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IO::Async::Timer::CounUsernContributed Perl DocuIO::Async::Timer::Countdown(3)

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\n";
	      $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
   is_expired
	  $expired = $timer->is_expired

       Returns true if the Timer has already expired.

   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.

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 v5.32.1			  2021-02-28	IO::Async::Timer::Countdown(3)

NAME | SYNOPSIS | DESCRIPTION | EVENTS | PARAMETERS | METHODS | EXAMPLES | AUTHOR

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