my $head = 0;  # Can only be modified by the lone writer thread
my $tail = 0;  # Can only be modified by the lone reader thread
my $size = 4;  # Can hold one less than $size
my @buf = (undef) x $size;

# Can only be called by the lone reader thread
sub is_empty {
    return $tail == $head;
}

# Can only be called by the lone reader thread
sub dequeue {
    return () if is_empty();
    my $val = $buf[$tail];
    $tail = ( $tail + 1 ) % @buf;
    return $val;
}

# Can only be called by the lone writer thread
sub is_full {
    return ($head + 1) % @buf == $tail;
}

# Can only be called by the lone writer thread
sub enqueue {
    my ($val) = @_;
    return 0 if is_full();
    $buf[$head] = $val;
    $head = ( $head + 1 ) % @buf;
    return 1;
}

##</code><code>##

package Data::RingBuffer;

sub new {
    my ($class, $size) = @_;
    return bless({
        head => 0,
        tail => 0,
        buf  => [ (undef) x $size ],
    }, $class);
}

sub is_empty {
    my ($self) = @_;
    return $self->{tail} == $self->{head};
}

sub dequeue {
    my ($self) = @_;
    my $buf = $self->{buf};
    return () if $self->is_empty();
    my $val = $buf->[$self->{tail}];
    $self->{tail} = ( $self->{tail} + 1 ) % @$buf;
    return $val;
}

sub is_full {
    my ($self) = @_;
    my $buf = $self->{buf};
    return ($self->{head} + 1) % @$buf == $self->{tail};
}

sub enqueue {
    my ($self, $val) = @_;
    my $buf = $self->{buf};
    return 0 if $self->is_full();
    $buf->[$self->{head}] = $val;
    $self->{head} = ( $self->{head} + 1 ) % @$buf;
    return 1;
}