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From "Pon Umapathy K.S." <>
Subject RE: Tomcat's ThreadPool and InheritableThreadLocal variables
Date Fri, 05 Dec 2003 06:18:44 GMT
> Likely, you can get better advice if you try to explain what problem it is
> you are using InheritableThreadLocal for :).

Let me explain what exactly i am trying to acheive.
 We have a web server which runs a suite of applications.There are a large
number of backend libraries which are used by these different
applications.The logging done in these libraries will need to go into a
different log location depending on the calling application(originates from
the application invoked from the User Interface).

The library code typically gets a reference to the current Logging context
by a call
 LoggerIf log=Logger.getCurrentInstance();

 The caller would have set the logging context for that thread before
calling the library code using
  Logger.setCurrentLogInstance(new LoggerImpl("fileName"));
 which sets the value of a InheritableThreadLocal variable to the specified
logger instance.

 Suppose a request sets the logging context using the thread it is running
in.After the request is processed,this var is not cleared.So,when a new
request is processed using the same thread(if the request processing does
not invlove setting the current logging context),the called backend
libraries would get the reference to the logging context set by the previous
request which was not cleared.

 Yes,i know that it's better to pass around the logger references and
all.But,i would like to see if i can achieve the same results without having
to pass around an explicit logger reference every time. :)

Currently,this is what i have planned to do:

 I am not allowed to touch the ActionServlet class.So,i wont be able to do
any preprocessing on a new request by which i can reset the logging
context.So,this is how i plan to do it:

 Have a Logger object in the ActionForm(to be used for that session).

The action class would do something like this for each request:

 // See if there is a logger for this session
 LoggerIf log=FormBean.getLogger();
 // No.So,create a new one and set the logging context for this thread
  log= Logger.setLogger(new LoggerImpl("fileName"));
 // set the logging context for this thread using the logger created for
this session


 // And before returning from the request,clear the logging context for the
 return screenId;

Have to test this out,though.But,it should work.

As an aside,should'nt this behaviour be corrected in tomcat to clear the
ThreadLocal variables once a request is done(because as i see it,a thread is
very much local to the request it is processing)?

> -----Original Message-----
> From: Bill Barker []
> Sent: Friday, December 05, 2003 11:19 AM
> To: Tomcat Users List
> Subject: Re: Tomcat's ThreadPool and InheritableThreadLocal variables
> Yoav is pretty much right.  And, this is pretty much true for Tomcat 4.1.x
> and Tomcat 5.0.x, since they all use the same threading code.
> Given the limitations of the 2.2 spec, the easiest is to use Request
> attributes to pass things along.  This works for includes, forwards, and
> even JSP tags (who can access the Request from the pageContext).
> It doesn't
> work if you want to pass them to generic Beans.  In this case,
> you can still
> use Request attributes, but you must set the attributes on the Beans
> explictly.
> Likely, you can get better advice if you try to explain what problem it is
> you are using InheritableThreadLocal for :).
> ----- Original Message -----
> From: "Pon Umapathy K.S." <>
> Newsgroups: gmane.comp.jakarta.tomcat.user
> Sent: Thursday, December 04, 2003 4:09 AM
> Subject: Tomcat's ThreadPool and InheritableThreadLocal variables
> > Hi,
> >  A query regarding InheritableThreadLocal variables in the
> tomcat context.
> >
> > To explain the problem i am facing:
> >  If i am correct,for each request,tomcat uses a thread from it's
> threadpool
> > to process the request.
> >  Suppose during one of these requests,i set the value of a
> > InheritableThreadLocal variable.Once this request is
> processed,the thread
> > will be available for use from the ThreadPool.Does tomcat reset
> the value
> of
> > the InheritableThreadLocal variable which was set by the
> previous request
> > processing?(it should,ideally). The tomcat version i am using is
> 3.3.1a.Also
> > use the struts framework model.
> >
> >  It seems to me that the InheritableThreadLocal value which was set by a
> > previous request on a thread is still retained when that thread
> is reused
> > for processing another request.Are there any known issues
> regarding this?
> >  Would be really helpful if someone can answer this.A bit
> urgent.Thanks in
> > advance.
> >
> > Regards,
> > Umapathy

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