Sharing data amongst VIs

[MartinMcD]

Hello everyone,

I have created a multiple-window application consisting of lots of independently running VIs. Each window receives data via a queue or notifier and process it in different ways.

The example image below shows an issue that crops up a lot and I am not sure if I am solving it the right way. My method works perfectly but it doesn't seem very efficient...

Within the main application there is a class which maintains a list of the active channels. That list is stored in a single-element queue. The children have access to a class member 'Get Channel List' which previews the data on the queue at any time. I use the class constant to hold the queue type and queue name just to be tidy - as you can see I do not pass any class wires in or out.

This works fine, but if I want to keep polling this list then it means each time I am having to have the overhead of trying to create the queue, finding out that it already exists so just getting the reference, then previewing the element (okay I could use event rather than poll but you see the point). I use DVR & In Place Element Structure in another case and I have the same issue there - I store the DVR in a queue in the same way.

I just wanted to check if what I have done is considered good or bad practice or whether there is a nicer way of doing this?

Thank you,

Martin

[Roderic]

Hi,

If you are using LV 2010, have you considered using network stream? I'm using it to share data beetwin VIs in different applications.

regards

Rodéric

[Yair]

First, it should be pointed that you have an uncontrolled memory allocation, because each call to Obtain Queue creates a new reference to the queue.

Second, if I understand what you want correctly, the easiest way is a VI which looks like this:

At first call it generates the SEQ (or DVR, in this example, because it has some advantages), then it just returns the same reference on every subsequent call. This doesn't handle a case where the queue was destroyed, so if you want to handle that, you can check the reference coming out of the feedback node for an error and generate a new one if there is an error (which would also happen on first call).

[Stagg54]

I use Yairs solution quite often and it works very well. (although I often use a shift register - I haven't quite adopted the feedback node yet).

I've always referred to it as a "self-intializing functional global constant".

[MartinMcD]

Crikey, thanks very much Yair for the post, I hadn't realised that a new reference was called each time (I now see it is written in the help, I just hadn't read it).

I am busy implementing your proposed method at the moment...

Thank you,

Martin

[jdunham]

Crikey, thanks very much Yair for the post, I hadn't realised that a new reference was called each time (I now see it is written in the help, I just hadn't read it).

I am busy implementing your proposed method at the moment...

Martin, why aren't you using a global variable? I mean, you are using a global variable, just one that is a lot more complex than the built-in version, but appears to have the same functionality.

I suppose if you have multiple places modifying the channel list the queue will act as a semaphore (mutex) but you could just use a semaphore for that.