package Thread::Queue;
use Thread qw(cond_wait cond_broadcast);

=head1 NAME

Thread::Queue - thread-safe queues

=head1 SYNOPSIS

    use Thread::Queue;
    my $q = new Thread::Queue;
    $q->enqueue("foo", "bar");
    my $foo = $q->dequeue;    # The "bar" is still in the queue.
    my $foo = $q->dequeue_nb; # returns "bar", or undef if the queue was
                              # empty
    my $left = $q->pending;   # returns the number of items still in the queue

=head1 DESCRIPTION

A queue, as implemented by C<Thread::Queue> is a thread-safe data structure
much like a list. Any number of threads can safely add elements to the end
of the list, or remove elements from the head of the list. (Queues don't
permit adding or removing elements from the middle of the list)

=head1 FUNCTIONS AND METHODS

=over 8

=item new

The C<new> function creates a new empty queue.

=item enqueue LIST

The C<enqueue> method adds a list of scalars on to the end of the queue.
The queue will grow as needed to accomodate the list.

=item dequeue

The C<dequeue> method removes a scalar from the head of the queue and
returns it. If the queue is currently empty, C<dequeue> will block the
thread until another thread C<enqueue>s a scalar.

=item dequeue_nb

The C<dequeue_nb> method, like the C<dequeue> method, removes a scalar from
the head of the queue and returns it. Unlike C<dequeue>, though,
C<dequeue_nb> won't block if the queue is empty, instead returning
C<undef>.

=item pending

The C<pending> method returns the number of items still in the queue.  (If
there can be multiple readers on the queue it's best to lock the queue
before checking to make sure that it stays in a consistent state)

=back

=head1 SEE ALSO

L<Thread>
  
=cut

sub new {
    my $class = shift;
    return bless [@_], $class;
}

sub dequeue {
    use attrs qw(locked method);
    my $q = shift;
    cond_wait $q until @$q;
    return shift @$q;
}

sub dequeue_nb {
  use attrs qw(locked method);
  my $q = shift;
  if (@$q) {
    return shift @$q;
  } else {
    return undef;
  }
}

sub enqueue {
    use attrs qw(locked method);
    my $q = shift;
    push(@$q, @_) and cond_broadcast $q;
}

sub pending {
  use attrs qw(locked method);
  my $q = shift;
  return scalar(@$q);
}

1;