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Hadoop is the distributed computing framework of Apache; hadoop-core contains the filesystem, job tracker and map/reduce modules
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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.util;

import java.util.ArrayList;

/** Utility to assist with generation of progress reports.  Applications build
 * a hierarchy of {@link Progress} instances, each modelling a phase of
 * execution.  The root is constructed with {@link #Progress()}.  Nodes for
 * sub-phases are created by calling {@link #addPhase()}.
 */
public class Progress {
  private String status = "";
  private float progress;
  private int currentPhase;
  private ArrayList phases = new ArrayList();
  private Progress parent;
  private float progressPerPhase;

  /** Creates a new root node. */
  public Progress() {}

  /** Adds a named node to the tree. */
  public Progress addPhase(String status) {
    Progress phase = addPhase();
    phase.setStatus(status);
    return phase;
  }

  /** Adds a node to the tree. */
  public synchronized Progress addPhase() {
    Progress phase = new Progress();
    phases.add(phase);
    phase.parent = this;
    progressPerPhase = 1.0f / (float)phases.size();
    return phase;
  }

  /** Called during execution to move to the next phase at this level in the
   * tree. */
  public synchronized void startNextPhase() {
    currentPhase++;
  }

  /** Returns the current sub-node executing. */
  public synchronized Progress phase() {
    return phases.get(currentPhase);
  }

  /** Completes this node, moving the parent node to its next child. */
  public void complete() {
    // we have to traverse up to our parent, so be careful about locking.
    Progress myParent;
    synchronized(this) {
      progress = 1.0f;
      myParent = parent;
    }
    if (myParent != null) {
      // this will synchronize on the parent, so we make sure we release
      // our lock before getting the parent's, since we're traversing 
      // against the normal traversal direction used by get() or toString().
      // We don't need transactional semantics, so we're OK doing this. 
      myParent.startNextPhase();
    }
  }

  /** Called during execution on a leaf node to set its progress. */
  public synchronized void set(float progress) {
    this.progress = progress;
  }

  /** Returns the overall progress of the root. */
  // this method probably does not need to be synchronized as getINternal() is synchronized 
  // and the node's parent never changes. Still, it doesn't hurt. 
  public synchronized float get() {
    Progress node = this;
    while (node.parent != null) {                 // find the root
      node = parent;
    }
    return node.getInternal();
  }

  /** Computes progress in this node. */
  private synchronized float getInternal() {
    int phaseCount = phases.size();
    if (phaseCount != 0) {
      float subProgress =
        currentPhase < phaseCount ? phase().getInternal() : 0.0f;
      return progressPerPhase*(currentPhase + subProgress);
    } else {
      return progress;
    }
  }

  public synchronized void setStatus(String status) {
    this.status = status;
  }

  public String toString() {
    StringBuffer result = new StringBuffer();
    toString(result);
    return result.toString();
  }

  private synchronized void toString(StringBuffer buffer) {
    buffer.append(status);
    if (phases.size() != 0 && currentPhase < phases.size()) {
      buffer.append(" > ");
      phase().toString(buffer);
    }
  }

}