchronized void close() {
367 final PingPongTransaction notLocked = lockedTx;
368 checkState(notLocked == null, "Attempted to close chain with outstanding transaction %s", notLocked);
370 // This is not reliable, but if we observe it to be null and the process has already completed,
371 // the backend transaction chain will throw the appropriate error.
372 checkState(shutdownTx == null, "Attempted to close an already-closed chain");
374 // This may be a reaction to our failure callback, in that case the backend is already shutdown
375 if (deadTx != null) {
376 LOG.debug("Delegate {} is already closed due to failure {}", delegate, deadTx);
380 // Force allocations on slow path, picking up a potentially-outstanding transaction
381 final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
384 // We have one more transaction, which needs to be processed somewhere. If we do not
385 // a transaction in-flight, we need to push it down ourselves.
386 // If there is an in-flight transaction we will schedule this last one into a dedicated
387 // slot. Allocation slow path will check its presence and fail, the in-flight path will
388 // pick it up, submit and immediately close the chain.
389 if (inflightTx == null) {
390 processTransaction(tx);
396 // Nothing outstanding, we can safely shutdown
402 public DOMDataTreeReadTransaction newReadOnlyTransaction() {
403 final PingPongTransaction tx = allocateTransaction();
405 return new DOMDataTreeReadTransaction() {
407 public FluentFuture<Optional<NormalizedNode<?, ?>>> read(
408 final LogicalDatastoreType store, final YangInstanceIdentifier path) {
409 return tx.getTransaction().read(store, path);
413 public FluentFuture<Boolean> exists(final LogicalDatastoreType store, final YangInstanceIdentifier path) {
414 return tx.getTransaction().exists(store, path);
418 public Object getIdentifier() {
419 return tx.getTransaction().getIdentifier();
423 public void close() {
424 readyTransaction(tx);
430 public DOMDataTreeReadWriteTransaction newReadWriteTransaction() {
431 final PingPongTransaction tx = allocateTransaction();
432 final DOMDataTreeReadWriteTransaction ret = new ForwardingDOMDataReadWriteTransaction() {
433 private boolean isOpen = true;
436 protected DOMDataTreeReadWriteTransaction delegate() {
437 return tx.getTransaction();
441 public FluentFuture<? extends CommitInfo> commit() {
442 readyTransaction(tx);
444 return tx.getCommitFuture().transform(ignored -> CommitInfo.empty(), MoreExecutors.directExecutor());
448 public boolean cancel() {
450 cancelTransaction(tx, this);
459 tx.recordFrontendTransaction(ret);
464 public DOMDataTreeWriteTransaction newWriteOnlyTransaction() {
465 return newReadWriteTransaction();