Shared variable, missing data, the same timestamp for two consecutiv​ely data

Question

hello
I have a problem with missing data when I read from a network published shared variable.
Host VI:
In a host VI on my Laptop (HP with WinXP Prof.) i'm writing data to the shared Variable "data". Between two consecutively write operations is a minimum of Milliseconds waiting time. I use that because I want to be sure that the timestamp for each new data value is different then the preview one (resolution shared variables is 1 ms)
Target VI:
the Target VI on a cRIO-9012 realtime device is reading only new data in the way that it compares the timestamp of a new value with the timestamp from the last value.
Problem:
rarely, I'm missing a datapoint (sometimes everything works fine for several hours, transferring thousands of data correctly before suddenly the failure happens). With some workaround I'm able to catch the missing data. I've discovered that the missing data has the exactly same timestamp then the last readed datapoint, therefore is ignored in my "legal" data.
To sum up, the missed value is written to the shared variable in the host, but the target ignores him because his timestamp is wrong, respectively the same as the last value has, despite the host waits every time for a minimum of 10 milliseconds before writing a new value.
Note:
The shared Variable is hosted on the Laptop and configured using buffering.
The example is simplified only to show the principle function, in real I use also a handshaking and I secure that there is no over- and underflow.
Simplified Example:
Question:
Has someone an idea why two consecutively data can have the same timestamp ?
Where is the (wrong) timestamp finally coming from (system?) ?
What would be a possible solution (at the moment with shared Variables) ?
-> I tried a workaround with clusters where each data gets a  unique ID. It works but it is slower than comparing timestamps and I could get performance problems.
Would it change something when I host the shared Variable on the RT-System ?
Thanks for your help
Regards
Reto
Solved!
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Answer 1

Hi Reto,
I had a look on your modified Example.
Because the Shared Variables didn`t work like Queues or Notifiers (No Event or Interrupt when a new value has been written. And for sure the´re not possible over a network) you will see the issue, that the code is reading the values more often with the same timestamp (Polling Problematic) if the reader is faster then the writer. And because the timestamp is written with the value you´re able to program like you do. Filter out whats duplicated when you have the same timestamp.
Everything is described in here:
http://zone.ni.com/devzone/cda/tut/p/id/4679#toc1
Laurent talked about a second depth of buffer. Please have also a look at the link. Somewhere in the middle of the tutorial you see the explanations of Buffer and RT-Buffer.
Regarding your question: Would it change something when I host the shared Variable on the RT-System? --> No
In my experiences, you should consider to place the Shared Variable Engine after asking some questions regarding the application.
You will find the Answers to this 3 Questions also in the link:
Does the application require datalogging and supervisory functionality?
Does the computing device have adequate processor and memory resources?
Which system is always online?
And you`re right the smalles time interval you can see in the timestamp is 1ms.!
What you also can do is working with an enabled "timed out". This might be more performance efficient than reading the timestamp.
What I don`t know and not find up to now, is if LabVIEW or the OS adds the timestamp. It´s taken from the system time, this looks like LabVIEW is taking the value and adds it. 
I hope this helps
Alex
NI Switzerland