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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