Re: Threading Model (Both) and cross apartment calls

From:

"Igor Tandetnik" <itandetnik@mvps.org>

Newsgroups:

microsoft.public.vc.atl

Date:

Tue, 3 Oct 2006 15:12:58 -0400

Message-ID:

<uRhq2Cy5GHA.2104@TK2MSFTNGP06.phx.gbl>

buddie84 <buddie84@gmail.com> wrote:

Component : COM- ATL
Threading model - "Both"
FTM / Free Threaded Marshalling supported

This component should support events using Connection points ..

The events may fired from another thread other than Main Thread , and
the outgoing argument IMyObj *pMyObj will be created in the event
thread (multithreaded apartment)

These are two scenarios of cross apartment calls and it should be
resolved :
a) Sink/outgoing interface pointer will be called from event thread
b) The outgoing argument(IMyObj) will be created in "event thread"
which is going to be called from the "main/client thread ".

Case (a) could be resolved using IConnectionPointImplMT ,which use the
marshaled sink .

Can any one suggest how can we resolve Case (b) ?

Case (b) should just work. Since you are now calling from MTA into STA
through a proxy, IMyObj pointer will be marshalled on its way to STA, so
STA thread will get a proxy to it. Any call will be marshalled back into
MTA, execute there, and return back to STA.

Will the COM Standard marshalling do the trick and the client could
safely use Interface by casting it to IDispatch* ?

MyEventImplementaion (VARIANT varMyObj)
{
IMyObj *pMyObj =(IMyObj *) V_DISPATCH(varMyObj);
}

Never downcast a COM interface: use QueryInterface instead.
--
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