Rename Text File Used By Two applications

Question

Dears,

I have an application that write to a text file every time an event fires, in the second application i want to rename this text file when it reach 2GB.
The problem that if i run the rename command at the moment of the write moment this may run an exception or lead to loos a data that did not written on the file.
If i Use Try and exception and the rename will occurs when there is no exception, is there is any probability that i loss any data?
Or Do You have any idea to prevent this?

Kind Regards