Jump to content

DereferenceByName Xnode ( -> operator in C)


Recommended Posts

Property nodes already do this? Granted it requires implementing the property, but I'm generally not a fan of pulling data from class wires via the cluster primitives as it makes it hard to track where data is consumed. 

Link to post
Share on other sites

The above bit is what gets tedious to setup for all of those property VIs, this would get used inside those VIs for outside access but for a lot of stuff I do I try to avoid the overhead of an additional VI call just to pull out a data value. Here's a clarification of the boilerplate I'm eliminating:

 

DerefBoilerplate.png

Link to post
Share on other sites

Oh right. I jumped to objects by analogy to the c languages, completely forgetting the hard boundary between clusters and objects in LV

Link to post
Share on other sites

Well the nice thing about his is that you dont have to copy the entire data structure, just the portions you care about. Note that he unbundles inside the IPE structure. For known names that you want to support (like always unbundle the thing called "waveform") the VIM would work, but its not arbitrary like the xnode could be.

Edited by smithd
Link to post
Share on other sites

I think it's extremely useful. I added DVR support to the latest version of LV-Signals which does something very similar:

LV-Signals.png

It only works with DVRs of clusters, and it looks like yours works with DVRs in general. Check out LV-Signals if you get a chance, the original use was to use it with LV-Create-Signals.xnode, which creates a DVR and a value change event for each element in the cluster.

https://github.com/erdosmiller/lv-signals

Edited by DTaylor
  • Like 1
Link to post
Share on other sites
On 7/15/2017 at 0:25 PM, UnlikelyNomad said:

Then I get the daunting task of scripting up the GenerateCode ability >_>

When you do this give LV-Scripting a chance: https://github.com/erdosmiller/lv-scripting

It has similar functionality to the LAVA Scripting Library: https://lavag.org/files/file/54-scripting-tools/ , but with a heavy emphasis on ease of use for code generation. The package has a dozen or so examples which likely cover everything you need for your XNode.

Link to post
Share on other sites

So cool, I would definitely use an XNode that does this.  Yes the VIM could work with the issues already mentioned, with copying the whole cluster in memory just to grab one element.  Props for the idea, and DTaylor's suggestion.

Link to post
Share on other sites

Oh sorry it was renamed Maleable VI, official feature in 2017 but was implemented as a custom XNode shipped with LabVIEW since around 8.2.

http://zone.ni.com/reference/en-XX/help/371361P-01/lvupgrade/labview_features/

VI Macro discussion before 2017 made VIMs official.

https://lavag.org/topic/19163-vi-macros/

It has some shared functionality with XNodes (type propagation for inputs and outputs) but other custom things like right click, adding removing terminals, and changing node size and icon at edit time can only be done as an XNode, not a VIM.

Link to post
Share on other sites
18 hours ago, infinitenothing said:

Maybe VIM could help?

 

Read DVR example.png

Read DVR.png

I use a lot of reference applications for things like buffers, etc. where pulling out everything everytime would become prohibitive. (As others have stated about my unbundle being inside the IPE). Perhaps the compiler would see the other items aren't pulled out and not copy everything, but if it copied my two gigs of full rate 50khz data when all I wanted was the current data size: boom. Memory fault.

Ultimately this XNode is going to become part of a palette of functionality that aids in development of by-reference designs that go beyond just type matching and maybe even someday others start using these and I never have to inherit code where a class instance stores state data in a FG, especially when that FG isn't part of the class. Preview of other coming attractions: Generics in LabVIEW. (With type restrictions!) All of these features will build on what I learn getting this "simple" introduction to XNodes working.

Link to post
Share on other sites

Was debugging enabled on the VI when it was ran?  I assume probing the cluster wire would force the string to be copied into another memory location.  Anyway that does sound good since one VIM that takes a few minutes to write could perform some of the same functionality as the XNode.  Still would require an unbundle by name, but a Read-Only DVR function could be pretty useful.  I think I made one during the 2017 beta replacing the icon now that I think about it.

Link to post
Share on other sites

Interesting, the same holds even if you do the following:

  • Pull out the string and read array size
  • pull out string and use split string (at char 0xFF) but only read offset
  • Inside of top (writing loop) in-place manipulate data of string (convert to byte array, replace element 0, byte array to string, rebundle)

To force labview to do an allocation, I had to go so far as to pull the data out of the DVR and manipulate it and use the manipulated data (I used the same byte array replace index + split string) . They really did a solid job with the optimization here.

1 hour ago, UnlikelyNomad said:

Was the compiler smart enough that it never put the string into the cluster in the first place? /snicker

Yes it actually did. And in typical labview fashion there are two copies (one for the data after the for loop, one to bundle it). You can get rid of the unnecessary copy through this embarrassing scheme:

sad.PNG

As impressive as the DVR optimization is, this is far more common and far more sad :(

Edited by smithd
Link to post
Share on other sites

I was testing a buffer I wrote for an application some months ago and pushed nearly 2 gigs of data into it 200 rows at a time and then read back the row count. LabVIEW's memory never went above 350megs. Definitely tricky to benchmark in LabVIEW sometimes. LabVIEW is great because it does a lot of stuff for you. LabVIEW sucks because it does a lot of stuff for you.

Edited by UnlikelyNomad
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Similar Content

    • By flarn2006
      LabVIEW's built-in XNode editing tools are enabled using a license file, rather than a simple INI toggle. Presumably they do this for stronger discouragement from unofficial use, as hacking one's way past that feels a lot more "shady" than just adding a line to a config file.
      But what about the Linux and Mac versions? They don't have a license manager, so how is XNode development enabled there? One might guess that those features simply aren't compiled into the released builds of those versions, but there is actually precedent to suggest otherwise. VI Scripting used to be similarly restricted using a license, but then they made it public. At the time, LabVIEW didn't have a toggle in the Options for it. But they didn't need to release a patch to add one. Instead, they simply published their formerly-internal license file, and set their activation server to accept requests to activate it. And yet, Linux/Mac users weren't out of luck: it turned out that for them, it actually was just a configuration key.
      The VI Scripting license had the internal name "LabVIEW_Scripting(_PKG)". The Linux/Mac configuration key was "Scripting_LabVIEWInternalTag".
      At 17:48 in this video, several XNode-related configuration keys are shown, likely found in strings in the EXE or resource files. One of them is called "XNodeDevelopment_LabVIEWInternalTag". Guess what the internal name of the XNode Development license is.
      I don't have the Linux/Mac version to test with, but I know a pattern when I see one. The following command was given in the readme for the VI Scripting package for Linux:
      echo -e "labview.Scripting_LabVIEWInternalTag:\tTrue" >> ~/.labviewrc Here are the Mac instructions:

      If you have either of those versions, it's probably worth a try: follow those instructions, but replace "Scripting" with "XNodeDevelopment", and see if you can open an XNode in the IDE, or create one from File->New. (Also, in the case of Mac, replace 8.6 with your actual LabVIEW version if necessary.)
      (Here's where I got my information about enabling scripting: https://forums.ni.com/t5/LabVIEW-APIs-Documents/LabVIEW-Scripting/ta-p/3535340?profile.language=en)
    • By Axelwlt
      Hi
      I am reading big TDMS files (~1GB) and I try to minimize memory usage.
      I read a signal once and I want to keep it for later usage, so I tried to write it to a DVR in the hope that I have only one instance of the data in memory.

      However the task manager tells me that uses 2 times more memory than it should.
      I think the problem is that the array is not deallocated although I don't need it after writing it to the DVR.
      Is there a solution to make sure I don't have copies of data?
    • By Ram Prakash
      Can anyone please tell what a DVR [ Data value reference ] is ? I want to know at what situation it will be used and what are the advantages we get by using DVR. I am really confused in this topic . If someone has any code in which they have worked with DVRs. kindly share it to me.
       
      Thank you.
    • By Zyl
      Hi everybody,
       
      I'm running into something I don't really understand. Maybe you can help me here !
      I've got a LVLIB that is used as an 'Interface': it exposes public VIs which wrap around public functions of a private class (see code attached) . The class is private because I want to force the users to use the 'interface' functions.
      In one of my interface VI, I create a DVR on the private class (Interface_init). The DVR is stored into a typedef (FClass_DVR.ctl) and this typedef is the 'reference' that link all the interface public functions.
      In TestCode.vi (which is not part of the lvlib and illustrates the standard code that a user can create to use my driver), I can call my public interface functions and link them without any problem.

      But as soon as I create an indicator on that reference (to create a state-machine-context-cluster for example), my TestCode VI breaks !

      The error returned is : This VI cannot use the LabVIEW class control because of library access scope. The LabVIEW class is a private library item and can only be accessed from inside the same library or libraries contained in that library.
      I understand that the class is private. But the DVR is contained into a public control. Using an In Place structure on that DVR into TestCode would not work, since the class is private. So why is the DVR control problematic at that point ? Creating it do not breaks any access protection...
      Am I missing something ?
      DVR Private POC.zip
    • By Brains
      Hi,
      Does anybody know the best way to make a copy of a byref object (open gds v4) at runtime and pass all the attributes values (including inherited attributes) to the new object?
      Thank you!
      Craig
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.