becketqin commented on a change in pull request #6594: [FLINK-9311] [pubsub] Added PubSub source connector with support for checkpointing (ATLEAST_ONCE) URL: https://github.com/apache/flink/pull/6594#discussion_r264638629
########## File path: flink-connectors/flink-connector-gcp-pubsub/src/main/java/org/apache/flink/streaming/connectors/gcp/pubsub/PubSubSource.java ########## @@ -0,0 +1,296 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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 org.apache.flink.streaming.connectors.gcp.pubsub; + +import org.apache.flink.api.common.functions.RuntimeContext; +import org.apache.flink.api.common.functions.StoppableFunction; +import org.apache.flink.api.common.serialization.DeserializationSchema; +import org.apache.flink.api.common.typeinfo.TypeInformation; +import org.apache.flink.api.java.typeutils.ResultTypeQueryable; +import org.apache.flink.configuration.Configuration; +import org.apache.flink.streaming.api.functions.source.MultipleIdsMessageAcknowledgingSourceBase; +import org.apache.flink.streaming.api.functions.source.ParallelSourceFunction; +import org.apache.flink.streaming.api.operators.StreamingRuntimeContext; +import org.apache.flink.streaming.connectors.gcp.pubsub.common.PubSubSubscriberFactory; +import org.apache.flink.util.Preconditions; + +import com.google.api.core.ApiFuture; +import com.google.auth.Credentials; +import com.google.cloud.pubsub.v1.Subscriber; +import com.google.cloud.pubsub.v1.stub.SubscriberStub; +import com.google.pubsub.v1.AcknowledgeRequest; +import com.google.pubsub.v1.ProjectSubscriptionName; +import com.google.pubsub.v1.PubsubMessage; +import com.google.pubsub.v1.PullRequest; +import com.google.pubsub.v1.PullResponse; +import com.google.pubsub.v1.ReceivedMessage; +import io.grpc.netty.shaded.io.netty.channel.EventLoopGroup; +import io.grpc.netty.shaded.io.netty.channel.nio.NioEventLoopGroup; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.io.IOException; +import java.util.List; +import java.util.concurrent.CancellationException; +import java.util.concurrent.TimeUnit; + +import static com.google.cloud.pubsub.v1.SubscriptionAdminSettings.defaultCredentialsProviderBuilder; + +/** + * PubSub Source, this Source will consume PubSub messages from a subscription and Acknowledge them on the next checkpoint. + * This ensures every message will get acknowledged at least once. + */ +public class PubSubSource<OUT> extends MultipleIdsMessageAcknowledgingSourceBase<OUT, String, String> + implements ResultTypeQueryable<OUT>, ParallelSourceFunction<OUT>, StoppableFunction { + private static final Logger LOG = LoggerFactory.getLogger(PubSubSource.class); + protected final DeserializationSchema<OUT> deserializationSchema; + protected final PubSubSubscriberFactory pubSubSubscriberFactory; + protected final Credentials credentials; + protected final String projectSubscriptionName; + protected final int maxMessagesPerPull; + + protected transient boolean deduplicateMessages; + protected transient SubscriberStub subscriber; + protected transient PullRequest pullRequest; + protected transient EventLoopGroup eventLoopGroup; + + protected transient volatile boolean isRunning; + protected transient volatile ApiFuture<PullResponse> messagesFuture; + + PubSubSource(DeserializationSchema<OUT> deserializationSchema, PubSubSubscriberFactory pubSubSubscriberFactory, Credentials credentials, String projectSubscriptionName, int maxMessagesPerPull) { + super(String.class); + this.deserializationSchema = deserializationSchema; + this.pubSubSubscriberFactory = pubSubSubscriberFactory; + this.credentials = credentials; + this.projectSubscriptionName = projectSubscriptionName; + this.maxMessagesPerPull = maxMessagesPerPull; + } + + @Override + public void open(Configuration configuration) throws Exception { + super.open(configuration); + if (hasNoCheckpointingEnabled(getRuntimeContext())) { + throw new IllegalArgumentException("The PubSubSource REQUIRES Checkpointing to be enabled and " + + "the checkpointing frequency must be MUCH lower than the PubSub timeout for it to retry a message."); + } + + getRuntimeContext().getMetricGroup().gauge("PubSubMessagesProcessedNotAcked", this::getOutstandingMessagesToAck); + + this.eventLoopGroup = new NioEventLoopGroup(); + this.subscriber = pubSubSubscriberFactory.getSubscriber(eventLoopGroup, credentials); + this.deduplicateMessages = getRuntimeContext().getNumberOfParallelSubtasks() == 1; + this.isRunning = true; + this.pullRequest = PullRequest.newBuilder() + .setMaxMessages(100) + .setReturnImmediately(false) + .setSubscription(projectSubscriptionName) + .build(); + } + + private boolean hasNoCheckpointingEnabled(RuntimeContext runtimeContext) { + return !(runtimeContext instanceof StreamingRuntimeContext && ((StreamingRuntimeContext) runtimeContext).isCheckpointingEnabled()); + } + + @Override + protected void acknowledgeSessionIDs(List<String> acknowledgementIds) { + if (acknowledgementIds.isEmpty() || !isRunning) { + return; + } + + AcknowledgeRequest acknowledgeRequest = + AcknowledgeRequest.newBuilder() + .setSubscription(projectSubscriptionName) + .addAllAckIds(acknowledgementIds) + .build(); + subscriber.acknowledgeCallable().call(acknowledgeRequest); + } + + @Override + public void run(SourceContext<OUT> sourceContext) throws Exception { + while (isRunning) { + messagesFuture = subscriber.pullCallable().futureCall(pullRequest); + try { + processMessage(sourceContext, messagesFuture.get().getReceivedMessagesList()); + } catch (InterruptedException | CancellationException e) { + awaitSubscriberTermination(); + return; + } + } + + awaitSubscriberTermination(); + } + + void processMessage(SourceContext<OUT> sourceContext, List<ReceivedMessage> messages) throws IOException { + synchronized (sourceContext.getCheckpointLock()) { + for (ReceivedMessage message : messages) { + sessionIds.add(message.getAckId()); + + PubsubMessage pubsubMessage = message.getMessage(); + if (deduplicateMessages && !addId(pubsubMessage.getMessageId())) { + // message is duplicate so just ignore it + return; + } + + OUT deserializedMessage = deserializeMessage(pubsubMessage); + if (deserializationSchema.isEndOfStream(deserializedMessage)) { + stop(); + return; + } + + sourceContext.collect(deserializedMessage); + } + + } + } + + private Integer getOutstandingMessagesToAck() { + return this.sessionIdsPerSnapshot + .stream() + .mapToInt(tuple -> tuple.f1.size()) + .sum() + this.sessionIds.size(); + } + + @Override + public void cancel() { + stop(); + } + + @Override + public void stop() { Review comment: Even the classes used in here are all thread safe, the thread safety is still a problem here. For example, `messageFuture` variable is assigned different instances all the time. If `messagesFuture.cancel()` is invoked on one instance, while the main thread is calling `get()` on another instance, the main thread may block on the future for long. As a result the Source task will not exit in time. Also, since the semantic of `stop` method is to stop gracefully. Usually we don't want the thread calling stop to execute the shutdown routine. This may complicate things. For example, what is the behavior of `subscriber.pullCallable().futureCall()` when the underlying `eventLoopGroup` has shutdown? Will it throw exception? If so, that exception is not caught in the current code and will cause the task to fail. So a simpler and usually safer way to do the shutdown is to just set a flag and ensure the main thread knows it is being shutting down (e.g. via interrupting). The main thread will then execute the shutdown routine by itself to do the cleanup. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
