org.apache.flink.runtime.state.GroupIterator 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.state;

import org.apache.flink.types.Pair;

import java.util.Collection;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.Queue;

/**
 * A key-value iterator over all possible groups within the same state storage (the same stat name).
 */
public class GroupIterator implements Iterator> {

	private final Queue>> groupIterators;

	/** The node for the current head group. */
	private volatile Iterator> headIterator;

	public GroupIterator(Collection>> iteratorCollection) {
		this.groupIterators = new LinkedList<>();
		for (Iterator> iterator : iteratorCollection) {
			if (iterator.hasNext()) {
				groupIterators.add(iterator);
			}
		}
		this.headIterator = this.groupIterators.poll();
	}

	@Override
	public boolean hasNext() {
		return !groupIterators.isEmpty() || (headIterator != null && headIterator.hasNext());
	}

	@Override
	public Pair next() {
		if (!headIterator.hasNext()) {
			if (!groupIterators.isEmpty()) {
				headIterator = groupIterators.poll();
			}
		}
		return headIterator.next();
	}

	@Override
	public void remove() {
		headIterator.remove();
	}
}