X-Git-Url: https://git.opendaylight.org/gerrit/gitweb?a=blobdiff_plain;f=opendaylight%2Fmd-sal%2Fsal-distributed-datastore%2Fsrc%2Fmain%2Fjava%2Forg%2Fopendaylight%2Fcontroller%2Fcluster%2Fdatabroker%2Factors%2Fdds%2FAbstractProxyTransaction.java;h=bf56376fcee3d538d483a063d652ae6d3d5a5654;hb=20ece8c549211d1c453f1763132bb0a0ca7be0e0;hp=803908d8c603848683d55d74d897c65bd9cd9931;hpb=db9a673c114febc785fbd324947ac2c3e3095d06;p=controller.git diff --git a/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/databroker/actors/dds/AbstractProxyTransaction.java b/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/databroker/actors/dds/AbstractProxyTransaction.java index 803908d8c6..bf56376fce 100644 --- a/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/databroker/actors/dds/AbstractProxyTransaction.java +++ b/opendaylight/md-sal/sal-distributed-datastore/src/main/java/org/opendaylight/controller/cluster/databroker/actors/dds/AbstractProxyTransaction.java @@ -8,17 +8,29 @@ package org.opendaylight.controller.cluster.databroker.actors.dds; import akka.actor.ActorRef; +import com.google.common.base.MoreObjects; import com.google.common.base.Optional; import com.google.common.base.Preconditions; +import com.google.common.base.Throwables; import com.google.common.base.Verify; +import com.google.common.collect.Iterables; import com.google.common.util.concurrent.CheckedFuture; import com.google.common.util.concurrent.ListenableFuture; 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.AbstractLocalTransactionRequest; +import org.opendaylight.controller.cluster.access.commands.IncrementTransactionSequenceRequest; import org.opendaylight.controller.cluster.access.commands.TransactionAbortRequest; import org.opendaylight.controller.cluster.access.commands.TransactionAbortSuccess; import org.opendaylight.controller.cluster.access.commands.TransactionCanCommitSuccess; @@ -26,8 +38,9 @@ import org.opendaylight.controller.cluster.access.commands.TransactionCommitSucc import org.opendaylight.controller.cluster.access.commands.TransactionDoCommitRequest; import org.opendaylight.controller.cluster.access.commands.TransactionPreCommitRequest; import org.opendaylight.controller.cluster.access.commands.TransactionPreCommitSuccess; +import org.opendaylight.controller.cluster.access.commands.TransactionPurgeRequest; 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; @@ -52,36 +65,150 @@ import org.slf4j.LoggerFactory; * @author Robert Varga */ abstract class AbstractProxyTransaction implements Identifiable { + /** + * Marker object used instead of read-type of requests, which are satisfied only once. This has a lower footprint + * and allows compressing multiple requests into a single entry. + */ + @NotThreadSafe private static final class IncrementSequence { - private long delta = 1; + private final long sequence; + private long delta = 0; + + IncrementSequence(final long sequence) { + this.sequence = sequence; + } long getDelta() { return delta; } + long getSequence() { + return sequence; + } + void incrementDelta() { delta++; } } - private static final Logger LOG = LoggerFactory.getLogger(AbstractProxyTransaction.class); + // 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; + } + } + + // 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 SEALED_UPDATER = + AtomicIntegerFieldUpdater.newUpdater(AbstractProxyTransaction.class, "sealed"); + private static final AtomicReferenceFieldUpdater 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 successfulRequests = new ArrayDeque<>(); private final ProxyHistory parent; - private AbstractProxyTransaction successor; + // Accessed from user thread only, which may not access this object concurrently private long sequence; - private boolean sealed; + + /* + * Atomic state-keeping is required to synchronize the process of propagating completed transaction state towards + * the backend -- which may include a successor. + * + * Successor, unlike {@link AbstractProxyTransaction#seal()} is triggered from the client actor thread, which means + * the successor placement needs to be atomic with regard to the application thread. + * + * In the common case, the application thread performs performs the seal operations and then "immediately" sends + * the corresponding message. The uncommon case is when the seal and send operations race with a connect completion + * 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. 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 int sealed = 0; + private volatile State state = OPEN; AbstractProxyTransaction(final ProxyHistory parent) { this.parent = Preconditions.checkNotNull(parent); } + final void executeInActor(final Runnable command) { + parent.context().executeInActor(behavior -> { + command.run(); + return behavior; + }); + } + final ActorRef localActor() { return parent.localActor(); } - private void incrementSequence(final long delta) { + final void incrementSequence(final long delta) { sequence += delta; LOG.debug("Transaction {} incremented sequence to {}", this, sequence); } @@ -93,16 +220,19 @@ abstract class AbstractProxyTransaction implements Identifiable data) { + checkReadWrite(); checkNotSealed(); doMerge(path, data); } final void write(final YangInstanceIdentifier path, final NormalizedNode data) { + checkReadWrite(); checkNotSealed(); doWrite(path, data); } @@ -117,6 +247,12 @@ abstract class AbstractProxyTransaction implements Identifiable request, final Consumer> callback, + final long enqueuedTicks) { + LOG.debug("Transaction proxy {} enqueing request {} callback {}", this, request, callback); + parent.enqueueRequest(request, callback, enqueuedTicks); + } + final void sendRequest(final TransactionRequest request, final Consumer> callback) { LOG.debug("Transaction proxy {} sending request {} callback {}", this, request, callback); parent.sendRequest(request, callback); @@ -126,30 +262,65 @@ abstract class AbstractProxyTransaction implements Identifiable req) { successfulRequests.add(Verify.verifyNotNull(req)); } - final void recordFinishedRequest() { + final void recordFinishedRequest(final Response response) { final Object last = successfulRequests.peekLast(); if (last instanceof IncrementSequence) { ((IncrementSequence) last).incrementDelta(); } else { - successfulRequests.addLast(new IncrementSequence()); + successfulRequests.addLast(new IncrementSequence(response.getSequence())); } } @@ -159,29 +330,51 @@ abstract class AbstractProxyTransaction implements Identifiable { + LOG.debug("Transaction {} abort completed with {}", getIdentifier(), resp); + enqueuePurge(); + }); } final void abort(final VotingFuture ret) { checkSealed(); - sendAbort(t -> { + sendDoAbort(t -> { if (t instanceof TransactionAbortSuccess) { ret.voteYes(); } else if (t instanceof RequestFailure) { - ret.voteNo(((RequestFailure) t).getCause()); + ret.voteNo(((RequestFailure) t).getCause().unwrap()); } else { ret.voteNo(new IllegalStateException("Unhandled response " + t.getClass())); } // This is a terminal request, hence we do not need to record it LOG.debug("Transaction {} abort completed", this); - parent.completeTransaction(this); + enqueuePurge(); }); } - final void sendAbort(final Consumer> callback) { + final void enqueueAbort(final Consumer> callback, final long enqueuedTicks) { + checkNotSealed(); + parent.abortTransaction(this); + + enqueueRequest(abortRequest(), resp -> { + LOG.debug("Transaction {} abort completed with {}", getIdentifier(), resp); + // Purge will be sent by the predecessor's callback + if (callback != null) { + callback.accept(resp); + } + }, enqueuedTicks); + } + + final void enqueueDoAbort(final Consumer> callback, final long enqueuedTicks) { + enqueueRequest(new TransactionAbortRequest(getIdentifier(), nextSequence(), localActor()), callback, + enqueuedTicks); + } + + final void sendDoAbort(final Consumer> callback) { sendRequest(new TransactionAbortRequest(getIdentifier(), nextSequence(), localActor()), callback); } @@ -192,45 +385,71 @@ abstract class AbstractProxyTransaction implements Identifiable directCommit() { + checkReadWrite(); checkSealed(); - final SettableFuture ret = SettableFuture.create(); - sendRequest(Verify.verifyNotNull(commitRequest(false)), t -> { - if (t instanceof TransactionCommitSuccess) { - ret.set(Boolean.TRUE); - } else if (t instanceof RequestFailure) { - ret.setException(((RequestFailure) t).getCause()); - } else { - ret.setException(new IllegalStateException("Unhandled response " + t.getClass())); + // Precludes startReconnect() from interfering with the fast path + synchronized (this) { + if (STATE_UPDATER.compareAndSet(this, SEALED, FLUSHED)) { + final SettableFuture ret = SettableFuture.create(); + sendRequest(Verify.verifyNotNull(commitRequest(false)), t -> { + if (t instanceof TransactionCommitSuccess) { + ret.set(Boolean.TRUE); + } else if (t instanceof RequestFailure) { + ret.setException(((RequestFailure) t).getCause().unwrap()); + } else { + ret.setException(new IllegalStateException("Unhandled response " + t.getClass())); + } + + // This is a terminal request, hence we do not need to record it + LOG.debug("Transaction {} directCommit completed", this); + enqueuePurge(); + }); + + return ret; } + } - // This is a terminal request, hence we do not need to record it - LOG.debug("Transaction {} directCommit completed", this); - parent.completeTransaction(this); - }); - return ret; + // We have had some interference with successor injection, wait for it to complete and defer to the successor. + return awaitSuccessor().directCommit(); } - - void canCommit(final VotingFuture ret) { + final void canCommit(final VotingFuture ret) { + checkReadWrite(); checkSealed(); - final TransactionRequest req = Verify.verifyNotNull(commitRequest(true)); - sendRequest(req, t -> { - if (t instanceof TransactionCanCommitSuccess) { - ret.voteYes(); - } else if (t instanceof RequestFailure) { - ret.voteNo(((RequestFailure) t).getCause()); - } else { - ret.voteNo(new IllegalStateException("Unhandled response " + t.getClass())); + // Precludes startReconnect() from interfering with the fast path + synchronized (this) { + if (STATE_UPDATER.compareAndSet(this, SEALED, FLUSHED)) { + final TransactionRequest req = Verify.verifyNotNull(commitRequest(true)); + + sendRequest(req, t -> { + if (t instanceof TransactionCanCommitSuccess) { + ret.voteYes(); + } else if (t instanceof RequestFailure) { + ret.voteNo(((RequestFailure) t).getCause().unwrap()); + } else { + ret.voteNo(new IllegalStateException("Unhandled response " + t.getClass())); + } + + recordSuccessfulRequest(req); + LOG.debug("Transaction {} canCommit completed", this); + }); + + return; } + } - recordSuccessfulRequest(req); - LOG.debug("Transaction {} canCommit completed", this); - }); + // We have had some interference with successor injection, wait for it to complete and defer to the successor. + awaitSuccessor().canCommit(ret); + } + + private AbstractProxyTransaction awaitSuccessor() { + return getSuccessorState().await(); } - void preCommit(final VotingFuture ret) { + final void preCommit(final VotingFuture ret) { + checkReadWrite(); checkSealed(); final TransactionRequest req = new TransactionPreCommitRequest(getIdentifier(), nextSequence(), @@ -239,47 +458,176 @@ abstract class AbstractProxyTransaction implements Identifiable) t).getCause()); + ret.voteNo(((RequestFailure) t).getCause().unwrap()); } else { ret.voteNo(new IllegalStateException("Unhandled response " + t.getClass())); } - recordSuccessfulRequest(req); - LOG.debug("Transaction {} preCommit completed", this); + onPreCommitComplete(req); }); } - void doCommit(final VotingFuture ret) { + private void onPreCommitComplete(final TransactionRequest req) { + /* + * The backend has agreed that the transaction has entered PRE_COMMIT phase, meaning it will be committed + * to storage after the timeout completes. + * + * All state has been replicated to the backend, hence we do not need to keep it around. Retain only + * the precommit request, so we know which request to use for resync. + */ + LOG.debug("Transaction {} preCommit completed, clearing successfulRequests", this); + successfulRequests.clear(); + + // TODO: this works, but can contain some useless state (like batched operations). Create an empty + // equivalent of this request and store that. + recordSuccessfulRequest(req); + } + + final void doCommit(final VotingFuture ret) { + checkReadWrite(); checkSealed(); sendRequest(new TransactionDoCommitRequest(getIdentifier(), nextSequence(), localActor()), t -> { if (t instanceof TransactionCommitSuccess) { ret.voteYes(); } else if (t instanceof RequestFailure) { - ret.voteNo(((RequestFailure) t).getCause()); + ret.voteNo(((RequestFailure) t).getCause().unwrap()); } else { ret.voteNo(new IllegalStateException("Unhandled response " + t.getClass())); } LOG.debug("Transaction {} doCommit completed", this); - parent.completeTransaction(this); + enqueuePurge(); }); } - final void replaySuccessfulRequests(final AbstractProxyTransaction successor) { - this.successor = Preconditions.checkNotNull(successor); + private void enqueuePurge() { + enqueuePurge(null); + } - for (Object obj : successfulRequests) { - if (obj instanceof TransactionRequest) { - LOG.debug("Forwarding request {} to successor {}", obj, successor); - successor.handleForwardedRemoteRequest((TransactionRequest) obj, null); - } else { - Verify.verify(obj instanceof IncrementSequence); - successor.incrementSequence(((IncrementSequence) obj).getDelta()); + final void enqueuePurge(final Consumer> callback) { + // Purge request are dispatched internally, hence should not wait + enqueuePurge(callback, parent.currentTime()); + } + + final void enqueuePurge(final Consumer> callback, final long enqueuedTicks) { + enqueueRequest(purgeRequest(), resp -> { + LOG.debug("Transaction {} purge completed", this); + parent.completeTransaction(this); + if (callback != null) { + callback.accept(resp); } - } - LOG.debug("{} replayed {} successful requests", getIdentifier(), successfulRequests.size()); + }, enqueuedTicks); + } + + private TransactionPurgeRequest purgeRequest() { successfulRequests.clear(); + return new TransactionPurgeRequest(getIdentifier(), nextSequence(), localActor()); + } + + // 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 enqueuedEntries) { + final SuccessorState local = getSuccessorState(); + local.setSuccessor(successor); + + // Replay successful requests first + if (!successfulRequests.isEmpty()) { + // We need to find a good timestamp to use for successful requests, as we do not want to time them out + // nor create timing inconsistencies in the queue -- requests are expected to be ordered by their enqueue + // time. We will pick the time of the first entry available. If there is none, we will just use current + // time, as all other requests will get enqueued afterwards. + final ConnectionEntry firstInQueue = Iterables.getFirst(enqueuedEntries, null); + final long now = firstInQueue != null ? firstInQueue.getEnqueuedTicks() : parent.currentTime(); + + for (Object obj : successfulRequests) { + if (obj instanceof TransactionRequest) { + LOG.debug("Forwarding successful request {} to successor {}", obj, successor); + successor.replayRequest((TransactionRequest) obj, resp -> { }, now); + } else { + Verify.verify(obj instanceof IncrementSequence); + final IncrementSequence increment = (IncrementSequence) obj; + successor.replayRequest(new IncrementTransactionSequenceRequest(getIdentifier(), + increment.getSequence(), localActor(), isSnapshotOnly(), increment.getDelta()), resp -> { }, + now); + LOG.debug("Incrementing sequence {} to successor {}", obj, successor); + } + } + LOG.debug("{} replayed {} successful requests", getIdentifier(), successfulRequests.size()); + successfulRequests.clear(); + } + + // Now replay whatever is in the connection + final Iterator 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("Replaying queued request {} to successor {}", req, successor); + successor.replayRequest((TransactionRequest) req, e.getCallback(), e.getEnqueuedTicks()); + it.remove(); + } + } + + /* + * 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. + */ + 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.ensureSealed(); + } + } + + /** + * Invoked from {@link #replayMessages(AbstractProxyTransaction, Iterable)} to have successor adopt an in-flight + * request. + * + *

+ * Note: this method is invoked by the predecessor on the successor. + * + * @param request Request which needs to be forwarded + * @param callback Callback to be invoked once the request completes + * @param enqueuedTicks ticker-based time stamp when the request was enqueued + */ + private void replayRequest(final TransactionRequest request, final Consumer> callback, + final long enqueuedTicks) { + if (request instanceof AbstractLocalTransactionRequest) { + handleReplayedLocalRequest((AbstractLocalTransactionRequest) request, callback, enqueuedTicks); + } else { + handleReplayedRemoteRequest(request, callback, enqueuedTicks); + } + } + + // 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() slow paths + local.finish(); } /** @@ -288,12 +636,13 @@ abstract class AbstractProxyTransaction implements Identifiable request, final Consumer> callback) - throws RequestException { - Preconditions.checkState(successor != null, "%s does not have a successor set", this); + final void forwardRequest(final TransactionRequest request, final Consumer> callback) { + forwardToSuccessor(getSuccessorState().getSuccessor(), request, callback); + } + final void forwardToSuccessor(final AbstractProxyTransaction successor, final TransactionRequest request, + final Consumer> callback) { if (successor instanceof LocalProxyTransaction) { forwardToLocal((LocalProxyTransaction)successor, request, callback); } else if (successor instanceof RemoteProxyTransaction) { @@ -303,46 +652,67 @@ abstract class AbstractProxyTransaction implements Identifiable data); + abstract void doMerge(YangInstanceIdentifier path, NormalizedNode data); - abstract void doWrite(final YangInstanceIdentifier path, final NormalizedNode data); + abstract void doWrite(YangInstanceIdentifier path, NormalizedNode data); - abstract CheckedFuture doExists(final YangInstanceIdentifier path); + abstract CheckedFuture doExists(YangInstanceIdentifier path); - abstract CheckedFuture>, ReadFailedException> doRead( - final YangInstanceIdentifier path); + abstract CheckedFuture>, ReadFailedException> doRead(YangInstanceIdentifier path); abstract void doSeal(); - abstract void doAbort(); + @GuardedBy("this") + abstract void flushState(AbstractProxyTransaction successor); + + abstract TransactionRequest abortRequest(); abstract TransactionRequest commitRequest(boolean coordinated); /** - * Invoked from {@link RemoteProxyTransaction} when it replays its successful requests to its successor. There is - * no equivalent of this call from {@link LocalProxyTransaction} because it does not send a request until all - * operations are packaged in the message. + * Replay a request originating in this proxy to a successor remote proxy. + */ + abstract void forwardToRemote(RemoteProxyTransaction successor, TransactionRequest request, + Consumer> callback); + + /** + * Replay a request originating in this proxy to a successor local proxy. + */ + abstract void forwardToLocal(LocalProxyTransaction successor, TransactionRequest request, + Consumer> callback); + + /** + * Invoked from {@link LocalProxyTransaction} when it replays its successful requests to its successor. * *

* Note: this method is invoked by the predecessor on the successor. * * @param request Request which needs to be forwarded * @param callback Callback to be invoked once the request completes + * @param enqueuedTicks Time stamp to use for enqueue time */ - abstract void handleForwardedRemoteRequest(TransactionRequest request, - @Nullable Consumer> callback); + abstract void handleReplayedLocalRequest(AbstractLocalTransactionRequest request, + @Nullable Consumer> callback, long enqueuedTicks); /** - * Replay a request originating in this proxy to a successor remote proxy. + * Invoked from {@link RemoteProxyTransaction} when it replays its successful requests to its successor. + * + *

+ * Note: this method is invoked by the predecessor on the successor. + * + * @param request Request which needs to be forwarded + * @param callback Callback to be invoked once the request completes + * @param enqueuedTicks Time stamp to use for enqueue time */ - abstract void forwardToRemote(RemoteProxyTransaction successor, TransactionRequest request, - Consumer> callback) throws RequestException; + abstract void handleReplayedRemoteRequest(TransactionRequest request, + @Nullable Consumer> callback, long enqueuedTicks); - /** - * Replay a request originating in this proxy to a successor local proxy. - */ - abstract void forwardToLocal(LocalProxyTransaction successor, TransactionRequest request, - Consumer> callback) throws RequestException; + @Override + public final String toString() { + return MoreObjects.toStringHelper(this).add("identifier", getIdentifier()).add("state", state).toString(); + } }