Re: Missing events

"Igor Tandetnik" <>
Thu, 3 Jan 2008 08:02:53 -0500
"spforeman" <> wrote in message

When the COM server starts it calls CoInitializeEx(NULL,
COINIT_MULTITHREADED); and then initialises the hardware (camera, lens
control etc). The server has a COM control that exposes a focus
method, which is what the main app calls to perform the focus.

As the focus routine can take a short while (up to 30s) a worker
thread is created to perform the routine described in my previous post
(steps 1-6) so that the function can return. Progress is monitored
via events. The worker thread is passed pointers to the hardware for
the camera and lens. Up until now these camera and lens objects have
not been COM based and have just used 3rd party API calls.

Is it ok for this worker thread to fire off the progress events (I
pass a pointer into the thread so it can do this) or should I be
posting messages back to the main control and getting it to fire the

It is OK if the worker thread also joins MTA (by calling CoInitializeEx
just like the main thread).

Either way this has all been working ok for about a year now...until a
few weeks ago when I was asked to use a new focus lens. The new lens
is controlled via a COM server, which I know is written in VB (if that
makes any difference). To try and keep the hardware abstracted I
created a new type of lens object that derives from the same base
class as the original lens object I had.

So this means that when my server is started it creates an object that
internally uses this new COM control. A pointer to this object is
then passed to the focus worker thread so it can control the lens.

Again, this is OK if the worker thread joins MTA. Be aware that the
events from the "lens server" will arrive on yet another thread from a
pool COM maintains on your behalf - not on your main or worker thread.
Make sure your lens wrapper class is thread-safe and prepared for this.
With best wishes,
    Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not
necessarily a good idea. It is hard to be sure where they are going to
land, and it could be dangerous sitting under them as they fly
overhead. -- RFC 1925

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