in reply to
Re^3: creating unknown number of threads and then join results
in thread creating unknown number of threads and then join results
I think I stumbled onto the answer. According to this article, the chdir command is not thread-safe. See http://www.perl.com/pub/2002/06/11/threads.html. See the section about 2/3 the way down titled "Altering Perls behavior to be thread-safe, ex::threads::cwd" . They give an example of how to "fix" it, too. In my script, I use "chdir" only if running the ClearCase commands, which explains why it is failing. I'll have to re-examine how I am doing that, or implement the fix in the article above.