Single-Process Shared Variable programmatic access

[ehrlich]

Hi,

I was wondering: Is there a way to programmatically access Single Process Shared Variables using the API similar to Network Shared SV? That would be a very handy feature and this post suggests there is:

https://forums.ni.com/t5/LabVIEW/programmatically-select-global-variable-object/m-p/1855565#M631304

But I couldn't find any example or what to use as "Link to Variable"

Thanks!

[Bob_Schor]

I'm pretty sure that the Open Variable Connection is designed for Network Shared Variables, not Single Process Variables.  The Link to Variable is just the URL to the deployed variable.  I created a tiny project with a Boolean Shared Variable called Test -- if I made it a Network Shared Variable and deployed it to my PC, I could access it just fine as the Snippet illustrates.  But if I made it a Single Process Variable (and got rid of the Network Shared Variable), I got Error -1950679035 on Open Variable Connection, Unable to located the SV on the Shared Variable Engine (which makes sense, it is not deployed there).  Incidentally, when I run this code, Start is False and End is True, as it should be.

Bob Schor

[Jacobson-ni]

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@Bob_Schor wrote:

I'm pretty sure that the Open Variable Connection is designed for Network Shared Variables, not Single Process Variables.  The Link to Variable is just the URL to the deployed variable.  I created a tiny project with a Boolean Shared Variable called Test -- if I made it a Network Shared Variable and deployed it to my PC, I could access it just fine as the Snippet illustrates.  But if I made it a Single Process Variable (and got rid of the Network Shared Variable), I got Error -1950679035 on Open Variable Connection, Unable to located the SV on the Shared Variable Engine (which makes sense, it is not deployed there).  Incidentally, when I run this code, Start is False and End is True, as it should be.

Bob Schor

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I found basically the same thing.  What I was not sure of was whether you should be able to read Single-Process Shared Variables.  

Looking at our help documentation for the Open Variable Connection, it opens connection to a shared variable.  The documentation for the Read Variable function is more specific and says that it reads from a, "network-published shared variable, I/O variable, or I/O variable container" which a SPSV is not.

http://zone.ni.com/reference/en-XX/help/371361L-01/lvcomm/sv_dynamic_open/

http://zone.ni.com/reference/en-XX/help/371361L-01/lvcomm/sv_dynamic_read/

Based on the Read Variable's help documentation I would say that it is probably not possible.  The problem I had was what the URL of the variable would be.  In the multivariable editor the URL is just ./<Library>/<Variable> and it would not be ni.var.psp or ni.var.io becuase the SPSV do not communicate using PSP and are not IO.

[ehrlich]

Thanks for the tests! It's a pity that this feature only works for network shared variables (which in my case are too slow to be used), would be really useful also for the single-process ones.

[crossrulz · Accepted solution]

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@ehrlich wrote:

Thanks for the tests! It's a pity that this feature only works for network shared variables (which in my case are too slow to be used), would be really useful also for the single-process ones.

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If you are not looking for network published, then you really should take a look at the Current Value Table (CVT).  It is a way of defining and excessing variables by name.  Developed by NI Systems Engineers and available for FREE on the LabVIEW Tools Network.

[ehrlich]

This looks very intersting. Thank you for the hint!