NAME
Async::Event::Interval - Scheduled and one-off asynchronous events
SYNOPSIS
A simple event that updates JSON data from a website using a shared scalar variable, while allowing the main application to continue running in the foreground. Multiple events can be simultaneously used if desired.
See "EXAMPLES" for other various functionality of this module.
use warnings;
use strict;
use Async::Event::Interval;
my $event = Async::Event::Interval->new(2, \&callback);
my $json = $event->shared_scalar;
$event->start;
while (1) {
print "$$json\n";
#... do other things
$event->restart if $event->error;
}
sub callback {
$$json = ...; # Fetch JSON from website
}DESCRIPTION
Very basic implementation of asynchronous events triggered by a timed interval. If a time of zero is specified, we'll run the event only once.
METHODS - EVENT OPERATION
new($delay, $callback, @params)
Returns a new Async::Event::Interval object. Does not create the event. Use start for that.
Parameters:
$delayMandatory: The interval on which to trigger your event callback, in seconds. Represent partial seconds as a floating point number. If zero is specified, we'll simply run the event once and stop.
$callbackMandatory: A reference to a subroutine that will be called every time the interval expires.
@paramsOptional, List: A list of parameters to pass to the callback. Note that these are not shared parameters and are a copy only, so changes to them in the main code will not be seen in the event, and vice-versa. See "shared_scalar" if you'd like to use variables that can be shared between the main application and the events.
start
Starts the event timer. Each time the interval is reached, the event callback is executed.
stop
Stops the event from being executed.
restart
Alias for start(). Re-starts a stop()ped event.
status
Returns the event's process ID (true) if it is running, 0 (false) if it isn't.
waiting
Returns true if the event is dormant and is ready for a start() or restart() command. Returns false if the event is already running.
error
Returns true if an event crashed unexpectedly in the background, and is ready for a start() or restart() command. Returns false if the event is not in an error state.
interval($seconds)
Gets/sets the delay time (in seconds) between each execution of the event's callback code. You can use this method to change the delay between calls during the event's lifecycle.
Parameters:
$secondsOptional, Integer: The number of seconds (can be floating point) to delay between executions.
Return: Integer, the number of seconds between execution runs. If we're in a run-once scenario, the return will be zero 0.
shared_scalar
Returns a reference to a scalar variable that can be shared between the main process and the events. This reference can be used within multiple events, and multiple shared scalars can be created by each event.
To read from or assign to the returned scalar, you must dereference it. Eg. $$shared_scalar = 1;.
METHODS - EVENT INFORMATION
errors
Returns the number of times a started or restarted event has crashed unexpectedly.
error_message
Returns the error message (if any) that caused the most recent event crash.
events
This is a class method that returns a hash reference that contains the data of all existing events.
$VAR1 = {
'0' => {
'shared_scalars' => {
'0x555A4654' => \'hello, world',
'0x4C534758' => \98
},
'pid' => 11859,
'runs' => 16,
'errors' => 0,
'interval' => 5,
},
'1' => {
'pid' => 11860,
'runs' => 447,
'errors' => 2,
'interval' => 0.6,
'error_message' => 'File notes.txt not found at scripts/write_file.pl line 227',
}
};id
Returns the integer ID of the event.
info
Returns a hash reference containing various data about the event. Eg.
$VAR1 = {
'shared_scalars' => {
'0x55435449' => \'hello, world!,
'0x43534644' => \98
},
'pid' => 6841,
'runs' => 4077,
'errors' => 0,
'interval' => 1.4,
};pid
Returns the Process ID that the event is running under
runs
Returns the number of executions of the event's callback routine.
SCENARIOS/EXAMPLES
Run once
Send in an interval of zero (0) to have your event run a single time. Call start() repeatedly for numerous individual/one-off runs.
use Async::Event::Interval
my $event = Async::Event::Interval->new(0, sub {print "hey\n";});
$event->start;
# Do stuff, then run the event again if it's done its previous task
$event->start if $event->waiting;Change delay interval during operation
Change the delay interval from 5 to 600 seconds after the event has fired 100 times
use Async::Event::Interval
my $event = Async::Event::Interval->new(5, sub {print "hey\n";});
$event->start;
while (1) {
if ($event->runs > 99 && $event->interval != 600) {
$event->interval(600);
}
#... do stuff
}Event error management
If an event crashes, print out error information and restart the event. If an event crashes five or more times, print the most recent error message and halt the program so you can figure out what's wrong with your callback code.
use Async::Event::Interval
my $event = Async::Event::Interval->new(5, sub {print "hey\n";});
$event->start;
while (1) {
#... do stuff
if ($event->errors >= 5) {
print $event->error_message;
exit;
}
if ($event->error) {
printf(
"Runs: %d, Runs errored: %d, Last error message: %s\n",
$event->runs,
$event->errors,
$event->error_message;
);
$event->restart;
}
}Event suicidal timeout
You can have your callback commit suicide if it takes too long to run. We use Perl's $SIG{ALRM} and alarm() to do this. In your main application, you can check the status of the event and restart it or whatever else you need.
my $event_timeout = 30;
my $event = Async::Event::Interval->new(
30,
sub {
local $SIG{ALRM} = sub { print "Committing suicide!\n"; kill 9, $$; };
alarm $event_timeout;
# Do stuff here. If it takes 30 seconds, we kill ourselves
alarm 0;
},
);Event parameters
You can send in a list of parameters to the event callback. Changing these within the main program will have no effect on the values sent into the event itself. These parameter variables are copies and are not shared. For shared variables, see "shared_scalar".
use Async::Event::Interval
my @params = qw(1 2 3);
my $event = Async::Event::Interval->new(
1,
\&callback,
@params
);
sub callback {
my ($one, $two, $three) = @_;
print "$one, $two, $three\n";
}Event crash: Restart event
use warnings;
use strict;
use Async::Event::Interval;
my $event = Async::Event::Interval->new(0.5, sub { kill 9, $$; });
$event->start;
sleep 1; # Do stuff
if ($event->error){
print "Event crashed, restarting\n";
$event->restart;
}Event crash: End program
use warnings;
use strict;
use Async::Event::Interval;
my $event = Async::Event::Interval->new(0.5, sub { kill 9, $$; });
$event->start;
sleep 1; # Do stuff
die "Event crashed, can't continue" if $event->error;Shared data across events
This software uses IPC::Shareable internally, so it's automatically installed for you already. You can use shared data for use across many processes and events, and if you use the same IPC key, even across multiple scripts.
Here's an example that uses a hash that's stored in shared memory, where the parent process (the script) and two other processes (the two events) all share and update the same hash.
use Async::Event::Interval;
use IPC::Shareable;
tie my %shared_data, 'IPC::Shareable', {
key => '123456789',
create => 1,
destroy => 1
};
$shared_data{$$}{called_count}++;
my $event_one = Async::Event::Interval->new(0.2, \&update);
my $event_two = Async::Event::Interval->new(1, \&update);
$event_one->start;
$event_two->start;
sleep 10;
$event_one->stop;
$event_two->stop;
for my $pid (keys %shared_data) {
printf(
"Process ID %d executed %d times\n",
$pid,
$shared_data{$pid}{called_count}
);
}
for my $event ($event_one, $event_two) {
printf(
"Event ID %d with PID %d ran %d times, with %d errors and an interval" .
" of %.2f seconds\n",
$event->id,
$event->pid,
$event->runs,
$event->errors,
$event->interval
);
}
sub update {
# Because each event runs in its own process, $$ will be set to the
# process ID of the calling event, even though they both call this
# same function
$shared_data{$$}{called_count}++;
}AUTHOR
Steve Bertrand, <steveb at cpan.org>
LICENSE AND COPYRIGHT
Copyright 2022 Steve Bertrand.
This program is free software; you can redistribute it and/or modify it under the terms of either: the GNU General Public License as published by the Free Software Foundation; or the Artistic License.
See http://dev.perl.org/licenses/ for more information.