# called when event loop idle (if applicable)
       my $w = AnyEvent->idle (cb => sub { ... });

       my $w = AnyEvent->condvar; # stores whether a condition was flagged
       $w->send; # wake up current and all future recv's
       $w->recv; # enters "main loop" till $condvar gets ->send
       # use a condvar in callback mode:
       $w->cb (sub { $_[0]->recv });