Queue inside Packed Project Library

[Vipin@AMP]

Hello Everyone,

I m facing an issue when I m using PPL in my TestStand Custom Step Type.

The issue is , I have two vis (Server and Client) inside same ppl, I want pass a queue reference from Server.vi to Client.vi using global variable. But when I m executing , getting error 1 - which is invalid queue ref. Can anyone tell me what would the reason for this and how to solve this issue.

I sincerely appreciate your time.

-Vipinraj KK

[crossrulz]

This usually points to a race condition where the client reads the global before the server can set it.

[JÞB · Accepted solution]

Name the queue! Then delete the global.  All better now.

[billko]

If you're relying on a global to distribute your references, you have to set it explicitly first, or it will just have the reference number of whatever it was when the global was created, which is, in all likelihood, not the same.

[Vipin@AMP]

I m doing same thing, 

I have 3 vis , 

1. Start Server.vi -- where I m creating and opening the queue ref

2. Write value.vi -- pass the value to the Tx queue

3. Read Value.vi -- get the value from Rx Queue

I m ensuring Start server.vi is executing first and also added a 2000ms delay.

Also I tried creating the queue with same name inside all three vis, but that also not working.

Note: These vis are inside same packed project library  .its called inside TestStand custom step.

[JÞB]

So..... What is keeping the vis that obtain a reference to the named queue from going idle?  You just may need to post some code.

[billko]

Does the library work outside of TestStand?

[Vipin@AMP · Accepted solution]

Its working now.

Please check the attached code and sequence.

[billko]

It would be good to include a description of the fix.  Since people come here for help, you could be helping someone fix their problem as well.  🙂

[avogadro5]

Reference issues between TestStand steps are usually one of 2 things in my experience - garbage collection or different application instances.

Future people stumbling here should try:

1. Make sure a VI is always running while holding a reference open (run async with an async VI step or in an async subsequence). LabVIEW may garbage collect a reference if there are no VIs running with the reference open.
2. Make sure both steps are calling the VIs in the same project (or no project). References from one project are not valid in another.