Github user tillrohrmann commented on a diff in the pull request: https://github.com/apache/flink/pull/1954#discussion_r70094658 --- Diff: flink-runtime/src/main/java/org/apache/flink/runtime/util/FixedSizeFifoQueue.java --- @@ -0,0 +1,55 @@ +/* + * 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.runtime.util; + +import java.util.concurrent.ArrayBlockingQueue; + +/** + * Adding element to full queue removes its head and then adds new element. It's why size of this queue is fixed. + * Example: + * <pre> + * {@code + * Queue q = new FixedSizeFifoQueue<Long>(2); + * q.add(1); // q = [1] + * q.add(2); // q = [1, 2] + * q.add(3); // q = [2, 3] + * q.peek(); // 2 + * } + * </pre> + */ +public class FixedSizeFifoQueue<E> extends ArrayBlockingQueue<E> { --- End diff -- I think it's not so efficient to use a `ArrayBlockingQueue` as the basis for the implementation because we don't need protection against concurrency. I think it would be great if we could use `ArrayDeque` instead.
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