Re: multithreaded dialog application

From:

"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>

Newsgroups:

microsoft.public.vc.mfc

Date:

Fri, 29 Jun 2007 11:37:22 -0400

Message-ID:

<LqGdnQXtlOqruhjbnZ2dnUVZ_qGjnZ2d@comcast.com>

Ryan wrote:

My application is a dialog app, with one parent dialog with spawns
several (up to 20 or so) child dialogs. There are basically three
channels of input to the dialogs: user actions and messages that come
in on two seperate threads via socket connections. At this point, all
the socket messages are posted to the main thread to be processed.
Nearly all the socket messages are simply passed on to a child dialog
(or 3 or 4 in some instances) to be processed.

The number of messages received from the sockets can be quite large
and since they come in on two seperate threads, I think it would be
more efficient to handle these messages in multiple threads (this is a
realtime application so we want to reduce latency in processing
messages as much as possible). There is some calculation that is done
to process the various messages that could be pushed to a worker
thread, but nearly every message results in a UI update as well.

My understanding is that there is no safe way to update the UI from
any threads other than the main thread. I'd like to know if this is
correct. It's not clear from what I read, but I'm hoping it may be
possible to create child dialogs in a seperate UI thread. If this
could be done for even one dialog, I believe we would derive
significant benefit from this. My concern is in still being able to
link the child dialog back to the parent dialog if they are in
seperate threads.

Can anyone give some advice on what possible options I have or if I am
really stuck posting everything to the main thread?

It's not clear what you are trying to fix. You can't have a parent
window in one thread and child windows in a different thread.

If you have significant latency then perhaps you have too many messages
stacking up between the threads. If that is the case look for ways to
combine messages. You may also be able to do the update painting more
efficiently: Are you painting more than you need to paint when you do an
update?

Your assumption that more threads would help is quite questionable. More
threads add more overhead and reduce the time available to the main
thread for painting. If you have only one network interface then there
is little or nothing to be gained by having multiple socket threads:
Only one network message can arrive at a time.

--
Scott McPhillips [MVP VC++]