[JDEV] JabberCOM in C++: The problem ...

[Scott Francis]

I've seen so many posts on this list lately about everyone saying how
they can't get JabberCOM to work in using Visual C++ ... So I thought
I'd shed some light on the problem.
Note that this was done without ATL or MFC, just plain-old C++ (win32).

First of all, the reason why your events aren't being called is an issue
with the JabberCOM object itself.  If you look through the JabberCOM
Delphi source, you'll see that after the initial connection is made to
the Jabber server, a second thread is launched to handle all network
communications.  It is also this thread that will fire events back to
the sink.  

The problem?  

Marshalling.  When you pass your sink to JabberCOM, it will work fine
from the thread that registered the sink, but when it's called from any
other thread you get the dreaded RPC_E_WRONG_THREAD error (which is what
is happening in JabberCOM).  When you call CoInitializeEx() make sure
you pass COINIT_MULTITHREADED to it.  The solution for me, was to
implement a free threaded marshaller object within my event sink.
Basically, you need to support some form of marshalling for your event
sink to work, I found that the free threaded marshaller would be the
easiest, because:

a) I knew I would be using JabberCOM in-process
b) it required me to add two lines of code to my source file, and
c) I didn't have to write my own marshaler.

Now doing these things solved the problem of getting JabberCOM to fire
my events.  The second thing you have to do is implement IDispatch.  The
reason you can't use ATL to implement IDispatch for you is because the
event interfaces in the JabberCOM IDL are not defined as dual (why?).
Therefore, you basically need to have a massive switch statement in your
IDispatch::Invoke() method, checking the DISPID's of the method being
invoked.  Then either call your function directly from IDispatch, or
hell, make it inline.  But at least it will be called.

Now, the third thing you have to do, is setup a Global Interface Table
to store your JabberSession IP.  Say you define your JabberSession IP as
global and you try to access it from your event sink, BOOM,
RPC_E_WRONG_THREAD, because your method is being called from the worker
thread in the JabberCOM object.  So what do you do?  Initialize a global
interface table in the main thread of your application, and upon
initializing your JabberSession, pass the interface pointer to
IGlobalInterfaceTable::RegisterInterfaceInGlobal() ... Then you can
access interface by using the GetInterfaceInGlobal() method.  Then go
nuts and use your Session object like crazy.

This should do it ... A couple notes as a summary ... I've talked to
pgmillard (JabberCOM author) about this, and I'm not sure, but I think
he said that he'd modify JabberCOM, so that events are fired from the
main thread, which would eliminate the need for almost everything here.
The only thing you'd then have to do is implement IDispatch.

As far as source code goes ... I'll see what I can do :)

Hope this helps everyone out there that is struggling with JabberCOM in
C++,

Scott.

--
Scott Francis
sfrancis at blueairnetworks.com
http://www.blueairnetworks.com/