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.controller.md.sal.dom.broker.impl;
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.base.Optional;
15 import com.google.common.util.concurrent.CheckedFuture;
16 import com.google.common.util.concurrent.FluentFuture;
17 import com.google.common.util.concurrent.FutureCallback;
18 import com.google.common.util.concurrent.MoreExecutors;
19 import java.util.AbstractMap.SimpleImmutableEntry;
20 import java.util.Map.Entry;
21 import java.util.concurrent.CancellationException;
22 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
23 import org.checkerframework.checker.lock.qual.GuardedBy;
24 import org.checkerframework.checker.lock.qual.Holding;
25 import org.eclipse.jdt.annotation.NonNull;
26 import org.opendaylight.controller.md.sal.common.api.data.AsyncTransaction;
27 import org.opendaylight.controller.md.sal.common.api.data.LogicalDatastoreType;
28 import org.opendaylight.controller.md.sal.common.api.data.ReadFailedException;
29 import org.opendaylight.controller.md.sal.common.api.data.TransactionChain;
30 import org.opendaylight.controller.md.sal.common.api.data.TransactionChainListener;
31 import org.opendaylight.controller.md.sal.dom.api.DOMDataBroker;
32 import org.opendaylight.controller.md.sal.dom.api.DOMDataReadOnlyTransaction;
33 import org.opendaylight.controller.md.sal.dom.api.DOMDataReadWriteTransaction;
34 import org.opendaylight.controller.md.sal.dom.api.DOMDataWriteTransaction;
35 import org.opendaylight.controller.md.sal.dom.api.DOMTransactionChain;
36 import org.opendaylight.controller.md.sal.dom.spi.ForwardingDOMDataReadWriteTransaction;
37 import org.opendaylight.mdsal.common.api.CommitInfo;
38 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
39 import org.opendaylight.yangtools.yang.data.api.schema.NormalizedNode;
40 import org.slf4j.Logger;
41 import org.slf4j.LoggerFactory;
44 * An implementation of {@link DOMTransactionChain}, which has a very specific
45 * behavior, which some users may find surprising. If keeps the general
46 * intent of the contract, but it makes sure there are never more than two
47 * transactions allocated at any given time: one of them is being committed,
48 * and while that is happening, the other one acts as the scratch pad. Once
49 * the committing transaction completes successfully, the scratch transaction
50 * is enqueued as soon as it is ready.
53 * This mode of operation means that there is no inherent isolation between
54 * the front-end transactions and transactions cannot be reasonably cancelled.
57 * It furthermore means that the transactions returned by {@link #newReadOnlyTransaction()}
58 * counts as an outstanding transaction and the user may not allocate multiple
59 * read-only transactions at the same time.
62 public final class PingPongTransactionChain implements DOMTransactionChain {
63 private static final Logger LOG = LoggerFactory.getLogger(PingPongTransactionChain.class);
64 private final TransactionChainListener listener;
65 private final DOMTransactionChain delegate;
68 private boolean failed;
70 private PingPongTransaction shutdownTx;
72 private Entry<PingPongTransaction, Throwable> deadTx;
75 * This updater is used to manipulate the "ready" transaction. We perform only atomic
78 private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> READY_UPDATER
79 = AtomicReferenceFieldUpdater
80 .newUpdater(PingPongTransactionChain.class, PingPongTransaction.class, "readyTx");
81 private volatile PingPongTransaction readyTx;
84 * This updater is used to manipulate the "locked" transaction. A locked transaction
85 * means we know that the user still holds a transaction and should at some point call
86 * us. We perform on compare-and-swap to ensure we properly detect when a user is
87 * attempting to allocated multiple transactions concurrently.
89 private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> LOCKED_UPDATER
90 = AtomicReferenceFieldUpdater
91 .newUpdater(PingPongTransactionChain.class, PingPongTransaction.class, "lockedTx");
92 private volatile PingPongTransaction lockedTx;
95 * This updater is used to manipulate the "inflight" transaction. There can be at most
96 * one of these at any given time. We perform only compare-and-swap on these.
98 private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> INFLIGHT_UPDATER
99 = AtomicReferenceFieldUpdater
100 .newUpdater(PingPongTransactionChain.class, PingPongTransaction.class, "inflightTx");
101 private volatile PingPongTransaction inflightTx;
103 PingPongTransactionChain(final DOMDataBroker broker, final TransactionChainListener listener) {
104 this.listener = requireNonNull(listener);
105 this.delegate = broker.createTransactionChain(new TransactionChainListener() {
107 public void onTransactionChainFailed(final TransactionChain<?, ?> chain,
108 final AsyncTransaction<?, ?> transaction, final Throwable cause) {
109 LOG.debug("Transaction chain {} reported failure in {}", chain, transaction, cause);
110 delegateFailed(chain, cause);
114 public void onTransactionChainSuccessful(final TransactionChain<?, ?> chain) {
115 delegateSuccessful(chain);
120 void delegateSuccessful(final TransactionChain<?, ?> chain) {
121 final Entry<PingPongTransaction, Throwable> canceled;
122 synchronized (this) {
123 // This looks weird, but we need not hold the lock while invoking callbacks
127 if (canceled == null) {
128 listener.onTransactionChainSuccessful(this);
132 // Backend shutdown successful, but we have a batch of transactions we have to report as dead due to the
133 // user calling cancel().
134 final PingPongTransaction tx = canceled.getKey();
135 final Throwable cause = canceled.getValue();
136 LOG.debug("Transaction chain {} successful, failing cancelled transaction {}", chain, tx, cause);
138 listener.onTransactionChainFailed(this, tx.getFrontendTransaction(), cause);
142 void delegateFailed(final TransactionChain<?, ?> chain, final Throwable cause) {
144 final DOMDataReadWriteTransaction frontend;
145 final PingPongTransaction tx = inflightTx;
147 LOG.warn("Transaction chain {} failed with no pending transactions", chain);
150 frontend = tx.getFrontendTransaction();
153 listener.onTransactionChainFailed(this, frontend, cause);
155 synchronized (this) {
159 * If we do not have a locked transaction, we need to ensure that
160 * the backend transaction is cancelled. Otherwise we can defer
161 * until the user calls us.
163 if (lockedTx == null) {
169 private synchronized PingPongTransaction slowAllocateTransaction() {
170 checkState(shutdownTx == null, "Transaction chain %s has been shut down", this);
172 if (deadTx != null) {
173 throw new IllegalStateException(
174 String.format("Transaction chain %s has failed due to transaction %s being canceled", this,
175 deadTx.getKey()), deadTx.getValue());
178 final DOMDataReadWriteTransaction delegateTx = delegate.newReadWriteTransaction();
179 final PingPongTransaction newTx = new PingPongTransaction(delegateTx);
181 if (!LOCKED_UPDATER.compareAndSet(this, null, newTx)) {
183 throw new IllegalStateException(
184 String.format("New transaction %s raced with transaction %s", newTx, lockedTx));
190 private PingPongTransaction allocateTransaction() {
191 // Step 1: acquire current state
192 final PingPongTransaction oldTx = READY_UPDATER.getAndSet(this, null);
194 // Slow path: allocate a delegate transaction
196 return slowAllocateTransaction();
199 // Fast path: reuse current transaction. We will check failures and similar on commit().
200 if (!LOCKED_UPDATER.compareAndSet(this, null, oldTx)) {
201 // Ouch. Delegate chain has not detected a duplicate transaction allocation. This is the best we can do.
202 oldTx.getTransaction().cancel();
203 throw new IllegalStateException(
204 String.format("Reusable transaction %s raced with transaction %s", oldTx, lockedTx));
211 * This forces allocateTransaction() on a slow path, which has to happen after
212 * this method has completed executing. Also inflightTx may be updated outside
213 * the lock, hence we need to re-check.
216 private void processIfReady() {
217 if (inflightTx == null) {
218 final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
220 processTransaction(tx);
226 * Process a ready transaction. The caller needs to ensure that
227 * each transaction is seen only once by this method.
229 * @param tx Transaction which needs processing.
232 private void processTransaction(final @NonNull PingPongTransaction tx) {
234 LOG.debug("Cancelling transaction {}", tx);
235 tx.getTransaction().cancel();
239 LOG.debug("Submitting transaction {}", tx);
240 if (!INFLIGHT_UPDATER.compareAndSet(this, null, tx)) {
241 LOG.warn("Submitting transaction {} while {} is still running", tx, inflightTx);
244 tx.getTransaction().commit().addCallback(new FutureCallback<CommitInfo>() {
246 public void onSuccess(final CommitInfo result) {
247 transactionSuccessful(tx, result);
251 public void onFailure(final Throwable throwable) {
252 transactionFailed(tx, throwable);
254 }, MoreExecutors.directExecutor());
258 * We got invoked from the data store thread. We need to do two things:
259 * 1) release the in-flight transaction
260 * 2) process the potential next transaction
262 * We have to perform 2) under lock. We could perform 1) without locking, but that means the CAS result may
263 * not be accurate, as a user thread may submit the ready transaction before we acquire the lock -- and checking
264 * for next transaction is not enough, as that may have also be allocated (as a result of a quick
265 * submit/allocate/submit between 1) and 2)). Hence we'd end up doing the following:
266 * 1) CAS of inflightTx
268 * 3) volatile read of inflightTx
270 * Rather than doing that, we keep this method synchronized, hence performing only:
272 * 2) CAS of inflightTx
274 * Since the user thread is barred from submitting the transaction (in processIfReady), we can then proceed with
275 * the knowledge that inflightTx is null -- processTransaction() will still do a CAS, but that is only for
278 private synchronized void processNextTransaction(final PingPongTransaction tx) {
279 final boolean success = INFLIGHT_UPDATER.compareAndSet(this, tx, null);
280 checkState(success, "Completed transaction %s while %s was submitted", tx, inflightTx);
282 final PingPongTransaction nextTx = READY_UPDATER.getAndSet(this, null);
283 if (nextTx != null) {
284 processTransaction(nextTx);
285 } else if (shutdownTx != null) {
286 processTransaction(shutdownTx);
292 void transactionSuccessful(final PingPongTransaction tx, final CommitInfo result) {
293 LOG.debug("Transaction {} completed successfully", tx);
295 tx.onSuccess(result);
296 processNextTransaction(tx);
299 void transactionFailed(final PingPongTransaction tx, final Throwable throwable) {
300 LOG.debug("Transaction {} failed", tx, throwable);
302 tx.onFailure(throwable);
303 processNextTransaction(tx);
306 void readyTransaction(final @NonNull PingPongTransaction tx) {
307 // First mark the transaction as not locked.
308 final boolean lockedMatch = LOCKED_UPDATER.compareAndSet(this, tx, null);
309 checkState(lockedMatch, "Attempted to submit transaction %s while we have %s", tx, lockedTx);
310 LOG.debug("Transaction {} unlocked", tx);
313 * The transaction is ready. It will then be picked up by either next allocation,
314 * or a background transaction completion callback.
316 final boolean success = READY_UPDATER.compareAndSet(this, null, tx);
317 checkState(success, "Transaction %s collided on ready state", tx, readyTx);
318 LOG.debug("Transaction {} readied", tx);
321 * We do not see a transaction being in-flight, so we need to take care of dispatching
322 * the transaction to the backend. We are in the ready case, we cannot short-cut
323 * the checking of readyTx, as an in-flight transaction may have completed between us
324 * setting the field above and us checking.
326 if (inflightTx == null) {
327 synchronized (this) {
334 * Transaction cancellation is a heavyweight operation. We only support cancelation of a locked transaction
335 * and return false for everything else. Cancelling such a transaction will result in all transactions in the
336 * batch to be cancelled.
338 * @param tx Backend shared transaction
339 * @param frontendTx transaction
340 * @param isOpen indicator whether the transaction was already closed
342 synchronized void cancelTransaction(final PingPongTransaction tx, final DOMDataReadWriteTransaction frontendTx) {
343 // Attempt to unlock the operation.
344 final boolean lockedMatch = LOCKED_UPDATER.compareAndSet(this, tx, null);
345 verify(lockedMatch, "Cancelling transaction %s collided with locked transaction %s", tx, lockedTx);
347 // Cancel the backend transaction, so we do not end up leaking it.
348 final boolean backendCancelled = tx.getTransaction().cancel();
351 // The transaction has failed, this is probably the user just clearing up the transaction they had. We have
352 // already cancelled the transaction anyway,
354 } else if (!backendCancelled) {
355 LOG.warn("Backend transaction cannot be cancelled during cancellation of {}, attempting to continue", tx);
358 // We have dealt with canceling the backend transaction and have unlocked the transaction. Since we are still
359 // inside the synchronized block, any allocations are blocking on the slow path. Now we have to decide the fate
360 // of this transaction chain.
362 // If there are no other frontend transactions in this batch we are aligned with backend state and we can
363 // continue processing.
364 if (frontendTx.equals(tx.getFrontendTransaction())) {
365 LOG.debug("Cancelled transaction {} was head of the batch, resuming processing", tx);
369 // There are multiple frontend transactions in this batch. We have to report them as failed, which dooms this
370 // transaction chain, too. Since we just came off of a locked transaction, we do not have a ready transaction
371 // at the moment, but there may be some transaction in-flight. So we proceed to shutdown the backend chain
372 // and mark the fact that we should be turning its completion into a failure.
373 deadTx = new SimpleImmutableEntry<>(tx, new CancellationException("Transaction " + frontendTx + " canceled")
374 .fillInStackTrace());
379 public synchronized void close() {
380 final PingPongTransaction notLocked = lockedTx;
381 checkState(notLocked == null, "Attempted to close chain with outstanding transaction %s", notLocked);
383 // This is not reliable, but if we observe it to be null and the process has already completed,
384 // the backend transaction chain will throw the appropriate error.
385 checkState(shutdownTx == null, "Attempted to close an already-closed chain");
387 // This may be a reaction to our failure callback, in that case the backend is already shutdown
388 if (deadTx != null) {
389 LOG.debug("Delegate {} is already closed due to failure {}", delegate, deadTx);
393 // Force allocations on slow path, picking up a potentially-outstanding transaction
394 final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
397 // We have one more transaction, which needs to be processed somewhere. If we do not
398 // a transaction in-flight, we need to push it down ourselves.
399 // If there is an in-flight transaction we will schedule this last one into a dedicated
400 // slot. Allocation slow path will check its presence and fail, the in-flight path will
401 // pick it up, submit and immediately close the chain.
402 if (inflightTx == null) {
403 processTransaction(tx);
409 // Nothing outstanding, we can safely shutdown
415 public DOMDataReadOnlyTransaction newReadOnlyTransaction() {
416 final PingPongTransaction tx = allocateTransaction();
418 return new DOMDataReadOnlyTransaction() {
420 public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> read(
421 final LogicalDatastoreType store, final YangInstanceIdentifier path) {
422 return tx.getTransaction().read(store, path);
426 public CheckedFuture<Boolean, ReadFailedException> exists(final LogicalDatastoreType store,
427 final YangInstanceIdentifier path) {
428 return tx.getTransaction().exists(store, path);
432 public Object getIdentifier() {
433 return tx.getTransaction().getIdentifier();
437 public void close() {
438 readyTransaction(tx);
444 public DOMDataReadWriteTransaction newReadWriteTransaction() {
445 final PingPongTransaction tx = allocateTransaction();
446 final DOMDataReadWriteTransaction ret = new ForwardingDOMDataReadWriteTransaction() {
447 private boolean isOpen = true;
450 protected DOMDataReadWriteTransaction delegate() {
451 return tx.getTransaction();
455 public FluentFuture<? extends CommitInfo> commit() {
456 readyTransaction(tx);
458 return FluentFuture.from(tx.getCommitFuture()).transformAsync(
459 ignored -> CommitInfo.emptyFluentFuture(), MoreExecutors.directExecutor());
463 public boolean cancel() {
465 cancelTransaction(tx, this);
474 tx.recordFrontendTransaction(ret);
479 public DOMDataWriteTransaction newWriteOnlyTransaction() {
480 return newReadWriteTransaction();