You're going to have to make sure that your program is aware of what it is doing, and that it can pick up where it left off. This is not necessarily trivial, especially if the work each function does is not entirely trackable.

Maybe this will do something useful:

#!/usr/bin/perl -w

use strict;

use constant RDELIM => "\x00";
use constant ADELIM => "\x01";

my @state;
my @f_state;
my $state_file = "saved.state";

$SIG{INT} = \&freeze;

sub freeze
{
        open (STATE, ">$state_file")
          || die "Could not save state to $state_file, sorry\n";

        foreach (@state)
        {
                my ($args, $vars) = @$_;
                print "@$args...@$vars\n";

                print STATE join(RDELIM, @$args);
                print STATE ADELIM;
                print STATE join(RDELIM, map { $$_ } @$vars);
                print STATE "\n";
        }

        close (STATE);

        exit (0);
}

sub thaw
{
        # If the file can't be opened, just restart
        open (STATE, $state_file) || return;

        @f_state = ();

        while (<STATE>)
        {
                chomp;
                push (@f_state,
                        [ map { [ split(RDELIM, $_) ] }
                          split(ADELIM, $_) ]);
        }

        close (STATE);
}

sub arg_push
{
        push(@state, [shift(@_), [@_]]);
}

sub arg_pop
{
        pop(@state);
}

sub arg_thaw
{
        my ($args,$vars) = @{shift(@f_state)};

        @{shift()} = @$args;

        foreach (@_)
        {
                $$_ = shift(@$vars);
        }
}

use constant DEPTH  => 4;

sub recurse
{
        my ($x,$y,$X,$Y);
        my @args = @_;

        arg_push(\@args, \$x, \$y);

        # If there is frozen data specified to at least
        # this depth...
        if (@f_state)
        {
                # ...use that instead.
                arg_thaw(\@args, \$X, \$Y);
                print "Resuming @args ($X,$Y)\n";
        }

        my ($what) = @args;

        $X = 0   unless (defined($X));
        $Y = 'a' unless (defined($Y));

        print "$what\n" if (@state == 3);

        if (length($what) <= DEPTH)
        {
                for my $x_iter ($X..'9')
                {
                        for my $y_iter ($Y..'z')
                        {
                                $x = $x_iter;   # Copy
                                $y = $y_iter;

                                recurse("$what$x_iter$y_iter");
                        }
                }
        }

        pop(@state);
}

thaw();
recurse('');
[download]

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