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From "Kumar, Kiran" <kku...@kheaa.com>
Subject RE: Problem with sharing sessions/ multithreading
Date Sun, 17 Apr 2005 16:43:38 GMT
here's what I did. and changing all the code to use this.
==========================================
	private static final String LOCK = "Lock";
	
	public Document getDocument(Map objectModel,String attrname)
	throws ParserConfigurationException
	{
         Request request = ObjectModelHelper.getRequest(objectModel);
         Session session = request.getSession(true);
         Document doc = (Document)session.getAttribute(attrname);
         if   (doc == null)
         {
              // It is possible for more than one thread to get here at 
			  // the same time with doc == null
              synchronized(LOCK)
              {     
                    // So check again. Only the first caller should 
					//	actually create the
document.
                    doc = (Document)session.getAttribute(attrname);
                    if (doc == null)
                    {     
                        DocumentBuilderFactory dbf  = 
	
DocumentBuilderFactory.newInstance();                                 
                        doc = dbf.newDocumentBuilder().newDocument();
                        session.setAttribute(attrname, doc);
                     }           
               }
         }
         return doc;
	}
=====================================

but why do we need static method??  please guide me



thanks

Kiran Kumar (Raj)
 
(502) 696-7203




-----Original Message-----
From: Ralph Goers [mailto:Ralph.Goers@dslextreme.com]
Sent: Sunday, April 17, 2005 12:27 PM
To: dev@cocoon.apache.org
Subject: Re: Problem with sharing sessions/ multithreading


Torsten Curdt wrote:

>
>Don't want to be picky ...but better don't use DCL
>
>http://www.javaworld.com/javaworld/jw-05-2001/jw-0525-double.html
>
>cheers
>  
>
Thanks, that article wasn't too helpful in figuring out why the 
technique doesn't work. However, it refreences an article from Alan 
Holub that does. From his description, the following version of the DCL 
should work fine.  I'm not sure the function actually has to be static. 
 From what I could tell synchronized should be sufficient.

Document getDocument()
{
        Request request = ObjectModelHelper.getRequest(objectModel);
        Session session = request.getSession(true);
        Document doc = (Document)session.getAttribute("myAttribute");
        if   (doc == null)
        {
             // It is possible for more than one thread to get here at 
the same time with doc == null
             syncronize(LOCK);
             {     // So check again. Only the first caller should 
actually create the document.
                   doc = (Document)session.getAttribute("myAttribute");
                   if (doc == null)
                   {     
                        DocumentBuilderFactory dbf  = 
DocumentBuilderFactory.newInstance();                             
                     
                        doc = buildDocument(dbf);
                        session.setAttribute("myAttribute", doc);
                    }                        
             }
        }
        return doc;
}

private static synchronized Document 
buildDocument(DocumentBuilderFactory dbf)
{
    return dbf.newDocumentBuilder().newDocument();
}

>--
>Torsten
>  
>

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