Application Builder - Use of Global Variables

Hello,
I have an application which consists one one main VI running for the user interface, and one VI running in the background dealing with CAN communications. These two VIs must communicate using global variables. In the main VI, I have to open a reference to the global variable VI in order to write data to it. The application works correctly in LabVIEW environment. However when I build the application using application builder, I receive an error with the open reference VI in opening the global variable VI. The error given is Error Code 7: File not found. The path to the Global variable VI is correct however. I am pretty sure of this because in my main VI, I open up other VIs based on the open reference function and a path.
Therefore:
1) I can open references to normal VIs and use properties such as run VI without a problem.
2) This does not work for my global variable vi.
Build settings:
Im dont understand all the build options completely but the settings I use are:
1) Single target file contening all the VIs
2) All the VIs I use are located in the same folder
I hope the explaination is clear enough.
Do you have any suggestion to explain what happens and how can I make it work correctly?
Thanks
Julien

Duplicate.
Try to take over the world!

Similar Messages

Application Builder - Use of Global Variables

Hello,
I have an application which consists one one main VI running for the user interface, and one VI running in the background dealing with CAN communications. These two VIs must communicate using global variables. In the main VI, I have to open a reference to the global variable VI in order to write data to it. The application works correctly in LabVIEW environment. However when I build the application using application builder, I receive an error with the open reference VI in opening the global variable VI. The error given is Error Code 7: File not found. The path to the Global variable VI is correct however. I am pretty sure of this because in my main VI, I open up other VIs based on the open reference function and a path.
Therefore:
1) I can open references to normal VIs and use properties such as run VI without a problem.
2) This does not work for my global variable vi.
Build settings:
Im dont understand all the build options completely but the settings I use are:
1) Single target file contening all the VIs
2) All the VIs I use are located in the same folder
I hope the explaination is clear enough.
Do you have any suggestion to explain what happens and how can I make it work correctly?
Thanks
Julien

Your usage sounds very weird. Normally, the best reason to use a standard global is that it's easy to use. You simply place it in the diagram and select the one you want. Your use case of opening a reference to the VI sounds weird.
You say that the path is correct. There is a very simple way to check this. Place a path indicator showing the path you built and you will see exactly. The most common reason for path problems in executables is if you build relative paths since the executable itself is treated as another directory, so you have an extra level. The common way to go around this is to use the Application.Kind property and if you're running in the RTE perform an extra strip. Another problem you might have is that if you are dynamically loading the VI, it will not get included in the build automatically. You have to include it manually either by selecting it as a support file or by including a VI which calls it normally.
After all that, though, my suggestion would simply be to avoid the global. If you need inter-VI communication you can use a lot of other global options like LV2 globals, named queues, notifiers, etc. or even use globals as they were intended and they will all probably be simpler than the way you currently use globals. Note that global communication in LabVIEW is very risky because you can easily create race conditions and it's important to look out for that.
Try to take over the world!

How can I programmatically create and use a global variable?

I have an app where the number of AI DAQmx tasks I create are specified in a config file. I have a monitor task that periodically looks at the latest values from all DAQ tasks. I've been doing this with a set of global variables because it was the simplest way to do it. But to do this, I have to explicitly create a separate AI task that uses the hard-coded global variable name for the DAQmx samples. I would prefer to only write one VI for the DAQ loop that writes to a global variable that I programmatically create based on the config file. The only solution I can think of is to use a global variable "pool" that is sized bigger than I expect to need, and then have a big switch case to select which one I want based on the task index. But this sounds pretty silly.

I tend to agree with Ben. I don't buy the concept of taking the asy way out (globals) because it very rarely will things remain static. You almost always have to extend the features and functionality of an application and then you will run into issues with sloppy and lazy implementations. The solutions offered may require a little time to learn but once you do it doesn't really require any extra effort.
Mark Yedinak
"Does anyone know where the love of God goes when the waves turn the minutes to hours?"
Wreck of the Edmund Fitzgerald - Gordon Lightfoot

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

How to Set and Use a global variable within a session?

Dear All,
I'm new to jsp, and would like to ask how to set and use a global variable within a session?
Thanks in advance.
Regards,
Cecil

With session.setAttribute("name",object) you can store a Attribute in the session object.
with session.getAttribute("name") you can get it.
That's it.
Regards,
Geri

How to use a global variable for reading a query resultset in JDBC lookup?

Hi Friends,
Using JDBC lookup, I am trying to read from a table Emp1 using a user defined function. In PI 7.0, this function returns values of a single column only even if you fire a " Select * " query. I am planning to use a global variable(array) that stores individual column values of the records returned by a "select *" query. Need pointers on as to how a global variable can be declared and used to acheive the above scenario. Kindly explain with an example. Any help would be appreciated.
Thanks,
Amit.

Hi Amit,
Sounds like a good idea but then you would need an external db and update the table in a thread safe way !.
Regarding your question as to how to work with global variable please refer https://www.sdn.sap.com/irj/scn/weblogs?blog=/pub/wlg/1352. [original link is broken] [original link is broken] [original link is broken]
Rgds
joel

What is the difference between using a global variable,passing a valuee and using a reference?

I have created a project that consists of several VIs. Only the main VI has a front panel and the others perform functions. The function VIs are dependent on controls on the main VI's front panel. I have several ways of passing the value of the controls. One is to use a global variable and just place it on the dependent VIs. Another option is to strictly connect the terminal from the control to a VI connector block and pass the value directly. My last option is to create a reference of the control and reference it inside the dependent VIs, but this would also require connections to be made to the VI block.
What are the advantages/disadvantages of these options?
-Stephen

5thGen wrote:
I have created a project that consists of several VIs. Only the main VI has a front panel and the others perform functions. The function VIs are dependent on controls on the main VI's front panel. I have several ways of passing the value of the controls.
1) One is to use a global variable and just place it on the dependent VIs.
2) Another option is to strictly connect the terminal from the control to a VI connector block and pass the value directly.
3) My last option is to create a reference of the control and reference it inside the dependent VIs, but this would also require connections to be made to the VI block.
What are the advantages/disadvantages of these options?
-Stephen
1) Globals are evil and introduce race conditions.
2) The sub-VI only get the value when it was called and updates that occur while the sub-VI is runing are not sensed by the sub-VI
3) This uses property node "value" or "value signaling" both of which run the user interface thread which is single-threaded and you incur a thread swap hit to performance. You also have a potential for race conditions.
The are various methods for sharing dat to/from sub-VI which include Queues and Action Engines.
I hope that hleps,
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

How to declare global variables using another global variable in ODI

I am declaring a gloabal variable using another global variable.
say for example:
I have a global variable empid.
I am decalaring another global variable empname in refreshing tab of global variables and the select statment is
select empname from emp where empno = #GLOBAL.empid -------if i write like this i am getting error as invalid character.
select empname from emp where empno = '#GLOBAL.empid'-------if i write like this i am getting error as invalid number.
I have kept the datatype as numeric and action as non persistent
Please help
Thank you in advance.

Hi,
You cant test/refresh empname standalone.
You need to create a new package drag and drop both variables and make them as refresh variable and execute that package and test.
Flow,
empid----> empname
Thanks,
Guru

Setting the value of an Application Item (setting a global variable);

In APEX 3.2.0.00.27, I need to initialize a global variable to 0 to implement a variable for testing to see if anything on the page has changed. Will update to 1 when certain select lists on the page are changed. Have read through some similar questions and replies within the forum as well as other blogs and sites. So, I believe what I am doing is the way to go about this. Unfortunately, my initialization of an application item/global isn't happening yet. here's a rundown of what has been implemented:
1) created an application item, G_CLASSIFICATION_ID_NEW in the shared components;
2) created Javascript (JS) function called by addLoadEvent in the page html header region so when the page loads, the G_CLASSIFICATION_ID_NEW global/application item should get set to 0 with the following JS and using AJAX and htmldb_GET:
<script type="text/javascript">
function initVars()
alert("before get initvars");
var get = new htmldb_Get(null,$x('pFlowId').value,null,22);
get.add('G_CLASSIFICATION_ID_NEW', 0);
gReturn = get.get();
if(gReturn){
alert(gReturn.value);
get = null;
alert("after get initvars");
alert("before call to initpage");
addLoadEvent(initVars());
</script>
I've used the htmldb_Get with success for populating other global variables and running On Demand Processes with onchange JS calls in the html form element attributes within select lists on the page. Afterwards, I can check the globals via the Session window and searching on Application Items. Unfortunately, I'm missing something because my G_CLASSIFICATION_ID_NEW never gets populated when I load the page. The alerts all popup when the page is loaded, so I know the script is being executed when the page loads. the alert(gReturn.value) comes back undefined. And, needless to say, the G_CLASSIFICATION_ID_NEW to 0 is not occurring.
I've tried the htmldb_Get with it calling an application process and without (set to null). From what I've read, you shouldn't need to call an on demand process to have the get.add set the global variable. Then again, this could be where I'm going wrong. however, as I've mentioned, this works for other functions called from an onchange to populate an application item, but the page has already loaded when the onchange(s) get executed. They may work because the page is already loaded when the onchange is called. My point here is that my other On demand processes are NOT setting or changing the global variables at all. The globals are getting set with the get.add(<app item>, <value>) portion of my other JS functions within the HTML Header region. So, I'm inclined to believe that I don't need the 'application_process=<some_odp>' parameter set, but if that's not true, please let me know. if so, what would need to be in the on demand process--ie, what would be the purpose of the get.add(<application item>, <value>) if I set the global variable in the on demand process because that's the only thing I could think of doing within an on demand process for this?
If somebody can point out what I'm not understanding or failing to do here, that would be great. I'm doing fine with APEX, but wouldn't consider myself a guru with it just yet. I'm definitely not a JS/AJAX guru, and when things like this go astray, I get bogged down because I'm not sure of the problem. So, I'm hoping you gurus who monitor this forum can get me going in the right direction.
thanks,
bob

Hi Jari,
Does that javascript work if you place it some of region footer on page 22 ?Yes. I cut it out of the html header of the page, and put it in the footer of the first region on the page. It initializes the variable. Putting it into the footer of the first region on the page should work for me instead of having an extra region on the page that's being picked up from page 0.
Is your page 22 authentication public ?No. This particular page is set for an ADMINISTRATOR only. That said, I am logged in as an administrator. So, I cannot see why setting authentication should make a difference as long as I have that authentication/authorization. Also, there will be other pages where I want to use this script or a similar script, but again, those pages will not be open to the public. the authentication will be "role" based where a user will not necessarily have to be an administrator, but they will have to have a certain role to access the page. Is there a known problem or something that precludes a html header JS script from doing an addloadevent when authentication is NOT public?
thank you,
bob

Use of global variables like g_cnt_transactions_transferred in the LSMW

Hi SapAll.
when i had a look at the some of the LSMW's whic use IDOC as the object of uploading data into SAP from external Files i have found in the coding under the step "Maintain Field Mapping and Conversion Rules" that they use some of the global variables like below
.if p_trfcpt = yes or sy-saprl >= '46A'.
EDI_DC40-DOCNUM = g_cnt_transactions_transferred + 1.
endif.
.EDI_DC40-CIMTYP = g_cimtyp.
.EDI_DC40-MESTYP = g_mestyp.
.EDI_DC40-MESCOD = g_mescod.
.if p_filept = yes.
EDI_DC40-SNDPOR = g_fileport.
elseif p_trfcpt = yes.
EDI_DC40-SNDPOR = g_trfcport.
endif.
my doubt is where i can find these variables 'g_cnt_transactions_transferred ','g_cimtyp','g_mescod','g_fileport','g_trfcport' in the LSMW and what is the use of the variable 'g_cnt_transactions_transferred ' in the LSMW.
I have treid to find out the above listed variables looking in step 'Maintain Field Mapping and Conversion Rules' under global variabels list and the other lists also but i couldnt found.
can any one help me in this ?
regards.
Seetha.

Hi Seetha,
In the LSMW Workbench go to the option user menu. And check the option display conversion program.
Now when you execute with the radio button on dislplay conversion program, you ll see the code that got generated in the background while you built your LSMW.
The global variables that you have mentioned are bound to be there in this program generated in the background..
You can put a break point here and see for yourself what the value of these global variables are at runtime.
File port, TRFC port , no. of transactions executed by one run of the LMSW Idoc program , message type are some of the fields that you have asked for .
Regards,
Arun

Using a global variable within a function

Hi all,
I'm trying to learn how to use global variables, but can't quite get it right:
Im trying to use two buttons, named UpButton and DownButton to control one global variable, p1
A text field, named "Value" displays p1.
Here's my code:
p1 = 0;
ButtonClick("UpButton", p1, 100,"Value");
ButtonClick("DownButton", p1,(-100),"Value");
function ButtonClick(ButtonName,Var,Increment,TextToChange){
                    sym.$(ButtonName).click(function(){
                    Var = Var + Increment;
                    sym.$(TextToChange).html(Var);
However, it seems to be treating p1 as two different variables.
Here's a link to the page to show you what I mean, apologies but this link wont work in google chrome because I'm using dropbox as a server temporarily
In other browsers you may need to click "Show all content" or similar to any security warnings...
https://dl.dropboxusercontent.com/u/83693404/ButtonTest/buttons.html
Here are the project files:
https://app.box.com/s/0shocivto8fl295h62uq
Any help greatly appreciated, sorry if this is a stupid question,
Katherine

Hi Katherine,
However, it seems to be treating p1 as two different variables.
Indeed, your code created two different variables in two different scopes (I guess it as to do with JavaScript closures, but do not ask me more, I am still a bit foggy about that idiosyncrasy ).
In JavaScript, a primitive parameter – this is the case here with p1, a Number value –, is passed by value. In other words, a copy of the value is made. Your code handles two copies of the value stored in p1.
This contrasts with an object parameter, which is passed by reference (address in memory), without copy. Your code would work if Numbers were passed by reference : the two Var (p1) would then point to the same address.
The intent behind your trial is a global variable.
1) Let us be as simple as possible :
Stage : document.compositionReady event handler
p1 = 0;
buttonClick = function( Increment)
p1 += Increment;
sym.$( "Value").html( p1);
Stage : DownButton.click event handler
buttonClick(-100);
Stage : UpButton.click event handler
buttonClick(100);
Without being preceded by the var keyword the variables are global.
So the Number variable p1 can be accessed inside function buttonClick.
And the Function variable buttonClick as well, is accessible inside click event handlers, everything (function definition +function calls) being inside the same symbol (Stage).
2) Now, suppose this is no longer the case : you want to access a variable from another symbol.
We create a new GraySquare symbol, instantiated both in the DownButton symbol (instance name DownSquare) and in the UpButton symbol (instance name DownSquare).
Stage : document.compositionReady event handler
p1 = 0;
sym.buttonClick = function( Increment)
p1 += Increment;
sym.$( "Value").html( p1);
The sym. prefix is now necessary to make the variable (here a Function, but you would proceed exactly the same with a String, Number or Boolean) accessible in other symbols.
DownButton symbol : DownSquare.click event handler
sym.getComposition().getStage().buttonClick( -100);
UpButton symbol : UpSquare.click event handler
sym.getComposition().getStage().buttonClick( 100);
From these other symbols, the sym.getComposition().getStage(). prefix is necessary to acces to our global variable (function).
The two examples are downloadable here : https://app.box.com/s/6vkyiqk7i8zwlw0j1wk1
Gil

Application builder (using OpenG source)

I just made a LV program and executable thing in LV8.2.0.
Only one function (for converting cluster->ini) from OpenG was used to make the program easily.
When I copy the program folder, so many OpenG (maybe related to the converting routine) codes were created in subVI folder.
My question is,
1. In distributing source code, Is there some DLL or convenient format file for OpenG not to copy many Vis?
2. In making executable program by NI-application builder, how to treat the OpenG library if I have only one Vi ?
And as other question,
3. In NI buidler, the external libraries (run-time/DAQ/VISA) may be rather big.
How can I make the whole program( application+libraries installer) as small as possible?

labmaster wrote:
1. In distributing source code, Is there some DLL or convenient format file for OpenG not to copy many Vis?
2. In making executable program by NI-application builder, how to treat the OpenG library if I have only one Vi ?
And as other question,
3. In NI buidler, the external libraries (run-time/DAQ/VISA) may be rather big.
How can I make the whole program( application+libraries installer) as small as possible?
3: The DAQmx installer has several versions the smallest being 40 MB? and the largest 150 or something.
I think the VISA installer has the same options.
Ton
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LabVIEW, programming like it should be!

Static used on global variable declaration

I have inherited a CVI project that contains a single .C file and a couple of .UIR files with their associated .H files.
Many of the global variables have STATIC in their declaration - I believe this is due to the fact the original developer originally had them inside various functions and at some point changed strategy to make them global, leaving the STATIC keyword in place when copy/pasting.
As I understand it the ONLY implication of STATIC on a global variable would be to keep its visibility only to the .C file in which it is declared. In this instance that is moot since there is only one .C file in the project.
Is there anything about LabWindows/CVI which I might not be aware of that makes this use of STATIC cause something different than if STATIC were not used?
Thanks for any input you might have since I'm new to CVI

Roberto and menchar said it well:
"static variables are declared at compile time and survive when their block of code terminates. If declared at function level, their value survives from one call of the function to another, so that they can be used over time to store permanent values locale to the function. If declared at module level, they are common to all functions in the module and are allocated outside the stack so that their values are not lost during program life. In every case they can be accessed and modified in values by functions in the program. If arrays, they cannot be dinamically changed in size."
"The static keyword can be used with a function name also, meaning the function name isn't exported to the linker, and the function is in scope only to code within the module."

Problems in syncronyzing two threads into Test Stand using a Global Variable (TestStand 4.1.1)

I have one thread that is doing TCPIP Aquisition into a Global variable defined in Teststand. And I have another thread that it supose to read it. All are in the same sequence and execution. The problem is that the aquisition thread got a lot of bytes, while the processing thread is reading always only a few. Do you know what the problem could be?
I will attach also some pictures just to be maybe more clear...
Attachments:
Implementation_pictures.zip ‏368 KB

I wasn't looking at your Sequence, I was looking at Receive_HDL_Block.JPG. What is that VI doing (the one with number 3 on the icon and Size_in_bytes as an input) ?
Where in teststand are you doing any checking?
I don't really understand your sequence.
You have a sequence (running in a new thread) (why), following by another called Receiver Handler (also running in a new thread) then two more sequences which seem to do some with transmitting something (also running as new threads). You are only waiting on one of these threads (the Receiver Handler). There does seem to be any loops in TestStand, you dont seem to be bothered about the other threads that you have running. What happens when this test sequence finally does stop, what is stopping the Threads that you have running.
Your pictures dont really seem to fit in with your Test Sequence, such as where does Test_005.vi fit into everything
The whole thing is a bit of a nightmare.
Maybe your best bet would be to scrap the lot and start again. Only this time have a better understanding of what you what to achieve, what would be best to put into Teststand and what to put into labview. Whether you really need all those new threads running.
Sorry to be so blunt.
Regards
Ray Farmer
Regards
Ray Farmer

Dealing with a turn based application with using a global static variable

Hi there. I read some articles about JavaFX concurrency,so as a newbie i have to practice on it. Now i'm trying to implement a turn based application that can be played among 3-6 players. Moreover, i use a scene imported from a .fxml file and i have to update it correctly depends on some calculations of each thread (in other word players ). My main issue is, i don't wanna use a while loop which checks the state of game like;
while( GameState != State.GAME_OVER ){
     currentPlayer = GameBoard.getNextPlayer();
     // do some actions,calculations etc.
So, i want to use worker threads instead of this while loop. I guess using Service class for iterating and assigning the next player will be suitable instead of using the while loop and Tasks for doing each player's calculation,or waiting for some responses from Human players on UI based,however, i'm struggling with two problems.
There should a global static variable ( like GameState which is an Enumarator ) determines the state of the game,so it should be updated and should be checked by each turn. Is there any way to do this ?
How can i get rid off this while loop ?
I will appreciate for every answer. Thanks anyway.

It shouldn't make too much difference. The basic idea is that you have a model class representing your game state (the Game class in jsmith's example). When a player makes a move, you update the state of the game. Since this will result in changes to the UI, this update should be performed on the FX Application Thread.
If the player making the move is a human player, the move will likely be made by a user action (button press or mouse click, etc); this will be handled on the FX Application thread anyway.
When the state of the game changes so it is the turn of an "artificial" player to make a move, have the object representing the artificial player calculate its next move, and then update the game state. Since this is a response to the game state changing (it's now the turn of the artificial player), this will also be on the FX Application Thread.
The only (slight) complexity comes if the calculation of the move for the artificial player takes a long time. You don't want to perform this long running calculation on the FX Application Thread. The cleanest way to manage this is to launch a Task which calculates the desired move, and then updates the game state when the move is ready. So, something like this:
GameState game = ... ;
// UI is bound to the game state.
ExecutorService executorService = ... ;
final Player currentPlayer = game.getCurrentPlayer() ;
final Task<Move> calculateMoveTask = new Task<Move>() {
     @Override
     public Move call() {
          Move move = // compute next move...
          return move ;
calculateMoveTask.setOnSucceeded(new EventHandler<WorkerStateEvent>() {
     @Override
     public void handle(WorkerStateEvent event) {
          gameState.makeMove(currentPlayer, calculateMoveTask.getValue());
executorService.submit(calculateMoveTask);
If you're doing more threading than that, you're probably doing it wrong... . There should also be no need for anything to be held as a "global" static variable (the idea above is the only structural modification you need to the example posted by jsmith).

Application Builder - Use of Global Variables

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