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LabVIEW
variant set attribute- how fast it is?
Solved!
Hello
On NI days there was presentation about variant atributes. There was example saying that variant can be used to remove duplicates from 1D array and this supposed to be very fast solution. I did some test and it seems that it isn't :
On the other hand variant is very fast at searching once all atrubutes are set up.
Som my question is how fast is process of setting variant atributes and how this variant structure is allocated and stored in memory.
VI snippets attached.
You should attach the actual VIs. Snippets do not reproduce all VI settings.
You should use "high resolution relative seconds" for the timing.
Make sure your code does not get deadstripped, because there is no output used
Well, the speed difference is not dramatic (not even an order of magnitude ;)) The dramatically simpler variant code is also worth something.
Your non-variant code is also highly optimized. If you would do something that more closely resembles what the variant version does (=search if each element has already be added to the output), it would be much slower, epsecially for large arrays.
Interestingly, if you would prepend a long constant string to all you strings, suddenly the variant gets faster. 😉
apapasd1sd wrote:What means code does not get deadstripped?
See e.g. figure 13 here. Dead code elimination removes code where executing it would no make a difference, e.g. if the output is not used. This typically only happens if you disable debugging, though. You should disable debugging, to eliminate general debugging overhead,
Don't underestimate the compiler. Sometimes it is difficult to devise a honest benchmark.
apapasd1sd wrote:When I create large array like 10000 elements by using initialise array it is stored as continious block in memory?
What If I create array in for loop with auto indexing enabled? Is this also continious block in memory ?
When I add using functions like insert into aray when app is working I think it is unlike that we still have continious block in memory. Is that true?
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LabVIEW stores variants as handles to a LabVIEW internal data structure. Variant data is made up of 4 bytes. - Could someone explain that to me??
Numeric arrays are always contiguous in memory, independent on how you create it. The loop where you generate the data can be simplified by using autoindexing. same difference, but less code.
When you use "insert into array", a new copy of the entire array typically needs to be made, because it always needs to be contiguous. Insert into array and delete from array are relatilvely slow because of this.
You are not really using variant data, just variant attributes. The variant itself is actually empty in your case. Variant attributes are stored internally as a red-black tree, giving very fast lookup, insert, and delete performance.
LabVIEW manages the memory for you.
However, if you make too many reallocations of evergrowing arrays, you might run out of contiguous memory and thus run out of memory, Memory fragmentation can cause problems.
I'd say the Remove duplicates test is flawed, as the test is unlikely to actually remove something. If you set the text to use 2 or 3 decimals you'll get some duplicates to remove.
/Y
