Hi Stuart,
Thanks for the reply. A few followup questions if you don't mind.
> 1) on any specific node, request.getSession() returns a different
object
> for each request. The sessionId() remains the same, but the actual object
> ID changes. This implies that it is a different representation of the
> session object.
>
Undertow returns a different facade for each request. Undertow uses its
internal representation of a session (io.undertow.server.session.Session)
that is stored in the session manager, and wraps a facade around it
(io.undertow.servlet.spec.HttpSessionImpl) that implements Servlet
semantics.
That's what I had assumed as well, based on the behaviour I had noticed.
Thanks for confirming.
>
> 2) if I persist a local copy of the HttpSession object between requests
> (ex: in a static map) and invalidate the session using the persisted
> object, my request.getSession() object is not updated (ex: the invalid flag
> is still set to false), but the session is dead. Trying to call
> request.getSession().invalidate() throws IllegalStateException as do
> calls to request.getSession().set/getAttribute()
>
I guess this could be considered a bug in that isNew will not throw an
IllegalStateException, which is the only place that the invalid flag is
used without also consulting the underlying session, but you sound as if
you expect the session to still work after it has been invalidated?
No - quite the opposite actually. I'm expecting that all session objects
to react the same after it has been invalidated. If I use one of the
facades from a prior request to invalidate the session, I would expect that
every facade would respect the same state. For instance, if I do the
following:
Request 1:
// store a copy of the session object to be available in a later request
static Session cachedSessionObj = request.getSession();
Request 2:
// invalidate the session from the cached object
cachedSessoinObject.invalidate();
// get a new session
Session newSession = request.getSession();
I would expect that cachedSessionObj.getId() != newSessoin.getId().
However, the request.getSession() doesn't get a new session object. Rather
it still returns the old (now invalidated) session object. So any logic
that is dependent on having a fresh session object fails (since the session
object is returned is actually the invalidated session).
There is no requirement that the same session is represented by a
single
java object, and especially it in a distributed environment this is not
possible. Even though we could keep the same facade around for all requests
this can encourage people to write apps that rely on this behaviour, and
also increases the likelihood that the facade will become tenured and
require a full GC to be reclaimed.
Understood.
> 3) over time, my JVM will actually crash with an
> EXCEPTION_ACCESS_VIOLATION in a GC process. This always seems to correlate
> with a thread that is trying to do some session invalidation via the
> persisted session copy.
>
This is a JVM bug. Which JVM are you using?
I'm running Oracle Hotspot Java 8x64 on a Windows platform (server 2016).
I've tried with both patch 131 and 151, and both exhibit the same
behaviour.
To implement this I would remove the WeakReference which will not work with
Undertow's session management strategy, and instead register a
listener to
remove the session from the local map when it is invalidated. If you really
want to access the underlying Undertow session you can
call io.undertow.servlet.spec.HttpSessionImpl#getSession() to return the
Underlying Undertow session, although it should not be necessary.
I've already removed the WeakReference as soon as I noticed that the
session facade returned by Undertow changed at each request. I am using a
session listener to remove it from the local map when it is invalidated,
but I need an ability for an JMS listener to be able to invalidate a
session object based on an id it receives.
How can I access Undertow's SessionManager from within my application? Is
there any way I can retrieve it from the CDI? I tried adding
the io.undertow.core module to my jboss-deployment-structure.xml, but yet I
can't access it via injection or
via: CDI.current().getBeanManager().getBeans(SessionManager.class); in both
cases it is unable to find the SessionManager class. Is there some other
way I can access it/retrieve it from within my application?
Thanks,
Eric
Is anyone able to explain this behaviour? Why is the session object
> always different between requests? Shouldn't it be the same request? What
> is Undertow doing with the session objects between requests? Is the
> Undertow object being passivated in some way and my attempt to invalidate
> if from within my cached version causing this kind of access violation? Is
> my cached object referencing memory that has been cleared by the GC (ex:
> does the request.getSession() object only a WeakReference to the actual
> Undertow object)?
>
>
> Finally, what would the recommended approach be to doing something like
> this? Using a distributed web-cache is unfortunately not an option at the
> moment. So give that, is there some way to access the Undertow session
> manager directly?
>
> Thanks for any insight. I thought we had a functional solution but in
> production (under real load), the intermittent JVM crashes are telling me
> that our solution is broken.
>
> Eric
>
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