[GitHub] [kafka] jolshan commented on a diff in pull request #13795: KAFKA-14462; [17/N] Add CoordinatorRuntime

["jolshan (via GitHub)" <gi...@apache.org>]

jolshan commented on code in PR #13795:
URL: https://github.com/apache/kafka/pull/13795#discussion_r1214835504


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group-coordinator/src/main/java/org/apache/kafka/coordinator/group/runtime/CoordinatorRuntime.java:
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@@ -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

Review Comment:
   nit: exposes



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