my %pending;

sub set_oneshot_timer {
  my ($event, $hence) = @_;
  my $session_id = $poe_kernel->get_active_session()->ID();
  return if exists $pending{$session_id}{$event};
  $poe_kernel->delay( $event, $hence );
  $pending{$session_id}{$event} = 1;
}

sub caught_oneshot_timer {
  my $event = shift;
  my $session_id = $poe_kernel->get_active_session()->ID();
  delete $pending{$session_id}{$event};
  delete $pending{$session_id} unless keys %{$pending{$session_id}};
}

##</code><code>##

sub some_event_handler {
  # set a timer for 10s from now, unless it's already set
  set_oneshot_timer( event_to_send => 10 );
}

sub handle_timer_event {
  # caught the timer; clear the flag
  caught_oneshot_timer($_[STATE]);
}