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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)
12-29-2011
Timer application in linux
