Fix a race PingPongTransactionChain

[controller.git] / opendaylight / md-sal / sal-dom-broker / src / main / java / org / opendaylight / controller / md / sal / dom / broker / impl / PingPongTransactionChain.java

diff --git a/opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/md/sal/dom/broker/impl/PingPongTransactionChain.java b/opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/md/sal/dom/broker/impl/PingPongTransactionChain.java
index b3c03b3185efa421b3913aba39362ef6f701bba0..c3a56ed454024b3cb316c1e5bec9d7184c897edc 100644 (file)
--- a/opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/md/sal/dom/broker/impl/PingPongTransactionChain.java
+++ b/opendaylight/md-sal/sal-dom-broker/src/main/java/org/opendaylight/controller/md/sal/dom/broker/impl/PingPongTransactionChain.java
@@ -55,8 +55,6 @@ public final class PingPongTransactionChain implements DOMTransactionChain {
     private static final Logger LOG = LoggerFactory.getLogger(PingPongTransactionChain.class);
     private final DOMTransactionChain delegate;
 
-    @GuardedBy("this")
-    private PingPongTransaction inflightTransaction;
     @GuardedBy("this")
     private boolean failed;
 
@@ -66,7 +64,6 @@ public final class PingPongTransactionChain implements DOMTransactionChain {
      */
     private static final AtomicReferenceFieldUpdater<PingPongTransactionChain, PingPongTransaction> READY_UPDATER =
             AtomicReferenceFieldUpdater.newUpdater(PingPongTransactionChain.class, PingPongTransaction.class, "readyTx");
-    @SuppressWarnings("unused") // Accessed via READY_UPDATER
     private volatile PingPongTransaction readyTx;
 
     /**
@@ -79,6 +76,14 @@ public final class PingPongTransactionChain implements DOMTransactionChain {
             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;
+
     PingPongTransactionChain(final DOMDataBroker broker, final TransactionChainListener listener) {
         this.delegate = broker.createTransactionChain(new TransactionChainListener() {
             @Override
@@ -86,14 +91,15 @@ public final class PingPongTransactionChain implements DOMTransactionChain {
                 LOG.debug("Delegate chain {} reported failure in {}", chain, transaction, cause);
 
                 final DOMDataReadWriteTransaction frontend;
-                if (inflightTransaction == null) {
+                final PingPongTransaction tx = inflightTx;
+                if (tx == null) {
                     LOG.warn("Transaction chain {} failed with no pending transactions", chain);
                     frontend = null;
                 } else {
-                    frontend = inflightTransaction.getFrontendTransaction();
+                    frontend = tx.getFrontendTransaction();
                 }
 
-                listener.onTransactionChainFailed(PingPongTransactionChain.this, frontend , cause);
+                listener.onTransactionChainFailed(PingPongTransactionChain.this, frontend, cause);
                 delegateFailed();
             }
 
@@ -150,7 +156,10 @@ public final class PingPongTransactionChain implements DOMTransactionChain {
         return oldTx;
     }
 
-    // This forces allocateTransaction() on a slow path
+    /*
+     * This forces allocateTransaction() on a slow path, which has to happen after
+     * this method has completed executing.
+     */
     @GuardedBy("this")
     private void processIfReady() {
         final PingPongTransaction tx = READY_UPDATER.getAndSet(this, null);
@@ -174,10 +183,11 @@ public final class PingPongTransactionChain implements DOMTransactionChain {
         }
 
         LOG.debug("Submitting transaction {}", tx);
-        final CheckedFuture<Void, ?> f = tx.getTransaction().submit();
-        inflightTransaction = tx;
+        if (!INFLIGHT_UPDATER.compareAndSet(this, null, tx)) {
+            LOG.warn("Submitting transaction {} while {} is still running", tx, inflightTx);
+        }
 
-        Futures.addCallback(f, new FutureCallback<Void>() {
+        Futures.addCallback(tx.getTransaction().submit(), new FutureCallback<Void>() {
             @Override
             public void onSuccess(final Void result) {
                 transactionSuccessful(tx, result);
@@ -193,10 +203,10 @@ public final class PingPongTransactionChain implements DOMTransactionChain {
     private void transactionSuccessful(final PingPongTransaction tx, final Void result) {
         LOG.debug("Transaction {} completed successfully", tx);
 
-        synchronized (this) {
-            Preconditions.checkState(inflightTransaction == tx, "Successful transaction %s while %s was submitted", tx, inflightTransaction);
+        final boolean success = INFLIGHT_UPDATER.compareAndSet(this, tx, null);
+        Preconditions.checkState(success, "Successful transaction %s while %s was submitted", tx, inflightTx);
 
-            inflightTransaction = null;
+        synchronized (this) {
             processIfReady();
         }
 
@@ -207,23 +217,35 @@ public final class PingPongTransactionChain implements DOMTransactionChain {
     private void transactionFailed(final PingPongTransaction tx, final Throwable t) {
         LOG.debug("Transaction {} failed", tx, t);
 
-        synchronized (this) {
-            Preconditions.checkState(inflightTransaction == tx, "Failed transaction %s while %s was submitted", tx, inflightTransaction);
-            inflightTransaction = null;
-        }
+        final boolean success = INFLIGHT_UPDATER.compareAndSet(this, tx, null);
+        Preconditions.checkState(success, "Failed transaction %s while %s was submitted", tx, inflightTx);
 
         tx.onFailure(t);
     }
 
     private void readyTransaction(final @Nonnull PingPongTransaction tx) {
+        // First mark the transaction as not locked.
         final boolean lockedMatch = LOCKED_UPDATER.compareAndSet(this, tx, null);
         Preconditions.checkState(lockedMatch, "Attempted to submit transaction %s while we have %s", tx, lockedTx);
-
         LOG.debug("Transaction {} unlocked", tx);
 
-        synchronized (this) {
-            if (inflightTransaction == null) {
-                processTransaction(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);
+        Preconditions.checkState(success, "Transaction %s collided on ready state", tx, readyTx);
+        LOG.debug("Transaction {} readied");
+
+        /*
+         * 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();
             }
         }
     }