We are certain that a vendor DLL is getting hung that takes down their
application. We cannot figure out how to tell if a DLL is hung
(stopped in code, running in a endless loop, etc). Is there a way to
detect if a DLL is running amok? We see it loaded using MSINFO.EXE but
it doesn't show any more than that. This is running on a Win2000
Server with all the latest Service Packs and HotFixes. The application
is a third party web based e-commerce package.

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Request for Question Clarification by answerguru-ga on 18 Dec 2002 14:45 PST

Hi there,

Can you define "hung"? Do you get an error message or see programs
closing? Or is there just a pause in activity every so often that goes
away after a little while?

answerguru-ga

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Clarification of Question by buyoguru-ga on 18 Dec 2002 16:10 PST

Hung means that the application stops working and only those users
that use that application are affected. The Web App uses several DLLs
as provided by the Vendor. Once in a great while the App (Web Stores)
stops working although everything seems to be OK; i.e the Data Base,
the Server, other Web pages, etc. So the OS and Data Base and other
tools seem to be OK. After beating this extensively and having a good
knowledge of Software and Hardware engineering, my only conclusion is
that a DLL created by the Vendor and used by the Users of the
E-Commerce store gets hung, bringing everything to a stop. My probblem
is identifying that the DLL is "hung" and which DLL (the store app has
several running).

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Clarification of Question by buyoguru-ga on 18 Dec 2002 16:17 PST

In addition, there are no error messages and no logs (including the
System and App Logs). Also, we have never seen it kick back on
although we typically react quickly when this happens because we have
many screaming customers calling and emailing so we never had the
chance past 30 minutes or so to see if the App starts to work again.
From my 20+ years of software development and systems management, this
is usually an indication that a process is in a loop or at an impasse,
maybe due to a system level error. Since these are shared DLLs, it is
logical that if the DLL gets "hung", all users of that DLL are also
hung.

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Request for Question Clarification by answerguru-ga on 18 Dec 2002 18:50 PST

I agree, from my experience that type of problem is usually present in
this type of situation. However, without any error logs I have not
come across any ways to detect which DLL is faulty. Of course, other
researchers may have insights that could help you so you may want to
let this question sit for a while..

answerguru-ga

It sounds like a problem that needs to be addressed by the vendor, one
way or the other.  What a DLL implements might be germane to
diagnostic techniques, ie. is it an ordinary DLL, or does it implement
COM interfaces?  You describe it as a "shared" DLL, but this is not
really a clear description.  From the surrounding discussion of "Web
stores" and "E-commerce" one might guess that the DLL is the
implementation of an ASP/Webclass project in VB 6.0.  Without knowing
more it's hard to suggest a way to determine whether the application
or the DLL is at fault.

If the DLL were in an infinite loop, then the Task Manager would
almost surely show the excess CPU cycles as being consumed by the
application.  You don't mention this, however, which leads me to think
that the application may be unable to allocate threads, database
connections, or some other kind of critical resource.

Despite not being able to diagnose the problem on the vendor's behalf,
I would certainly try to have them address the issue.  Depending on
their size, they may have previously diagnosed the problem for another
customer, and unless they are comparable in size to Microsoft, they
probably value your opinion of them and their product.

regards, mathtalk-ga

I agree and appreciate your thoughts. The app does not show in the
Task Manager; I wish it did for the reasons you pointed out. If you go
to MSINFO.EXE, Software > Loaded Modules, you see several of the
Vendors DLLs loaded and running. However MSINFO does not tell you the
resources that the process is utilizing. If nothing else, this tells
me that I know as much as anyone else and have no where to go with the
problem but back to the Vendor who may be reluctant or at least
critical of the thought that this provokes. They are a small/medium
size vendor.

Note that a dll, can hang in two ways. 

Endless loop which means it will use ressources from the CPU, and in
worst case all CPU ressources.

Stuck in code, in which case it does not use CPU ressources, but stops
responding.

You can download Faber Toys from
http://www.faberbox.com/fabertoys.asp?action=download (Freeware) and
watch the vendors DLLs.

Note that if the application runs within IIS on windows 2000 it might
be a problem MTS/COM+ not being able to running the application. Use
the windows MTS or COM+ tools see how the dll is configured and/or how
it runs as well as set up logging.

TMJ