'Thread-shared' variable across JSPs

Hi folks,
I'd really appreciate some help with something - I'd like to have a variable that each JSP on my site can access, so if, say, 5 people are on my site at a given time, and one of them changes it, the changes will be seen by the other visitors.
For example, it's an online game andthe current maximum score is always shown at the top right, on each page refresh the score of the player who is currently winning is shown...
I understand that your run-of-the-mill variable on a JSP page is a per-page variable... how can I create a.... er... not-per-page variable? (As you can tell my lack of relevant terminology has somewhat hampered my googling so far!) :os :oD

Thannks bbaldino - I've had a bit of a read about Application Scope variables, and they do seem to do what I am after, I think.... hopefully Uncle Google will work with me on the rest!
Thanks again!

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Sharing variable across Threads created by ThreadFactory

Hi,
I am initializing an ExecutorService as:
static ExecutorService service =
Executors.newFixedThreadPool(16, new ThreadFactory() {
@Override
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
t.setContextClassLoader("<<My_Class_Loader");
return t;
Now, I have to initialize a service that should be initialized only once that all the Callables submitted to this ExecutorService can use. The variable needed to be shared across the Threads must have "My_Class_Loader" as its ContextClassLoader. How can I do that? Thanks in advance.

Something like this:
Thread t = new MyThread(r, ccl); // ccl = your context class loader
public class MyThread extends Thread
private MyVariable myVariable;
public MyThread(Runnable r, ClassLoader ccl)
    super(r);
    this.setContextClassLoader(ccl);
    myVariable = ...; // your class loader stuff
public MyVariable getMyVariable()
    return myVariable;
// ... then runnables can go:
((MyThread)Thread.currentThread()).getMyVariable();

How to access variables across JSP and JavaScript?

Hi,
I have some .js files and in those files, some of the methods need to access to the variables that I'd declare in the jsp files. How do I do it?
Anne

You can do it this way, but I'm not sure if this is what you had in mind.
Say you had a java variable called XString. And you wanted to display
the value of XString in a javascript Alert. Here's how:
<html>
<body>
<% String XString = "Hi There!"; %>
</body>
<script language="javascript">
alert("<%=XString%>");
</html>Hope This Help,
P.

Sharing variables in jsp

plz help me..
i have declared a variable in a jsp page and i want to make this variable known to another jsp ..both jsp are in same directory..actually i m making a project but i m new in jsp and i have a need like this..plz write ur suggestive snippet so that i can understand.
thanks

A variable declared in a JSP is not visible to the other JSPs, no matter where they are.
What you can do, is use one of 3 scopes:
request - For all resources involved in servicing the same request
session - For all resources involved in a session
application - For all resources in the application
Put your data as an attribute in one of these scopes, depending on how long you want the data to be available and which resources, and then fetch it from the scope when you need it.
//in your first JSP
request.setAttribute("mySharedValue", "TheValue");
//in your second JSP
String sharedValue = request.getAttribute("mySharedValue");Similarly, you can work with the session and application scopes...
People on the forum help others voluntarily, it's not their job.
Help them help you.
Learn how to ask questions first: http://faq.javaranch.com/java/HowToAskQuestionsOnJavaRanch
(Yes I know it's on JavaRanch but I think it applies everywhere)
----------------------------------------------------------------

Sharing User Defined Variables across projects

Hi,
I'm wondering if it's possible to share User Defined Variables across projects. What I have in mind is that I would like to have my User Defined Variables configured in a central location and then insert them into my projects as linked variables so that they update automatically when I change their values. For example, I define a variable named Product_Version that has its value set to 9. Then I insert this variable into all my projects as a linked variable. After 2 months the product version changes to 10, so I change the value of the variable to 10 in the location where it is stored and it is automatically updated in all the projects. Can this be done somehow? I'm new to RoboHelp and I can't find any answer. I've been searching for the solution for some time in the product help, on the Internet to no avail. I even contacted Adobe Support and they redirected me to this forum I used Help and Manual before and their way of dealing with user variables was pretty simple.

Hi there
Unfortunately RoboHelp doesn't offer up a way to allow this, At least, not directly.
However, I do believe I found a way to make it happen, The variables are stored in a file named rhvariable.apj. So what you could do is to add this file as a Baggage File to each of your projects that will share the variables.
Now you would create a Shared Location as well as a new Category in your Resource Manager. This will create a common location to store the apj file.
Add the Baggage File to the location. Repeat the process for all projects that are sharing the variables.
Now, when the variable gets changed in any of the participating projects, the shared location should be updated and you can accomplish the goal.
However, note that even though you will have what you are wanting, it will still require opening each of the participating projects, synchronizing the APJ file and generating the output in order to update it all. No way I'm aware of to escape that.
Cheers,,, Rick

Problems with communication across a network using shared variables

I have two programs(projects) running on two different computers connected with a LAN. I am using LabVIEW 8.0, and the DSC-module. The program on one of the computers have measurements that I want to collect and show on the program running on the other computer on the network. I choose the indicator where I want to show the data, select ''Properties'', ''Data binding'', ''Shared Variable Engine (NI-PSP)'', ''Network Items'' and then browse for a Network...but the problem is that in my ''Network Neighborhood'' There is only one computer...and that is the one I am one...not the computer on my Network that I want to communicate with....
Have anyone any suggestions on how to solve this?
Kind regards Mari

Mari,
Check this link regarding trouble shooting network-published shared variables:
http://digital.ni.com/public.nsf/websearch/6E37AC5435E44F9F862570D2005FEF25?OpenDocument
This might be a firewall issue, so I would check that first.
Frode

Binding shared variable in executable across network

I can't seem to get a shared variable to bind from an executable on another computer back to a source variable on the main machine.
I can get the remote variable to change with programmatic access. Is it possible to have shared variables in an executable bind to a PSP URL on another computer? This is labview 2011.
I can see everything with NI Distributed System Manager, and the programmatic access changes the remote variable, so it's not a network issue.
Thanks for any insights. This just doesn't seem to work the way NI's online white papers say it shoud.

What I don't understand is why after binding to a specific URL, the "Shared Variable Deployment" screen of the application builder makes the target "my computer".
I probably could get this to work if I changed the network address of "my computer" in the ini file created in Application Builder?
This seem a strange way for this binding process to work. If the absolute target (for shared variable bound to another variable and referencing "absolute") was retained when the VI goes through the application builder, it would make for sense.
I can't get this to work any way with using bound variables. The only way this works is using programmatic access to shared variables in the built app, and I don't consider this the same thing.
My conclusion is that shared variable binding and appropriate absolute references to deployed variable libraries do not survive passing through the application builder with their absolute references intact.

Serializing read/write operations of network-published shared variables

Hi all,
I'm developing a distributed application (PC + CompactRIO), and using shared variables (SVs) for inter-device communication. Here's my journey so far:
Intended procedure
PC parses file
PC writes processed file data (custom cluster, large) into the 1st SV
PC writes a "grab data" signal/command (enum) into the 2nd SV
cRIO polls the 2nd SV
cRIO sees the command, then reacts by reading the 1st SV
Steps #2 and #3 were sequenced, using error wires.
Unexpected results
Even after the command is transmitted and the cRIO sees it, the cRIO could not read the data (which I wrote BEFORE the command) -- LabVIEW reported that the buffer was empty.
The operation succeeded when I placed a wait (5 seconds) between steps #2 and #3.
Questions
What am I doing wrong, and how do I achieve my desired outcome?
Is SV I/O asynchronous by design?
Is it possible to use event-driven programming to handle SV access? (i.e. does LabVIEW signal when the new SV value has propagated across the network?)

BillMe wrote:
Why do you have to "notify" the other end that data is available? The subscriber can simply sit in a loop doing a timed read just as if using a queue or notifier IPC. If it doesn't time out, you got new data. If it does time out, do some other processing if needed and then loop back for another timed read.
My sytem architecture is command-driven -- the cRIO listens for instructions from the PC interface (sent as an enum via one SV), and performs tasks (motor control) in response. One of the commands (the one described in this thread) happens to be "download a new motion profile from the PC, by reading the other SV". Given that the cRIO is already polling the command channel, I felt that there's no need to also poll the data channel (especially since the "download" command is issued very infrequenty). Plus, I thought that polling two channels would increase the chances of race conditions or illegal state transitions, particularly if the app is developed over a long term.
I am also new to LabVIEW, so my current programming style will heavily reflect my C++/Qt background while I get a feel for LabVIEW's strengths and weaknesses -- Qt is a heavily event-driven framework (even for networking!), where polling often means you're doing something wrong.
Still, thank you for pointing out that I can use timeouts to determine if new data has arrived -- my subscriber current writes a null command back into the SV when it has consumed the command, but you showed me that I don't have to.

Issues with Shared Variables in Systems Running for Extended Periods of Time

I am designing a large SCADA system using LabVIEW DSC and cRIOs. My plan is to use shared variables to communicate the majority of the information across my network (much like "tags" in a normal SCADA system).
I'm wondering if anyone has experienced issues (connection failures, etc...) with shared variables running on systems for months (both real-time and windows based PCs) without the cRIO or PC being restarted/redeploying the variables. What is the stability of the Shared Variable Engine over extended periods of time?
Thank you for the input.
--CLD--
LV 6.1, 8.6.1, 2011 SP1, 2012 SP1

I have a system with 2 cRIO's each with Ethercat extension chassis. Each cRIO hosts ~100 NSV's and is running the scan engine at 40 Hz.
Each cRIO is coupled to a HMI that has front panel control bindings to NSV's hosted on the cRIO as well as a windows hosted mirror library (used for citadel db logging) that is also bound to the cRIO NSV library. The cRIO's have monay months of contiguous run time without reboot and I closely monitor cpu and memory usage and also rt performance metrics and will log faults if there are any such events. I also use NSV's for messaging from the HMI to the cRIO for such things as setting zero offset values and deploying configuration parameters. My overall findings are that the SV engine and the PSP are stable and efficient (especially NSV<->NSV and NSV<->HMI binding)

Dsc 8.2.1 cannot write to shared variables error 1950679035

I am getting error 1950679035 ni_tagger_write when I try to write to my shared variables. I recently upgraded from labview 8.2 to 8.2.1. I also upgraded to DSC 8.2.1. During the install, I had to upgrade my computer to SP2 (windows xp), which installed mdac 2.8 sp1 for use with dsc 8.2.1.
I have the windows firewall turned off, I checked with our IT dept and no upgrades were completed overnight (as the program worked yesterday using 8.2). I checked and MAX will get a connection with the fieldpoint unit. Everything is deployed from my machine, currently running under the dev environment.
I have looked at this thread, but I was not able to get anywhere, http://digital.ni.com/public.nsf/websearch/0D7B86F4B4D19A5E86256F9A006EECB1?OpenDocument and here.
Even though I have windows firewall turned off, I added all of the execptions to the windows firewall list.
It appears that the shared variable library is deploying correctly, as the the windows says that it has (when you run a vi). I am progmatically deploying the vi.
I looked at the variable manager and I attached a screenshot below. I am not sure if that means that it did not deploy correctly or not.?? (I was only watching a couple of the variables, I have about 20 total)
thanks
Kenny
Attachments:
variable manager.jpg ‏55 KB

It appears that my problem has been solved. Apparently our network had an internal error for a quick second and my nic did not like it. So after I restarted again (fourth of the morning) it started working now.
Kenny

Using a Meter control in LV Touch Panel, and using shared variables that are custom controls.

I Just started using LV touch Panel module with an NI TPC-2106.
I have two differenct problems:
1) I was planning on using the "Meter" control quite a bit. I can set up the meter exactly how I like on the host PC, but on the touch Panel computer it seems to ignore my adjustments, mainly the start and end of the scale - i.e. I would like control to run from 0 to 360 with 0 straight up, using the entire circle. However, on the Touch panel computer it always puts 0 at about 7 o'clock and 360 at about 5 o'clock. I have also tried adding markers to no avail.
2) I am communicating with a compact fieldpoint controller. I can creat a shared variable that is a simple double with no problems. However, I have some shared variables that use a custom control for the variable type - bascially a cluster with a couble doubles, a time stamp, and an enumeration. It lets me drag the shared variable into my diagram, but it seems to ignore it when I run it.

Ipshita_C,
- I am using LV 8.6.1f1and LV Touch Panel 8.6.1.
- I have attached a simplified VI that shows how I want to use the meter. Notice that the placement of the endpoitns does not work correctly on the touch panel, and that it ignores the arbitrary markers that I placed.
- I also have included an XY graph control that displays on the TPC with margins around the graph area that I removed from the graph control.
- For the shared variable, it appears to be an issue related to the touch panel, not fieldpoint. I found another thread in this forum that mentioned that clusters containing Enumerations do not work in shared variables on the touch panel. I changed the enumeration to an integer and it now works fine.
In general, there seem to be a disappointing number of limitations in the touch panel implementation. My biggest concern is that I have not found any documentation from NI that lists these limitations. I seem to have to try things out and see what works and what does not work. Can you point me to a comprehensive list of touch panel modules limitations?
Attachments:
test 2.vi ‏10 KB

Modbus Ethernet read and write to a Eurotherm 6180XIO Modbus server using LV8.2 shared variables

I am having EXTREME difficulty trying to establish communications with a Modbus device using LV8.2 shared variables. The device is a Eurotherm 6180XIO Datalogger configured as a Modbus master. The PC and a cFP-1804 are slaves. All IP addresses are set correctly. This approach using shared variables would seem simple, but I can't find any examples or proper guidance on how to get it working. I am trying to avoid having to mess around with TCP/IP, OPC, or any other old-fashioned method.
I have read many threads on related topics but none directly apply to this situation. I have created a library containing a Modbus I/O server and shared variables bound to read and write holding registers. I have followed all recommended tips for creating such variables but I can neither read or write data. All data types are U16 due to Modbus protocol limitations. I have also applied the LV x10 factor in the most significant digit in the register offset (6 digits instead of 5).
I have a cFP-1804 on the same network which reads into the datalogger OK. The registers I use are 31000 (for CH0 on module 0, 31002 for CH1, etc) and the data can be read as FLOAT32. I have updated the firmwate on the 1804 to the latest level. I cannot even get shared variables to read SGL values. Using registers 301001 for CH0 and 301002 for CH1 I can only read U16 values, and not a 2-word SGL.
Third party Modbus simulation software is able to write to and read from registers very easily, but not LabVIEW.
Some questions are:
- do I use a Modbus master or slave as an I/O server in the library as a target for binding the shared variables?
- is there some other wierd translation in register offsets between LabVIEW and traditional Modbus?
- is this actually possible using shared variables or am I wasting my time?

Sending the whole 60-character string using a string or array would be the most efficient. I have tried both methods, and these only cause the datalogger to flag a message log but no text is displayed.
For a string variable, I have used the following binding "My Computer\Modbus Test.lvlib\ModbusServer6180\442305", where ModbusServer6180 is a Modbus I/O server configured with the logger IP address, and 42304 is the register offset at the start of the text block in the logger. I need to write to 30 consecutive registers starting with this one. I am not using buffering and have not enabled single writer.
Can anyone confirm whether this method should work in 8.2?
Does the string need a special termination character?

Using Shared Variables and Initialize Front Panel Binding (to PSP)

Hi,
I use LV DSC RT 8.2.1
I have a Vacuum System That includes signals from - Pumps failure, Valves status, Vacuum gauge, start Pump ...
Each signal is read by a FieldPoint.
All the relevant FieldPoint Channels are read by the Server (a computer in the Ethernet Network) and published to the network in the form of Shared Variables.
I have a client VI that is reading the Shared Variables published by the Server using Front Panel Binding.
Problem :
Some of the Bindings are in the mode 'Write &Read' and that causes some initialization problems.
For example - Valve #1 is Open, and then a User start running the Client VI, (the Valve #1 Status mode is 'Write & Read")
if in the VI the status of Valve #1 is closed (before running it) then the Valve status is changing to Closed.
I want the Client VI to first read the Physical status of the instrument and then to change the Value if the User changes it.
But that's seems to be a problem when using Front Panel Binding... (is it?)
I know I can Deploy a lvlib in the Client Side and Item Bind to the Shared Variables or Use DataSocket.
(Is DataSocket is a Reliable method when connecting to Shared Variables? What are the disadvantages when using DataSocket?)
What is recommended by those of you that are experienced or by NI ?
Sincerely Yours,
Amitai Abramson.

Amitai Abramson,
Hello and thanks for using the NI Forums.
I'm glad that you've read the Using the LabVIEW Shared Variable Tutorial on our website. Check out these other resources:
Network Variable Technical Overview
Troubleshooting Network-Published Shared Variables
Why Do I See Unexpected Value Change Events for Shared Variables Using LabVIEW DSC?
All You Need to Know About Shared Variables
Creating a Value Change Event for Shared Variables
Alternative Method for Using Shared Variables Between Systems in LabVIEW 8.x
What Is The Difference Between Using Shared Variables And DataSocket VIs To Access OPC Tags?
The issue that you are seeing by having "Write & Read" bound items on both the server and client side is essentially a race condition, you don't know which one is being read/written at what time. To resolve this issue I would take a look at some of the documents below.
Using a Local, Global, or Shared Variable in Parallel Loops Can Cause Race Conditions
Using Local and Global Variables Carefully
Tutorial: Local Variable, Global Variable, and Race Conditions
Locking a Shared Resource or Variable in LabVIEW Using Semaphores
You mentioned not wanting to have two sets of shared variables (one on each side), but this is a great method to resovle this issue, that, or you can develope some sort of hand shaking to prevent these race conditions.
I would suggest that in the future when using these forums you try to ask only one question per thread and make it more concise. It's hard to tackle multiple questions and such broad questions as "I want to know all the ways that I can connect to Shared Variables, and I want to know the advantages and disadvantages." I suggest this because we want you to get your questions answered and more concise questions will result in quicker and better answers.
Message Edited by Ben S on 10-01-2009 06:05 PM
Ben Sisney
FlexRIO V&V Engineer
National Instruments

Deploying Shared Variables to Remote Target?

I have a 2-application server/client setup where my client(s) merely read information "published" by the server via a Network-Shared Shared Variable. If I run my server on a "clean machine" (i.e. no LabVIEW development) and I "publish" the shared variable library (via the "Library : Deploy Library" Application method) to the localhost, I have no problems whatsoever reading the data in the client (the path of the .lvlib file provided to the Invoke Method VI is an absolute path to the .lvlib file, BTW). However, I'm having a bear of a time getting the server to deploy the library to a machine running a second client on the same network - to do this I still use the same absolute path to my .lvlib file for the first input to the method (it's in the same place on the target as well as on the host, not that I know what this means for a targeted host) and I specify the IP Address of the target machine on the second input. There is no firewall on either machine (I removed it because I was getting nowhere and needed to eliminate a possible source of problems) and my router doesn't filter traffic going across the local subnet. Am I not using the programmatic publishing correctly to publish to another target (from within the server), or can anyone point out any problems in my usage?
By the way, if I publish to the local host (127.0.0.1 or the host machine's IP address) I do not get an error out of the "Invoke Node" VI. However, when I try to publish to a network target (both machines have the Variable Manager running and both machines work fine if both server and client are on the same machine) I get error code 1 and the message: "Invoke Node in MyServer.vi<APPEND> Method Name: <b>Library : Deploy Library</b>" which is anything but helpful.
Any help would be greatly appreciated!
-Danny

Hi Arun,
I hope you're doing well. I'd like to clarify the architecture that you are actually using. It sounds like you are deploying a network-published shared variable library on two seperate host PCs. You are then attempting to read data from both of these hosts from a RT target using the Datasocket VIs. The RT target seems to be reading from the shared variables from one of the hosts just fine, but you can't read from the other host. Are both hosts deploying their libraries in an executable as mentioned in previous posts, or is the deployment process done through the LabVIEW development system? Also, when you connect to the hosts using Datasocket, how are you entering in the addresses for each item? Lastly, it might help to know whether you have LabVIEW and LabVIEW Real-Time versions 8.0 or 8.0.1. If you could provide some more information on your set up, we can try to give some suggestions. Thanks!
Thaison V
Applications Engineer
National Instruments

Deploy Shared Variables

I'm having an issue with using SVE. I'm using LV 8.6 (cannot upgrade to 2010 at this time, have to "make it work").
I've used shared variables before with an HMI and PXI but my setup is different now:
PXI (called my target) that "talks" to different controllers via Modbus TCP/IP. Separate PC to interface to the PXI to provide a user-interface (called my host).
I've run across posts talking about calling the Deploy Library method in the top-level VI of the application. I want the PXI to deploy the shared variables since it will be running constantly and the PC is optional. Do I "manually" transfer the shared variable library, in this case called the NetworkVars, to the PXI so the PXI application can find it? The PXI will be running independently once the program is completely developed.
I've used Labview a long time but have never had to do much with networking/sharing.
Thanks for any help.
Solved!
Go to Solution.

I still cannot figure this out, have read NUMEROUS white papers, help entries, etc. but I cannot get it to work properly.
PXI system with analog I/O, TCP/IP connections to Watlow controllers. This is where I set up NI-PSP variables, autodeploy enabled, run as startup when I transfer the program to the PXI.
Separate computer running an interface program to the PXI, the front panel controls and indicators are "bound" to the PSP variables.
I download to the PXI, reboot it, start my PC program and there is no communication. The PSP LEDs on the bound items are all green but there is nothing going back and forth, UNLESS I run the PXI program on the other development computer.
I know I'm missing something simple, just getting a little aggravated! LabVIEW 8.6, no DSC module, just the RT module.

'Thread-shared' variable across JSPs

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