On Fri, 13 Dec 2002, Eric Noriega wrote:
> I'm not sure if there has been a change in the spec., but my
> understanding was that multiple instance of the servlet would be
> created. Each one is a single thread class, but there can be
> multiple of them. The cost is in the class turnover, not in the
> fact that each request is blocked.
It's not so much a change in the spec, but rather a detail that isn't
covered in the spec. That is, SingleThreadModel is discussed in the
spec, as to how it is to behave, but not how it is to be implemented.
A particular implementation could create a single instance that blocks
when another request/thread comes through, or they could create a pool
of instances to handle (some number of) multiple simultaneous
requests/threads.
So servlet containers have a choice how to implement it. And that
includes a particular servlet container changing how it implements it
between versions. And, in fact, I think this is what happened, I just
saw a post about it on the tomcat-user list, Tomcat 3.x did it one way
(no pool of instances), Tomcat 4.x did it another (a pool of
instances) -- or something like that. That could explain the behavior
being seen here.
BTW, have I included in this thread yet my comment about how
SingleThreadModel is a bad solution and should be avoided? :-). Check
the list archives for more info on this.
> Adrian Janssen wrote:
>
> >The servlet is blocked with one thread inside it. When you make the
> >call with another browser window it starts NEW SECOND thread. This
> >thread is NOT LET INTO the servlet because it implements the
> >SingleThreadModel and there is ALREADY ONE THREAD INSIDE IT.
> >
> >The 4.1 on W2K seems to be incorrect - it should behave like 3.2.1
> >on linux!!!!
> >
> >>-----Original Message-----
> >>From: Patricio Vera S. [SMTP:[EMAIL PROTECTED]]
> >>Sent: 10 December 2002 03:22
> >>To: [EMAIL PROTECTED]
> >>Subject: Re: servlet implementing SingleThreadModel
> >>
> >> That's is the idea, block the servlet so when call with another
> >>browser instance force to execute a new thread....
> >>
> >> It's semms ok in tomcat 4.1 on W2K but not in tomcat 3.2.1 on linux.
> >>
> >>Saludos,
> >>Patricio Vera S.
> >>
> >>
> >>----- Original Message -----
> >>From: "Partha Ranjan Das" <[EMAIL PROTECTED]>
> >>To: <[EMAIL PROTECTED]>
> >>Sent: Tuesday, December 10, 2002 3:10 AM
> >>Subject: Re: servlet implementing SingleThreadModel
> >>
> >>
> >>>if (sOpcion.equals("SS")) {
> >>>
> >>>>> while ( true )
> >>>>> ;
> >>>>> }
> >>>>>
> >>>What does this code do? it will loop eternally.
> >>>
> >>>-----Original Message-----
> >>>From: Adrian Janssen [mailto:[EMAIL PROTECTED]]
> >>>Sent: Tuesday, December 10, 2002 12:27 PM
> >>>To: [EMAIL PROTECTED]
> >>>Subject: Re: servlet implementing SingleThreadModel
> >>>
> >>>
> >>>SingleThreadModel means that only one thread is allowed to run in your
> >>>servlet at a time. So what is happening is with your first call to the
> >>>servlet a thread starts to execute in the servlet - but it never leaves
> >>>
> >>the
> >>
> >>>servlet, as per yopur code. It thereby blocks the second call which will
> >>>start a new thread that will try to run through the servlet but due to
> >>>
> >>the
> >>
> >>>fact the thread from the first call is still running in the servlet the
> >>>second call's thread is blocked due to the restrictions of the
> >>>SingleThreadModel.
> >>>
> >>>So if anything the W2K implementation seems like it might be incorrect,
> >>>
> >>but
> >>
> >>>I suspect that it is setup differently, perhaps with a very short
> >>>
> >>timeout.
> >>
> >>>Cheers
> >>>Adrian
Milt Epstein
Research Programmer
Integration and Software Engineering (ISE)
Campus Information Technologies and Educational Services (CITES)
University of Illinois at Urbana-Champaign (UIUC)
[EMAIL PROTECTED]
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