Github user tillrohrmann commented on a diff in the pull request:
https://github.com/apache/flink/pull/2837#discussion_r88886636
--- Diff:
flink-runtime/src/main/java/org/apache/flink/runtime/util/EvictingBoundedList.java
---
@@ -0,0 +1,139 @@
+/*
+ * 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 org.apache.flink.util.Preconditions;
+
+import java.util.ConcurrentModificationException;
+import java.util.Iterator;
+
+/**
+ * This class implements a list (array based) that is physically bounded
in maximum size, but can virtually grow beyond
+ * the bounded size. When the list grows beyond the size bound, elements
are dropped from the head of the list (FIFO
+ * order). If dropped elements are accessed, a default element is returned
instead.
+ * <p>
+ * TODO this class could eventually implement the whole actual List
interface.
+ *
+ * @param <T> type of the list elements
+ */
+public class EvictingBoundedList<T> implements Iterable<T> {
+
+ private final T defaultElement;
+ private final Object[] elements;
+ private int idx;
+ private int count;
+ private long modCount;
+
+ public EvictingBoundedList(int sizeLimit) {
+ this(sizeLimit, null);
+ }
+
+ public EvictingBoundedList(int sizeLimit, T defaultElement) {
+ this.elements = new Object[sizeLimit];
+ this.defaultElement = defaultElement;
+ this.idx = 0;
+ this.count = 0;
+ this.modCount = 0;
+ }
+
+ public int size() {
+ return count;
+ }
+
+ public boolean isEmpty() {
+ return 0 == count;
+ }
+
+ public boolean add(T t) {
+ elements[idx] = t;
+ idx = (idx + 1) % elements.length;
+ ++count;
+ ++modCount;
+ return true;
+ }
+
+ public void clear() {
+ if (!isEmpty()) {
+ for (int i = 0; i < elements.length; ++i) {
+ elements[i] = null;
+ }
+ count = 0;
+ idx = 0;
+ ++modCount;
+ }
+ }
+
+ public T get(int index) {
+ Preconditions.checkArgument(index >= 0 && index < count);
+ return isDroppedIndex(index) ? getDefaultElement() :
accessInternal(index % elements.length);
+ }
+
+ public T set(int index, T element) {
+ Preconditions.checkArgument(index >= 0 && index < count);
+ ++modCount;
+ if (isDroppedIndex(index)) {
+ return getDefaultElement();
+ } else {
+ int idx = index % elements.length;
+ T old = accessInternal(idx);
+ elements[idx] = element;
+ return old;
+ }
+ }
+
+ public T getDefaultElement() {
+ return defaultElement;
+ }
+
+ private boolean isDroppedIndex(int idx) {
+ return idx < count - elements.length;
+ }
+
+ @SuppressWarnings("unchecked")
+ private T accessInternal(int arrayIndex) {
+ return (T) elements[arrayIndex];
+ }
+
+ @Override
+ public Iterator<T> iterator() {
+ return new Iterator<T>() {
+
+ int pos = 0;
+ final long oldModCount = modCount;
+
+ @Override
+ public boolean hasNext() {
+ return pos < count;
+ }
+
+ @Override
+ public T next() {
+ if (oldModCount != modCount) {
+ throw new
ConcurrentModificationException();
+ }
+ return get(pos++);
--- End diff --
I think we should throw an `NoSuchElementException` if we see an
`IllegalArgumentException` here.
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