I'm sorry, but you have an unconstrained flat out loop creating hundreds of thousands of threads ... and you wonder why it runs out of memory?

Why are you storing the thread handles when you're detaching them?

Did you not see me ask which version of Perl you are using?

... but its the only way I know of ensuring a fresh thread each time.

What on earth do you mean by a "fresh thread"? And why are you so certain that you need them?