Draft...
Planning on using BackgroundDRB? Take a long look at the alternatives first
Ask yourself, do you really need a complex solution like BackgroundDRB? Most likely you don't, so use a simple daemonized process instead, see this snippet about the daemons gem for more information.
Heck, even a simple Ruby script run by cron every 5 minutes will be more stable than BackgroundDRB and require less work.
Even if you really need to process a lot of data asynchronously in the background, I wouldn't recommend BackgroundDRB, it's riddled with bugs and unstable in production, so use the BJ plugin instead.
Anyway, continue reading if you want to use BackgroundDRB...
Installing the prerequisites:
$ sudo gem install chronic packet
Installing backgroundrb
$ cd rails_project
$ git clone git://gitorious.org/backgroundrb/mainline.git vendor/plugins/backgroundrb
You can also get the latest stable version from the Subversion repository:
svn co http://svn.devjavu.com/backgroundrb/trunk vendor/plugins/backgroundrb
Setup backgroundrb
rake backgroundrb:setup
Create a worker
./script/generate worker feeds_worker
class FeedsWorker < BackgrounDRb::MetaWorker
set_worker_name :feeds_worker
def create(args = nil)
# this method is called, when worker is loaded for the first time
logger.info "Created feeds worker"
end
def update(data)
logger.info "Updating #{Feed.count} feeds."
seconds = Benchmark.realtime do
thread_pool.defer do
Feed.update_all()
end
end
logger.info "Update took #{'%.5f' % seconds}."
end
end
Starting backgroundrb
First configure backgroundrb by opening config/backgroundrb.yml in your editor:
:backgroundrb:
:ip: 0.0.0.0
:development:
:backgroundrb:
:port: 11111 # use port 11111
:log: foreground # foreground mode,print log messages on console
:production:
:backgroundrb:
:port: 22222 # use port 22222
Next, start backgroundrb in development mode:
./script/backgroundrb -e development &
Call your worker
From the command line:
$ script/console
Loading development environment (Rails 2.0.2)
>> MiddleMan.worker(:feeds_worker).update()
When things go wrong
Asynchronous programming is complex, so expect bugs...
Rule #1 know who you're calling.
If you give your MiddleMan the wrong name of your worker, he'll just spit this crap at you:
You have a nil object when you didn't expect it!
The error occurred while evaluating nil.send_request
/usr/local/lib/ruby/gems/1.8/gems/packet-0.1.5/lib/packet/packet_master.rb:44:in ask_worker'
/Users/christian/Documents/Projects/xxx/vendor/plugins/backgroundrb/server/lib/master_worker.rb:104:in process_work'
/Users/christian/Documents/Projects/xxx/vendor/plugins/backgroundrb/server/lib/master_worker.rb:35:in receive_data'
/usr/local/lib/ruby/gems/1.8/gems/packet-0.1.5/lib/packet/packet_parser.rb:29:in call'
/usr/local/lib/ruby/gems/1.8/gems/packet-0.1.5/lib/packet/packet_parser.rb:29:in extract'
/Users/christian/Documents/Projects/xxx/vendor/plugins/backgroundrb/server/lib/master_worker.rb:31:in receive_data'
So for example this command would generate the above mentioned error:
MiddleMan.worker(:illegal_worker).update()
It's always nice to see a cryptic error messages such as this, it really deserves an award.
Check for bugs and bug fixes
Going to production
Starting the daemon:
./script/backgroundrb -e production start
Configuring your task to run periodically
The following example makes backgroundrb call the FeedsWorker's update method once every 15 minutes:
:production:
:backgroundrb:
:port: 22222 # use port 22222
:lazy_load: true # do not load models eagerly
:debug_log: false # disable log workers and other logging
# Cron based scheduling
:schedules:
:feeds_worker:
:update:
:trigger_args: * */15 * * * *
:data: "Hello world"
At the time of writing, the cron scheduler seems to be broken, so I prefer hard-coding the interval in the worker's create method:
def create
add_periodic_timer(15.minutes) { update }
end
If using Vlad or Capistrano, it's also a good idea to fix script/backgroundrb by changing these lines:
pid_file = "#{RAILS_HOME}/../../shared/pids/backgroundrb_#{CONFIG_FILE[:backgroundrb][:port]}.pid"
SERVER_LOGGER = "#{RAILS_HOME}/../../shared/log/backgroundrb_server_#{CONFIG_FILE[:backgroundrb][:port]}.log"