Subj : Re: Hyper Threading / Multi-Threaded Queue / Application Freezes
To   : comp.programming.threads
From : junker98
Date : Wed Apr 20 2005 06:37 am

"Shaw" <nwshaw@gmail.com> wrote in message news:<1113316445.845312.71210@z14g2000cwz.googlegroups.com>...
> have an MFC application which contains a queue which is accessed by
> multiple threads.  The main application thread is used to add items to
> the queue, while I have a worker thread which is used for taking items
> from the queue and passing them to another application.
> 
> The queue is implemented using the MFC CList class, and add/remove
> operations are guarded by a critical section, therefore access to the
> queue is synchronized ( I hope ).
> 
> My problem is this program has run great on 100's of machines for well
> over 12months, however recently has been tested on a Hyper-Threaded XP
> SP2 machine - and for some reasons the application locks up
> periodically.  By "locks up", I mean the application frame freezes (not
> responding) for up to 10-20secs at a time and then returns to normal
> again.  Seems there is some sort of livelock/deadlocal between the
> add/remove operations - however I can't work it out.
> 
> Is there a problem with critical sections and multi threads on HT
> machines?  Anyone had similar problems to this before?
>  
> I can post code snippets if needs be...
>  
> Help (pls)
>  
> Wal

Have you tried running your application on a true multiprocessor box?
Running threaded code on a Hyperthreaded or Multiprocessor machine
will often expose threading bugs that go undetected on Uniprocessor
machines.

I've had numerous experiences with multithreaded code developed on a
single processor machine crashing or hanging when run on
multiprocessor machines due to the increased concurrency of these
systems.

If it runs fine on a multiprocessor box I'd suspect a problem with
Hyperthreading, but if this is not possible to test, I'd spend a bit
of time with the debugger trying to figure out what is going wrong.

Does you code do anything else aside from the add/remove operations
while holding the critical section? Is it definitely the
synchronisation of this queue that is causing the hang?

.