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>