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/*_##########################################################################
  _##
  _##  Copyright (C) 2012  Pcap4J.org
  _##
  _##########################################################################
*/

package org.pcap4j.util;

import java.io.IOException;
import java.io.ObjectOutputStream;
import java.io.Serializable;

/**
 * @author Kaito Yamada
 * @since pcap4j 0.9.6
 * @param  the type of value this class returns.
 */
public final class LazyValue implements Serializable {

  /** */
  private static final long serialVersionUID = 1379102837076225509L;

  private final transient BuildValueCommand command;
  private final transient Object thisLock = new Object();

  private volatile T1 value = null;

  /** @param command command */
  public LazyValue(BuildValueCommand command) {
    this.command = command;
  }

  /** @return value */
  public T1 getValue() {
    T1 result = value;
    if (result == null) {
      synchronized (thisLock) {
        result = value;
        if (result == null) {
          value = command.buildValue();
        }
      }
    }
    return value;
  }

  private void writeObject(ObjectOutputStream out) throws IOException {
    getValue();
    if (value == null) {
      throw new AssertionError();
    }
    out.defaultWriteObject();
  }

  /**
   * @author Kaito Yamada
   * @since pcap4j 0.9.6
   * @param  the type of value to build.
   */
  public interface BuildValueCommand {

    /** @return value */
    public T2 buildValue();
  }
}