org.apache.flink.runtime.util.BoundedFIFOQueue Maven / Gradle / Ivy
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* 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.io.Serializable;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Queue;
/**
* {@code BoundedFIFOQueue} collects elements up to given amount. Reaching this limit will result in
* removing the oldest element from this queue (First-In/First-Out; FIFO).
*
* @param The type of elements collected.
*/
public class BoundedFIFOQueue implements Iterable, Serializable {
private static final long serialVersionUID = -890727339944580409L;
private final int maxSize;
private final Queue elements;
/**
* Creates a {@code BoundedFIFOQueue} with the given maximum size.
*
* @param maxSize The maximum size of this queue. Exceeding this limit would result in removing
* the oldest element (FIFO).
* @throws IllegalArgumentException If {@code maxSize} is less than 0.
*/
public BoundedFIFOQueue(int maxSize) {
Preconditions.checkArgument(maxSize >= 0, "The maximum size should be at least 0.");
this.maxSize = maxSize;
this.elements = new LinkedList<>();
}
/**
* Adds an element to the end of the queue. An element will be removed from the head of the
* queue if the queue would exceed its maximum size by adding the new element.
*
* @param element The element that should be added to the end of the queue.
* @throws NullPointerException If {@code null} is passed as an element.
*/
public void add(T element) {
Preconditions.checkNotNull(element);
if (elements.add(element) && elements.size() > maxSize) {
elements.poll();
}
}
/**
* Returns the number of currently stored elements.
*
* @return The number of currently stored elements.
*/
public int size() {
return this.elements.size();
}
/**
* Returns the {@code BoundedFIFOQueue}'s {@link Iterator}.
*
* @return The queue's {@code Iterator}.
*/
@Override
public Iterator iterator() {
return elements.iterator();
}
}