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
$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 v5.18.2 2014-05-14 IO::Async::Timer::Countdown(3)
