String order - TCP

[cristina.lopez]

Good Morning,  

I expose my problem:  

I transmit a string beetwen TCP (TCP Write), but when I read this string (TCP Read) it is not always in the same order as it was sent, sometimes yes, sometimes not, how can I read the string exactly? in the same order that was sent?  

Thank you.   A greeting

[GerdW]

Hi Cristina,

can you attach a VI demonstrating that behaviour?

[rolfk]

You need to explain in more detail what you are doing. TCP is a stream based protocol and one of its guarantees is that the data arrives in the same order as it was sent. If that does not appear so you have probably a race condition in your sender where you try to send from different locations in parallel through the same connection refnum and while you think you enforce a specific order you don't since LabVIEW is happily executing code that has no data flow dependency in parallel with each other and then it is pure randomness which function is scheduled earlier. You may think that if you single step through the code there only is always the one code function executing but that is because LabVIEW has to sequentially highlight the functions since humans are pretty bad to interpret multiple things happening in parallel. When you disable single stepping LabVIEW executes the code again with full speed and not necessarily in the same order as what you saw in single step mode debugging.

[wiebe@CARYA]

That's not normal behaviour. Must be something you're doing.

Do you send one string (e.g. one send)? Or 

Do you send the string from multiple parallel loops?

Some code would help.

[cristina.lopez]

Hello,

firstly thanks to answer.

I'm attaching a image of program, I'm communicating my computer with a sb-rio

Thanks.

[GerdW]

Hi Cristina,

are you sure you ALWAYS send/receive just 4 bytes?

[jwscs]

can it be that you still have something in the buffer from "before"?

so you get the "0" from an earlier send as first char of your 4?

[cristina.lopez]

The string is composed from 2W00 or 2W02 or 2W10 or 2W11 

This is 4 byte , not?

[cristina.lopez]

I thought so , but  I don't know how can i check this.

Do you know?

[cristina.lopez]

Or how i can clean the buffer?