Trap #1: LOCK_UN

        # Process A

        open DATAFILE, "+< $datafile" or die ...;
        flock DATAFILE, LOCK_EX;

        seek DATAFILE, 0, 2;
        print DATAFILE, $newdata;

        flock DATAFILE, LOCK_UN;

        # do something else for awhile

• The $newdata might still be in the standard I/O buffer when the file is unlocked!

• Or some of it might still be in the buffer

• Result: Other processes see a garbled file

• When process A exits, the buffer is flushed

• Even though some other process holds the lock by then!

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Copyright © 2003 M. J. Dominus