import com.google.common.util.concurrent.SettableFuture;
import java.util.ArrayDeque;
import java.util.Deque;
+import java.util.Iterator;
import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
+import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
import java.util.function.Consumer;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.GuardedBy;
import javax.annotation.concurrent.NotThreadSafe;
+import org.opendaylight.controller.cluster.access.client.ConnectionEntry;
import org.opendaylight.controller.cluster.access.commands.TransactionAbortRequest;
import org.opendaylight.controller.cluster.access.commands.TransactionAbortSuccess;
import org.opendaylight.controller.cluster.access.commands.TransactionCanCommitSuccess;
import org.opendaylight.controller.cluster.access.commands.TransactionPreCommitRequest;
import org.opendaylight.controller.cluster.access.commands.TransactionPreCommitSuccess;
import org.opendaylight.controller.cluster.access.commands.TransactionRequest;
-import org.opendaylight.controller.cluster.access.concepts.RequestException;
+import org.opendaylight.controller.cluster.access.concepts.Request;
import org.opendaylight.controller.cluster.access.concepts.RequestFailure;
import org.opendaylight.controller.cluster.access.concepts.Response;
import org.opendaylight.controller.cluster.access.concepts.TransactionIdentifier;
}
}
- private enum SealState {
- /**
- * The user has not sealed the transaction yet.
- */
- OPEN,
- /**
- * The user has sealed the transaction, but has not issued a canCommit().
- */
- SEALED,
- /**
- * The user has sealed the transaction and has issued a canCommit().
- */
- FLUSHED,
+ // Generic state base class. Direct instances are used for fast paths, sub-class is used for successor transitions
+ private static class State {
+ private final String string;
+
+ State(final String string) {
+ this.string = Preconditions.checkNotNull(string);
+ }
+
+ @Override
+ public final String toString() {
+ return string;
+ }
}
- private static final Logger LOG = LoggerFactory.getLogger(AbstractProxyTransaction.class);
+ // State class used when a successor has interfered. Contains coordinator latch, the successor and previous state
+ private static final class SuccessorState extends State {
+ private final CountDownLatch latch = new CountDownLatch(1);
+ private AbstractProxyTransaction successor;
+ private State prevState;
+
+ SuccessorState() {
+ super("successor");
+ }
+
+ // Synchronize with succession process and return the successor
+ AbstractProxyTransaction await() {
+ try {
+ latch.await();
+ } catch (InterruptedException e) {
+ LOG.warn("Interrupted while waiting for latch of {}", successor);
+ throw Throwables.propagate(e);
+ }
+ return successor;
+ }
+
+ void finish() {
+ latch.countDown();
+ }
+
+ State getPrevState() {
+ return prevState;
+ }
+
+ void setPrevState(final State prevState) {
+ Verify.verify(this.prevState == null);
+ this.prevState = Preconditions.checkNotNull(prevState);
+ }
+
+ // To be called from safe contexts, where successor is known to be completed
+ AbstractProxyTransaction getSuccessor() {
+ return Verify.verifyNotNull(successor);
+ }
+ void setSuccessor(final AbstractProxyTransaction successor) {
+ Verify.verify(this.successor == null);
+ this.successor = Preconditions.checkNotNull(successor);
+ }
+ }
+
+ private static final Logger LOG = LoggerFactory.getLogger(AbstractProxyTransaction.class);
+ private static final AtomicIntegerFieldUpdater<AbstractProxyTransaction> SEALED_UPDATER =
+ AtomicIntegerFieldUpdater.newUpdater(AbstractProxyTransaction.class, "sealed");
+ private static final AtomicReferenceFieldUpdater<AbstractProxyTransaction, State> STATE_UPDATER =
+ AtomicReferenceFieldUpdater.newUpdater(AbstractProxyTransaction.class, State.class, "state");
+ private static final State OPEN = new State("open");
+ private static final State SEALED = new State("sealed");
+ private static final State FLUSHED = new State("flushed");
+
+ // Touched from client actor thread only
private final Deque<Object> successfulRequests = new ArrayDeque<>();
private final ProxyHistory parent;
+ // Accessed from user thread only, which may not access this object concurrently
+ private long sequence;
+
/*
* Atomic state-keeping is required to synchronize the process of propagating completed transaction state towards
* the backend -- which may include a successor.
* or timeout, when a successor is injected.
*
* This leaves the problem of needing to completely transferring state just after all queued messages are replayed
- * after a successor was injected, so that it can be properly sealed if we are racing.
+ * after a successor was injected, so that it can be properly sealed if we are racing. Further complication comes
+ * from lock ordering, where the successor injection works with a locked queue and locks proxy objects -- leading
+ * to a potential AB-BA deadlock in case of a naive implementation.
+ *
+ * For tracking user-visible state we use a single volatile int, which is flipped atomically from 0 to 1 exactly
+ * once in {@link AbstractProxyTransaction#seal()}. That keeps common operations fast, as they need to perform
+ * only a single volatile read to assert state correctness.
+ *
+ * For synchronizing client actor (successor-injecting) and user (commit-driving) thread, we keep a separate state
+ * variable. It uses pre-allocated objects for fast paths (i.e. no successor present) and a per-transition object
+ * for slow paths (when successor is injected/present).
*/
- private volatile SealState sealed = SealState.OPEN;
- @GuardedBy("this")
- private AbstractProxyTransaction successor;
- @GuardedBy("this")
- private CountDownLatch successorLatch;
-
- // Accessed from user thread only, which may not access this object concurrently
- private long sequence;
-
+ private volatile int sealed = 0;
+ private volatile State state = OPEN;
AbstractProxyTransaction(final ProxyHistory parent) {
this.parent = Preconditions.checkNotNull(parent);
* Seal this transaction before it is either committed or aborted.
*/
final void seal() {
- final CountDownLatch localLatch;
-
- synchronized (this) {
- checkNotSealed();
- doSeal();
-
- // Fast path: no successor
- if (successor == null) {
- sealed = SealState.SEALED;
- parent.onTransactionSealed(this);
- return;
- }
-
- localLatch = successorLatch;
- }
-
- // Slow path: wait for the latch
- LOG.debug("{} waiting on successor latch", getIdentifier());
- try {
- localLatch.await();
- } catch (InterruptedException e) {
- LOG.warn("{} interrupted while waiting for latch", getIdentifier());
- throw Throwables.propagate(e);
- }
-
- synchronized (this) {
- LOG.debug("{} reacquired lock", getIdentifier());
-
+ // Transition user-visible state first
+ final boolean success = SEALED_UPDATER.compareAndSet(this, 0, 1);
+ Preconditions.checkState(success, "Proxy %s was already sealed", getIdentifier());
+ doSeal();
+ parent.onTransactionSealed(this);
+
+ // Now deal with state transfer, which can occur via successor or a follow-up canCommit() or directCommit().
+ if (!STATE_UPDATER.compareAndSet(this, OPEN, SEALED)) {
+ // Slow path: wait for the successor to complete
+ final AbstractProxyTransaction successor = awaitSuccessor();
+
+ // At this point the successor has completed transition and is possibly visible by the user thread, which is
+ // still stuck here. The successor has not seen final part of our state, nor the fact it is sealed.
+ // Propagate state and seal the successor.
flushState(successor);
successor.seal();
-
- sealed = SealState.FLUSHED;
- parent.onTransactionSealed(this);
}
}
private void checkNotSealed() {
- Preconditions.checkState(sealed == SealState.OPEN, "Transaction %s has already been sealed", getIdentifier());
+ Preconditions.checkState(sealed == 0, "Transaction %s has already been sealed", getIdentifier());
}
- private SealState checkSealed() {
- final SealState local = sealed;
- Preconditions.checkState(local != SealState.OPEN, "Transaction %s has not been sealed yet", getIdentifier());
- return local;
+ private void checkSealed() {
+ Preconditions.checkState(sealed != 0, "Transaction %s has not been sealed yet", getIdentifier());
+ }
+
+ private SuccessorState getSuccessorState() {
+ final State local = state;
+ Verify.verify(local instanceof SuccessorState, "State %s has unexpected class", local);
+ return (SuccessorState) local;
}
final void recordSuccessfulRequest(final @Nonnull TransactionRequest<?> req) {
* @return Future completion
*/
final ListenableFuture<Boolean> directCommit() {
- final CountDownLatch localLatch;
+ checkSealed();
+ // Precludes startReconnect() from interfering with the fast path
synchronized (this) {
- final SealState local = checkSealed();
-
- // Fast path: no successor asserted
- if (successor == null) {
- Verify.verify(local == SealState.SEALED);
-
+ if (STATE_UPDATER.compareAndSet(this, SEALED, FLUSHED)) {
final SettableFuture<Boolean> ret = SettableFuture.create();
sendRequest(Verify.verifyNotNull(commitRequest(false)), t -> {
if (t instanceof TransactionCommitSuccess) {
parent.completeTransaction(this);
});
- sealed = SealState.FLUSHED;
return ret;
}
-
- // We have a successor, take its latch
- localLatch = successorLatch;
- }
-
- // Slow path: we need to wait for the successor to completely propagate
- LOG.debug("{} waiting on successor latch", getIdentifier());
- try {
- localLatch.await();
- } catch (InterruptedException e) {
- LOG.warn("{} interrupted while waiting for latch", getIdentifier());
- throw Throwables.propagate(e);
}
- synchronized (this) {
- LOG.debug("{} reacquired lock", getIdentifier());
-
- final SealState local = sealed;
- Verify.verify(local == SealState.FLUSHED);
-
- return successor.directCommit();
- }
+ // We have had some interference with successor injection, wait for it to complete and defer to the successor.
+ return awaitSuccessor().directCommit();
}
final void canCommit(final VotingFuture<?> ret) {
- final CountDownLatch localLatch;
+ checkSealed();
+ // Precludes startReconnect() from interfering with the fast path
synchronized (this) {
- final SealState local = checkSealed();
-
- // Fast path: no successor asserted
- if (successor == null) {
- Verify.verify(local == SealState.SEALED);
-
+ if (STATE_UPDATER.compareAndSet(this, SEALED, FLUSHED)) {
final TransactionRequest<?> req = Verify.verifyNotNull(commitRequest(true));
+
sendRequest(req, t -> {
if (t instanceof TransactionCanCommitSuccess) {
ret.voteYes();
LOG.debug("Transaction {} canCommit completed", this);
});
- sealed = SealState.FLUSHED;
return;
}
-
- // We have a successor, take its latch
- localLatch = successorLatch;
- }
-
- // Slow path: we need to wait for the successor to completely propagate
- LOG.debug("{} waiting on successor latch", getIdentifier());
- try {
- localLatch.await();
- } catch (InterruptedException e) {
- LOG.warn("{} interrupted while waiting for latch", getIdentifier());
- throw Throwables.propagate(e);
}
- synchronized (this) {
- LOG.debug("{} reacquired lock", getIdentifier());
-
- final SealState local = sealed;
- Verify.verify(local == SealState.FLUSHED);
+ // We have had some interference with successor injection, wait for it to complete and defer to the successor.
+ awaitSuccessor().canCommit(ret);
+ }
- successor.canCommit(ret);
- }
+ private AbstractProxyTransaction awaitSuccessor() {
+ return getSuccessorState().await();
}
final void preCommit(final VotingFuture<?> ret) {
});
}
- void doCommit(final VotingFuture<?> ret) {
+ final void doCommit(final VotingFuture<?> ret) {
checkSealed();
sendRequest(new TransactionDoCommitRequest(getIdentifier(), nextSequence(), localActor()), t -> {
});
}
- final synchronized void startReconnect(final AbstractProxyTransaction successor) {
- Preconditions.checkState(this.successor == null);
- this.successor = Preconditions.checkNotNull(successor);
+ // Called with the connection unlocked
+ final synchronized void startReconnect() {
+ // At this point canCommit/directCommit are blocked, we assert a new successor state, retrieving the previous
+ // state. This method is called with the queue still unlocked.
+ final SuccessorState nextState = new SuccessorState();
+ final State prevState = STATE_UPDATER.getAndSet(this, nextState);
+
+ LOG.debug("Start reconnect of proxy {} previous state {}", this, prevState);
+ Verify.verify(!(prevState instanceof SuccessorState), "Proxy %s duplicate reconnect attempt after %s", this,
+ prevState);
+
+ // We have asserted a slow-path state, seal(), canCommit(), directCommit() are forced to slow paths, which will
+ // wait until we unblock nextState's latch before accessing state. Now we record prevState for later use and we
+ // are done.
+ nextState.setPrevState(prevState);
+ }
+
+ // Called with the connection locked
+ final void replayMessages(final AbstractProxyTransaction successor,
+ final Iterable<ConnectionEntry> enqueuedEntries) {
+ final SuccessorState local = getSuccessorState();
+ local.setSuccessor(successor);
+ // Replay successful requests first
for (Object obj : successfulRequests) {
if (obj instanceof TransactionRequest) {
- LOG.debug("Forwarding request {} to successor {}", obj, successor);
+ LOG.debug("Forwarding successful request {} to successor {}", obj, successor);
successor.handleForwardedRemoteRequest((TransactionRequest<?>) obj, null);
} else {
Verify.verify(obj instanceof IncrementSequence);
LOG.debug("{} replayed {} successful requests", getIdentifier(), successfulRequests.size());
successfulRequests.clear();
+ // Now replay whatever is in the connection
+ final Iterator<ConnectionEntry> it = enqueuedEntries.iterator();
+ while (it.hasNext()) {
+ final ConnectionEntry e = it.next();
+ final Request<?, ?> req = e.getRequest();
+
+ if (getIdentifier().equals(req.getTarget())) {
+ Verify.verify(req instanceof TransactionRequest, "Unhandled request %s", req);
+ LOG.debug("Forwarding queued request{} to successor {}", req, successor);
+ successor.handleForwardedRemoteRequest((TransactionRequest<?>) req, e.getCallback());
+ it.remove();
+ }
+ }
+
/*
- * Before releasing the lock we need to make sure that a call to seal() blocks until we have completed
- * finishConnect().
+ * Check the state at which we have started the reconnect attempt. State transitions triggered while we were
+ * reconnecting have been forced to slow paths, which will be unlocked once we unblock the state latch
+ * at the end of this method.
*/
- successorLatch = new CountDownLatch(1);
- }
-
- final synchronized void finishReconnect() {
- Preconditions.checkState(successorLatch != null);
-
- if (sealed == SealState.SEALED) {
- /*
- * If this proxy is in the 'sealed, have not sent canCommit' state. If so, we need to forward current
- * leftover state to the successor now.
- */
+ final State prevState = local.getPrevState();
+ if (SEALED.equals(prevState)) {
+ LOG.debug("Proxy {} reconnected while being sealed, propagating state to successor {}", this, successor);
flushState(successor);
successor.seal();
- sealed = SealState.FLUSHED;
}
+ }
+
+ // Called with the connection locked
+ final void finishReconnect() {
+ final SuccessorState local = getSuccessorState();
+ LOG.debug("Finishing reconnect of proxy {}", this);
- // All done, release the latch, unblocking seal() and canCommit()
- successorLatch.countDown();
+ // All done, release the latch, unblocking seal() and canCommit() slow paths
+ local.finish();
}
/**
*
* @param request Request to be forwarded
* @param callback Original callback
- * @throws RequestException when the request is unhandled by the successor
*/
- final synchronized void replayRequest(final TransactionRequest<?> request,
- final Consumer<Response<?, ?>> callback) {
- Preconditions.checkState(successor != null, "%s does not have a successor set", this);
+ final void replayRequest(final TransactionRequest<?> request, final Consumer<Response<?, ?>> callback) {
+ final AbstractProxyTransaction successor = getSuccessorState().getSuccessor();
if (successor instanceof LocalProxyTransaction) {
forwardToLocal((LocalProxyTransaction)successor, request, callback);
Code Review / controller.git / blobdiff