Re: COM Object performance in different Threads

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"Ben Childs" <bchilds@wpidotedu> wrote in message
news:%23UFJquPcFHA.720@xxxxxxxxxxxxxxxxxxxxxxx
> Hi,
>
> I am writing an application in C# (VS.NET 2002) that runs performance
> intensive analyses on data sets. In order to keep the UI responsive I have
> created a seperate thread to do the analysis.
>
> I am using my own DLLS to load the data sets from files and run the
> analyses. But I have run into a bit of a problem. If I load the data set
> in the main thread and then run the analysis in the seperate thread the
> analysis takes about 20 times longer than usual. In addition when I try to
> display the results in the gui they take forever to display. So it seems
> that accessing COM objects from different threads than they were created
> in is really slow. Is there any way around this?
>
> One solution for me would be to create a thread that handled all of the
> com objects, however this would be a lot of work and I was wondering if
> there was a simple solution.
>
> Thanks,
>
> -Ben Childs

I see two fundamental problems here.
When you create an instance of a COM object in the main (UI) thread , your
COM methods will execute on the UI thread, irrespective the thread that is
calling a method.
When you calls a method from the UI thread itself, the call is said to be a
direct call, however, when called from another thread (passing the reference
to the objects CCW to the other thread) the call must be marshaled to the UI
thread, this marshaling is done by posting windows messages to the UI
thread's message queue where they are picked up and dispatched to you COM
method which executes the call obviously on the UI thread. The marshalin
overhead make the call somewhat slower, but in general this is not such an
issue.
However, in your scenario, where you are updating the UI from the auxiliary
thread (using Control.BeginInvoke I hope, but I'm afraid you don't) things
get even more slower as the UI thread has to update the UI AND run the
analysis code, in the mean time your auxiliary thread is doing almost
nothing.

One possible solution for this is to:
- create an aux. thread,
- initialize this thread to enter a STA,
- start the thread,
- create an instance of your COM object on this thread and call the COM
methods from here,
- marshal the calls to the UI thread by calling Control.BeginInvoke to
update the UI.

Willy.



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