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From Simon Waddington <si...@viafone.com>
Subject RE: init() and destroy() in XSP
Date Sat, 02 Jun 2001 01:09:59 GMT
This is kind of late in the conversation... but there's a race condition in
your code.  The thread that finds initialized zero could get suspended
before setting it to one.  Its unlikely but could happen.  Then another
thread will also find it zero and both threads will end up performing
initialization.  

Code modifying shared data should be synchronized to achieve "test and set"
semantics:

<xsp:page>
<xsp:logic>
  boolean initialized = false;
  public synchronized void doInitialization () {
     if (!initialized) {
        // Do initialization here

	  // if init code successful (assuming it can fail)
	  initialized = true;
     }
  }
</xsp:logic>

<page>
<xsp:logic>
   doInitialization ();

   // rest of page
</xsp:logic>
</xsp:page>

If you don't like the method call overhead then make the variable an object
and synchronize the section around the test-and-set operation on it - or one
some other appropriate object.   In this case syncrhonization may seem like
a pain in the butt, but without it once in a blue moon your code will fail -
if initializing twice on those blue moon occasions isn't a big deal then
throw caution to the wind and leave it out, otherwise I'm afraid you'll need
it.
        

-----Original Message-----
From: Matthew Cordes [mailto:cordes@cs.usm.maine.edu]
Sent: Friday, June 01, 2001 1:12 PM
To: cocoon-users@xml.apache.org
Subject: Re: init() and destroy() in XSP


There is no init method, i'm just suggesting:

<xsp:page>
<xsp:logic>
    int initialized = 0;
</xsp:logic>

<page>
<xsp:logic>
    if ( initialized == 0 )
    {
        // do init stuff here

        initialized = 1;  // this block will never be reached again.
    }
</xsp:logic>
</page>
</xsp:page>

Hope this helps. Perhaps someone else has another idea?

-matt


----- Original Message -----
From: "Frans Thamura" <fth4mura@yahoo.com>
To: <cocoon-users@xml.apache.org>
Sent: Friday, June 01, 2001 1:24 AM
Subject: Re: init() and destroy() in XSP


> Matt,
> I don't understand, I need your help.
>
> I create a lot of xsp:page, but never find init()
> Would you give the simple work sample?
>
> Frans
> ----- Original Message -----
> From: "Matthew Cordes" <cordes@cs.usm.maine.edu>
> To: <cocoon-users@xml.apache.org>
> Sent: Friday, June 01, 2001 3:01 PM
> Subject: Re: init() and destroy() in XSP
>
>
> > There are work-arounds though:
> >
> > INIT:
> > Make a global variable, set it to null, inside your <xsp:page> block
check
> > to see if it is null and do init stuff, then set it to something else.
> >
> > DESTROY:
> > wouldn't  overloading void finalize() { ... } work here?
> >
> > -matt
> >
> >
> >
> > ----- Original Message -----
> > From: "Frans Thamura" <fth4mura@yahoo.com>
> > To: <cocoon-users@xml.apache.org>
> > Sent: Thursday, May 31, 2001 11:38 PM
> > Subject: Re: init() and destroy() in XSP
> >
> >
> > > Ya, one of cocoon problem is no init and destroy
> > >
> > > ----- Original Message -----
> > > From: "Polley Christopher W" <PolleyChristopherW@JohnDeere.com>
> > > To: <cocoon-users@xml.apache.org>
> > > Sent: Friday, May 04, 2001 9:16 PM
> > > Subject: init() and destroy() in XSP
> > >
> > >
> > > > Hello, all:
> > > >
> > > > I have an XSP page in which  I would like to do some setup (open
JDBC
> > > > connection, create prepared statements) upon instantiation and
cleanup
> > > > (close ps's and connection) upon destruction.
> > > >
> > > > In its previous life as a jsp page, it used jspInit() and
> jspDestroy(),
> > > and
> > > > in a servlet it could use init() and destroy().
> > > >
> > > > I found XSPPage.init(parameters), which I can override to do the
> > > > initialization, but I am unclear on the tail end of the xsp life
> cycle.
> > > How
> > > > & when is it destroyed (in Cocoon 1.8.1) ?  How is this type of
thing
> > done
> > > > in XSP?
> > > >
> > > > I suppose that in this case, in which I am only doing JDBC stuff, I
> > could
> > > > try the sql taglib, but am unclear on how that would be done.  Can
> > > > <?cocoon-process type="sql"?> safely be placed ahead of
> <?cocoon-process
> > > > type="xsp"?>? What would the resultant xsp-servlet look like?
> > > >
> > > >
> > > > Thanks,
> > > > Chris
> > > >
> > > >
> > >
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