package test.lang;
 
import org.apache.log4j.Category;
import org.apache.log4j.BasicConfigurator;
 
import java.util.Random;
 
/**
  * The purpose of this class is to :
  * 
  * Show how we can use threaded inner classes safely accessing the
  * "carrying/supporting" class attributes !
  *     
  * @author  <a href="mailto:tsmets@altern.org">Thomas SMETS, Brussels</a>
  * @version 0.1.15 pre-final
  */
class Parent
{
  Category log = Category.getInstance (Parent.class);
  Random random = new Random (System.currentTimeMillis ());
  
  Object o;
  String SharedObject = null;
  boolean isBusy = false;
  public static final long MAX_ITER = 200;  
  
  Inner i1, i2;
 
  Parent()
  {
    log.info ("Parent created");
    i1 = new Inner(1);
    i2 = new Inner(2);
    o = new Object ();
  }
  
  public void  go ()
  {  
    log.info ("Parent::go( )");
    i1.start ();
    i2.start ();
  }
 
  public void getBusyFlag(int callerNbr)
  {
    log.info ("Requesting the busy-flag (Thread is " + callerNbr + ")");
    synchronized (o)
    {
      while (isBusy)
      {
        try 
        {
          log.info ("Thread " + callerNbr + " is waitng");
          o.wait ();
        }
        catch (Exception ex) 
        {
          log.info ("Thread " + callerNbr + " wait has been disturbed");
        }
      }
      
      if (!isBusy)
      {
        isBusy = true;
        log.info ("Busy flag has been given to Thread : " + callerNbr);
        return;
      }  
    }
  }
  
  public boolean isFlagBusy ()  {    return isBusy;  }  
  
  public void releaseFlag(int callerNbr)
  {
    synchronized (o)
    {
      log.info ("Releasing the flag : " + callerNbr);
      isBusy = false;
      o.notifyAll();    
    }
  }
 
  public static void main(String[] args)
  {
    BasicConfigurator.resetConfiguration ();
    BasicConfigurator.configure ();
    new Parent().go();
  }
  
  
  class Inner
    extends Thread
  {
    int Nbr;
    Category ilog = null;
    
    Inner ()         
    {      
      Nbr = 0;    
      ilog = Category.getInstance (Inner.class);
    }    
    Inner (int i)    
    {
      this();
      Nbr = i;    
    }  
    
    public void run()
    {
      ilog.info (Nbr + " Inner::run()");
      while(true)
      { 
        getBusyFlag(Nbr);        
        try 
        {          
          if (SharedObject != null)
            ilog.fatal ("SharedObject is not null (Thread : "+ Nbr +"). First part is " 
                        + SharedObject.substring ( 0, 
                                                   (SharedObject.length ()<20)?
                                                    SharedObject.length ():
                                                    20) );                     
          for (int i = 0; i<MAX_ITER; i++)   
          {          
            SharedObject += new Integer (Nbr).toString ();            
            try 
            {
              Thread.sleep (20);
            }
            catch (Exception ex) 
            {
            }            
          }
          
          SharedObject = null;
          releaseFlag(Nbr);
        }
        catch (Exception ex) 
        {
          ilog.warn ("I have been woken up (Thread : "+ Nbr +"). Exception is " 
                    + ex.getClass ().getName () );
        }
        
      }
    }
  }    // End of inner class
  
}