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local/lib/perl5/IO/Async/Timer/Countdown.pm  view on Meta::CPAN

The object implements a countdown timer, which invokes its callback after the
given period from when it was started. After it has expired the Timer may be
started again, when it will wait the same period then invoke the callback
again. A timer that is currently running may be stopped or reset.

For a C<Timer> object that repeatedly runs a callback at regular intervals,
see instead L<IO::Async::Timer::Periodic>. For a C<Timer> that invokes its
callback at a fixed time in the future, see L<IO::Async::Timer::Absolute>.

=cut

=head1 EVENTS

The following events are invoked, either using subclass methods or CODE
references in parameters:

=head2 on_expire

Invoked when the timer expires.

=cut

=head1 PARAMETERS

The following named parameters may be passed to C<new> or C<configure>:

=head2 on_expire => CODE

CODE reference for the C<on_expire> event.

=head2 delay => NUM

The delay in seconds after starting the timer until it expires. Cannot be
changed if the timer is running. A timer with a zero delay expires
"immediately".

=head2 remove_on_expire => BOOL

Optional. If true, remove this timer object from its parent notifier or
containing loop when it expires. Defaults to false.

Once constructed, the timer object will need to be added to the C<Loop> before
it will work. It will also need to be started by the C<start> method.

=cut

sub configure
{
   my $self = shift;
   my %params = @_;

   foreach (qw( remove_on_expire )) {
      $self->{$_} = delete $params{$_} if exists $params{$_};
   }

   if( exists $params{on_expire} ) {
      my $on_expire = delete $params{on_expire};
      ref $on_expire or croak "Expected 'on_expire' as a reference";

      $self->{on_expire} = $on_expire;
      undef $self->{cb}; # Will be lazily constructed when needed
   }

   if( exists $params{delay} ) {
      $self->is_running and croak "Cannot configure 'delay' of a running timer\n";

      my $delay = delete $params{delay};
      $delay >= 0 or croak "Expected a 'delay' as a non-negative number";

      $self->{delay} = $delay;
   }

   unless( $self->can_event( 'on_expire' ) ) {
      croak 'Expected either a on_expire callback or an ->on_expire method';
   }

   $self->SUPER::configure( %params );
}

=head1 METHODS

=cut

=head2 is_expired

   $expired = $timer->is_expired

Returns true if the Timer has already expired.

=cut

sub is_expired
{
   my $self = shift;
   return $self->{expired};
}

sub _make_cb
{
   my $self = shift;

   return $self->_capture_weakself( sub {
      my $self = shift or return;

      undef $self->{id};
      $self->{expired} = 1;

      $self->remove_from_parent if $self->{remove_on_expire};

      $self->invoke_event( "on_expire" );
   } );
}

sub _make_enqueueargs
{
   my $self = shift;

   undef $self->{expired};
   return after => $self->{delay};
}

=head2 reset

   $timer->reset

If the timer is running, restart the countdown period from now. If the timer
is not running, this method has no effect.

=cut

sub reset
{
   my $self = shift;

   my $loop = $self->loop or croak "Cannot reset a Timer that is not in a Loop";

   return if !$self->is_running;

   $self->stop;
   $self->start;
}

=head1 EXAMPLES

=head2 Watchdog Timer

Because the C<reset> method restarts a running countdown timer back to its
full period, it can be used to implement a watchdog timer. This is a timer
which will not expire provided the method is called at least as often as it
is configured. If the method fails to be called, the timer will eventually
expire and run its callback.

For example, to expire an accepted connection after 30 seconds of inactivity:

 ...

 on_accept => sub {
    my ( $newclient ) = @_;

    my $watchdog = IO::Async::Timer::Countdown->new(
       delay => 30,

       on_expire => sub {
          my $self = shift;

          my $stream = $self->parent;
          $stream->close;
       },
    );

    my $stream = IO::Async::Stream->new(
       handle => $newclient,

       on_read => sub {
          my ( $self, $buffref, $eof ) = @_;
          $watchdog->reset;

          ...