Your attempt at making a semaphore file is not having any effect. The race condition caused by reading and writing separately goes like this:

	Process A	Process B
1	readdata()
2		readdata()
3		writedata()
4	writedata()

Process B's work is overwritten.

You should open the file once to read and write, flock it (blocking), read, process, and write. Close releases the lock.

To use a semaphore file, you should do a blocking sysopen with O_EXCL, and unlink the file when you're done. There's no need to use both methods.

I think you also have a problem with autovivifying globals in your subroutines, then expecting later lexicals to appear in their place. use warnings; use strict;.