Whilst Entity Beans may not be 100% thread safe( you can't use the
synchronized keyword) the spec does suggest (and it is the default behavior)
that they should be Non Reentrant, Session Beans are always Non reentrant.
If they are non reentrant then threading is not a problem.
If you allow an Entity been to be reentrant then you open it up to
multithreading... with no synchronized keyword allowed then you better be
sure of what you are doing.
Hope it helps
Karl
-----Original Message-----
From: Jorgen Thelin [mailto:[EMAIL PROTECTED]]
Sent: 22 July 2000 13:15
To: [EMAIL PROTECTED]
Subject: Re: Is a Proxy is thread-safe?
Thibault Cuvillier <[EMAIL PROTECTED]> writes:
>Hi,
>
>2 short questions:
>
>Is a proxy to an EJB instance is thread safe?
It depends exactly how you define "thread safe"!
The EJB architecture and specification says that an EJB *instance* can
only be used by one thread at one, so in that sense the answer is NO.
There is a slight trick here, as there is not always a one-to-one
mapping between EJB *references* (proxies) and EJB *instances*.
As an example a stateless session bean reference may well use a
different instance on each call [depending on the exact instance pooling
implementation and policy of the server, etc, etc], so the answer may
well be YES in that case, but is probably implementation-specific.
The EJB spec does not (AFAIK) preclude an EJB reference being created on
one thread and being passed to and used from another thread [provided
you do not get simultaneous use from multiple threads], so in that sense
the answer is MAYBE, and probably YES.
.... HOWEVER, all the "caller context" information (current transaction,
current security credentials) is basically thread-based, so the second
thread may well not be making a call with exactly the same context
environment, so in that sense the answer is MAYBE, but probably NO.
[It can depend to some extent exactly how the server has been
implemented whether this is a problem or not.]
Overall, I would *tend* to say EJB *references* (proxies) ARE NOT thread
safe in the normal expected definition of such things - i.e. don't write
programs relying on it.
Put another way, as a developer you do always have to aware of threading
issues in the client tier, and be particularly conscious that you make
an EJB call from the right thread -- just as you have to with Swing GUI
coding.
[Note, this is completely different from the question of whether an
actual bean instance (on the server-side) can create threads, but lets
not get into that discussion again!]
>Is a proxy to an EJB Home is thread safe ?
Most probably YES, but it may well be implementation-specific in
reality.
Again, the "caller context" *may* play a part, and the underlying
middleware itself may not be able to cope with simultaneous calls, but I
very much doubt this will be a problem with any proper middleware.
So I would *tend* to say EJB Home references (proxies) *should* be
thread safe, but check with your server vendor for confirmation.
I am not sure the spec is explicit about this matter though, so whether
it is safe to rely on this situation for all servers is perhaps
debatable.
Surely the whole point of the EJB spec is to define an architecture that
allows your programs to work identically on *any* EJB server, so if it
is not defined in the spec, it should really be regarded as server-
specific IMHO.
[No doubt someone will point us to the appropriate place in the spec if
it *is* actually specified somewhere!]
>
>I cannot find any information in the spec, and I read a lot of different
>responses.
>Is it middleware dependant ?
>
>Any idea?
>Tibo.
>
Hope that helps, rather than just confusing the matter even more!
- Jorgen
----------------------------------------------------------------------
| Orbware Ltd http://www.orbware.com/ |
| --- Enterprise technology for the "real world" --- |
| Try the OrCAS EJB server -- Completely free for development use. |
----------------------------------------------------------------------
===========================================================================
To unsubscribe, send email to [EMAIL PROTECTED] and include in the body
of the message "signoff EJB-INTEREST". For general help, send email to
[EMAIL PROTECTED] and include in the body of the message "help".
===========================================================================
To unsubscribe, send email to [EMAIL PROTECTED] and include in the body
of the message "signoff EJB-INTEREST". For general help, send email to
[EMAIL PROTECTED] and include in the body of the message "help".
