Slow imc COM (ActiveX)-libraries inside LabView

Question

Hi
I'm using the imc COM (ActiveX)-libraries inside labview. The key command is the "automation open" block from LabView and selecting the desired ActiveX class.
Here his the definition of one of this function:
Function DChannel.GetDataDouble( StartIndex As Long, Count As Long,
                Data As Double() ) As Long
Copies the specified samples in an array of 8Byte real numbers.
Parameters
StartIndex
Index of the 1st sample to copy. The first sample in a channel has an index of 1.
Count
Number of samples to copy.
Data
Array to receive the values. See remarks section.
Return Value
Number of valid samples in <Data>. May be smaller than <count>, when there are not enough samples in the channel (StartIndex + Count -1 > Length).
The problem and also question is why the parameter Data apears as a variant when I use a invoke node for the above method (should be double()??)
When using large Data arrays the libraries are very slow in comparison with VB6. I tested the same functions in VB6 and LabView. In VB6 the COM libraries are very fast! Does anybody know how to improve performance with COM Variants?
Thank you

Answer 1

I'm not sure you can do anything about the speed as long as you use ActiveX. At least that was the answer I got when I asked a similar question here. It seems that there is a lot of data copying between memory spaces that goes on between ActiveX and LabVIEW and, if there is much data involved, it can take a while. Search these forums for the terms safearray or "safe array" or marshal data and you will find more info on what you are up against.