Problem with polling for new files

There is a problem I've encounted while running a few tests with my Directory Polling actor.

If a file is being written to--for example, a large data file is being copied to the data directory--when the directory is checked for new files, the yet-to-be-complete data file will be flagged as a new file, and passed on to the other actors.

This causes a big problem, since the file then being written to SRB etc may not be complete.

Solution may be to check each file every second until the lastModified value has remained the same for a number of iterations. However i don't like this solution, as it add's a constraint that each file takes at least n seconds to process, although this wouldn't be a problem for large data sets that aren't produced rapidly.