O Monks,

I have a script that looks essentially like this:

while(@array1) {
    ONE: while(@array1) {
        my $item = shift @array1;
        # Do various things with $item, some of which will _possibly_
        # push @array1, ...
        # and/or
        # push @array2, ...
    }
    TWO: while(@array2) {
        my $item = shift @array2;
        # Do various things with $item, some of which will _possibly_
        # push @array2, ...
        # and/or
        # push @array1, ...
    }
}
[download]

The idea here is that I'm acting on items, which includes collecting more items to act on. The problem is that ONE runs for a long, long time (a few days, so far), and I don't want to spend so much time on @array1 and neglect @array2: I want to get some of the "various things" done to @array2 also. So I'm looking for ideas on how to get my code to switch off to TWO even before ONE ends.

One thing I thought of is to use an incrementer, something like this:

while(@array1 or @array2) {
    my $i = 0;
    ONE: while(@array1 and $i < $some_large_number/10) {
        $i++;
        my $item = shift @array1;
        # Do various things (as above)
    }
    $i = 0;
    TWO: while(@array2 and $i < $some_large_number) {
        $i++;
        my $item = shift @array2;
        # Do various things (as above)
    }
}
[download]

Another idea I had was to use threading: handle ONE and TWO in separate threads, and have each wait for the other until both arrays are empty. The problem with using threading is twofold: I don't know how to use threading (though I can learn, of course), and it comes with a big nasty warning.

A third idea I had was to combine the two arrays, something like this:

while(@array) {
    my $item = shift @array;
    if (used_to_be_in_array1($item)) {
        # Do various array1ish things with $item, some of which will _
+possibly_: push @array, ...
    } elsif (used_to_be_in_array2($item)) {
        # Do various array2ish things with $item, some of which will _
+possibly_: push @array, ...
    } else {
        warn $item;
    }
}
[download]

But I may be missing some pros and cons of each of those approaches — and of course there is probably yet another and better way that I haven't thought of. So I seek your advice on this issue. What do you recommend (and why) for handling both my arrays instead of spending a lot of time on one of them?

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