/*
 * File    : NonDaemonTaskRunner.java
 * Created : 29-Dec-2003
 * By      : parg
 * 
 * Azureus - a Java Bittorrent client
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details ( see the LICENSE file ).
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package org.gudy.azureus2.core3.util;

/**
 * @author parg
 *
 */

import java.util.*;

public class 
NonDaemonTaskRunner 
{
	public static final int	LINGER_PERIOD	= 2500;
	
	protected static NonDaemonTaskRunner	singleton;
	protected static AEMonitor				class_mon		= new AEMonitor( "NonDaemonTaskRunner:class" );
	
	protected Stack			tasks		= new Stack();
	protected AEMonitor		tasks_mon	= new AEMonitor( "NonDaemonTaskRunner:tasks" );
	protected AESemaphore	task_sem	= new AESemaphore("NonDaemonTaskRunner");
	
	protected List		wait_until_idle_list	= new ArrayList();
	
	protected Thread	current_thread;
	
	protected static NonDaemonTaskRunner
	getSingleton()
	{
		try{
			class_mon.enter();
		
			if ( singleton == null ){
				
				singleton = new NonDaemonTaskRunner();
			}
			
			return( singleton );

		}finally{
		
			class_mon.exit();
		}
	}
	
	public static Object
	run(
		NonDaemonTask	target )
	
		throws Throwable
	{
		return(getSingleton().runSupport( target, false ));
	}
	
	public static Object
	runAsync(
		NonDaemonTask	target )
	
		throws Throwable
	{
		return(getSingleton().runSupport( target, true ));
	}
	
	protected Object
	runSupport(
		NonDaemonTask	target,
		boolean			async )
	
		throws Throwable
	{
			// is this a recursive call? if so, run directly
		
		if ( current_thread == Thread.currentThread()){
			
			return( target.run());
		}
		
		taskWrapper	wrapper = new taskWrapper( target );
		
		try{
			tasks_mon.enter();
			
			tasks.push( wrapper );
			
			task_sem.release();
			
			if ( current_thread == null ){
				
				final AESemaphore wait_sem = new AESemaphore("NonDaemonTaskRunnerTask");
				
				current_thread = new AEThread("NonDaemonTaskRunner" )
					{
						public void
						runSupport()
						{
							wait_sem.release();
							
							// System.out.println( "non daemon starts" );
							
							while(true){
								
								task_sem.reserve(LINGER_PERIOD);
																
								taskWrapper t			= null;
								
								try{
									tasks_mon.enter();
									
									if ( tasks.isEmpty()){
	
										current_thread = null;
											
										for (int i=0;i<wait_until_idle_list.size();i++){
											
											((AESemaphore)wait_until_idle_list.get(i)).release();
										}
										
										wait_until_idle_list.clear();
										
										break;
										
									}else{
										
										t = (taskWrapper)tasks.pop();
									}
								}finally{
									
									tasks_mon.exit();
								}
								
								t.run();
							}
													
							// System.out.println( "non daemon ends" );
						}
					};
						
				current_thread.setDaemon(false);
				
				current_thread.start();	
				
				wait_sem.reserve();
			}
		}finally{
			
			tasks_mon.exit();
		}
		
		if ( async ){
			
			return( null );
		}
		
		return( wrapper.waitForResult());
	}
	
	protected class
	taskWrapper
	{
		protected NonDaemonTask		task;
		protected AESemaphore		sem;
		
		protected Object	  	result;
		protected Throwable  	exception;
		
		protected
		taskWrapper(
			NonDaemonTask	_task )
		{
			task		= _task;
			sem			= new AESemaphore("NonDaemonTaskRunner::taskWrapper");
		}
		
		protected void
		run()
		{
			try{
				result = task.run();
				
			}catch( Throwable e ){
								
				exception	= e;
				
			}finally{
		
				sem.release();
			}
		}
		
		protected Object
		waitForResult()
		
			throws Throwable
		{
			sem.reserve();
			
			if ( exception != null ){
							
				throw( exception );
			}
			
			return( result );
		}
	}
	
	public static void
	waitUntilIdle()
	{
		getSingleton().waitUntilIdleSupport();
	}
	
	protected void
	waitUntilIdleSupport()
	{
		AESemaphore	sem;
		
		try{
			tasks_mon.enter();
			
			if ( current_thread == null ){
				
				return;
			}
			
			sem = new AESemaphore("NDTR::idleWaiter");
			
			wait_until_idle_list.add( sem );
			
		}finally{
			
			tasks_mon.exit();
		}
		
		sem.reserve();
	}
}
