array blink indicator

[Da5idF]

Hello,

Given: Can't assign attributes for individual elements of an array.

But we can, obviously, have different values for each element of an array.

In attempt to make a blinking progress bar (where only one element is blinking), I:

1) Used an array of color boxes (I think you suggested this in another post).

2) Constructed an actor that blinks a color box.

   a. Parameters are fgd, bgd, blink rate and a reference to the color box to be blinked.

   b. This works for individual color boxes (where I can easily get a reference to them).

3) I can't, and I've tried, find a way to get a reference to an element of an array (that I can then pass to this actor).

Note: I'm not trying to change the attributes of elements of this array, only their values via a reference.

Q: Is this reality? Or is there an entirely different way to do this?

Thanks in advance,

Dave

[RavensFan]

You take a reference to an entire array of color boxes.  The value property is an array of values.  Change the value of individual elements within that array.  (Replace Array Element).

[Da5idF]

Thanks again!

Here's the working code. Is this doing a read-mod-write on the whole array? Just to overwrite one element?

-Dave

The reason this could be important is that other threads may be accessing (and wanting to blink) other elements of the array. I can see a way to coordinate this, but I don't want to do that if it isn't necessary.

[RavensFan]

Yes.  But if you have conflicts because of other stuff accessing it at the same time, you need a better architecture.

I know of at least three options, I'll put them in the order I would use them if it was my project.

1.  Older, but still good.  A functional global variable.  Commands to read an array element or set an array element.  It is a single run while loop where the data is stored in the FGV in an uninitialized shift register.  Because the subVI is non-reentrant, only 1 location can access it at a time.

2.  A data value reference.  Came about in more recent versions of LabVIEW, you pass a reference to the data around,  Use an In Place Element structure to access the data.  It puts a lock on the data so that other locations can't interfere at the same time.

3.  Single element Queue.  Data is in a queue.  Any place that needs it dequeues the array, modifies it, then re-enqueues it.  Other places can't conflict because if they try to read it at the same time, the queue will be empty and will wait for it to be re-enqueued.  I don't think this is used as much now that Data Value References exist.

[Da5idF]

RavensFan,

Thanks again... three ways of making a mutex. I'll use method (2).

But is it true... that the whole array is read-mod-write?

-Dave

[RavensFan]

I'd say yes and no.

Certainly for method 3.

With method 1 with the FGV, you could create a command that is modify element and use another input to tell which index you are modifying.  Then you'd just use Replace Array Subset within that case to act on a specific index.

For Method 2, the In Place Element structure has the ability to also read and replace one or more specific indices.

[Da5idF]

This is working:

Thank you!

-Dave

[RavensFan]

That will work as long as you aren't trying to do that in 2 or more places at the same time.

That is effectively doing the same thing as what you are doing in message 13.

Now if you wrapped that in a non-reentrant subVI and always use that subVI when setting the value of an array element, you'll be okay.

[Da5idF]

Maybe I'm beating a dead horse here, but I'd like this color box blink actor to be agnostic to whether the indicator is a scalar, an element in an array, or in the primary circumstance I'm considering, an element in an array of clusters.

As I understand it, the techniques we've discussed require the blink actor to know how the indicator is "declared".

If I could just pass a reference to a single color box to the actor, regardless of how it's arranged, I'd be good. But I don't yet see a way to get that reference if the color box is in an array (I know how to do this if the CB is an element in a cluster or if it's a scalar).

"Giving up" in this case might mean using a variant and then having the actor figure things out. But it seems so unnecessarily ugly.

What am I missing?

Thanks,

Dave

[Da5idF]

And this use case shouldn't be that uncommon.

1) If I had an array of numerics, where each numeric represents the same process parameter type (temp let's say) measured at different points on a production line and

2) I wanted to use an actor for each element in the array (to update those elements asynchronously to each other) and

3) I wanted the actor to work on scalars or on an array (so I could reuse that code), I'd have the same problem to solve, right?

I must be missing something obvious.

-Dave

PS: Maybe the "scalar" should be an 1D array with only one element in it? That would be a weird work around.