[GitHub] [kafka] jolshan commented on a diff in pull request #13505: KAFKA-14462; [5/N] Add EventAccumulator

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

jolshan commented on code in PR #13505:
URL: https://github.com/apache/kafka/pull/13505#discussion_r1163201442


##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/runtime/EventAccumulator.java:
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@@ -0,0 +1,256 @@
+/*
+ * 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 java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.Queue;
+import java.util.Random;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * A concurrent event accumulator which group events per key and ensure that only one
+ * event with a given key can't be processed concurrently.
+ *
+ * This class is threadsafe.
+ *
+ * @param <K> The type of the key of the event.
+ * @param <T> The type of the event itself. It implements the {{@link Event}} interface.
+ *
+ * There are a few examples about how to use it in the unit tests.
+ */
+public class EventAccumulator<K, T extends EventAccumulator.Event<K>> implements AutoCloseable {
+
+    /**
+     * The interface which must be implemented by all events.
+     *
+     * @param <K> The type of the key of the event.
+     */
+    public interface Event<K> {
+        K key();
+    }
+
+    /**
+     * The random generator used by this class.
+     */
+    private final Random random;
+
+    /**
+     * The map of queues keyed by K.
+     */
+    private final Map<K, Queue<T>> queues;
+
+    /**
+     * The list of available keys. Keys in this list can
+     * be delivered to pollers.
+     */
+    private final List<K> availableKeys;
+
+    /**
+     * The set of keys that are being processed.
+     */
+    private final Set<K> inflightKeys;
+
+    /**
+     * The lock for protecting access to the resources.
+     */
+    private final ReentrantLock lock;
+
+    /**
+     * The condition variable for waking up poller threads.
+     */
+    private final Condition condition;
+
+    /**
+     * The number of events in the queue.
+     */
+    private int size;
+
+    /**
+     * A boolean indicated whether the queue is closed.

Review Comment:
   This is for the whole accumulator right? Not an individual queue? There's a few other instances of queue used both for size and for closed throughout the comments.



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