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From Dakota Jack <dakota.j...@gmail.com>
Subject Re: How to run servlet for every 30 minutes in Tomcat 4.1.30
Date Wed, 22 Dec 2004 07:58:14 GMT
"[OT]Threads and Servlets Question" on the struts-user list.

Jack


On Tue, 21 Dec 2004 18:17:40 -0500, Frank W. Zammetti
<fzlists@omnytex.com> wrote:
> It's interesting, Craig and I had an exchange about threads in servlet
> containers last week... I can't find a link to the thread unfortunately.
> 
> Anyway, the basic idea behind that "don't spawn your own threads inside
> a servlet container" admonishment is based more on the fact that it's
> quite easy to screw up doing so, more than it has to do with virtually
> anything else.
> 
> You want the servlet container to manager resources for you, and you
> lose that by spawning your own threads.  The container isn't aware of
> the threads, so it can't control them for things like graceful shutdowns
> or simply trying to control resource utilization.  Many people,
> including me, tend to ignore that warning when the situation warrants
> it, but you have to be extra-careful.
> 
> For instance, you don't under any circumstances want to hold on to
> references to response, request or session objects because you don't
> manage them.  You also, unless you really have a need and know what your
> doing, want to spawn threads to handle requests at all.  Any threads you
> do spawn in a container should tend to be independent units of
> execution.  If your use case fits that description, you can get away
> with it relatively safely.
> 
> That being said, spawning things like daemon threads for low-level
> behind-the-scenes type processing is generally OK, so long as you are
> careful (i.e., be sure no runaway processing can occur, make sure it
> will shut down gracefully, etc).  You might be able to use something
> like that in this case, you'll have to decide.  If your using Struts,
> you can spawn the thread from a plug-in, as I've done in the past, but
> there are non-Struts equivalents (worse comes to worse, just do it in a
> servlet.init()).  Do yourself a favor and make the thread processing
> functional independent of your app essentially, and even make it so it's
> not aware it's running in a servlet container.  But again, caution is
> the key.  If you make it a demon thread and set it's priority as low as
> you can and be sure to not hold on to a reference to it, I've found that
> works just fine under a number of app servers on a numeber of OSs.
> 
> The bottom-line is that really that psuedo-rule is around because people
> tend to shoot themselves in the foot when using threads a bit too often,
> so better to advise against getting into a situation where you might do
> that.  But, if your confident in your ability, and believe the use case
> really warrants it, you CAN do it, and relatively safely.
> 
> --
> Frank W. Zammetti
> Founder and Chief Software Architect
> Omnytex Technologies
> http://www.omnytex.com
> 
> Dennis Payne wrote:
> > It is possible to create a servlet thread in the init() method.  That
> > thread sould stay alive and run something every thirty minutes.  The
> > issue of pushing information out to the user remins the same.  The
> > servlet and the thread cannot do that.  On the other hand, it is
> > possible to setup java script on the page to detect 30 minute intervals
> > to pull a page from the server.
> >
> > It is an awful lot of work for so little a result... It is best just to
> > put a java process into cron or task scheduler and have the user run the
> > report when they want the info.
> >
> >
> >>>>jukka.uusisalo@dnainternet.net 12-21-2004 14:44 >>>
> >
> > Jorge Sopena wrote:
> >
> >>Why is bad using own threads inside web application?
> >>Aren't all the servlet request actually a thread in Tomcat?
> >>I can't find a reason why it's so bad solution.
> >
> >
> > I think that comes from J2EE specs. I do not remember is threads just
> > forbidden but if you follow specs, you do not know and you do not have
> > to know how application server uses threads and controls thread
> > behaviour. If portability is issue for your application, it is better
> > to
> > not use threads.
> >
> >  >
> >
> >>In that way, you manage to have a single and independent
> >
> > application.
> >
> >>Maybe I don't know some thread behaviour in Tomcat...
> >>
> >
> >
> > After all, I have use threads in web application with tomcat :) and I
> > haven't have any problems or strange thread behaviour. Sometimes whole
> >
> > concurrent programming and syncronizing my own threads causes troubles
> >
> > but nothing due tomcat.
> >
> > Back to original question.
> >
> >
> >> bernhard.slominski@zooplus.com wrote:
> >>I am using Tomcat4.1.30 version.
> >>I have to develop a client application which looks in the database
> >
> > every 30
> >
> >>minutes,
> >
> >
> > ApplicationContextListener + Timer + TimerTask
> >
> >
> >
> >>to retrieve the status of an order and send the status to the remote
> >
> > client.
> >
> >>Again waits for the
> >>The client's response and insert the repsonse back to the database.
> >
> >
> > What is that remote client? Is actually another server and your
> > application is client. If so, just add client code for server in
> > TimerTask (http-, web service- or whatever client).
> >
> > - Jukka -
> >
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> >
> >
> >
> >
> 
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> 


-- 
"You can lead a horse to water but you cannot make it float on its back."

~Dakota Jack~

"You can't wake a person who is pretending to be asleep."

~Native Proverb~

"Each man is good in His sight. It is not necessary for eagles to be crows."

~Hunkesni (Sitting Bull), Hunkpapa Sioux~

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