Ok, thanks.
If I have a multithreaded application but use COM objects only within the secondary thread is pythoncom.CoInitialize() still required? So if I understand correctly, I could go the route I'm headed, but my code might be simpler and more reliable if I setup an event handler for the DataChange event of the group (as Graham pointed out). If that is the case, where might I go to learn about how to set that up? I appreciate your help! Jeff -----Original Message----------------------------------- Message: 4 Date: Mon, 03 Dec 2007 14:33:11 -0800 From: Tim Roberts <[EMAIL PROTECTED]> Subject: Re: [python-win32] problem accessing OPC clients from thread To: Python-Win32 List <python-win32@python.org> Message-ID: <[EMAIL PROTECTED]> Content-Type: text/plain; charset=UTF-8 Jeff Peery wrote: > > Graham, > > thanks for the beta! I think my main problem is that I don?t really > understand this code; I didn?t write it. Could you recommend a > book/website that describes what these functions like > ?group.OPCItems.AddItem? do? For example I don?t really know what a > ?group? is or what the addItem() parameters are, or how to interpret > that error code that you interpreted, and I?m not really sure if this > code will work for other OPC servers other than the automation direct > server. > Although I can understand your frustration, I want to make sure you understand that the trouble you reported has nothing to do with the OPC tools or their usage. It is quite complicated to use COM objects in a multithreaded application. A COM object is allowed to declare itself as single-threaded; in that case, COM takes extra steps to transfer control over to a single thread before calling that object. To do that, COM has to have some per-thread data structures to communicate between threads. The way that setup gets done is by calling the CoInitialize API (exposed in Python as pythoncom.CoInitialize). If a multithreaded application expects to use COM objects in several threads, it is REQUIRED to call CoInitialize from every thread. The pywin32 library will call CoInitialize on the main thread for you, but YOU are responsible for calling it from your secondary threads. -- Tim Roberts, [EMAIL PROTECTED] Providenza & Boekelheide, Inc.
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