🚀 go-pugleaf

In article <4014dcf8$1@newsgroups.borland.com>, Richard Bibby wrote:
> I have an application that generates Crystal Reports document. Along the way
> it creates an xml document (TXMLDocument) and a com object.
> 
> This app works fine... and i have a single procedure call that does all the
> hard work.
> 
> The problem occurs when i start to use the wm_copydata message.
> 
> I want other apps to be able to send a message to mine so that they can use
> my app as a sort of  "crystal reports print server"
> 
> I have create a message method connected to the wm_copydata message.  The
> message identifies the document to be printed.
> 
> However i am getting all sorts of problems in the wm_copydata message
> method.  It does not appear to like my call to create a  xml document.
> 
> The second line here throws an exception:
> 
>         //create DOM document instance
>         Reply := TXMLDocument.Create( nil );

And what is the exception message? 

> Reply is declared as IXMLDocument.
> 
> I can place this code anywhere in my app, and it works. It just doesn't work
> in the wm_copydata message method.

COM things sometimes do not work properly inside cross-process message 
handlers since COM uses messages itself internally for marshalling data 
between threads. Sometimes this can be fixed simply be using the correct 
method to send the message (i.e. SendMessageTimeout with SMTO_NORMAL, not with 
SMTO_BLOCK. Do not use SendMessage!). If this does not work in your case one 
option is to make a copy of the passed data into local memory, call 
ReplyMessage to release the sender thread, and then process the data. An 
equivalent method would be to post a message to self in the receiving program 
(with the address of the local memory block) and process the data in the 
handler for this message. Both techniques decouple the original sender from 
processing the request. 


--
Peter Below (TeamB)  
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