How can I tell when a process has finished writing to a file?

I have a process which has been spawned from a shell. It is running as a background process and exporting a DB to a CSV file in /tmp. How can I tell when the background process has completed (finished / quit) or if the CSV file lock has closed? I plan to FTP the file to another host once it's written, but I need the complete file before I start the file transfer.