Article: Functional Globals in LabVIEW 8.5 - No Loop, No Joke

Hello Everyone,
I've written another article on my blog:
Functional Globals in LabVIEW 8.5 - No Loop, No Joke
I hope you find it interesting
Thanks,
-Jim
Message Edited by Jim Kring on 09-07-2007 08:24 AM

Thank you for your attention!
I've opened the fixed vi and all seems to be ok, but in few mouse click all messed up again causing strange floating wire and a LV crash.
If you are brave please try the following procedure (save and close all of your work..!):
Open your fixed vi.
CTRL-E to display the block diagram.
Rigth click on the upper (DBL) feedback node and change it to "Globally Initialize".
Right click again on the same feedback node and select "Move Initializer One Loop Out".
Select the feedback node, the "+", the "+1" and the other (blue, INT32) feedback node.
Then perform the "Horizontal Centers" alignement.
(in my case) voila! Move one of the 2 feedback node and see what happen....
Now try to close and save the vi.
I run LV on a NI PXIe-8106 so I think that this kind of hw is fully compatible with NI software... :-)
I suspect that in this case the problem is not at a graphic level but reflect a corruption of internal data LV data.
Attachments:
Broken wire.jpg ‏54 KB
Error3.jpg ‏60 KB

Similar Messages

Software timing - Functional Global?

I was reading NI Intermediate manual to prepare for the CLD exam, and noticed that they used Functional global variable in combination with timed loop for the software timing. Also, the error handling was implemented using functional global.
However, I was reading in one post( not this forum) that the functional global is obsolete, can anyone shed any light on this issue, why would the functional global be obsolete: and if it is, what are acceptable design for software timing.
Thank you.

Cory K wrote:
I dont see why a global would be obsolete.
There are some instances when using a global variable is the best option, especially in cases when a resource will be used on several different computers.
A functional global variable isn't the same thing as a global variable. A functional global variable is what was used before global variables were introduced in LabVIEW 3. It is the heart of an Action Engine.
As for their obsolesence... Hah! That's all I have to say on that.
As to the original post: I'm a tad suspicious. What kind of software timing and error handling is being done with a functional global variable? Can you post the code?

How can I activate a functional global without displaying a LabVIEW VI ??

Hello. I'm using Teststand and have been got stuck on a problem now.
Whenever I communicate to a LabVIEW VI which is activated as a functional global, I purposely displayed the LabVIEW VI on front pannel to make sure the data communication.
However once I released the check mark 'Show VI front pannel when called' , the data transmission including receiving vanished. As a matter of fact, always the numeric data resturns ' 0 '.
So the data communication must be transacted with a shift resgister function at each step in Teststand, so it always provides a command to the functional global VI for an e-num item selector.
Therefore it looks the shift register function doesn't work at the point anymore in the functional global VI.
Otherwise as long as I suspend the VI as a display, checking on the box 'Show VI front pannel when called' , I exactly can make sure the data communication , receiving the command and returning the data.
Have you heard that kind of unusal problem before?
Do you think it happened due to data communication or just simply Teststand applicational error?
If it has some useful information, I try to fix them.
Thank you.
Noriyuki

hirose wrote:
Hello. I'm using Teststand and have been got stuck on a problem now.
Whenever I communicate to a LabVIEW VI which is activated as a functional global, I purposely displayed the LabVIEW VI on front pannel to make sure the data communication.
However once I released the check mark 'Show VI front pannel when called' , the data transmission including receiving vanished. As a matter of fact, always the numeric data resturns ' 0 '.
So the data communication must be transacted with a shift resgister function at each step in Teststand, so it always provides a command to the functional global VI for an e-num item selector.
Therefore it looks the shift register function doesn't work at the point anymore in the functional global VI.
Otherwise as long as I suspend the VI as a display, checking on the box 'Show VI front pannel when called' , I exactly can make sure the data communication , receiving the command and returning the data.
Have you heard that kind of unusal problem before?
Do you think it happened due to data communication or just simply Teststand applicational error?
If it has some useful information, I try to fix them.
Thank you.
Noriyuki
I'm not sure about the current versions of TestStand but in previous versions you had the possibility to preload certain test steps or initializer VIs. TestStand made sure to keep them in memory for the entire duration of the particular test sequence. You create such an initializer VI and call your init method in there and mark that step as preload. On loading the sequence or initializing it your step gets called and stays in memory for the entire duration. I would be surprised if TestStand doesn't support this anymore.
Rolf Kalbermatter
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

Using functional global variables to transfer data between touch screen device and other targets

Hi,
We are currently developing a control system that will operate on a cRIO with a touch screen interface. During development we have been using functional global variables (FGVs) to handle most of the settings/data etc, however we have just realised that we may have an issue updating the data on the touch screen, and vice versa.
Previously we have implemented similar programs using shared variables, however we were wondering if there is anyway to implement FGVs in a similar manner, whether it'd be a combination of FGVs and shared variables.
Regards,
Mike
Software version: Labview 8.2.1

See this thread on LAVA about sharing FGV's across projects. THis should be extendable to cross paltforms (I believe).
You also may want to concider an upgrade to LV 8.5.1. We have found a number of performance related issues with LV 8.2.1 and RT.
If you decide not to upgrade, just remeber what I wrote (above) when you have reason to question the performance.
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

What's wrong with a "regular" global in this case? AND WIl ActiveX objects stored in functional globals remain valid (when used in an executable)?

I've written a plugin layer for a LV executable. When this layer makes a call to the plugins' initialization functions, I want each plugin library to be able to initialize and maintain its own global memory (where things like VISA resource names or ActiveX objects are stored). However, I've found that I can't manage to keep my global VIs "alive." I'm inclined to switch to functional globals, but I suspect that this will be a problem for things like ActiveX objects (that in this particular case reference a CAN interface). I believe that the functional global will indeed store the object from run to run, it's just that I'm somehow disinclined to think that the object will remain valid. I think you'll have to re-initialize it. Can anyone speak for or against this hunch? (If you can't tell, I'm trying to avoid building a whole little test executable just to debug this problem.)
I suppose the more profound question is "Why don't the globals stay in memory?" I'm attaching an image of what the application layer that calls the plugins' intializations looks like. Next I'm attaching an example of an actual initialization routine. You'll notice that I've even gone so far as to explicitly open the ref to the global VI that I want to keep in memory. Then I just leave it there dangling - but it still gets dropped! In my mind I shouldn't even have to do this, since the dynamically-called subVI "MC_CMO Init.vi" actually initializes the globals and runs with AutoDisposeRef = False.
Lastly, this is my first-ever attempt at writting plugin software. So if you look at my code and have any criticisms/pointers, I'll greatly appreciate them.
Thanks in advance,
Nick
"You keep using that word. I do not think it means what you think it means." - Inigo Montoya
Attachments:
AppLayer.JPG ‏60 KB
InitPlugin.JPG ‏103 KB

I am not sure if I follow you completely on your work-around.
Everything I have to say on this topic is based on obesrvations and threads I have read on Info-LabVIEW. Therefore it is subject to corecttion by those who know better.
LV is smart enough to know when "something" that had been opened, can be closed. It is not perfect.
If for instance you open a VISA refnum and pass the refnum to a LV2 AS A REFNUM the refnum in the LV2 stay alive as long as the VI's are running.
If you start another VI that uses the LV2 to fetch the refnum, it should get a valid ref as long as it starts before the first goes idle.
You then be able to work with refnum usign the VI launched second as long as stays active.
I often create action engine that can be invoked where required throughout an application. If the action engines get a ref in one state (like init) and use it another, I will generally write a "tester" that calls the action engine action to test the engine. In this case, my "tester" stays live and it keeps the ref's fresh.
I suspect if you tried to trick LV you could. If you type cast the ref nums to I32 and stored those in a LV2, I could see how LV could loose track of the resource sharing, but that is something I would avoid.
So I encourage you to do some experimenting with keeping track of who's running when to see if your work-around will work.
If you think you understand it better than I explained it, please post.
Trying to help,
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Functional global variable question

Hello,
I fully understand how a functional global variable (FGV) works and its purpose but I have one last question.
How do I guarantee (or how is it guaranteed) that my sub-VI (the FGV one) is not re-entrant, in other words, how am I sure that when an instance of the FGV is running it does not loose the processor to others? Is this an option that I can choose in a sub-VI or is it related to the while loop or case strucure that compose a FGV?
Joao

Hi Joao,
For a little more background on configuring reentrancy and the options you have available if you do want to make a subVI reentrant:
LabVIEW Help: Reentrancy: Allowing Simultaneous Calls to the Same SubVI
http://zone.ni.com/reference/en-XX/help/371361K-01/lvconcepts/reentrancy/
As Lynn said, all new SubVIs will be non-reentrant by default.
Regards,
Tom L.

Functional global variable

I would like to ask to the experts a question about functional global variables.
In the labview basics 2 course was said that a functional global variable is not reentrant.
My purpose is to implement a code in such a way.2 main vi's. The first vi deals with some hardware that writes data in an output file with 1 Hz rate (more or less 1Hz, I cannot decide it).
The second vi deals with a different hardware (thermocouples). This works at a different rate (I cannot match exactly the different rates). I would like to write the data from the second hardware in the same output file of the first vi.
I am thinking to use a functional global variable to pass the information from the second vi to the first vi. In this way I am using the data from the thermocouples at a rate given by the first vi. But at the same time in the global variable the data are written at a rate given by the second vi.
My question is: what exactly happens if the subvi (functional global variable) is called exactly at the same time? As you can understand it's not really important if I read the temperature with an error of 1 second, but I would not like the execution would stop or something like that.
A functional global variable is a subVI that is not reentrant. This means that when
the subVI is called from multiple locations, the same copy of the subVI is used.
Therefore, only one call to the subVI can occur at a time.functional global variable is a subVI that is not reentrant. This means that whenthe subVI is called from multiple locations, the same copy of the subVI is used.Therefore, only one call to the subVI can occur at a time.

A couple of quick comments to add to this thread.
FG's can be involved in Race Conditions if two callers attempt to direct set the same value. An Action Engine (well what do you expect?) can be coded to help with those situations.
Example:
In arecent app I needed to set the heaters to "0" if an over-pressure condition was detected. The Heater set points where driven by a PID. The safety conditions where controlled by a process monitoring the input values.
So how do I keep the PID from setting the heater when the rig is not safe?
A Safety AE !
Actions used by the pressure monitoring set the Safety AE in an "go-safe" state where setting the heaters results in a null op.
This particular pattern (two writters) screams for an AE to coordinate the vaious actions. Do this same thing with queues could get tricky.
So for the Q in this thread we have a pattern of "two source of info, one sink for each" that screams for a queue.
BTW:
The AE Nugget linked above addresses what happens when two callers attempt to call the same non-re-entrant sub-VI.
Have fun,
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Global.vi vs functional global

Hi,
I'm making an application with one data acquistion VI and a bunch of user interface screens which includes about 50 global variables. On another forum, it was mentioned to me that some expierenced LabVIEW users avoid globals altogether and if they need one they use a functional global. I was wondering what the advantages and disadvantages of using functional globals vs. using regular global variables were in a fairly large application like the one I'm making. Any advice would be appreciated.
Thanks in advance!
Jason

napview wrote:
One thing for sure when to switch to global variables is:
1) to have a pop-up panel for user inputs
2) run out of room on the calling vi, even when using tabs
But the big drawback of it is slowing down the processing time when they are called and in active state (passing data or in a loop). And YES, ALWAYS avoid using them if possible because local variables are ALWAYS faster, stack pointer inherently, common sense.
I can't say I understood what you're saying, but I fail to see the relation between locals and globals. In general, using locals as a means of data storage is bad form - you're better off using wires as much as possible with the same exceptions which were described in the other thread for globals and a few exceptions which are only relevant for locals.
You are correct that locals are faster than globals (although I wouldn't jump to conclusions as to why, probably the locking is simpler to handle), but globals should be used when you want a global means of communication, not just because you run out of room on your FP. If you want to avoid running out of room, either use tabs and hide the controls or use wires instead of locals. In any case, both globals and locals have some disadvantages which can be overcome by using functional globals.
Try to take over the world!

RT executable causes functional global variable VIs to become non-reentrant

Hi,
I am having a small issue with functional global variables (Repositories). The attached VI is a sample functional global variable I created that stores double precision numeric values. The VI properties are set to normal execution. I use this VI to pass data between loops running in real time on a PXI platform. When running my application from the project explorer (not creating executable) the VI functions as it should and passes data between my loops with no issues. But when I create a real time executable of my application and run it on the PXI, it does not share data between instances of the VI. My work around this issue is to change the VI properties execution priority to Subroutine but it forces me to modify my VI slightly for this to work (I have to remove the property node). I am not sure why this is happing. I have seen some applications with this VI that appear to function normally in development and in executable with the VI properties execution priority set to Normal. Any comments or suggestions are welcomed.
I am running LabVIEW 2009, PXI-8186, and Windows XP
Thanks
Attachments:
RT Repository DBL Numeric Command Ver 2.ctl ‏5 KB
RT Repository DBL Numeric Element Ver 2.ctl ‏5 KB
RT Repository DBL Numeric Ver 2.vi ‏25 KB

Many properties require the front panel to be loaded in memory; the property you're using, NumItems, appears to be one of them (look at the help, you'll see that it says "Loads the front panel into memory.") However, VIs running in an executable on RT do not have front panels, so those property nodes will not work. If you were to log the error out terminal from the property node in your executable, you should see that an error occurs. As a result, you're getting a 0 value out of the property node, causing your VI to output unexpected results.
My recommendation is that you replace the property node with the function GetNumericInfo found in vi.lib\utility\VariantDataType. It has an output called EnumNames. Take the size of the EnumNames array and use that in place of the output from the property node. This will work on RT.
Note that this has nothing to do with re-entrancy, and the key hint is that the VI works when you remove the property node.

Will more function globals or sub vis slow down realtime DAQ or display

I need to do high sampling rate DAQ with varient data process and display.
Shall I intend to put all the code into one vi to accelarate the speed, or can I use more function global or sub vis to make the structure looks more reasonable.
Just worry how the compiler handle the data transfer when call function global or sub vis.
Will it creat new data copy and slow down the speed. Thanks.

The other 2 loops in charge of the data processing and display will keep checking the version of the 2 function global.
For high performance, you want to avoid this sort of thing. Basically, you're polling the functional global to see if it has new data. Polling will eat the CPU unless you include WAIT periods, but doing that slows your responsiveness.
Consider using custom events.
For the sake of discussion, let's say you need to process data in the TIME domain (1) and the FREQUENCY domain (2).
You create two events: NEW TIME DATA and NEW FREQ DATA, each carrying an array of DBL (the time-domain data from the DAQ).
The DAQ routine, when it gets a new data block fires both these events, feeding it the new data.
Your TIME DOMAIN loop (1) has registered for one event. When that event is triggered, the code accepts the data, and does whatever it needs to do (filters the time domain, graphs it, writes to file, averages, whatever).
Another loop (2) has registered for the OTHER event. When THAT event is triggered, the code accepts the data, performs FFT on it, and does whatever it needs to do (filters the frequency domain, graphs it, writes to file, averages, whatever).
Or you could do the same thing with queues.
When the use changes conditions, you change which event you listen to, or which queue you consume from.
The idea is that you want to avoid polling. Let the system tell YOU when data is available. Don't be asking the system if it's available.
Steve Bird
Culverson Software - Elegant software that is a pleasure to use.
Culverson.com
Blog for (mostly LabVIEW) programmers: Tips And Tricks

Do I need to use a semaphore when reading/writing a functional global from reentrant VIs?

I have a program that spawns multiple reentrant VIs running simultaneously. These VIs write their status to a functional global. The VI that monitors them periodically polls this global to check out how they're doing and takes action based on their collective status. (BTW, I'll mention that this monitoring VI is NOT the parent that spawned the reentrants, just in case this might affect memory management as it pertains to my question.)
Anyway, 90% of the time, stuff goes off without a hitch. However, once in a while the whole thing hangs. I'm wondering if there's any chance that I've overlooked something and that some kind of collision is occurring at the global. If that's the case, then should I be setting a semaphore for the global read/writes?
And, if this is a problem, then there is something deep about functional globals that I don't yet understand. My notion of them is that they should negate the need for a semaphore, since there is only one global instance, which cannot be simultaneously called by the various reentrants. Indeed, this is arguably THE WHOLE POINT about functional globals, is it not? Or am I missing something?
Thanks,
Nick
"You keep using that word. I do not think it means what you think it means." - Inigo Montoya

Thanks Uwe,
This is a good hunch. However, functional globals typically run at "subroutine" priority. With this priority, it is not possible to select a specific execution system; it is always "same as caller."
I will try your suggestion by switching to "time-critical" priority. However, I do not know if this could lead to a different set of issues (non-determinism?). It will probably take a little while to hear back from my guys on whether this makes a difference or not, because the error is sporadic, and sometimes doesn't come along for quite a while.
While probing all of this, I looked at the execution settings for my reentrant VI. It has standard settings: "normal" priority, running in the "same as caller" execution system. My impression has always been that LV creates the clones with unique names. This allows the clones to be in the same execution system with no problem, and the fact that the execution dialog allows me to choose "same as caller" for a reentrant VI supports this assertion. This is logical, since there could potentially be many more clones than available execution systems. "Preallocate clone for each instance" is selected, which is what I want, I think, though I don't know if it matters in my application.
In summary, I am trying out your suggestion, but with skepticism. Any other suggestions from anyone out there? Any misunderstandings on my part that need clarification?
Thanks,
Nick
"You keep using that word. I do not think it means what you think it means." - Inigo Montoya

Functional Global Variable in the CLAD sample Exam

Hello,
A question in the CLAD sample exam #2 keeps puzzling me. It's question number 32 about FGVs:
32. Which is not an important part of creating a Functional Global Variable?
a. Using Shift Registers to store information
b. Changing the VI’s execution settings to Reentrant
c. Setting the VI to inline into calling VIs
d. Setting the While Loop to stop after one iteration
The answer given is the following
32.Correct Answer: B
Topic: Functional Global Variables
Justification: It is not necessary to inline functional global variables into their calling VIs. In fact, inlining requires that the subVI be reentrant, which is forbidden for functional global variables.
Clearly, for an FGV to work properly, the VI must NOT be reentrant. So I would have selected answer B, but the justification seems to clearly point to answer C as well, doesn't it? Is it a typo, a subtlety in the wording? I am stuck on this one!
Solved!
Go to Solution.

Well, inlining requires reentrant. Therefore, the best answer should technically be C. This looks like one of those rejected/retired questions since it isn't quite right and/or left up to too much interpretation.
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How to use functional global with a large amount of variables?

Hi all,
I'm currently developping a LV program which control and acquired data from a device. Up to now I used global variables ( very conveniente to use for experimental parameters). But now my program is become to be too large and I have too much "global" variables to continue to use a global.vi.
I'm wondering if functional global can help me. If someone has an exemple of how use functional global with a large amount of variables...
thanks

I agree with Ben.
Using queues is better than a number of Globals or Action Engines (Functional Globals). If you need to pass data to a sub-vi, you can simply wire the queue out to a queue control of a sub-vi, or a reference. See attached example of passing data to a sub-vi using a queue. The example is an extremely simple, undocumented tid-bit of code that sends the loop count to the consumer VI.
Run the main program called QueueProducer.vi.
R
Attachments:
QueueProducer.vi ‏18 KB
QueueConsumer.vi ‏14 KB

Multiple copies of functional global using vi references

I have several producers aquiring data into a functional global (one functional global per producer). These functional globals are identical except for the name. Would it work to have only one functional global VI and obtain a separate reference for each producer? The matching consumer would also use the proper reference to consume the data.
The functional global contains an array of the data which must be parsed by the consumer. It is possible that the array of data may not contain a complete set of data on a single "store" operation by the producer. The consumer, of course is written to check for a complete data record before completing processing on the record.
Solved!
Go to Solution.

Les__Bartel wrote:
tst wrote:
Regardless of whether there is a better way, the answer to the question is yes. The FGV needs to be reentrant and the reference you open needs to be reentrant too and then you can use the CBR node to run the specific copy of the FGV.
I thought a reentrant vi would not maintain the state of the uninitialized shift register from one call to the next.
A reentrant VI will maintain the state of its uninitialized shift registers. However, you need to be really careful how you do this. First of all, you need to make sure it is set to Preallocate Clones. What will happen in this situation is that each different place you call that subVI will each be a different clone. This means that each call will have its own data. The problem with this is that you can't share the data across multiple instances and therefore multiple loops. If you don't believe me, go play with the Mean Point By Point VI.
So what happens if you set it to shared clones? A big freakin' mess. You will have no control over which clone will be called where and there will be some major data corruption.
This is why FGVs are almost always non-reentrant.
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Functional global set as reentrant vi in CLD sample?

In the CLD atm sample question attached. It set its functional global as a reentrant vi...
Now let me get this right , a non reentrant vi, no matter how many times it's called, stores its data into one location. So a functional global should be a nonreentrant vi so the functional global can SET the same data in the same place, and GET the same data in the same place.
Whereas a nonreentrant vi creates clones everytime it is called, and each clone stores a different set of data in a different place. So a functional global should not be a reentrant vi because it cannot retrieve the same copy of data; there are many different data sets stored in different places, the functional global would not know which data set to retrieve.
But how come this CLD sample set its functional global as reentrant vi and it works???
Attachments:
ATM Simulator LV86.zip ‏116 KB

richjoh wrote:
In your VI code "Shared clone is selected"
Below are past from the LV manual --
"Memory Usage - Only allocates clone VIs for the maximum number of simultaneous calls to the reentrant VI. Decreases memory usage..."
"Execution Speed - Creates clone VIs on demand. Slightly decreases execution speed and speed may vary per call.."
...and Preallocate is versa of above.
Yes the only reason to use Reentrant in any LV example is to keep separate copies in memory. This author uses the reentrant VI to track 3 different transaction in his example (looks like an banking ATM, I have not run it as yet). The author reentrant is for "deposit", "withdrawal" and "pin entry". Ctrl+F, the VI is used in 4 instances, one of them is to Get current action, the other 3 are Set.
IMHO, the example is overblown. Wonder how long it took the author to create it?
The reason it works is all access is sequential.
Overblown, yes. Reminds of the kid trying to show-off by climbing over the fence to pose next to the lion's cage. It will bite them eventually.
Keep It Simple Sir has clearly bee violated.
I will watch for someone who can explain WHY that was a good decision unless they felt there would 500 of these ATM GUIs running in parallel.
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Article: Functional Globals in LabVIEW 8.5 - No Loop, No Joke

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