Shared variable synchronization

Hi,
I am trying to send data between computers. I have used shared variable to do this and to avoid race condition I have append "?sync=true" in URL to synchronize access to shared data. But when I run Send and Read VI, race condition sometimes still appears? Even when I run both VIs on same PC.
I have attached VIs, if someone would like to try it.
Thanks,
andrej
Attachments:
SV.zip ‏53 KB

You maybe running into a race condition even though you are appending
the '?sync=true' tag is because the synchronous operation only ensures
that the dataflow proceeds after the the datasocket has communicated the
update to the shared variable engine. The race condition maybe caused
due to the time that the shared variable engine takes to update the
variable. The second iteration of the while loop may still read the
value of the SVRead variable from the previous iteration which might
cause a race condition. To avoid this possibility, I implemented a
tri-state SVRead variable. Instead of using a boolean, I used an
integer to check the status so that the Sender/Receiver do not wait for
the same value of SVRead which could potentially cause a race condition.
Assuming that the SVRead variable will be initialized to a '0' Value,
refer to the following image for more information on how the SVread
values are being cycled.
Also, I am attaching the editted version of your VIs so that you can test it out.
Please let me know if this helps in resolving the race condition.
Mehak D.
Attachments:
SV.zip ‏84 KB

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How do you synchronize accesses to a LabVIEW Shared Variable?

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Thanks!
-Danny
Message Edited by texasdiaz on 02-23-2006 02:52 AM

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From the annals of the weird:
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Shared Variable VI development on machine other than server

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http://www.ni.com/white-paper/4679/en
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Hi Marcus,
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Does OPC UA Shared Variable Server support Alarm&Event and historical access?

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Hi iCat,
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Industrial Communications Product Support Engineer
National Instruments

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David Thomson Original Code Consulting
www.originalcode.com
National Instruments Alliance Program Member
Certified LabVIEW Architect
There are 10 kinds of people: those who understand binary, and those who don't.
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Anna,
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Thanks,
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David Thomson Original Code Consulting
www.originalcode.com
National Instruments Alliance Program Member
Certified LabVIEW Architect
There are 10 kinds of people: those who understand binary, and those who don't.

Issue with use of shared variables in Crystal Reports 2008 Offline Viewer

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Please re-post if this is still an issue or purchase a case and have a dedicated support engineer work with you directly:
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Why should you explicitly open and close shared variable connections?

I'm looking into switching over from the old Datasocket API to the new Shared Variable API for programmatic access to shared variables, and I noticed that LV doesn't seem to have any problems executing Shared Variable Reads & Writes without first opening the connection explicitly. That is, I can just drop in a shared varaible Read VI, wire a constant to the refnum input, and it will work. I'm wondering, then, what benefits are offered by explicitly opening the conenction ahead of time...?
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Thanks in advance.

I'd expect there's a very small number of people at NI that would know the answer to the detail you're asking for. But, let's try to extrapolate from this rather old post to see if we can understand what they're forming their impression on.
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Is there a way to reset the shared variable engine?

I would like to be able to reset the SVE in a manner that is equivalent to what occurs during a hardware reset.
My motivation for doing so is as follows:
I have an cRIO app with lots of IOV's and NSV's that operate via the SV API and also with plenty of static nodes. I am finding
that on first run, from the DE, my CPU%=~55%. On all subsequent
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Anybody have any ideas?

Hello,
If you redeploy your library, does that bring your CPU usage back down? perhaps you can use that as a suitable workaround? How exactly are you setting the initial value of your shared variables?
Tejinder Gill
National Instruments
Applications Engineer
Visit ni.com/gettingstarted for step-by-step help in setting up your system.

Are clusters or individual elements better for shared variables?

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Thanks for any help. I'm so stuck on this fence, and I can't figure out which side to fall off!
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Thanks Tim, that is a great source that I somehow missed in my hunt for information regarding my dilemna...
I have to wonder though, does that 25 number also include the I/O points on your cRIO? Anyone know that particular? Most of the I/O points are network shared by default during initial configuration, and you could very quickly exceed 25 variables on an 8 slot rack (such as the one I use, a 9074). Now I'm a bit worried that I'm overusing the variable engine, even before the communications clusters get figured in...

Print-time charting with shared variables on a report without groups...

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The setting up of the two formulas ({@onchngof} and {@showval}) will be different for my situation, as all of the subreports run off of date information relative to when the report is ran. I've got all of the subreports that the shared variables originate in early in the report; but where to from here?
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As always, any help is greatly appreciated!

Let me ask couple of questions before trying to resolve this.
1. The chart you are trying to built is placed in which section and is it on Main report or sub-report of its own. This is needed because if you are trying to access shared variables values in Main report, the section should be below the sub-report placed sections.
2. Try pacing few test formulas in Main report and make sure the correct values are being pulled in on Main report.
If you are successfully pulling the variable values on the report, try creating a simple chart in report footer with the values you have pulled and see if its taking you somewhere...
Would need more information on how those variables are being accessed form sub to main or sub to other sub for example are you making an array of those variables and splitting or bringing it in as separate...

How do I setup shared variables between executables created in sepparate projects

Hello,
I have several sepparate projects with their own respective executable files and I would like to be able for these executable files to all share the same variable (one program controls the value of the variable, while the others read from it).
I got this setup to work on my personal computer (by being able to access variable manager, etc), but I need to deploy these executables on different computers that don't have the labview development program. What steps do I need to do in order for me to be able to put these executables on any computer (I'm assuming I need to setup a path for the shared variable that is always in the same folder, etc)
Thanks
Vlad
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Hi Vlad,
I think this article may answer some of your questions regarding shared variables in deployed applications.
http://zone.ni.com/devzone/cda/tut/p/id/9900
It sounds like you already have your executables built, but this article may answer some questions about deploying them to other machines.
http://zone.ni.com/devzone/cda/tut/p/id/3303
Jeff S.
National Instruments

How to use shared variables to address multiple Watlow controllers on the same COM port

Hello,
I am trying to use LabVIEW 2010 to control 4 Watlow temperature controllers on one COM port. 3 are Model 96 and 1 is an EZ zone controller. Each controller has a unique modbus address, and I am trying to read from and write to individual registers (such as closed loop setpoint) using shared variables. I am getting return data when reading (although the data appears to be invalid), but am unable to change the value in the register by writing. How can I be sure that the Modbus server is sending commands to the correct controller?
Chuck
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Peter,
Thanks for the reply. I have actually solved that problem. I realized that the Modbus server address has to be the same as the controller's Modbus address.
I have, however, run into another problem. Perhaps you could help me with that. I have a system with 4 Watlow controllers, 3 are series 96 controllers, one is PID only and 2 are ramping. The 4th controller is an EZ zone. I am using RS485 for communications and the controllers are all wired in parallel for communications and power.
I have set up 2 Modbus servers for 2 of the controllers.
This is the first I have ever worked with Modbus based communications. I have successfully programmed using the Modbus read/write VIs, and am wanting to move to shared variables. My questions right now revolve around addressing, Modbus I/O servers and COM ports. Specifically, at this point, I know the addresses need to match up between the server and the slave device (Watlow controller in my case), how many servers can I create and use on one COM port? If the number is limited, is there a way I can specify an address that I want the server to talk to? Will the broadcast mode work to request data values from the controllers?
I'd appreciate any information you can help me with, or if you could point me to some sort of concise 'How-To' for Modbus communication.
Thanks.
Chuck

How to add a new Shared Variable programmatically to an existing and deployed library?

Hi there!
I am trying to accomplish this on both LabVIEW 8.6 and LabVIEW 2010 and seems like it's not any different in this situation.
My case: A project has a library with 4 Shared Variables (SVs). The library and the variables are deployed (visible in Distributed System Manager 8.6/2010). I want to add 2 more variables into this library. It is possible to do this manually from Project Explorer window's options menu. But while running an application it has to be done programmatically. Can I provide the library reference to the one currently existing without creating a new one?
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Any tips?
Thanks ahead!
Vaibhav

<<<<>>>>
As the above two images show, while a library does not exist, it is easy to use the "CreateOrAddLibraryToProject.vi" which will add a new library to the project (if it doesn't exist on file system, a new library will be created) and that way, using the reference (the green wire going out from the function and the Case Structure, can be used to add Shared Variables to the library. The problem was what to do when a library already exists in the project, how to add more variables to it. I was looking for a way to get a library reference, and somehow I could not see it inside a Project's property (VI Server functions). Hence I posted the question. And upon continuing my search, I found it on the Application's property list.
I hope it was useful for someone else as well. And thanks for the replies. Please share a better idea if you have.
Vaibhav

Shared variable synchronization

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