AHeise commented on code in PR #152: URL: https://github.com/apache/flink-connector-kafka/pull/152#discussion_r1957073671
########## flink-connector-kafka/src/main/java/org/apache/flink/connector/kafka/sink/internal/BackchannelFactory.java: ########## @@ -0,0 +1,123 @@ +/* + * 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.connector.kafka.sink.internal; + +import org.apache.flink.annotation.Internal; +import org.apache.flink.api.java.tuple.Tuple3; + +import javax.annotation.concurrent.ThreadSafe; + +import java.util.Map; +import java.util.concurrent.ConcurrentHashMap; +import java.util.function.Function; + +/** + * Creates and manages backchannels for the Kafka sink. The backchannels are used to communicate + * between the Kafka committer and writer. + * + * <p>Each backchannel is uniquely identified by the subtask id, attempt number, and transactional + * id prefix. The subtask id prevents concurrent subtasks of the same sink from conflicting. The + * attempt number prevents conflicts for task-local recovery. The transactional id prefix prevents + * conflicts between multiple Kafka sinks. + */ +@Internal +@ThreadSafe +public class BackchannelFactory { + private static final BackchannelFactory INSTANCE = new BackchannelFactory(); + + /** Gets the singleton instance of the {@link BackchannelFactory}. */ + public static BackchannelFactory getInstance() { + return INSTANCE; + } + + private BackchannelFactory() {} + + /** + * The map of backchannels, keyed by the subtask id and transactional id prefix to uniquely + * identify the backchannel while establishing the connection. + */ + private final Map<Tuple3<Integer, Integer, String>, BackchannelImpl<?>> backchannels = + new ConcurrentHashMap<>(); + + /** + * Gets a {@link ReadableBackchannel} for the given subtask, attempt, and transactional id + * prefix. + * + * <p>If this method is called twice with the same arguments, it will throw an exception as it + * indicates that the transactional id prefix is being reused for multiple Kafka sinks. + * + * <p>If the corresponding {@link #getWritableBackchannel(int, int, String)} is called, the + * {@link ReadableBackchannel#isEstablished()} will return true. + */ + @SuppressWarnings("unchecked") + public <T> ReadableBackchannel<T> getReadableBackchannel( + int subtaskId, int attemptNumber, String transactionalIdPrefix) { + return (ReadableBackchannel<T>) + getBackchannel( + subtaskId, + attemptNumber, Review Comment: Yes, but I'm now convinced that it's needed for all fail-over scenarios where the TM isn't restarted. That should be rather common and necessarily result in conflicts without the attempt number. -- 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. To unsubscribe, e-mail: issues-unsubscr...@flink.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
