Croney part of Monolyth

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Latest release

0.2.0

Date: github

README.md

PHP-based CRON scheduler

Don't you hate having to juggle a gazillion cronjobs for each application? We sure do! We also hate having to adhere to a library-specific code format to circumvent this problem (e.g. Symfony, Laravel... you know who you are).

You know what we'd like to do? We just want to register a bunch of callables and have a central script figure it out. Hello Croney!

Installation

Composer (recommended)

composer require monomelodies/croney

Manual

  1. Download or clone the repository;
  2. Add the namespace Croney for the path path/to/croney/src to your PSR-4 autoloader.

Setting up the executable

Croney needs to run periodically, so create a simple executable that we will add as a cronjob:

#!/usr/bin/php
<?php

// Let's assume this is in bin/cron.
// It's empty for now.
$ chmod a+x bin/cron
$ crontab -e

How often you let Croney run is up to you. The default assumption is every minute since it is the smallest interval possible on Unix-like systems. We'll see how to optimise this to e.g. every five minutes later on. For now, register the cronjob with * * * * *, i.e. every minute.

The Scheduler class

At Croney's core is an instance of the Scheduler class. This is what is used to run tasks and it takes care (as the name implies) of scheduling them.

In your bin/cron file:

#!/usr/bin/php
<?php
use Croney\Scheduler;
$schedule = new Scheduler;

Adding tasks

The Scheduler extends ArrayObject, so to add a task simply set it. The value should be a callable:

#!/usr/bin/php
<?php
// ...
$schedule['some-task'] = function () {
// ...perform the task...
};

This task gets run every minute (or whatever interval you set your cronjob to). A task can be any callable, including class methods (even static ones), but the $this property is bound to the scheduler itself (for utility purposes as we'll see shortly), so it's usually best to use an actual lambda.

If your task is stored e.g. inside a class method, just call it from the lambda instead of passing it directly. The usage of $this would be ambiguous otherwise, which might lead to complications down the road.

When you've setup all your tasks, call process on the Scheduler to actually run them:

<?php

// ...
$schedule->process();

Running tasks at specific intervals or times

To have more control over when exactly a task is run, you call the at method on the bound $this object:

<?php
$scheduler['some-task'] = function () {
$this->at('Y-m-d H:m');
};

The parameter to at is a PHP date string which, when parsed using the run's start time, should preg_match it. The above example runs the task every minute (which is the default assuming your cronjob runs every minute). To run a task every five minutes instead, you'd write something like this:

<?php

$scheduler['some-task'] = function () {
    // Note the double escape for \d in the regex.
    $this->at('Y-m-d H:[0-5][05]');
};

Note that the date function works with placeholders, so if you need to regex on e.g. a decimal (\d) you would need to double-escape it. See the PHP manual page for date for a list of all valid placeholders.

preg_match is called without checking string position, i.e. if you would pass only 'H' as the date to match it would run on the hour, but also every minute (since 00-24 are all valid minutes and it would match 'i' as well) and also every day, month and (for all practical purposes since I'm not expecting this library to still be alive by the year 2399 ;)) all years. So be as specific as you need!

Note that the seconds part is irrelevant due to the granularity of cron and should be omitted or your task will likely never run (since the date it is compared to also doesn't include seconds). Also note that at breaks off the task if it's not due yet, so it should in almost all cases be the first statement in a task.

Any operations prior to at will always be executed. In rare cases this might be intentional, but normally it really won't be. Trust us.

Running the script less often

We mentioned earlier how you can also choose to run the cronjob less often than every minute, say every five minutes. If you only have tasks that run every five minutes (or multiples of that), that's fine and no further configuration is required. But what if you want to run your cronjob every five minutes, but still be able to schedule tasks based on minutes?

An example of this would be a cronjob that runs every five minutes, defining five tasks, each of which is run one minute after the previous task.

On the Scheduler object, call the setDuration method. This takes a single integer parameter: the number of minutes the script is meant to run.

<?php

$scheduler->setDuration(5); // Runs for five minutes

(As you'll have guessed, the default value here is 1.)

When you call process, the tasks will actually be run 5 times (once every minute) and executed when the time is there. E.g.:

<?php

// ...

// First task, runs only on the first loop
$scheduler['first-task'] = function () {
    $this->at('H:00');
};
// Second task, runs only on the second loop
$scheduler['second-task'] = function () {
    $this->at('H:01');
};
// etc.

Croney calls PHP's sleep function in between loops.

Croney tries to calculate the actual number of seconds to sleep, so if the tasks from the first loop took, say, 3 seconds in total it sleeps for 57 seconds before the next loop. Note however that this is not exact and does not guarantee that your task will run exactly on the dot. If your task involves time-based operations make sure to "round down" the time to the expected value.

In theory, you could let your script run at midnight on January the first and calculate everything from there. In the real world, this is obviously not practical since any error whatsoever means you have to wait a whole year to see if your fix solved the problem!

Typical values are every 5 or 10 minutes, maybe 30 or 60 on very busy servers.

Long running tasks

Typically a task runs in (micro)seconds, but sometimes one of your tasks will be "long running". If this is intentional (e.g. a periodic cleanup operation of user-uploaded files) you would obviously runAt it at a safe interval, and you should take care limit stuff in your task itself (e.g. "max 100 files per run"). Still, every so often you'll need to write a task that should run often, but might in extreme cases take longer than expected to do so.

A fictional example: a task that reads a mailbox (e.g. to push them into a ticketing system). If that mailbox explodes for whatever reason (let's be positive and imagine your application became really popular overnight ;)) this would pose a problem: the previous run might still be reading mails as the next run starts, causing mails to be handled twice. Obviously not desirable.

Croney "locks" each task prior to running, and does not attempt to re-run as long as it is locked. If a run fails due to locking, a warning is logged and the task is retried periodically for as long as the cronjob runs. If the task couldn't be run before the cronjob ends, an error is logged.

The locking is done based on an MD5 hash of the reflected callable, so any changes between runs will invalidate any existing locks.

Error handling

You can pass an instance of Monolog\Logger as an argument to the Scheduler constructor. This will then be used to log any messages triggered by tasks, in the way that you specified.

If no logger was defined, all messages go to STDERR.

The logger is available inside task callables via $this->logger, so individual tasks can also log to whatever you configured it with.

Development

During development, you probably want to run tasks when testing (not just at a specific time), and also probably just a specific task. Croney as of version 0.3 comes with two command line flags for this:

--all Use this flag to run all tasks, regardless of specified scheduling. Do not do this in production!

--job=jobname Run only the specified jobname. If the job is scheduled for particular times, you'll likely want to use this in conjunction with the --all (or -a) flag.

You might also want to receive some more verbose feedback on what's going on. To accomplish this, call your executable with the --verbose (or -v) flag.