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HBase is the <a href="http://hadoop.apache.org"&rt;Hadoop</a&rt; database. Use it when you need random, realtime read/write access to your Big Data. This project's goal is the hosting of very large tables -- billions of rows X millions of columns -- atop clusters of commodity hardware.

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/*
 * Copyright 2011 The Apache Software Foundation
 *
 * 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.hadoop.hbase.coprocessor;

import org.apache.hadoop.hbase.CoprocessorEnvironment;

/**
 * Carries the execution state for a given invocation of an Observer coprocessor
 * ({@link RegionObserver}, {@link MasterObserver}, or {@link WALObserver})
 * method.  The same ObserverContext instance is passed sequentially to all loaded
 * coprocessors for a given Observer method trigger, with the
 * CoprocessorEnvironment reference swapped out for each
 * coprocessor.
 * @param  The {@link CoprocessorEnvironment} subclass applicable to the
 *     revelant Observer interface.
 */
public class ObserverContext {
  private E env;
  private boolean bypass;
  private boolean complete;

  public ObserverContext() {
  }

  public E getEnvironment() {
    return env;
  }

  public void prepare(E env) {
    this.env = env;
  }

  /**
   * Call to indicate that the current coprocessor's return value should be
   * used in place of the normal HBase obtained value.
   */
  public void bypass() {
    bypass = true;
  }

  /**
   * Call to indicate that additional coprocessors further down the execution
   * chain do not need to be invoked.  Implies that this coprocessor's response
   * is definitive.
   */
  public void complete() {
    complete = true;
  }

  /**
   * For use by the coprocessor framework.
   * @return true if {@link ObserverContext#bypass()}
   *     was called by one of the loaded coprocessors, false otherwise.
   */
  public boolean shouldBypass() {
    boolean current = bypass;
    bypass = false;
    return current;
  }

  /**
   * For use by the coprocessor framework.
   * @return true if {@link ObserverContext#complete()}
   *     was called by one of the loaded coprocessors, false otherwise.
   */
  public boolean shouldComplete() {
    boolean current = complete;
    complete = false;
    return current;
  }

  /**
   * Instantiates a new ObserverContext instance if the passed reference is
   * null and sets the environment in the new or existing instance.
   * This allows deferring the instantiation of a ObserverContext until it is
   * actually needed.
   *
   * @param env The coprocessor environment to set
   * @param context An existing ObserverContext instance to use, or null
   *     to create a new instance
   * @param  The environment type for the context
   * @return An instance of ObserverContext with the environment set
   */
  public static  ObserverContext createAndPrepare(
      T env, ObserverContext context) {
    if (context == null) {
      context = new ObserverContext();
    }
    context.prepare(env);
    return context;
  }
}