[osg-users] Threading and such, Was: Re: [osg-submissions] Platformindependentmatrixmultiplicationoptimization

Mathias Fröhlich M.Froehlich at science-computing.de
Wed Sep 24 00:31:33 PDT 2008

Hi James,

I have moved that to osg-users. No longer in any way a submission related 
thing ...

On Wednesday 24 September 2008 00:15, James Killian wrote:
> I have had an opportunity to work with a case where I need a many-to-one
> relationship.  So for example lets say there are several threads working in
> tandem, and they simply make a function/method call, and at any given
> timeslice a single thread will process all the calls that happened in its
> own thread.  There is a win32 way to handle this without the need of any
> critical sections, mutex, semaphore, setevent, etc...  This would be done
> VIA passing function pointers (i.e. these could be cpp methods too) in the
> APC queue.  What then happens is during the context switch the OS processes
> all method calls passed in (this can work with parameters too) and calls
> the methods in the same single thread.   This works best for cases where
> there is work to be done from a single point.
> Ideally the client code would be easier to write, and with all atomic
> operations make the synchronization more efficient than using other
> synchronization techniques.  The downside of course is trying to have some
> generic form of this technique for other platforms, but there may be a
> possibility of this happening.
> So this is the idea.  The thing which I am not sure about is if this could
> be useful when culling works together with opengl (or other similar
> serialization processes).  I also do not know if the gain would be
> significant for these cases.  One thing is for certain... the absence of
> critical sections is good in that it decreases the chance for deadlocks.
> The client code would have a method to handle outside thread calls.  This
> method simply invokes some ThreadCall(bool
> wait_for_return,thread,instance,func ptr, ... parms) and then the actual
> method would auto-magically be called on the thread (whatever parameter
> which was passed in as thread) timeslice interval .
> If this sounds like a cool technique to pursue then I could see what I can
> do to provide more info.

What you are talking about is some kind of queue that can be filled by many 
threads and emptied by a single thread at a specified time.
So what you basically need to do is, have either a lockless queue 
implementation or a mutex that protects that queue. Note that even if you do 
not see that fact behind the win32 api, that must happen inside that APC 
queue anyway. So you have exactly the same serialization points than you have 
in any case ...
For lockless queues/lists, google for RCU/list/queue to see how this can be 
done. It is relatively simple using atomic compare and swap operations.

But anyway, I do still not see where you want that serialized events to be 
And where this sould happen in osg and for what reason?
I am sure I miss something important...

May be you put that in your application library for your use???



Dr. Mathias Fröhlich, science + computing ag, Software Solutions
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