Labview: creating subVIs makes the Block Diagram expand

Question

I wrote a rather complicated piece of code in Labview (with many loops and other sequences). Therefore I want to create many subVIs to make my code more clear.

When I have a loop in the code I want to have in a subVI, the icon of the newly created subVI appears far away form my original piece of code, causing my Block Diagram to expand.

Why does it happen and how can I avoid it?

The piece of code I want to turn into a subVI:

The same fragment of my Block Diagram after I created the subVI:

And here is my newly created subVI - approximately 1 m to the right at 1 m down in comparison with the first piece of code:

Answer 1

Thanks for adding images -- that is quite an inflation of the block diagram.

I don't know why LabVIEW is behaving that way, but my guess is that the control and indicator references are contributing.

As for ways to prevent it from happening, aside from refactoring the code (which is likely necessary anyway), you can try turning off automatic wire routing: Tools » Options » Block Diagram » Uncheck 'Enable automatic wire routing'.

Avoid creating subVIs that contain terminals in a structure

However, to move the block diagram's complexity into a sub VI will require some refactoring because you want to include a while loop that changes behavior based on front panel input (like the stop abs 2 boolean button). Otherwise, whatever value stop abs 2 has when the new sub VI executes will not change while it's running.

The LabVIEW Help reiterates this point: "Because the terminal remains on the original block diagram and the terminal is wired to the new subVI, the subVI does not update the value of the terminal on every iteration of the loop inside the subVI."

Here is an illustration.

Communicating with running subVIs

To send input and receive output from a sub VI while it is executing requires some data synchronization like queues or notifiers. Typical design patterns for this include:

• Producer/Consumer on the targeted and simple side, to
• Queued Message Handler in the middle, to
• Actor Framework on the general and complex side.