Why does this keep duplicating values?

Question

Hi, I have this sub vi that reads opc values(addresses) from a server across a local network. It uses a data socket read within a for loop to pass these values into an array. The problem i have is every so often it duplicates the same value rather than just reading the exact address in the opc array.
e.g.
123      123
103      103
110      103
121      110
Which may values that i save in a spread sheet out of sequence. Anyone knows whats wrong here?
Stuart
Attachments:
RandD Cell room Software Project.llb ‏415 KB

Answer 1

Your code has a lot of issues.
First do a block diagram cleanup, you have a lot of wires with unnecessary bends and sections of code scattered all over the place.
Why do you have 13? stop buttons.  Then proceed to crash your code by wiring the real Stop button to a Stop LabVIEW stop sign?  That is like hitting the abort button on the toolbar.  Not a good way to stop a program.
I think you are seeing the effects of a race condition caused by the use of local variables.  You are writing to an indicator on one loop and reading from its local variable in another loop.  Depending on where each independent parallel loop is in its execution, you could read duplicate values (i.e., the indicator was not updated in between), or miss a value (indicator updated twice without being read.)  You should be using a producer/consumer architecture with queues to pass data if you want to avoid this problem.
I would suggest spending more time on the forums reading up on race conditions, queues, and the LabVIEW style guide.
Message Edited by Ravens Fan on 01-28-2010 11:24 AM