Clockwork - a clock process to replace cron [![Build Status](https://secure.travis-ci.org/tomykaira/clockwork.png?branch=master)](http://travis-ci.org/tomykaira/clockwork) [![Dependency Status](https://gemnasium.com/tomykaira/clockwork.png)](https://gemnasium.com/tomykaira/clockwork)
===========================================

Cron is non-ideal for running scheduled application tasks, especially in an app
deployed to multiple machines.  [More details.](http://adam.heroku.com/past/2010/4/13/rethinking_cron/)

Clockwork is a cron replacement.  It runs as a lightweight, long-running Ruby
process which sits alongside your web processes (Mongrel/Thin) and your worker
processes (DJ/Resque/Minion/Stalker) to schedule recurring work at particular
times or dates.  For example, refreshing feeds on an hourly basis, or send
reminder emails on a nightly basis, or generating invoices once a month on the
1st.

Quickstart
----------

Create clock.rb:

```ruby
require 'clockwork'
module Clockwork
  handler do |job|
    puts "Running #{job}"
  end

  # handler receives the time when job is prepared to run in the 2nd argument
  # handler do |job, time|
  #   puts "Running #{job}, at #{time}"
  # end

  every(10.seconds, 'frequent.job')
  every(3.minutes, 'less.frequent.job')
  every(1.hour, 'hourly.job')

  every(1.day, 'midnight.job', :at => '00:00')
end
```

Run it with the clockwork binary:

```
$ clockwork clock.rb
Starting clock for 4 events: [ frequent.job less.frequent.job hourly.job midnight.job ]
Triggering frequent.job
```

If you need to load your entire environment for your jobs, simply add:

```ruby
require './config/boot'
require './config/environment'
```

under the `require 'clockwork'` declaration.

Quickstart for Heroku
---------------------

Clockwork fits well with heroku's cedar stack.

Consider to use [clockwork-init.sh](https://gist.github.com/1312172) to create
a new project for heroku.

Use with queueing
-----------------

The clock process only makes sense as a place to schedule work to be done, not
to do the work.  It avoids locking by running as a single process, but this
makes it impossible to parallelize.  For doing the work, you should be using a
job queueing system, such as
[Delayed Job](http://www.therailsway.com/2009/7/22/do-it-later-with-delayed-job),
[Beanstalk/Stalker](http://adam.heroku.com/past/2010/4/24/beanstalk_a_simple_and_fast_queueing_backend/),
[RabbitMQ/Minion](http://adamblog.heroku.com/past/2009/9/28/background_jobs_with_rabbitmq_and_minion/),
[Resque](http://github.com/blog/542-introducing-resque), or
[Sidekiq](https://github.com/mperham/sidekiq).  This design allows a
simple clock process with no locks, but also offers near infinite horizontal
scalability.

For example, if you're using Beanstalk/Staker:

```ruby
require 'stalker'

module Clockwork
  handler { |job| Stalker.enqueue(job) }

  every(1.hour, 'feeds.refresh')
  every(1.day, 'reminders.send', :at => '01:30')
end
```

Using a queueing system which doesn't require that your full application be
loaded is preferable, because the clock process can keep a tiny memory
footprint.  If you're using DJ or Resque, however, you can go ahead and load
your full application enviroment, and use per-event blocks to call DJ or Resque
enqueue methods.  For example, with DJ/Rails:

```ruby
require 'config/boot'
require 'config/environment'

every(1.hour, 'feeds.refresh') { Feed.send_later(:refresh) }
every(1.day, 'reminders.send', :at => '01:30') { Reminder.send_later(:send_reminders) }
```

Parameters
----------

### :at

`:at` parameter the hour and minute specifies when the event occur.

The simplest example:

```ruby
every(1.day, 'reminders.send', :at => '01:30')
```

You can omit 0 of the hour:

```ruby
every(1.day, 'reminders.send', :at => '1:30')
```

The wildcard for hour and minute is supported:

```ruby
every(1.hour, 'reminders.send', :at => '**:30')
every(10.seconds, 'frequent.job', :at => '9:**')
```

You can set more than one timing:

```ruby
every(1.hour, 'reminders.send', :at => ['12:00', '18:00'])
# send reminders at noon and evening
```

You can specify the day of week to run:

```ruby
every(1.week, 'myjob', :at => 'Monday 16:20')
```

You can also specify a timezone (default is the local timezone):

```ruby
every(1.day, 'reminders.send', :at => '00:00', :tz => 'UTC')
# Runs the job each day at midnight, UTC.
# The value for :tz can be anything supported by [TZInfo](http://tzinfo.rubyforge.org/)
```

### :if

`:if` parameter is invoked every time the task is ready to run, and run if the
return value is true.

Run on every first day of month.

```ruby
Clockwork.every(1.day, 'myjob', :if => lambda { |t| t.day == 1 })
```

The argument is an instance of `ActiveSupport::TimeWithZone` if the `:tz` option is set. Otherwise, it's an instance of `Time`.

This argument cannot be omitted.  Please use _ as placeholder if not needed.

```ruby
Clockwork.every(1.second, 'myjob', :if => lambda { |_| true })
```

### :thread

A handler with `:thread` parameter runs in a different thread.

If a job is long running or IO-intensive, this option will be useful to keep the clock precise.

Configuration
-----------------------

Clockwork exposes a couple of configuration options you may change:

### :logger

By default Clockwork logs to STDOUT. In case you prefer to make it to use our
own logger implementation you have to specify the `logger` configuration option. See example below.

### :sleep_timeout

Clockwork wakes up once a second (by default) and performs its duties. If that
is the rare case you need to tweak the number of seconds it sleeps then you have
the `sleep_timeout` configuration option to set like shown below.

### :tz

This is the default timezone to use for all events.  When not specified this defaults to the local
timezone.  Specifying :tz in the the parameters for an event overrides anything set here.

### :max_threads

Clockwork runs handlers in threads. If it exceeds `max_threads`, it will warn you about missing
jobs.

### Configuration example

```ruby
module Clockwork
  configure do |config|
    config[:sleep_timeout] = 5
    config[:logger] = Logger.new(log_file_path)
    config[:tz] = 'EST'
    config[:max_threads] = 15
  end
end
```

### error_handler

You can add error_handler to define your own logging or error rescue.

```ruby
module Clockwork
  error_handler do |error|
    Airbrake.notify_or_ignore(error)
  end
end
```

Current specifications are as follows.

- defining error_handler does not disable original logging
- errors from error_handler itself do not rescued, and stop clockwork

Any suggestion about these specifications is welcome.

Old style
---------

`include Clockwork` is old style.
That is still supported, but not recommended, because it taint global namespace.



Anatomy of a clock file
-----------------------

clock.rb is standard Ruby.  Since we include the Clockwork module (the
clockwork binary does this automatically, or you can do it explicitly), this
exposes a small DSL ("handler" and "every") to define the handler for events,
and then the events themselves.

The handler typically looks like this:

```ruby
handler { |job| enqueue_your_job(job) }
```

This block will be invoked every time an event is triggered, with the job name
passed in.  In most cases, you should be able to pass the job name directly
through to your queueing system.

The second part of the file are the events, which roughly resembles a crontab:

```ruby
every(5.minutes, 'thing.do')
every(1.hour, 'otherthing.do')
```

In the first line of this example, an event will be triggered once every five
minutes, passing the job name 'thing.do' into the handler.  The handler shown
above would thus call enqueue_your_job('thing.do').

You can also pass a custom block to the handler, for job queueing systems that
rely on classes rather than job names (i.e. DJ and Resque).  In this case, you
need not define a general event handler, and instead provide one with each
event:

```ruby
every(5.minutes, 'thing.do') { Thing.send_later(:do) }
```

If you provide a custom handler for the block, the job name is used only for
logging.

You can also use blocks to do more complex checks:

```ruby
every(1.day, 'check.leap.year') do
  Stalker.enqueue('leap.year.party') if Time.now.year % 4 == 0
end
```

In production
-------------

Only one clock process should ever be running across your whole application
deployment.  For example, if your app is running on three VPS machines (two app
servers and one database), your app machines might have the following process
topography:

* App server 1: 3 web (thin start), 3 workers (rake jobs:work), 1 clock (clockwork clock.rb)
* App server 2: 3 web (thin start), 3 workers (rake jobs:work)

You should use Monit, God, Upstart, or Inittab to keep your clock process
running the same way you keep your web and workers running.

Daemonization
-------------

Thanks to @fddayan, `clockworkd` executes clockwork script in as a daemon.

You need `daemons` gem to use `clockworkd`.  It is not automatically installed, please install by yourself.

Then,

```
clockworkd -c YOUR_CLOCK.rb start
```

For more details, see help shown by `clockworkd`.

Issues and Pull requests
------------------------

Let us know bugs you found as an issue from [Issues · tomykaira/clockwork](https://github.com/tomykaira/clockwork/issues).

For a bug fix or a feature request, please send a pull-request.
Do not forget to add tests to show how your feature works, or what bug is fixed.
All existing tests and new tests must pass (TravisCI is watching).

We want to provide simple and customizable core, so superficial changes will not be merged (e.g. supporting new event registration style).
In most case, directly operating `Manager` realizes an idea, without touching the core.
If you get up with a new usage, please create a gist page or an article on your website, then add to the following "Use cases" section.
This tool is already used in various environment, so backward-incompatible requests will be mostly rejected.

Use cases
---------

Feel free to add your idea or experience and send a pull-request.

- [Sending errors to Airbrake](https://github.com/tomykaira/clockwork/issues/58)
- [Read events from a database](https://github.com/tomykaira/clockwork/issues/25)

Meta
----

Created by Adam Wiggins

Inspired by [rufus-scheduler](https://github.com/jmettraux/rufus-scheduler) and [resque-scheduler](https://github.com/bvandenbos/resque-scheduler)

Design assistance from Peter van Hardenberg and Matthew Soldo

Patches contributed by Mark McGranaghan and Lukáš Konarovský

Released under the MIT License: http://www.opensource.org/licenses/mit-license.php

http://github.com/tomykaira/clockwork