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sub _init
{
   my $self = shift;
   my ( $params ) = @_;
   $self->SUPER::_init( @_ );

   $params->{code} = sub {
      my ( $type, $timeout, @data ) = @_;

      if( my $code = $METHODS{$type} ) {
         local $SIG{ALRM} = sub { die "Timed out\n" };

         alarm( $timeout );
         my @ret = eval { $code->( @data ) };
         alarm( 0 );

         die $@ if $@;
         return @ret;
      }
      else {
         die "Unrecognised resolver request '$type'";
      }
   };

   $params->{idle_timeout} = 30;
   $params->{min_workers}  = 0;

   $started = 1;
}

=head1 METHODS

The following methods documented with a trailing call to C<< ->get >> return
L<Future> instances.

=cut

=head2 resolve

   @result = $loop->resolve( %params )->get

Performs a single name resolution operation, as given by the keys in the hash.

The C<%params> hash keys the following keys:

=over 8

=item type => STRING

Name of the resolution operation to perform. See BUILT-IN RESOLVERS for the
list of available operations.

=item data => ARRAY

Arguments to pass to the resolver function. Exact meaning depends on the
specific function chosen by the C<type>; see BUILT-IN RESOLVERS.

=item timeout => NUMBER

Optional. Timeout in seconds, after which the resolver operation will abort
with a timeout exception. If not supplied, a default of 10 seconds will apply.

=back

On failure, the fail category name is C<resolve>; the details give the
individual resolver function name (e.g. C<getaddrinfo>), followed by other
error details specific to the resolver in question.

 ->fail( $message, resolve => $type => @details )

=head2 resolve (void)

   $resolver->resolve( %params )

When not returning a future, additional parameters can be given containing the
continuations to invoke on success or failure:

=over 8

=item on_resolved => CODE

A continuation that is invoked when the resolver function returns a successful
result. It will be passed the array returned by the resolver function.

 $on_resolved->( @result )

=item on_error => CODE

A continuation that is invoked when the resolver function fails. It will be
passed the exception thrown by the function.

=back

=cut

sub resolve
{
   my $self = shift;
   my %args = @_;

   my $type = $args{type};
   defined $type or croak "Expected 'type'";

   if( $type eq "getaddrinfo_hash" ) {
      $type = "getaddrinfo";
   }

   exists $METHODS{$type} or croak "Expected 'type' to be an existing resolver method, got '$type'";

   my $on_resolved;
   if( $on_resolved = $args{on_resolved} ) {
      ref $on_resolved or croak "Expected 'on_resolved' to be a reference";
   }
   elsif( !defined wantarray ) {
      croak "Expected 'on_resolved' or to return a Future";
   }

   my $on_error;
   if( $on_error = $args{on_error} ) {
      ref $on_error or croak "Expected 'on_error' to be a reference";