[python-win32] problem accessing OPC clients from thread

[Jeff Peery]

Hello,
  I'm getting in a bit over my head here and need some help. I'm running a simple wxpython application that runs a thread in the background. The thread is supposed to read and write data to/from an OPC server - which I use to communicate to a PLC (programmable logic controller, for process automation). My OPC module works well for just reading and writing to the OPC server; however when I try to read and write to the OPC server from within the thread it doesn't work. I get this error:
   
  Here's the snippet from my thread:
  # connect to server 
  opcServerName = 'the server name goes here'
  opcItemName = 'the opc item goes here'
  (server, group) = myOPC.connectServer(opcServerName)
  item = myOPC.addItem(opcItemName, group)
  value = myOPC.readItemValue(item)
  # the value return a tuple of info including a value and timestamp and quality

  Here's the error that's returned:
  line 124, in readItemValue
    return opcItem.Read(0x1)
  File "<COMObject AddItem>", line 3, in Read
  File "C:\Python25\lib\site-packages\win32com\client\dynamic.py", line 258, in _ApplyTypes_
    result = self._oleobj_.InvokeTypes(*(dispid, LCID, wFlags, retType, argTypes) + args)
com_error: (-2147352567, 'Exception occurred.', (0, None, None, None, 0, -2147221008), None)
   
  I attached my OPC module, if its important to include the wxapp I can do that to, but it's pretty apparent that the problem only happens when I call my OPC funcitons from within a thread... 
   
  I suppose its also worthwhile to mention that I need to access the OPC module from within a thread (thats not the main applications thread) because I'm trying to aquire data from a PLC and I want to do that continuously and not lock up my program.
   
  Any ideas on how I might get this thing to work within the thread? Thanks!
   
   
  Jeff

       
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