Re: [SunONE-JATO] Frame Loading

Question

Divakar,
A very challenging scenario for all app servers, especially J2EE web
containers, is concurrent access to session. The HttpSession API does
not provide an interface for either the container vendor or the
developer to manage concurrency issues or events discretely; therefore,
there is little JATO or any framework can do to help you with
concurrency issues AND not add container behavior. The container
vendors have to rely upon implementation details to manage these complex
scenarios. Be that as it may (which is mostly my opinion anyways), the
iAS engineers have worked long and hard the last year from iAS 6.0 sp2
thru 6.5 to deal with issues around session concurrency; the discussion
of which can be fairly verbose. What is important and in some ways
unfortunate, is that the handling on these concurrency scenarios is
different between releases. I believe that there is no blocking/locking
in sp2 and earlier (resembling NetDynamics 3.x behavior). In sp3 (your
case) concurrent access was serialized (resembling in some ways
NetDynamics 4.x and 5.x) In sp4 it was changed again and finally in 6.5
it was improved to ensure data coherency and stability with locking
while eliminating locks within the same JVM. If you would like details
email me offline at [matthew.stevens@s...] and I will see what I can do.
No matter what version of iAS you are using, please ensure that your
application is deployed with Sticky load-balancing such that request
process is handled by the same JVM per session. In this way, you avoid
the 'distributed' computing problem of locking across processes and
machines. In other words, you have far less chance of hung request
threads if you use sticky load-balancing.
You need to establish some debug techniques in your development
environment for J2EE to assess hangs or latencies (there are plenty of
synchronous APIs in any J2EE container so this is not just an iAS thing
or Session concurrency thing). If you are on Solaris you may issue a
kill -3 PID
of the JVM running the web container. Sending this SIGQUIT signal to
the JVM will trap the JVM and result in a full thread dump to the
STDERR. For instance, for iAS you would find the JVM (.kjs) spawned by
the kjs script and send it a SIGQUIT. You should very easily see in the
stack traces of the threads, your own thread which is above the dispatch
to your module servlet [ie. you will see the
<ApplicationServletBase.processRequest()] stack frame in the stack trace.
If you are on Win32 you can run the iAS engines in the foreground by
invoking iAS from the command line [kas -debug] in which case the KJS
will appear in its own console window which you can CTRLBREAK to see the
stack trace.
In this way, you can see what your web container is doing while it is
latent or hung.
In your case, you will probably see your request thread blocked in calls
to PlatformNASSession or PlatformLITESession. These two classes are the
HttpSession implementations for iAS. The 'NAS' session uses the HA
Dsync sub-system for replicated attribute backing store and the 'LITE'
session uses an regular HashTable for the backing store.
Again, concurrency issues are FAR MORE complex with the distributed
implementation. Therefore, as an isolation technique, you may want to
confirm that you are using session-impl=lite in your iAS deployment
descriptor so as to avoid the Dsync implementation. Using Session LITE
should eliminate the hangs during concurrent frame loads.
Is it possible for you to upgrade to iAS 6.5? What about iAS 6.0 sp4?
Please remember to leverage the JATO front controller events, even if it
is for debug. You have the onBeforeRequest event where you could
intercept the front controller before it has bothered with the
HttpSession APIs. For isolation purposes, you could enter a critical
section from your derived onBeforeRequest event to see whether
concurrency is an issue in your case.
I hope this "frames" the problem space for you 8-) Please post any
questions or results from your testing and we can try to help further.
The best information we can use to help you is the stack trace for the
hang condition.
thanks,
matt
padiyar wrote:
I am facing problems with FrameSet loading.
I have a frameset having two frames and src defined
for both. Sometimes one of the frames doesnt get loaded.
I am using iAS 6.0 with SP3 and JATO 1.2
<FRAMESET COLS="200,*" BORDER=0 FRAMEBORDER=no>
<FRAME NAME="Frame1" SRC="../AppName/pgMenu" MARGINHEIGHT=0
MARGINWIDTH=10 SCROLLING=auto NORESIZE >
<FRAME NAME="Frame2" SRC="../AppName/pgDetail" MARGINHEIGHT=6
MARGINWIDTH=12 SCROLLING=auto RESIZE >
</FRAMESET>
From the kjs logs i noticed that onAfterRequest is not getting called
while first frame's viewbean is being executed and kjs just hangs.
If I set the SRC for one of the frames as viewbean and the other one
a blank.html and trigger the loading of second frame using javascript
on load of the first frame it works fine. But i dont
want to go for this approach.
Did anybody faced this problem and know how to fix this without using
javascripts?
Thanks,
Divakar
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Answer 1

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