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 com.google.common.base.Optional;
11 import com.google.common.base.Preconditions;
12 import com.google.common.util.concurrent.CheckedFuture;
13 import com.google.common.util.concurrent.FutureCallback;
14 import com.google.common.util.concurrent.Futures;
15 import com.google.common.util.concurrent.ListenableFuture;
16 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
17 import javax.annotation.Nonnull;
18 import javax.annotation.concurrent.GuardedBy;
19 import org.opendaylight.controller.md.sal.common.api.TransactionStatus;
20 import org.opendaylight.controller.md.sal.common.api.data.AsyncTransaction;
21 import org.opendaylight.controller.md.sal.common.api.data.LogicalDatastoreType;
22 import org.opendaylight.controller.md.sal.common.api.data.ReadFailedException;
23 import org.opendaylight.controller.md.sal.common.api.data.TransactionChain;
24 import org.opendaylight.controller.md.sal.common.api.data.TransactionChainListener;
25 import org.opendaylight.controller.md.sal.common.api.data.TransactionCommitFailedException;
26 import org.opendaylight.controller.md.sal.dom.api.DOMDataBroker;
27 import org.opendaylight.controller.md.sal.dom.api.DOMDataReadOnlyTransaction;
28 import org.opendaylight.controller.md.sal.dom.api.DOMDataReadWriteTransaction;
29 import org.opendaylight.controller.md.sal.dom.api.DOMDataWriteTransaction;
30 import org.opendaylight.controller.md.sal.dom.api.DOMTransactionChain;
31 import org.opendaylight.controller.md.sal.dom.spi.ForwardingDOMDataReadWriteTransaction;
32 import org.opendaylight.yangtools.yang.common.RpcResult;
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
40 * behavior, which some users may find surprising. If keeps the general
41 * intent of the contract, but it makes sure there are never more than two
42 * transactions allocated at any given time: one of them is being committed,
43 * and while that is happening, the other one acts as the scratch pad. Once
44 * the committing transaction completes successfully, the scratch transaction
45 * is enqueued as soon as it is ready.
47 * This mode of operation means that there is no inherent isolation between
48 * the front-end transactions and transactions cannot be reasonably cancelled.
50 * It furthermore means that the transactions returned by {@link #newReadOnlyTransaction()}
51 * counts as an outstanding transaction and the user may not allocate multiple
52 * read-only transactions at the same time.
54 public final class PingPongTransactionChain implements DOMTransactionChain {
55 private static final Logger LOG = LoggerFactory.getLogger(PingPongTransactionChain.class);
56 private final DOMTransactionChain delegate;
59 private boolean failed;
62 * This updater is used to manipulate the "ready" transaction. We perform only atomic
65 private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> READY_UPDATER =
66 AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class, "readyTx");
67 private volatile PingPongTransaction readyTx;
70 * This updater is used to manipulate the "locked" transaction. A locked transaction
71 * means we know that the user still holds a transaction and should at some point call
72 * us. We perform on compare-and-swap to ensure we properly detect when a user is
73 * attempting to allocated multiple transactions concurrently.
75 private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> LOCKED_UPDATER =
76 AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class, "lockedTx");
77 private volatile PingPongTransaction lockedTx;
80 * This updater is used to manipulate the "inflight" transaction. There can be at most
81 * one of these at any given time. We perform only compare-and-swap on these.
83 private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> INFLIGHT_UPDATER =
84 AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class, "inflightTx");
85 private volatile PingPongTransaction inflightTx;
87 PingPongTransactionChain(final DOMDataBroker broker, final TransactionChainListener listener) {
88 this.delegate = broker.createTransactionChain(new TransactionChainListener() {
90 public void onTransactionChainFailed(final TransactionChain<?, ?> chain, final AsyncTransaction<?, ?> transaction, final Throwable cause) {
91 LOG.debug("Delegate chain {} reported failure in {}", chain, transaction, cause);
93 final DOMDataReadWriteTransaction frontend;
94 final PingPongTransaction tx = inflightTx;
96 LOG.warn("Transaction chain {} failed with no pending transactions", chain);
99 frontend = tx.getFrontendTransaction();
102 listener.onTransactionChainFailed(PingPongTransactionChain.this, frontend, cause);
107 public void onTransactionChainSuccessful(final TransactionChain<?, ?> chain) {
108 listener.onTransactionChainSuccessful(PingPongTransactionChain.this);
113 private synchronized void delegateFailed() {
117 * If we do not have a locked transaction, we need to ensure that
118 * the backend transaction is cancelled. Otherwise we can defer
119 * until the user calls us.
121 if (lockedTx == null) {
126 private synchronized PingPongTransaction slowAllocateTransaction() {
127 final DOMDataReadWriteTransaction delegateTx = delegate.newReadWriteTransaction();
128 final PingPongTransaction newTx = new PingPongTransaction(delegateTx);
130 if (!LOCKED_UPDATER.compareAndSet(this, null, newTx)) {
132 throw new IllegalStateException(String.format("New transaction %s raced with transacion %s", newTx, lockedTx));
138 private PingPongTransaction allocateTransaction() {
139 // Step 1: acquire current state
140 final PingPongTransaction oldTx = READY_UPDATER.getAndSet(this, null);
142 // Slow path: allocate a delegate transaction
144 return slowAllocateTransaction();
147 // Fast path: reuse current transaction. We will check
148 // failures and similar on submit().
149 if (!LOCKED_UPDATER.compareAndSet(this, null, oldTx)) {
150 // Ouch. Delegate chain has not detected a duplicate
151 // transaction allocation. This is the best we can do.
152 oldTx.getTransaction().cancel();
153 throw new IllegalStateException(String.format("Reusable transaction %s raced with transaction %s", oldTx, lockedTx));
160 * This forces allocateTransaction() on a slow path, which has to happen after
161 * this method has completed executing. Also inflightTx may be updated outside
162 * the lock, hence we need to re-check.
165 private void processIfReady() {
166 if (inflightTx == null) {
167 final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
169 processTransaction(tx);
175 * Process a ready transaction. The caller needs to ensure that
176 * each transaction is seen only once by this method.
178 * @param tx Transaction which needs processing.
181 private void processTransaction(@Nonnull final PingPongTransaction tx) {
183 LOG.debug("Cancelling transaction {}", tx);
184 tx.getTransaction().cancel();
188 LOG.debug("Submitting transaction {}", tx);
189 if (!INFLIGHT_UPDATER.compareAndSet(this, null, tx)) {
190 LOG.warn("Submitting transaction {} while {} is still running", tx, inflightTx);
193 Futures.addCallback(tx.getTransaction().submit(), new FutureCallback<Void>() {
195 public void onSuccess(final Void result) {
196 transactionSuccessful(tx, result);
200 public void onFailure(final Throwable t) {
201 transactionFailed(tx, t);
206 private void transactionSuccessful(final PingPongTransaction tx, final Void result) {
207 LOG.debug("Transaction {} completed successfully", tx);
209 final boolean success = INFLIGHT_UPDATER.compareAndSet(this, tx, null);
210 Preconditions.checkState(success, "Successful transaction %s while %s was submitted", tx, inflightTx);
212 synchronized (this) {
216 // Can run unsynchronized
217 tx.onSuccess(result);
220 private void transactionFailed(final PingPongTransaction tx, final Throwable t) {
221 LOG.debug("Transaction {} failed", tx, t);
223 final boolean success = INFLIGHT_UPDATER.compareAndSet(this, tx, null);
224 Preconditions.checkState(success, "Failed transaction %s while %s was submitted", tx, inflightTx);
229 private void readyTransaction(@Nonnull final PingPongTransaction tx) {
230 // First mark the transaction as not locked.
231 final boolean lockedMatch = LOCKED_UPDATER.compareAndSet(this, tx, null);
232 Preconditions.checkState(lockedMatch, "Attempted to submit transaction %s while we have %s", tx, lockedTx);
233 LOG.debug("Transaction {} unlocked", tx);
236 * The transaction is ready. It will then be picked up by either next allocation,
237 * or a background transaction completion callback.
239 final boolean success = READY_UPDATER.compareAndSet(this, null, tx);
240 Preconditions.checkState(success, "Transaction %s collided on ready state", tx, readyTx);
241 LOG.debug("Transaction {} readied", tx);
244 * We do not see a transaction being in-flight, so we need to take care of dispatching
245 * the transaction to the backend. We are in the ready case, we cannot short-cut
246 * the checking of readyTx, as an in-flight transaction may have completed between us
247 * setting the field above and us checking.
249 if (inflightTx == null) {
250 synchronized (this) {
257 public synchronized void close() {
258 final PingPongTransaction notLocked = lockedTx;
259 Preconditions.checkState(notLocked == null, "Attempted to close chain with outstanding transaction %s", notLocked);
261 // Force allocations on slow path. We will complete the rest
262 final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
264 // Make sure no transaction is outstanding. Otherwise sleep a bit and retry
265 while (inflightTx != null) {
266 LOG.debug("Busy-waiting for in-flight transaction {} to complete", inflightTx);
271 // If we have an outstanding transaction, send it down
273 processTransaction(tx);
276 // All done, close the delegate. All new allocations should fail.
281 public DOMDataReadOnlyTransaction newReadOnlyTransaction() {
282 final PingPongTransaction tx = allocateTransaction();
284 return new DOMDataReadOnlyTransaction() {
286 public CheckedFuture<Optional<NormalizedNode<?, ?>>, ReadFailedException> read(final LogicalDatastoreType store,
287 final YangInstanceIdentifier path) {
288 return tx.getTransaction().read(store, path);
292 public CheckedFuture<Boolean, ReadFailedException> exists(final LogicalDatastoreType store,
293 final YangInstanceIdentifier path) {
294 return tx.getTransaction().exists(store, path);
298 public Object getIdentifier() {
299 return tx.getTransaction().getIdentifier();
303 public void close() {
304 readyTransaction(tx);
310 public DOMDataReadWriteTransaction newReadWriteTransaction() {
311 final PingPongTransaction tx = allocateTransaction();
312 final DOMDataReadWriteTransaction ret = new ForwardingDOMDataReadWriteTransaction() {
314 protected DOMDataReadWriteTransaction delegate() {
315 return tx.getTransaction();
319 public CheckedFuture<Void, TransactionCommitFailedException> submit() {
320 readyTransaction(tx);
321 return tx.getSubmitFuture();
325 public ListenableFuture<RpcResult<TransactionStatus>> commit() {
326 readyTransaction(tx);
327 return tx.getCommitFuture();
331 public boolean cancel() {
332 throw new UnsupportedOperationException("Transaction cancellation is not supported");
336 tx.recordFrontendTransaction(ret);
341 public DOMDataWriteTransaction newWriteOnlyTransaction() {
342 return newReadWriteTransaction();