start/stop local variables question

[chuman]

Hello,

Attached, please fine 2 similar vi. In whileStoop.vi, I can start or stop the program at any x+y values.  But, in eventStoop.vi, I cannot use stop when program is executing (program will terminate when x+y =10).  Why does start/stop local variable not work in my eventStoop.vi? 

Thanks,
Chuman

[jon_mcbee]

In regards to the eventStoop.vi.  When you hit the start/stop boolean control you enter the start/stop state of your event structure.  Once you are in this state the boolean control will not register until whatever code in that state has executed. Once the state has finished executing control goes back to the outer while loop and it waits for you to trigger the event structure again.  That said, I dont know what the aim or purpose of this program is, I am guessing its main purpose is to help you learn?  Since your aim is to learn, one thing you should try to stay away from is the use of local variables.  They could cause race conidtions and they break the data flow paradigm that good LabVIEW code is supposed to adhere to.  One artifact of your use of local variables is that you had to use sequence structures to force your code to operate correctly.  It is better to enforce this using dataflow (aka wires).  The event structure approach is probably not the best way to solve this problem.  You should try and remove the local variables and sequence structures from your while loop version.  I hope I answered your question.

[RavensFan · Accepted solution]

It is a bad idea to have an event structure that contains code that takes a long time to execute such as the while loops inside the case in your situation.

It probably doesn't stop because you have Lock Front Panel until the event for this case completes checked.  So when the Start/Stop button is pressed, the even case executes and the while loops begin running.  But because the front panel is locked, it can't detect the change in Start/Stop again which is necessary to stop the inner while loops.