single frame sequence structure

[VI_Joe]

The following code came from the security system sample CLD exam.  I don't understand why a single frame sequence structure was used in this case?  Can anyone explaine?

Thanks in advance.

[smercurio_fc]

It's to prevent a race condition. Presumably, that indicator can get updated in another case, but the shift register would not. In that case you want to see if the indicator data is different before the indicator gets updated with the contents of the shift register. Without the frame the indicator could be updated before the local variable gets read.

I'm also kind of surprised to see the method being used to construct the path that way in a sample CLD exam. Paths should not be specified using strings. (Waving finger in the air) Bad programmer, bad programmer. 

[Vsh]

Well, VI Joe,

It is to avoid race around condition 

It makes sure that the data from the indicator Zone status Indicators is read through its local variable before a new data being written to the same indicator. 

Perhaps it could have been avoided by having a shift register for storing old data. But the developer might have thought that its unnecessary  to add another shift register for a simple value change comparison at a single case 

[DFGray · Accepted solution]

Although I do not know (even though I work at NI), that code looks like the kind of polling code that was common before the event structure showed up.  Proper use of the event structure would eliminate the need for the locals and this check.