Chronic

Scheduling thingy for Perl6

Synopsis

# Static configuration;

use Chronic;

react {
    # Every minute
    whenever Chronic.every() -> $v {
        say "One: $v";
    }
    # Every five minutes
    whenever Chronic.every(minute => '*/5') -> $v {
        say "Five: $v";
    }
    # At 21:31 every day
    whenever Chronic.every(minute => 31, hour => 21) -> $v {
        say "21:31 $v";
    }

}

# Dynamic configuration

use Chronic;

my @events = (
    {
        schedule => {},
        code     => sub ($v) { say "One: $v" },
    },
    {
        schedule => { minute => '*/2' },
        code     => sub ($v) { say "Two: $v" },
    },
    {
        schedule => { minute => '*/5' },
        code     => sub ($v) { say "Five: $v" },
    },
    {
        schedule => { minute => 31, hour => 21 },
        code     => sub ($v) {  say "21:31 $v"; },
    },
);

for @events -> $event {
    Chronic.every(|$event<schedule>).tap($event<code>);
}

# This has the effect of waiting forever
Chronic.supply.wait;

Description

This module provides a low-level scheduling mechanism, that be used to create cron-like schedules, the specifications can be provided as cron expression strings, lists of integer values or L of values.

There is a single class method every that takes a schedule specification and returns a Supply that will emit a value (a DateTime) on the schedule specified.

This can be used to build custom scheduling services like cron with additional code to read the specification from a file and arrange the execution of the required thing or it could be used in a larger program that may require to execute some code asynchronously periodically.

There is a single base Supply that emits an event at a 1 second frequency in order to preserve the accuracy of the timings (in testing it may drift by up to 59 seconds on a long run due to system latency if it didn't match the seconds too,) so this may be a problem on a heavily loaded single core computer. The sub-minute granularity isn't provided for in the interface as it is easily achieved anyway with a basic supply, it isn't supported by a standard cron and I think most code that would want to be executed with that frequency would be more highly optimised then this may allow.

Installation

Assuming you have a working perl6 installation you should be able to install this with ufo :

ufo
make test
make install

ufo can be installed with panda for rakudo:

panda install ufo

Or you can install directly with "panda":

# From the source directory

panda install .

# Remote installation

panda install Chronic

Other install mechanisms may be become available in the future.

Support

This should be considered experimental software until such time that Perl 6 reaches an official release. However suggestions/patches are welcomed via github at

https://github.com/jonathanstowe/Chronic

Licence

Please see the LICENCE file in the distribution

(C) Jonathan Stowe 2015