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=head2 without_cancel

   $future = $f1->without_cancel

I<Since version 0.30.>

Returns a new sequencing C<Future> that will complete with the success or
failure of the original future, but if cancelled, will not cancel the
original. This may be useful if the original future represents an operation
that is being shared among multiple sequences; cancelling one should not
prevent the others from running too.

=cut

sub without_cancel
{
   my $self = shift;
   my $new = $self->new;

   $self->on_ready( sub {
      my $self = shift;
      if( $self->failure ) {
         $new->fail( $self->failure );
      }
      else {
         $new->done( $self->get );
      }
   });

   return $new;
}

=head1 CONVERGENT FUTURES

The following constructors all take a list of component futures, and return a
new future whose readiness somehow depends on the readiness of those
components. The first derived class component future will be used as the
prototype for constructing the return value, so it respects subclassing
correctly, or failing that a plain C<Future>.

=cut

sub _new_convergent
{
   shift; # ignore this class
   my ( $subs ) = @_;

   foreach my $sub ( @$subs ) {
      blessed $sub and $sub->isa( "Future" ) or Carp::croak "Expected a Future, got $_";
   }

   # Find the best prototype. Ideally anything derived if we can find one.
   my $self;
   ref($_) eq "Future" or $self = $_->new, last for @$subs;

   # No derived ones; just have to be a basic class then
   $self ||= Future->new;

   $self->{subs} = $subs;

   # This might be called by a DESTROY during global destruction so it should
   # be as defensive as possible (see RT88967)
   $self->on_cancel( sub {
      foreach my $sub ( @$subs ) {
         $sub->cancel if $sub and !$sub->{ready};
      }
   } );

   return $self;
}

=head2 wait_all

   $future = Future->wait_all( @subfutures )

Returns a new C<Future> instance that will indicate it is ready once all of
the sub future objects given to it indicate that they are ready, either by
success, failure or cancellation. Its result will be a list of its component
futures.

When given an empty list this constructor returns a new immediately-done
future.

This constructor would primarily be used by users of asynchronous interfaces.

=cut

sub wait_all
{
   my $class = shift;
   my @subs = @_;

   unless( @subs ) {
      my $self = $class->done;
      $self->{subs} = [];
      return $self;
   }

   my $self = Future->_new_convergent( \@subs );

   my $pending = 0;
   $_->{ready} or $pending++ for @subs;

   # Look for immediate ready
   if( !$pending ) {
      $self->{result} = [ @subs ];
      $self->_mark_ready( "wait_all" );
      return $self;
   }

   weaken( my $weakself = $self );
   my $sub_on_ready = sub {
      return unless $weakself;

      $pending--;
      $pending and return;

      $weakself->{result} = [ @subs ];
      $weakself->_mark_ready( "wait_all" );
   };