Thank you all (Laurent R, perlfan, Tanktalus) for your ideas! Tanktalus, I think you misunderstood my arrays' schema, but no matter: I think I will end up using something based directly on one of your ideas:

while(@array1 or @array2) {
    while(@array2) {
        my $item = shift @array2;
        # Do various things
    }
    if(@array1) {
        my $item = shift @array1;
        # Do various things
    }
}
[download]

This avoids the need for me to learn to use threads or Coro. And (it's especially good for me at this juncture. My script has (as I mentioned) been running for days, building up `@array2` without doing anything with it really, but I stored the array elements in a file, so now I can read that file and start acting on it immediately. Even after my current list of `@array2` items is exhausted,) I'm more interested really in `@array2` items than in `@array1` items, so this is a good solution for me. Thanks again.