org.apache.flink.runtime.jobmanager.scheduler.LifoSetQueue Maven / Gradle / Ivy
/*
* 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.jobmanager.scheduler;
import java.util.AbstractQueue;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Queue;
/**
* A queue that returns elements in LIFO order and simultaneously maintains set characteristics, i.e., elements
* that are already in the queue may not be added another time.
*
* @param The type of the elements in the queue.
*/
public class LifoSetQueue extends AbstractQueue implements Queue {
private final ArrayList lifo = new ArrayList();
private final HashSet set = new HashSet();
@Override
public boolean offer(E e) {
if (e == null) {
throw new NullPointerException();
}
if (set.add(e)) {
lifo.add(e);
}
return true;
}
@Override
public E poll() {
int size = lifo.size();
if (size > 0) {
E element = lifo.remove(size-1);
set.remove(element);
return element;
} else {
return null;
}
}
@Override
public E peek() {
int size = lifo.size();
if (size > 0) {
return lifo.get(size-1);
} else {
return null;
}
}
@Override
public Iterator iterator() {
return new Iterator() {
private int currentPos = lifo.size() - 1;
private int posToRemove = -1;
@Override
public boolean hasNext() {
return currentPos >= 0;
}
@Override
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
} else {
posToRemove = currentPos;
return lifo.get(currentPos--);
}
}
@Override
public void remove() {
if (posToRemove == -1) {
throw new NoSuchElementException();
} else {
E element = lifo.remove(posToRemove);
set.remove(element);
}
}
};
}
@Override
public int size() {
return lifo.size();
}
}