dajac commented on code in PR #13795: URL: https://github.com/apache/kafka/pull/13795#discussion_r1217658963
########## group-coordinator/src/main/java/org/apache/kafka/coordinator/group/runtime/CoordinatorRuntime.java: ########## @@ -0,0 +1,959 @@ +/* + * 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 expose 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. + */ +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, + + /** + * The coordinator is being loaded. + */ + LOADING, + + /** + * The coordinator is active and can service requests. + */ + ACTIVE, + + /** + * The coordinator is closed. + */ + CLOSED, + + /** + * The coordinator has failed. + */ + FAILED + } + + /** + * CoordinatorContext holds all the metadata around a coordinator state machine. + */ + class CoordinatorContext { + /** + * The topic partition backing the coordinator. + */ + final TopicPartition tp; + + /** + * The snapshot registry backing the coordinator. + */ + final SnapshotRegistry snapshotRegistry; + + /** + * The deferred event queue used to park events waiting + * on records to be committed. + */ + final DeferredEventQueue deferredEventQueue; + + /** + * The current state. + */ + volatile CoordinatorState state; + + /** + * The actual state machine. + */ + volatile S coordinator; + + /** + * The current epoch of the coordinator. This represents + * the epoch of the partition leader. + */ + volatile int epoch; + + /** + * The last offset written to the partition. + */ + volatile long lastWrittenOffset; + + /** + * The last offset committed. This represents the high + * watermark of the partition. + */ + volatile long lastCommittedOffset; + + /** + * Constructor. + * + * @param tp The topic partition of the coordinator. + */ + private CoordinatorContext( + TopicPartition tp + ) { + this.tp = tp; + this.snapshotRegistry = new SnapshotRegistry(logContext); + this.deferredEventQueue = new DeferredEventQueue(logContext); + this.state = CoordinatorState.INITIAL; + this.epoch = -1; + this.lastWrittenOffset = 0L; + this.lastCommittedOffset = 0L; + } + + /** + * Updates the last written offset. This also create a new snapshot + * in the snapshot registry. + * + * @param offset The new last written offset. + */ + private void updateLastWrittenOffset( + long offset + ) { + if (offset <= lastWrittenOffset) { + throw new IllegalStateException("New committed offset " + offset + " of " + tp + + " must be larger than " + lastWrittenOffset + "."); + } + + log.debug("Update last written offset of {} to {}.", tp, offset); + lastWrittenOffset = offset; + snapshotRegistry.getOrCreateSnapshot(offset); + } + + /** + * Reverts the last written offset. This also reverts the snapshot + * registry to this offset. All the changes applied after the offset + * are lost. + * + * @param offset The offset to revert to. + */ + private void revertLastWrittenOffset( + long offset + ) { + log.debug("Revert last written offset of {} to {}.", tp, offset); + lastWrittenOffset = offset; + snapshotRegistry.revertToSnapshot(offset); + } + + /** + * Updates the last committed offset. This completes all the deferred + * events waiting on this offset. This also cleanups all the snapshots + * prior to this offset. + * + * @param offset The new last committed offset. + */ + private void updateLastCommittedOffset( + long offset + ) { + if (offset <= lastCommittedOffset) { + throw new IllegalStateException("New committed offset " + offset + " of " + tp + + " must be larger than " + lastCommittedOffset + "."); + } + + log.debug("Update committed offset of {} to {}.", tp, offset); + lastCommittedOffset = offset; + deferredEventQueue.completeUpTo(offset); + snapshotRegistry.deleteSnapshotsUpTo(offset); + } + + /** + * Closes this coordinator. All the deferred events are failed + * with a NOT_COORDINATOR error. + */ + private void close() { + log.debug("Closing coordinator for " + tp + "."); + state = CoordinatorState.CLOSED; + deferredEventQueue.failAll(Errors.NOT_COORDINATOR.exception()); + coordinator.onUnloaded(); + log.debug("Coordinator for " + tp + " closed."); + } + } + + /** + * A coordinator write operation. + * + * @param <S> The type of the coordinator state machine. + * @param <T> The type of the response. + * @param <U> The type of the records. + */ + interface CoordinatorWriteOperation<S, T, U> { + /** + * Generates the records needed to implement this coordinator write operation. In general, + * this operation should not modify the hard state of the coordinator. That modifications + * will happen later on, when the records generated by this function are applied to the + * coordinator. + * + * @param state The coordinator state machine. + * @return A result containing a list of records and the RPC result. + * @throws KafkaException + */ + CoordinatorResult<T, U> generateRecordsAndResult(S state) throws KafkaException; Review Comment: I think that I will use `coordinator` to stay consistent with the rest of the class. -- 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: jira-unsubscr...@kafka.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
