jolshan commented on code in PR #13795: URL: https://github.com/apache/kafka/pull/13795#discussion_r1218533754
########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/runtime/CoordinatorRuntime.java: ########## @@ -0,0 +1,1009 @@ +/* + * 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.kafka.coordinator.group.runtime; + +import org.apache.kafka.common.KafkaException; +import org.apache.kafka.common.TopicPartition; +import org.apache.kafka.common.errors.CoordinatorLoadInProgressException; +import org.apache.kafka.common.errors.NotCoordinatorException; +import org.apache.kafka.common.protocol.Errors; +import org.apache.kafka.common.utils.LogContext; +import org.apache.kafka.deferred.DeferredEvent; +import org.apache.kafka.deferred.DeferredEventQueue; +import org.apache.kafka.timeline.SnapshotRegistry; +import org.slf4j.Logger; + +import java.util.HashSet; +import java.util.OptionalLong; +import java.util.Set; +import java.util.concurrent.CompletableFuture; +import java.util.concurrent.ConcurrentHashMap; + +/** + * The CoordinatorRuntime provides a framework to implement coordinators such as the group coordinator + * or the transaction coordinator. + * + * The runtime framework maps each underlying partitions (e.g. __consumer_offsets) that that broker is a + * leader of to a coordinator replicated state machine. A replicated state machine holds the hard and soft + * state of all the objects (e.g. groups or offsets) assigned to the partition. The hard state is stored in + * timeline datastructures backed by a SnapshotRegistry. The runtime supports two type of operations + * on state machines: (1) Writes and (2) Reads. + * + * (1) A write operation, aka a request, can read the full and potentially **uncommitted** state from state + * machine to handle the operation. A write operation typically generates a response and a list of + * records. The records are applies to the state machine and persisted to the partition. The response + * is parked until the records are committed and delivered when they are. + * + * (2) A read operation, aka a request, can only read the committed state from the state machine to handle + * the operation. A read operation typically generates a response that is immediately completed. + * + * The runtime framework exposes an asynchronous, future based, API to the world. All the operations + * are executed by an CoordinatorEventProcessor. The processor guarantees that operations for a + * single partition or state machine are not processed concurrently. + * + * @param <S> The type of the state machine. + * @param <U> The type of the record. + */ +public class CoordinatorRuntime<S extends Coordinator<U>, U> { + + /** + * Builder to create a CoordinatorRuntime. + * + * @param <S> The type of the state machine. + * @param <U> The type of the record. + */ + public static class Builder<S extends Coordinator<U>, U> { + private LogContext logContext; + private CoordinatorEventProcessor eventProcessor; + private PartitionWriter<U> partitionWriter; + private CoordinatorLoader<U> loader; + private CoordinatorBuilderSupplier<S, U> coordinatorBuilderSupplier; + + public Builder<S, U> withLogContext(LogContext logContext) { + this.logContext = logContext; + return this; + } + + public Builder<S, U> withEventProcessor(CoordinatorEventProcessor eventProcessor) { + this.eventProcessor = eventProcessor; + return this; + } + + public Builder<S, U> withPartitionWriter(PartitionWriter<U> partitionWriter) { + this.partitionWriter = partitionWriter; + return this; + } + + public Builder<S, U> withLoader(CoordinatorLoader<U> loader) { + this.loader = loader; + return this; + } + + public Builder<S, U> withCoordinatorStateMachineSupplier(CoordinatorBuilderSupplier<S, U> coordinatorBuilderSupplier) { + this.coordinatorBuilderSupplier = coordinatorBuilderSupplier; + return this; + } + + public CoordinatorRuntime<S, U> build() { + if (logContext == null) + logContext = new LogContext(); + if (eventProcessor == null) + throw new IllegalArgumentException("Event processor must be set."); + if (partitionWriter == null) + throw new IllegalArgumentException("Partition write must be set."); + if (loader == null) + throw new IllegalArgumentException("Loader must be set."); + if (coordinatorBuilderSupplier == null) + throw new IllegalArgumentException("State machine supplier must be set."); + + return new CoordinatorRuntime<>( + logContext, + eventProcessor, + partitionWriter, + loader, + coordinatorBuilderSupplier + ); + } + } + + /** + * The various state that a coordinator for a partition can be in. + */ + enum CoordinatorState { + /** + * Initial state when a coordinator is created. + */ + INITIAL { + @Override + boolean canTransitionFrom(CoordinatorState state) { + return false; + } + }, + + /** + * The coordinator is being loaded. + */ + LOADING { + @Override + boolean canTransitionFrom(CoordinatorState state) { + return state == INITIAL || state == CLOSED || state == FAILED; Review Comment: so we can go from closed/failed back to loading? -- This is an automated message from the Apache Git Service. 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