File Locking

Trap #3: Shutting the Barn Door etc.

Solution 2:

        open S, "> somefile.sem" or die ...;
        flock S, LOCK_EX or die ...;
        open F, "> somefile" or die ...;
        # Now write F
        close F;
        close S;

Use a semaphore file
The file you lock need not be the one that has the data in it
The semaphore file solution solves a lot of locking problems