IO::Async::Timer::Countdown(3pm)			User Contributed Perl Documentation			  IO::Async::Timer::Countdown(3pm)

NAME

       "IO::Async::Timer::Countdown" - event callback after a fixed delay

SYNOPSIS

	use IO::Async::Timer::Countdown;

	use IO::Async::Loop;
	my $loop = IO::Async::Loop->new;

	my $timer = IO::Async::Timer::Countdown->new(
	   delay => 10,

	   on_expire => sub {
	      print "Sorry, your time's up
";
	      $loop->stop;
	   },
	);

	$timer->start;

	$loop->add( $timer );

	$loop->run;

DESCRIPTION

       This subclass of IO::Async::Timer implements one-shot fixed delays.  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 "Timer" object that repeatedly runs a callback at regular intervals, see instead IO::Async::Timer::Periodic. For a "Timer" that
       invokes its callback at a fixed time in the future, see IO::Async::Timer::Absolute.

EVENTS

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

   on_expire
       Invoked when the timer expires.

PARAMETERS

       The following named parameters may be passed to "new" or "configure":

       on_expire => CODE
	       CODE reference for the "on_expire" event.

       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".

       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 "Loop" before it will work. It will also need to be started by the "start"
       method.

METHODS

   $expired = $timer->is_expired
       Returns true if the Timer has already expired.

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

EXAMPLES

   Watchdog Timer
       Because the "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;

		 ...
	      },

	      on_closed => sub {
		 $watchdog->stop;
	      },
	   ) );

	   $stream->add_child( $watchdog );
	   $watchdog->start;

	   $loop->add( $watchdog );
	}

       Rather than setting up a lexical variable to store the Stream so that the Timer's "on_expire" closure can call "close" on it, the
       parent/child relationship between the two Notifier objects is used. At the time the Timer "on_expire" closure is invoked, it will have been
       added as a child notifier of the Stream; this means the Timer's "parent" method will return the Stream Notifier. This enables it to call
       "close" without needing to capture a lexical variable, which would create a cyclic reference.

   Fixed-Delay Repeating Timer
       The "on_expire" event fires a fixed delay after the "start" method has begun the countdown. The "start" method can be invoked again at some
       point during the "on_expire" handling code, to create a timer that invokes its code regularly a fixed delay after the previous invocation
       has finished. This creates an arrangement similar to an IO::Async::Timer::Periodic, except that it will wait until the previous invocation
       has indicated it is finished, before starting the countdown for the next call.

	my $timer = IO::Async::Timer::Countdown->new(
	   delay => 60,

	   on_expire => sub {
	      my $self = shift;

	      start_some_operation(
		 on_complete => sub { $self->start },
	      );
	   },
	);

	$timer->start;
	$loop->add( $timer );

       This example invokes the "start_some_operation" function 60 seconds after the previous iteration has indicated it has finished.

AUTHOR

       Paul Evans <leonerd@leonerd.org.uk>

perl v5.14.2							    2012-10-24					  IO::Async::Timer::Countdown(3pm)