our $PID_IDLE;
our $WNOHANG;

sub _child_wait {
   while (0 < (my $pid = waitpid -1, $WNOHANG)) {
      $_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
                         (values %{ $PID_CB{0}    || {} });
   }

   undef $PID_IDLE;
}

sub _sigchld {
   # make sure we deliver these changes "synchronous" with the event loop.
   $CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
      undef $CHLD_DELAY_W;
      &_child_wait;
   });
}

sub child {
   my (undef, %arg) = @_;

   defined (my $pid = $arg{pid} + 0)
      or Carp::croak "required option 'pid' is missing";

   $PID_CB{$pid}{$arg{cb}} = $arg{cb};

   unless ($WNOHANG) {
      $WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
   }

   unless ($CHLD_W) {
      $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
      # child could be a zombie already, so make at least one round
      &_sigchld;
   }

   bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
}

sub AnyEvent::Base::Child::DESTROY {
   my ($pid, $cb) = @{$_[0]};

   delete $PID_CB{$pid}{$cb};
   delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };

   undef $CHLD_W unless keys %PID_CB;
}

package AnyEvent::CondVar;

our @ISA = AnyEvent::CondVar::Base::;

package AnyEvent::CondVar::Base;

use overload
   '&{}'    => sub { my $self = shift; sub { $self->send (@_) } },
   fallback => 1;

sub _send {
   # nop
}

sub send {
   my $cv = shift;
   $cv->{_ae_sent} = [@_];
   (delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
   $cv->_send;
}

sub croak {
   $_[0]{_ae_croak} = $_[1];
   $_[0]->send;
}

sub ready {
   $_[0]{_ae_sent}
}

sub _wait {
   AnyEvent->one_event while !$_[0]{_ae_sent};
}

sub recv {
   $_[0]->_wait;

   Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
   wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
}

sub cb {
   $_[0]{_ae_cb} = $_[1] if @_ > 1;
   $_[0]{_ae_cb}
}

sub begin {
   ++$_[0]{_ae_counter};
   $_[0]{_ae_end_cb} = $_[1] if @_ > 1;
}