Workling gives your Rails App a simple API that you can use to make code run in the background, outside of the your request.
You can configure how the background code will be run. Currently, workling supports Starling, BackgroundJob and Spawn Runners. Workling is a bit like Actve* for background work: you can write your code once, then swap in any of the supported background Runners later. This keeps things flexible.
The easiest way of getting started with workling is like this:
script/plugin install git@github.com:purzelrakete/workling.git
script/plugin install git://github.com/tra/spawn.git
If you're on an older Rails version, there's also a subversion mirror wor workling (I'll do my best to keep it synched) at:
script/plugin install http://svn.playtype.net/plugins/workling/
This is pretty easy. Just put cow_worker.rb into into app/workers, and subclass Workling::Base:
# handle asynchronous mooing.
class CowWorker < Workling::Base
def moo(options)
cow = Cow.find(options[:id])
logger.info("about to moo.")
cow.moo
end
end
Make sure you have exactly one hash parameter in your methods, workling passes the job :uid into here. Btw, in case you want to follow along with the Mooing, grab 'cows-not-kittens' off github, it's an example workling project. Look at the branches, there's one for each Runner.
Next, you'll want to call your workling in a controller. Your controller might looks like this:
class CowsController < ApplicationController
# milking has the side effect of causing
# the cow to moo. we don't want to
# wait for this while milking, though,
# it would be a terrible waste ouf our time.
def milk
@cow = Cow.find(params[:id])
CowWorker.asynch_moo(:id => @cow.id)
end
end
Notice the asynch_moo call to CowWorker. This will call the moo method on the CowWorker in the background, passing any parameters you like on. In fact, workling will call whatever comes after asynch_ as a method on the worker instance.
All worker classes must inherit from this class, and be saved in app/workers. The Worker is loaded once, at which point the instance method 'create' is called.
Calling async_my_method on the worker class will trigger background work. This means that the loaded Worker instance will receive a call to the method my_method(:uid => "thisjobsuid2348732947923").
If an exception is raised in your Worker, it will not be propagated to the calling code by workling. This is because the code is called asynchronously, meaning that exceptions may be raised after the calling code has already returned. If you need your calling code to handle exceptional situations, you have to pass the error into the return store.
Workling does log all exceptions that propagate out of the worker methods.
All workers have a logger method which returns the default logger, so you can log like this:
logger.info("about to moo.")
Workling automatically detects and uses Spawn, if installed. Spawn basically forks Rails every time you invoke a workling. To see what sort of characteristics this has, go into script/console, and run this:
>> fork { sleep 100 }
=> 1060 (the pid is returned)
You'll see that this executes pretty much instantly. Run 'top' in another terminal window, and look for the new ruby process. This might be around 30 MB. This tells you that using spawn as a runner will result low latency, but will take at least 30MB for each request you make.
You cannot run your workers on a remote machine or cluster them with spawn. You also have no persistence: if you've fired of a lot of work and everything dies, there's no way of picking up where you left off.
If you want cross machine jobs with low latency and a low memory overhead, you might want to look into using the Starling Runner.
As of 27. September 2008, the recommended Starling setup is as follows:
gem sources -a http://gems.github.com/
sudo gem install starling-starling
mkdir /var/spool/starling
The robot Co-Op Memcached Gem version 1.5.0 has several bugs, which have been fixed in the fiveruns-memcache-client gem. The starling-starling gem will install this as a dependency. Refer to the fiveruns README to see what the exact fixes are.
The Rubyforge Starling gem is also out of date. Currently, the most authorative Project is starling-starling on github (27. September 2008).
Workling will now automatically detect and use Starling, unless you have also installed Spawn. If you have Spawn installed, you need to tell Workling to use Starling by putting this in your environment.rb:
Workling::Remote.dispatcher = Workling::Remote::Runners::StarlingRunner.new
Here's what you need to get up and started in development mode.
sudo starling -d -p 22122
script/workling_starling_client start
Workling copies a file called starling.yml into your applications config directory. You can delete this file if you're not planning to use Starling. The config file tells Workling on which port Starling is listening.
Notice that the default production port is 15151. This means you'll need to start Starling with -p 15151 on production.
You can also use this config file to pass configuration options to the memcache client which workling uses to connect to starling:
development:
listens_on: localhost:22122
memcache_options:
<memcachesetting>: <value>
Starling comes with it's own script, starling_top. If you want statistics specific to workling, run:
script/starling_status.rb
You might wonder what exactly starling does. Here's a little snippet you can play with to illustrate how it works:
4 # Put messages onto a queue:
5 require 'memcache'
6 starling = MemCache.new('localhost:22122')
7 starling.set('my_queue', 1)
8
9 # Get messages from the queue:
10 require 'memcache'
11 starling = MemCache.new('localhost:22122')
12 loop { puts starling.get('my_queue') }
13
If you don't want to bother with seperate processes, are not worried about latence or memory footprint, then you might want to use Bj to power workling.
Install the Bj plugin like this:
1 ./script/plugin install http://codeforpeople.rubyforge.org/svn/rails/plugins/bj
2 ./script/bj setup
Workling will now automatically detect and use Bj, unless you have also installed Starling. If you have Starling installed, you need to tell Workling to use Bj by putting this in your environment.rb:
Workling::Remote.dispatcher = Workling::Remote::Runners::BackgroundjobRunner.new
Your worklings can write back to a return store. This allows you to write progress indicators, or access results from your workling. As above, this is fairly slim. Again, you can swap in any return store implementation you like without changing your code. They all behave like memcached. For tests, there is a memory return store, for production use there is currently a starling return store. You can easily add a new return store (over the database for instance) by subclassing Workling::Return::Store::Base. Configure it like this in your test environment:
Workling::Return::Store.instance = Workling::Return::Store::MemoryReturnStore.new
Here is an example workling that crawls an addressbook and puts results in a return store. Worling makes sure you have options[:uid] in your hash - pass this into the return store with your results.
require 'blackbook'
class NetworkWorker < Workling::Base
def search(options)
results = Blackbook.get(options[:key], options[:username], options[:password])
Workling::Return.set(options[:uid], results)
end
end
call your workling as above:
@uid = NetworkWorker.asynch_search(:key => :gmail, :username => "foo@gmail.com", :password => "bar")
you can now use the @uid to query the return store:
results = Workling::Return.get(@uid)
of course, you can use this for progress indicators. just put the progress into the return store.
enjoy!
Copyright (c) 2008 play/type GmbH, released under the MIT license