Your program logic is wrong, or at least very weird. The only place where you try to remove elements from your @t array is in SafeExit, and there you remove the wrong elements. You use the global $count variable to remove the elements, but $count never gets reset to 0 so you will basically remove a random element from @t, or at least not a joined element. I recommend using a hash keyed by the thread id over using some array.

Also, looking at the Thread documentation, it clearly recommends the ->eval method over the ->join method if you want to prevent dieing.