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Hive is a data warehouse infrastructure built on top of Hadoop see http://wiki.apache.org/hadoop/Hive

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/**
 * 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.hive.ql;

import java.io.Serializable;
import java.util.LinkedList;
import java.util.Queue;

import org.apache.hadoop.hive.ql.exec.Task;
import org.apache.hadoop.mapred.JobConf;

/**
 * DriverContext.
 *
 */
public class DriverContext {

  Queue> runnable = new LinkedList>();

  // how many jobs have been started
  int curJobNo;

  Context ctx;

  public DriverContext() {
    this.runnable = null;
    this.ctx = null;
  }

  public DriverContext(Queue> runnable, Context ctx) {
    this.runnable = runnable;
    this.ctx = ctx;
  }

  public Queue> getRunnable() {
    return runnable;
  }

  /**
   * Checks if a task can be launched.
   *
   * @param tsk
   *          the task to be checked
   * @return true if the task is launchable, false otherwise
   */

  public static boolean isLaunchable(Task tsk) {
    // A launchable task is one that hasn't been queued, hasn't been
    // initialized, and is runnable.
    return !tsk.getQueued() && !tsk.getInitialized() && tsk.isRunnable();
  }

  public void addToRunnable(Task tsk) {
    runnable.add(tsk);
    tsk.setQueued();
  }

  public int getCurJobNo() {
    return curJobNo;
  }

  public Context getCtx() {
    return ctx;
  }

  public void incCurJobNo(int amount) {
    this.curJobNo = this.curJobNo + amount;
  }
  
}