topic Re: Interrupting sequence structures in LabVIEW

Interrupting sequence structures

KFod — Sun, 28 Jun 2015 18:13:09 GMT

Say, for example, I have a case structure with two cases. In each case, there is a sequence structure. If case 1 is true and the program is running that particular sequence, would switching to case 2 immediately cut off the sequence from case 1 and leave it incomplete in favor of executing the sequence from case 2?

Re: Interrupting sequence structures

RavensFan — Sun, 28 Jun 2015 18:16:00 GMT

No.

How would the program know that it should be in case 2 until case 1 ends, the loop iterates, and it has a chance to read the condition that determines which case to execute?

I would recommend looking at the online LabVIEW tutorials
LabVIEW Introduction Course - Three Hours
LabVIEW Introduction Course - Six Hours

Re: Interrupting sequence structures

KFod — Sun, 28 Jun 2015 18:22:51 GMT

The program would know that it should switch to case 2 based on another input that is outside of the structures, like a user controlled boolean, for example. All of this would be going on inside a while loop, by the way.

I apologize for not adding those details earlier.

Re: Interrupting sequence structures

RavensFan — Sun, 28 Jun 2015 18:31:16 GMT

No. Which case gets executed is determined by the value in the wire going into the selector terminal at the beginning of the case structure. Where or how that value is getting into the wire is irrelevant.

That wire doesn't execute again, and the selector doesn't determine which case to execute until the current iteration of the loop ends, which includes all code inside that loop ending, including all code inside any internal structures such as the case structure. Only then will the loop iterate again, the value travels down that wire into the case structure selector terminal, and then the appropriate case of the case structure begins executing.

This is all basic dataflow rules that LabVIEW executes, and you need to take those tutorials to begin understanding that. Set up and example in code, then run it with highlight execution turned on and follow along.

Re: Interrupting sequence structures

altenbach — Sun, 28 Jun 2015 18:33:58 GMT

you need to learn the basics of dataflow. Sequence structures need to complete, they cannot be interrupted. While the code is inside the sequence, it cannot read controls outside of it, unless that other control is in a parallel loop.

What you need is a state machine. This not only eliminates the sequence structures, it will also make the code logical and maintainable.

Re: Interrupting sequence structures

palanivel — Sun, 28 Jun 2015 18:32:42 GMT

It is suggested that not to use sequence structure unnecessarily..... it's not possible to abort in case of developing applications where emergency is major criteria

Pls mention your expected result and actual results clearly

Snap /vi attachment will be useful

Re: Interrupting sequence structures

KFod — Sun, 28 Jun 2015 18:34:02 GMT

I'll have to look at the tutorial videos again. Is there a way to interrupt the sequence before it completes, by any chance?

Re: Interrupting sequence structures

Dennis_Knutson — Sun, 28 Jun 2015 18:36:54 GMT

Three different people have said no. I'll be the fourth to say the same thing.

Re: Interrupting sequence structures

palanivel — Sun, 28 Jun 2015 18:38:39 GMT

No way ......
You need to have some variable and case inside sequence
variable has to decide whether case to run / not....

Here "variable" takes its value from your interrupt signal...

Re: Interrupting sequence structures

natasftw — Sun, 28 Jun 2015 20:02:23 GMT

@palanivel wrote:
No way ......
You need to have some variable and case inside sequence
variable has to decide whether case to run / not....

Here "variable" takes its value from your interrupt signal...

This is bad advice. Alone, variables and sequence structures are dangerous to use if you don't understand them. You don't fix bad architecture by making it worse. Avoid doing something like this... ever.

You've been told by multiple people that you can't stop the sequence structure once it's started. That's a general dataflow principle. It's going to run. The best advice you've been given in this thread is to take a look at a state machine architecture. It's exactly what you're describing and doesn't require making your achitecture even worse to accomplish your goals.

Re: Interrupting sequence structures

palanivel — Sun, 28 Jun 2015 20:07:42 GMT

Pls look at my previous post... which I have suggested...

If his project needs that and if it is unavoidable I have given a way In different way....
I mentioned it's not recommended

Thought thanks for your suggestion....

Re: Interrupting sequence structures

palanivel — Sun, 28 Jun 2015 20:10:04 GMT

pls look at this post suggested earlier @nataswft

It is suggested that not to use sequence structure unnecessarily..... it's not possible to abort in case of developing applications where emergency is major criteria

Re: Interrupting sequence structures

altenbach — Sun, 28 Jun 2015 20:14:18 GMT

@palanivel wrote:
Pls look at my previous post... which I have suggested...

@palanivel wrote:
@PLS look at this post suggested earlier @nataswft

Please (NOT pls!) don't clutter the forum with repetitive and trivial posts that have little to do with solving the problem.

And please use full words, this is not twitter.

Re: Interrupting sequence structures

natasftw — Sun, 28 Jun 2015 20:43:06 GMT

I've seen a lot of your posts.

Here's the problem. There's no such thing as a project where this is unavoidable. If he needs to abort his sequential tasks in the middle, the solution isn't to further muddy the architecture. It's to fix the architecture.

Most of your posts are trying to find a way to use tools poorly in the fear that helping them choose the correct tool won't go over well. You're not helping anyone when you do this. You're essentially saying "it's not recommended to use a hammer with your screw, but maybe if you use your left hand instead of your right it'll work alright?" That doesn't make sense. Don't advocate for bad design. Don't find workarounds for bad design and suggest the bad design can't be avoided. That's a terrible habit. Instead, show people the tools that are available that solve their problem. Not only is it possible to change the architecture here, it's REQUIRED. Pointing me to your other posts won't change this.