Why not use File::Basename instead of split?

$att_file won't have a slash, and if $current_thread_id is $$, it won't contain a slash either, so there's no need for s/\//_/g/. But for those days when you do need somethign like that, take advantage of the fact that you can use any character as the delimiters: s|/|_|g.

What's the code in tmpFileName()?

--
TTTATCGGTCGTTATATAGATGTTTGCA