Request Deallocati​on?

Question

I am looking at a couple of subvi that pull and process a large 2d array.  At the end of each subvi, the Request Deallocation is used.  Is that neccessary?  Is it a good practice?
Kudos and Accepted as Solution are welcome!

Answer 1

jyang72211 wrote:
[...]  My question is
How do I prevent labview to allocate mulitple copies for the same array when the array is being passed in and out of different subvi? 
Passing data in and out usually does not force LabVIEW to copy the data: You can verify with   Tools >> Profile >> Show Buffer Allocations...   that LabVIEW reuses the data on the wire and no copy will be made -> This is no use case for "Request Deallocation".
jyang72211 wrote:  [...]
If I have a state machine, [...]  If I have 3 states with subvi plus the main state machine with shift register, would I have 4 copies of the same array in memory?
It depends on how the subVIs are allocating buffers.  Again, use Show Buffer Allocations...  in all subVIs. If no allocations take place, you do not have to worry. On the other hand: If you are unsure if the subVI allocates a buffer (e.g. because you might make a small change to it that forces LabVIEW to copy and you do not consider this at wiring time), you could place a "Request Deallocation" on the subVIs block diagram.  If there is a chance to free any memory, LabVIEW will do so when this VI finishes.  If there is nothing to deallocate -> "Request Deallocation" should be merely a "no operation".