some process writin file - check if complete

Hi folks...

some process is writing a file....
as soon as the process starts the file comes there, and its growin..

now i in another script want to ftp the file. i don't know if the file is complete or not.

the process which writes the file is some other application and hence can't integrate both...

is there a way to check the completion of the file....

thanks in advance
s a d e