PopExecutor.java

/*
 * 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.geode.redis.internal.executor.list;

import java.util.List;

import org.apache.geode.cache.Region;

import org.apache.geode.redis.internal.ByteArrayWrapper;
import org.apache.geode.redis.internal.Coder;
import org.apache.geode.redis.internal.Command;
import org.apache.geode.redis.internal.ExecutionHandlerContext;
import org.apache.geode.redis.internal.Extendable;
import org.apache.geode.redis.internal.RedisDataType;

public abstract class PopExecutor extends ListExecutor implements Extendable {

  @Override
  public void executeCommand(Command command, ExecutionHandlerContext context) {
    List<byte[]> commandElems = command.getProcessedCommand();

    if (commandElems.size() < 2) {
      command.setResponse(Coder.getErrorResponse(context.getByteBufAllocator(), getArgsError()));
      return;
    }

    ByteArrayWrapper key = command.getKey();

    checkDataType(key, RedisDataType.REDIS_LIST, context);
    Region keyRegion = getRegion(context, key);

    if (keyRegion == null || keyRegion.size() == LIST_EMPTY_SIZE) {
      command.setResponse(Coder.getNilResponse(context.getByteBufAllocator()));
      return;
    }

    String indexKey = popType() == ListDirection.LEFT ? "head" : "tail";
    String oppositeKey = popType() == ListDirection.RIGHT ? "head" : "tail";
    Integer index = 0;
    int originalIndex = index;
    int incr = popType() == ListDirection.LEFT ? 1 : -1;
    ByteArrayWrapper valueWrapper = null;

    /**
     * 
     * First attempt to hop over an index by moving the index down one in the meta data region. The
     * desired index to remove is held within the field index
     * 
     */

    boolean indexChanged = false;
    do {
      index = (Integer) keyRegion.get(indexKey);
      Integer opp = (Integer) keyRegion.get(oppositeKey);
      if (index.equals(opp))
        break;
      indexChanged = keyRegion.replace(indexKey, index, index + incr);
    } while (!indexChanged);

    /**
     * 
     * Now attempt to remove the value of the index. We must do a get to ensure a returned value and
     * then call remove with the value to ensure no one else has removed it first. Otherwise, try
     * other indexes
     * 
     */

    boolean removed = false;
    int i = 0;
    do {
      valueWrapper = (ByteArrayWrapper) keyRegion.get(index);
      if (valueWrapper != null)
        removed = keyRegion.remove(index, valueWrapper);

      /**
       * 
       * If remove has passed, our job is done and we can break and stop looking for a value
       * 
       */

      if (removed)
        break;

      /**
       * 
       * If the index has not been removed, we need to look at other indexes. Two cases exist:
       * 
       * ************************** FIRST MISS *********************************** Push occurring at
       * the same time, further index update first | This is location of miss | | | | V V [-4] [X]
       * [-2] [-1] [0] [1] [2] <-- Direction of index update If this is the first miss, the index is
       * re obtained from the meta region and that index is trying. However, if the index in the
       * meta data region is not further out, that index is not used and moves on to the second case
       * **************************************************************************
       * 
       * ************************* SUBSEQUENT MISSES ****************************** Push occurring
       * at the same time, further index update first | This is location of miss | | | | V V [-4]
       * [X] [-2] [-1] [0] [1] [2] Direction of index update --> If this is not the first miss then
       * we move down to the other end of the list which means the next not empty index will be
       * attempted to be removed
       * **************************************************************************
       * 
       * If it is the case that the list is empty, it will exit this loop
       * 
       */

      index += incr;
      Integer metaIndex = (Integer) keyRegion.get(indexKey);
      if (i < 1 && (popType() == ListDirection.LEFT && metaIndex < originalIndex
          || popType() == ListDirection.RIGHT && metaIndex > originalIndex))
        index = metaIndex;
      i++;
    } while (!removed && keyRegion.size() != LIST_EMPTY_SIZE);
    if (valueWrapper != null)
      command.setResponse(
          Coder.getBulkStringResponse(context.getByteBufAllocator(), valueWrapper.toBytes()));
    else
      command.setResponse(Coder.getNilResponse(context.getByteBufAllocator()));
  }

  protected abstract ListDirection popType();

}