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/*
* Copyright 2016 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.cloud.pubsub.v1;
import com.google.api.core.ApiClock;
import com.google.api.core.ApiFutureCallback;
import com.google.api.core.ApiFutures;
import com.google.api.core.InternalApi;
import com.google.api.core.SettableApiFuture;
import com.google.api.gax.batching.FlowController;
import com.google.api.gax.batching.FlowController.FlowControlException;
import com.google.api.gax.core.Distribution;
import com.google.common.primitives.Ints;
import com.google.common.util.concurrent.MoreExecutors;
import com.google.pubsub.v1.PubsubMessage;
import com.google.pubsub.v1.ReceivedMessage;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.Executor;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.logging.Level;
import java.util.logging.Logger;
import org.threeten.bp.Duration;
import org.threeten.bp.Instant;
import org.threeten.bp.temporal.ChronoUnit;
/**
* Dispatches messages to a message receiver while handling the messages acking and lease
* extensions.
*/
class MessageDispatcher {
private static final Logger logger = Logger.getLogger(MessageDispatcher.class.getName());
private static final double PERCENTILE_FOR_ACK_DEADLINE_UPDATES = 99.9;
@InternalApi static final Duration PENDING_ACKS_SEND_DELAY = Duration.ofMillis(100);
private final Executor executor;
private final ScheduledExecutorService systemExecutor;
private final ApiClock clock;
private final Duration ackExpirationPadding;
private final Duration maxAckExtensionPeriod;
private final MessageReceiver receiver;
private final AckProcessor ackProcessor;
private final FlowController flowController;
private final MessageWaiter messagesWaiter;
// Maps ID to "total expiration time". If it takes longer than this, stop extending.
private final ConcurrentMap pendingMessages = new ConcurrentHashMap<>();
private final LinkedBlockingQueue pendingAcks = new LinkedBlockingQueue<>();
private final LinkedBlockingQueue pendingNacks = new LinkedBlockingQueue<>();
private final LinkedBlockingQueue pendingReceipts = new LinkedBlockingQueue<>();
// The deadline should be set before use. Here, set it to something unreasonable,
// so we fail loudly if we mess up.
private final AtomicInteger messageDeadlineSeconds = new AtomicInteger(60);
private final AtomicBoolean extendDeadline = new AtomicBoolean(true);
private final Lock jobLock;
private ScheduledFuture backgroundJob;
// To keep track of number of seconds the receiver takes to process messages.
private final Distribution ackLatencyDistribution;
/** Stores the data needed to asynchronously modify acknowledgement deadlines. */
static class PendingModifyAckDeadline {
final List ackIds;
final int deadlineExtensionSeconds;
PendingModifyAckDeadline(int deadlineExtensionSeconds, String... ackIds) {
this(deadlineExtensionSeconds, Arrays.asList(ackIds));
}
private PendingModifyAckDeadline(int deadlineExtensionSeconds, Collection ackIds) {
this.ackIds = new ArrayList(ackIds);
this.deadlineExtensionSeconds = deadlineExtensionSeconds;
}
@Override
public String toString() {
return String.format(
"PendingModifyAckDeadline{extension: %d sec, ackIds: %s}",
deadlineExtensionSeconds, ackIds);
}
}
/** Internal representation of a reply to a Pubsub message, to be sent back to the service. */
public enum AckReply {
ACK,
NACK
}
/** Handles callbacks for acking/nacking messages from the {@link MessageReceiver}. */
private class AckHandler implements ApiFutureCallback {
private final String ackId;
private final int outstandingBytes;
private final long receivedTimeMillis;
private final Instant totalExpiration;
private AckHandler(String ackId, int outstandingBytes, Instant totalExpiration) {
this.ackId = ackId;
this.outstandingBytes = outstandingBytes;
this.receivedTimeMillis = clock.millisTime();
this.totalExpiration = totalExpiration;
}
/** Stop extending deadlines for this message and free flow control. */
private void forget() {
if (pendingMessages.remove(ackId) == null) {
/*
* We're forgetting the message for the second time. Probably because we ran out of total
* expiration, forget the message, then the user finishes working on the message, and forget
* again. Turn the second forget into a no-op so we don't free twice.
*/
return;
}
flowController.release(1, outstandingBytes);
messagesWaiter.incrementPendingMessages(-1);
}
@Override
public void onFailure(Throwable t) {
logger.log(
Level.WARNING,
"MessageReceiver failed to processes ack ID: " + ackId + ", the message will be nacked.",
t);
pendingNacks.add(ackId);
forget();
}
@Override
public void onSuccess(AckReply reply) {
LinkedBlockingQueue destination;
switch (reply) {
case ACK:
destination = pendingAcks;
// Record the latency rounded to the next closest integer.
ackLatencyDistribution.record(
Ints.saturatedCast(
(long) Math.ceil((clock.millisTime() - receivedTimeMillis) / 1000D)));
break;
case NACK:
destination = pendingNacks;
break;
default:
throw new IllegalArgumentException(String.format("AckReply: %s not supported", reply));
}
destination.add(ackId);
forget();
}
}
interface AckProcessor {
void sendAckOperations(
List acksToSend, List ackDeadlineExtensions);
}
MessageDispatcher(
MessageReceiver receiver,
AckProcessor ackProcessor,
Duration ackExpirationPadding,
Duration maxAckExtensionPeriod,
Distribution ackLatencyDistribution,
FlowController flowController,
Executor executor,
ScheduledExecutorService systemExecutor,
ApiClock clock) {
this.executor = executor;
this.systemExecutor = systemExecutor;
this.ackExpirationPadding = ackExpirationPadding;
this.maxAckExtensionPeriod = maxAckExtensionPeriod;
this.receiver = receiver;
this.ackProcessor = ackProcessor;
this.flowController = flowController;
// 601 buckets of 1s resolution from 0s to MAX_ACK_DEADLINE_SECONDS
this.ackLatencyDistribution = ackLatencyDistribution;
jobLock = new ReentrantLock();
messagesWaiter = new MessageWaiter();
this.clock = clock;
}
void start() {
final Runnable setExtendDeadline =
new Runnable() {
@Override
public void run() {
extendDeadline.set(true);
}
};
jobLock.lock();
try {
// Do not adjust deadline concurrently with extendDeadline or processOutstandingAckOperations.
// The following sequence can happen:
// 0. Initially, deadline = 1 min
// 1. Thread A (TA) wants to send receipts, reads deadline = 1m, but stalls before actually
// sending request
// 2. Thread B (TB) adjusts deadline to 2m
// 3. TB calls extendDeadline, modack all messages to 2m, schedules next extension in 2m
// 4. TA sends request, modacking messages to 1m.
// Then messages will expire too early.
// This can be resolved by adding locks in the right places, but at that point,
// we might as well do things sequentially.
backgroundJob =
systemExecutor.scheduleWithFixedDelay(
new Runnable() {
@Override
public void run() {
try {
if (extendDeadline.getAndSet(false)) {
int newDeadlineSec = computeDeadlineSeconds();
messageDeadlineSeconds.set(newDeadlineSec);
extendDeadlines();
// Don't bother cancelling this when we stop. It'd just set an atomic boolean.
systemExecutor.schedule(
setExtendDeadline,
newDeadlineSec - ackExpirationPadding.getSeconds(),
TimeUnit.SECONDS);
}
processOutstandingAckOperations();
} catch (Throwable t) {
// Catch everything so that one run failing doesn't prevent subsequent runs.
logger.log(Level.WARNING, "failed to run periodic job", t);
}
}
},
PENDING_ACKS_SEND_DELAY.toMillis(),
PENDING_ACKS_SEND_DELAY.toMillis(),
TimeUnit.MILLISECONDS);
} finally {
jobLock.unlock();
}
}
void stop() {
messagesWaiter.waitNoMessages();
jobLock.lock();
try {
if (backgroundJob != null) {
backgroundJob.cancel(false);
backgroundJob = null;
}
} finally {
jobLock.unlock();
}
processOutstandingAckOperations();
}
@InternalApi
void setMessageDeadlineSeconds(int sec) {
messageDeadlineSeconds.set(sec);
}
@InternalApi
int getMessageDeadlineSeconds() {
return messageDeadlineSeconds.get();
}
private static class OutstandingMessage {
private final ReceivedMessage receivedMessage;
private final AckHandler ackHandler;
private OutstandingMessage(ReceivedMessage receivedMessage, AckHandler ackHandler) {
this.receivedMessage = receivedMessage;
this.ackHandler = ackHandler;
}
}
void processReceivedMessages(List messages) {
Instant totalExpiration = now().plus(maxAckExtensionPeriod);
List outstandingBatch = new ArrayList<>(messages.size());
for (ReceivedMessage message : messages) {
AckHandler ackHandler =
new AckHandler(
message.getAckId(), message.getMessage().getSerializedSize(), totalExpiration);
if (pendingMessages.putIfAbsent(message.getAckId(), ackHandler) != null) {
// putIfAbsent puts ackHandler if ackID isn't previously mapped, then return the
// previously-mapped element.
// If the previous element is not null, we already have the message and the new one is
// definitely a duplicate.
// Don't nack this, because that'd also nack the one we already have in queue.
// Don't update the existing one's total expiration either. If the user "loses" the message,
// we want to eventually
// totally expire so that pubsub service sends us the message again.
continue;
}
outstandingBatch.add(new OutstandingMessage(message, ackHandler));
pendingReceipts.add(message.getAckId());
}
processBatch(outstandingBatch);
}
private void processBatch(List batch) {
messagesWaiter.incrementPendingMessages(batch.size());
for (OutstandingMessage message : batch) {
// This is a blocking flow controller. We have already incremented MessageWaiter, so
// shutdown will block on processing of all these messages anyway.
try {
flowController.reserve(1, message.receivedMessage.getMessage().getSerializedSize());
} catch (FlowControlException unexpectedException) {
// This should be a blocking flow controller and never throw an exception.
throw new IllegalStateException("Flow control unexpected exception", unexpectedException);
}
processOutstandingMessage(message.receivedMessage.getMessage(), message.ackHandler);
}
}
private void processOutstandingMessage(final PubsubMessage message, final AckHandler ackHandler) {
final SettableApiFuture response = SettableApiFuture.create();
final AckReplyConsumer consumer =
new AckReplyConsumer() {
@Override
public void ack() {
response.set(AckReply.ACK);
}
@Override
public void nack() {
response.set(AckReply.NACK);
}
};
ApiFutures.addCallback(response, ackHandler, MoreExecutors.directExecutor());
executor.execute(
new Runnable() {
@Override
public void run() {
try {
if (ackHandler
.totalExpiration
.plusSeconds(messageDeadlineSeconds.get())
.isBefore(now())) {
// Message expired while waiting. We don't extend these messages anymore,
// so it was probably sent to someone else. Don't work on it.
// Don't nack it either, because we'd be nacking someone else's message.
ackHandler.forget();
return;
}
receiver.receiveMessage(message, consumer);
} catch (Exception e) {
response.setException(e);
}
}
});
}
/** Compute the ideal deadline, set subsequent modacks to this deadline, and return it. */
@InternalApi
int computeDeadlineSeconds() {
int sec = ackLatencyDistribution.getPercentile(PERCENTILE_FOR_ACK_DEADLINE_UPDATES);
// Use Ints.constrainToRange when we get guava 21.
if (sec < Subscriber.MIN_ACK_DEADLINE_SECONDS) {
sec = Subscriber.MIN_ACK_DEADLINE_SECONDS;
} else if (sec > Subscriber.MAX_ACK_DEADLINE_SECONDS) {
sec = Subscriber.MAX_ACK_DEADLINE_SECONDS;
}
return sec;
}
@InternalApi
void extendDeadlines() {
int extendSeconds = getMessageDeadlineSeconds();
List modacks = new ArrayList<>();
PendingModifyAckDeadline modack = new PendingModifyAckDeadline(extendSeconds);
Instant now = now();
Instant extendTo = now.plusSeconds(extendSeconds);
for (Map.Entry entry : pendingMessages.entrySet()) {
String ackId = entry.getKey();
Instant totalExpiration = entry.getValue().totalExpiration;
if (totalExpiration.isAfter(extendTo)) {
modack.ackIds.add(ackId);
continue;
}
// forget removes from pendingMessages; this is OK, concurrent maps can
// handle concurrent iterations and modifications.
entry.getValue().forget();
if (totalExpiration.isAfter(now)) {
int sec = Math.max(1, (int) now.until(totalExpiration, ChronoUnit.SECONDS));
modacks.add(new PendingModifyAckDeadline(sec, ackId));
}
}
logger.log(Level.FINER, "Sending {0} modacks", modack.ackIds.size() + modacks.size());
modacks.add(modack);
List acksToSend = Collections.emptyList();
ackProcessor.sendAckOperations(acksToSend, modacks);
}
@InternalApi
void processOutstandingAckOperations() {
List modifyAckDeadlinesToSend = new ArrayList<>();
List acksToSend = new ArrayList<>();
pendingAcks.drainTo(acksToSend);
logger.log(Level.FINER, "Sending {0} acks", acksToSend.size());
PendingModifyAckDeadline nacksToSend = new PendingModifyAckDeadline(0);
pendingNacks.drainTo(nacksToSend.ackIds);
logger.log(Level.FINER, "Sending {0} nacks", nacksToSend.ackIds.size());
if (!nacksToSend.ackIds.isEmpty()) {
modifyAckDeadlinesToSend.add(nacksToSend);
}
PendingModifyAckDeadline receiptsToSend =
new PendingModifyAckDeadline(getMessageDeadlineSeconds());
pendingReceipts.drainTo(receiptsToSend.ackIds);
logger.log(Level.FINER, "Sending {0} receipts", receiptsToSend.ackIds.size());
if (!receiptsToSend.ackIds.isEmpty()) {
modifyAckDeadlinesToSend.add(receiptsToSend);
}
ackProcessor.sendAckOperations(acksToSend, modifyAckDeadlinesToSend);
}
private Instant now() {
return Instant.ofEpochMilli(clock.millisTime());
}
}
