Hi Mike,

Thanks for your posting. From your description, you've a service process
which expose a remote object as a MessageHandler. Other process (appdomain)
can get that remote object via remoting activation and call the method on
it to send message in the service process. But currrently you're concerning
about the speed the of the method call , yes?

Based on my experience, such cross-boundary calls( cross-appdomain,
cross-process ...) does need some additional time than a normal method
call. In fact, when we invoke a method on a remote object, the first step
occurs on the remote object's client side proxy in the client appdomain,
the proxy generate a Message object represent the method call then the
message go through several sinks and channels , and at the server
process(appdomain) the message is regenerated into stack based method call
on the actual object. So that'll take more time than a normal pure stack
based method call.

In addition, I notice that you're using the sendmessage  in your service
process. Since the SendMessage method will block the method call until the
the message's target window finish processing the message, I suggest you
can try use PostMessage or other async means instead which won't block the
method call. Also, you can also try remotely call a very simple method
(without send message) to see how long it will take and compare with the
method which send messages. That can also help to verify whether it's the
remote message exchange that eat the most times in a complete remote method
call.

Thanks.

Regards,

Steven Cheng
Microsoft Online Support