Many experienced programmers do not understand races either. For instance every select() loop has a race condition - between you being notified and you trying to respond, the data may have gone. Early versions of Apache suffered from this problem, one request could tie up several children.

A related bug warning. The examples in the documentation and in the Perl Cookbook of using flock with DB_File are not safe. It was discovered last fall that the first page of the database is read before you have a chance of locking the dbm, and in some cases BerkeleyDB will close and reopen the file behind your back.