OT - Ted, thanks for the info about the Aspect workshop. It was excellent.
Do you see anyone interested in integrating it into the J2EE framework? I
would love to see this in security authorization especially because
customers I see always end up growing their own.
>From: Ted Neward <[EMAIL PROTECTED]>
>Reply-To: Ted Neward <[EMAIL PROTECTED]>
>To: [EMAIL PROTECTED]
>Subject: Re: EJB reference in Java Pet Store(thread safe???)
>Date: Sat, 12 Jan 2002 01:42:37 -0800
>
>Section 6.5.6 of EJB 1.1 supports your view:
>
>"IF a client-invoked business method is in progress on an instance when
>another client-invoked call, from the same or different client, arrives at
>the same instance, the container must throw the java.rmi.RemoteException to
>the second client."
>
>In the EJB 2.0 spec, though (assuming the Aug 14 2001 release is still the
>final release), there is a footnote at the bottom of the page after that
>exact same sentence (this time in section 7.5.6, p 76) that states that the
>container may queue or serialize the calls, implying that the calls will
>simply block until the first call completes. Hence my posting.
>
>Net result--clients cannot assume anything, and had better synch
>themselves,
>which I believe is exactly your point. We've come to violent agreement. :)
>
>Ted Neward
>{.NET || Java} Course Author & Instructor, DevelopMentor
>(http://www.develop.com)
>http://www.javageeks.com/tneward
>
>----- Original Message -----
>From: "Ian McCallion" <[EMAIL PROTECTED]>
>To: "Ted Neward" <[EMAIL PROTECTED]>
>Sent: Friday, January 11, 2002 4:29 AM
>Subject: Re: [EJB-INT] EJB reference in Java Pet Store(thread safe???)
>
>
> > Ted Neward wrote:
> > >
> > > They *could* become a shared resource, however, if the client runs
>multiple
> > > threads against the same session bean reference, which is quite common
>in
> > > servlet applications....
> > >
> > > The EJB Spec guarantees that only one method call at a time will be
>allowed
> > > on any Bean, IIRC, so other callers will be blocked on any bean method
>until
> > > the first method completes and returns.
> >
> > No. The spec guarantees only one method call at a time will be allowed,
>but
> > containers don't do the synchronisation. So if you don't synchronize
>access to
> > EJBs (EJBHomes and EJBObjects) from servlets you'll get exceptions
>raised
>when
> > race conditions occur. This is not necessarily simply a matter of
>putting
> > synchronize() blocks around the calls to the EJB for two reasons:
> >
> > 1. For very high thruput applications synchronizing calls to EJBHome may
>cause a
> > bottleneck, so get a new copy of the EJBHome object whenever needed.
> >
> > 2. When viewing a page containing buttons that invoke your servlet a web
>user
> > can click the buttons multiple times and if this happens your servlet
>will
>get
> > multiple requests from the user that may be processed in parallel on
>different
> > threads. This potentially nasty situation that can cause several
>problems - not
> > just the problem of parallel invocations of EJBs, so cast your
>synchronization
> > net wide, and carefully choose the object to synchronize on - the
>EJBObject may
> > not be appropriate since it may not always exist.
> >
> > Ian
> >
> > ========================================
> > Ian McCallion
> > Alexis Systems Limited
> > Romsey, UK
> > Tel: +44 1794 514883
> > Fax: +44 1794 501692
> > ========================================
> >
>
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