Question - Launch Event Handler - Asynchronous call

[matrixx567]

Hy,

I have a question to the Launch Event Handler.vi. I saw this code (image below) in the QControl Launch Event Handler and also in the Actor Framework's Launch VI. This is a general question to improve my skills. I know what this code does and how it works but I don't fully understand the reasons behind this code.

The VI is non-reentrant and the shift-register stores the reference between calls. So the VI reference is only opened once between different calls.

Is this the only advantage you have over the straight-forward implementation with opening the VI reference before the Start Async Call every time. Are there other reasons too (e.g., performance)?

Greets

Martin

[TheQ · Accepted solution]

I have been trying to find @AristosQueue's post about it in Actor Framework but haven't found it yet.  I'll post it when I find it.

It is a performance help.  The Open Reference is the expensive part of this operation and therefore, it only has to happen once for all Actors (or in this case, all QControls).  All other calls can use the same reference. It does cause one leaked reference to occur but only on the first call.  In exchange, this operation is a lot faster.

[matrixx567]

Thank you for the answer. This was also my first guess.

Greets

Martin

[drjdpowell · Accepted solution]

If you look in the AF launch code, there is a comment and a link to the relevant conversation.  It's for reasons of performance AND to avoid being blocked by "Root Loop", which is the problem that certain things, including the User having a menu open, block opening a reference for an async call.

[matrixx567]

Hy,

I also found an interesting blog article about the Root Loop.