Scheduling thingy for Raku
# 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;
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 Junctions of values.
There is a class method every that takes a schedule specification
and returns a Supply that will emit a value (a DateTime) on
the schedule specified. There is also a method at (also a class
method) that returns a Promise that will be kept at a specified point
in time (as opposed to Promise.in which will return a Promise that
will be kept after a specified number of seconds.)
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.
If you have a working Rakudo you can install directly with zef:
# From the source directory
zef install .
# Remote installation
zef install Chronic
Suggestions/patches are welcomed via github at https://github.com/jonathanstowe/Chronic
This is free software.
Please see the LICENCE file in the distribution.
© Jonathan Stowe 2015, 2016, 2017, 2019, 2020