| /* |
| * 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.calcite.linq4j; |
| |
| import java.util.concurrent.atomic.AtomicInteger; |
| |
| /** |
| * Enumerator that keeps some recent and some "future" values. |
| * |
| * @param <E> Row value |
| */ |
| public class MemoryEnumerator<E> implements Enumerator<MemoryFactory.Memory<E>> { |
| private final Enumerator<E> enumerator; |
| private final MemoryFactory<E> memoryFactory; |
| private final AtomicInteger prevCounter; |
| private final AtomicInteger postCounter; |
| |
| /** |
| * Creates a MemoryEnumerator. |
| * |
| * <p>Use factory method {@link MemoryEnumerable#enumerator()}. |
| * |
| * @param enumerator The Enumerator that memory should be "wrapped" around |
| * @param history Number of present steps to remember |
| * @param future Number of future steps to "remember" |
| */ |
| MemoryEnumerator(Enumerator<E> enumerator, int history, int future) { |
| this.enumerator = enumerator; |
| this.memoryFactory = new MemoryFactory<>(history, future); |
| this.prevCounter = new AtomicInteger(future); |
| this.postCounter = new AtomicInteger(future); |
| } |
| |
| @Override public MemoryFactory.Memory<E> current() { |
| return memoryFactory.create(); |
| } |
| |
| @Override public boolean moveNext() { |
| if (prevCounter.get() > 0) { |
| boolean lastMove = false; |
| while (prevCounter.getAndDecrement() >= 0) { |
| lastMove = moveNextInternal(); |
| } |
| return lastMove; |
| } else { |
| return moveNextInternal(); |
| } |
| } |
| |
| private boolean moveNextInternal() { |
| final boolean moveNext = enumerator.moveNext(); |
| if (moveNext) { |
| memoryFactory.add(enumerator.current()); |
| return true; |
| } else { |
| // Check if we have to add "history" additional values |
| if (postCounter.getAndDecrement() > 0) { |
| memoryFactory.add(null); |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| @Override public void reset() { |
| enumerator.reset(); |
| } |
| |
| @Override public void close() { |
| enumerator.close(); |
| } |
| } |