FileGetSize() problem

Hello.
I want to check the size of a particular file that still creating.
For doing this, I'm using FileGetSize() in a while loop..

But there is a problem. It turns out that the function is not updated with the new size of the file (while it is still written)

I do not know what to do ..

What I want to do is to know if the file continues to be written. If not then know that it happens.

I can not do this because of this problem the function ..