Can you make "testb" faster than "testa" while still preserving the order? If you help me do that, then I can rewrite my script using queues and hope that it resolves my intermittent crashes.

#!/opt/perl/bin/perl
use strict;
use threads;
use Thread::Queue;
use Thread::Semaphore;
use threads::shared;
use Time::HiRes       qw( time );

my $iterations = 100;
my $chunksize = 50;
my $threads = 5;
my $aoutput = "a.txt";
my $boutput = "b.txt";

my $q;
my $s;
my $outq;

my %data = ();
foreach('a'..'z') {
    $data{$_} = $_ x 200;
}
testa();
testb();
system($^O eq 'MSWin32' ? 'fc' : 'diff',$aoutput,$boutput);

sub testa {
    my $t0 = time;
    $q = Thread::Queue->new;
    $s = Thread::Semaphore->new($threads);
    my ($outth) = threads->create(\&outputa);
    inputa();
    $q->end;
    $outth->join();
    printf STDERR "testa done in %0.02f seconds\n",time - $t0;
}

sub worka {
    my ($data) = @_;
    my @ret = ();
    foreach my $chunk(@$data) {
        my %output = ();
        foreach my $key(keys %$chunk) {
            if($key eq '.') {
                $output{$key} = $$chunk{$key};
                next;
            }
            my $val = $$chunk{$key};
            my $uc = uc($key);
            $val =~ s/$key/$uc/g;
            $output{$key} = $val;
        }
        push(@ret,\%output);
    }
    return(\@ret);
}

sub inputa {
    foreach my $a(1..$iterations) {
        my @chunk = ();
        foreach my $b(1..$chunksize) {
            my %adata = %data;
            $adata{'.'} = $a * $b;
            push(@chunk,\%adata);
        }
        $s->down();
        my ($th) = threads->create(\&worka,\@chunk);
        $q->enqueue($th);
    }
}

sub outputa {
    open(my $fh,'>',$aoutput);
    while(1) {
        my $th = $q->dequeue();
        last unless(defined $th);
        my ($output) = $th->join();
        $s->up();
        foreach my $data(@$output) {
            foreach my $key(sort keys %$data) {
                print {$fh} $$data{$key};
            }
            print {$fh} "\n";
        }
    }
    close($fh);
}

sub testb {
    my $t0 = time;
    $q = Thread::Queue->new;
    $outq = Thread::Queue->new;
    $s = Thread::Semaphore->new($threads);
    my @threads = ();
    foreach(1..$threads) {
        my $th = threads->create(\&workb);
        push(@threads,$th);
    }
    my ($outth) = threads->create(\&outputb);
    inputb();
    $q->end;
    $outq->end;
    $_->join() foreach(@threads,$outth);
    printf STDERR "testb done in %0.02f seconds\n",time - $t0;
}

sub workb {
    while(1) {
        my $arr = $q->dequeue;
        last unless(defined $arr);
        $s->up();
        my ($input,$output,$sem) = @$arr;
        foreach my $data(@$input) {
            my %ret :shared = ();
            foreach my $key(keys %$data) {
                if($key eq '.') {
                    $ret{$key} = $$data{$key};
                    next;
                }
                my $val = $$data{$key};
                my $uc = uc($key);
                $val =~ s/$key/$uc/g;
                $ret{$key} = $val;
            }
            push(@$output,\%ret);
        }
        $sem->up();
    }
}

sub inputb {
    foreach my $a(1..$iterations) {
        my @input = ();
        foreach my $b(1..$chunksize) {
            my %bdata = %data;
            $bdata{'.'} = $a * $b;
            push(@input,\%bdata);
        }
        my @output :shared = ();
        my $sem = Thread::Semaphore->new(0);
        $s->down();
        $outq->enqueue([\@output,$sem]);
        $q->enqueue([\@input,\@output,$sem]);
    }
}

sub outputb {
    open(my $fh,'>',$boutput);
    while(1) {
        my $arr = $outq->dequeue;
        last unless(defined $arr);
        my ($output,$sem) = @$arr;
        $sem->down();
        foreach my $data(@$output) {
            foreach my $key(sort keys %$data) {
                print {$fh} $$data{$key};
            }
            print {$fh} "\n";
        }
    }
    close($fh);
}
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