MongoMapper, MongoDB and EventMachine - mongodb

Question

I am using DaemonKit to create an AMQP listener. Whenever a message comes across the wire, I would like to log it to MongoDB. I have moved my Rails MongoDB configs over and the connection works fine. When I try to create a new model, I get an error in the Model.create method.
IOError when attempting to close socket connected to localhost:27017: #<IOError: closed stream>
/Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/connection.rb:856:in `rescue in send_message_on_socket': Operation failed with the following exception: closed stream (Mongo::ConnectionFailure)
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/connection.rb:843:in `send_message_on_socket'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/connection.rb:483:in `block in receive_message'
from <internal:prelude>:10:in `synchronize'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/connection.rb:482:in `receive_message'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/cursor.rb:407:in `block in send_initial_query'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/connection.rb:609:in `instrument'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/cursor.rb:406:in `send_initial_query'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/cursor.rb:371:in `refresh'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/cursor.rb:87:in `next_document'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/cursor.rb:248:in `each'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/cursor.rb:267:in `to_a'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/mongo-1.3.1/lib/mongo/cursor.rb:267:in `to_a'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/plucky-0.3.8/lib/plucky/query.rb:76:in `all'
from /Volumes/External/Projects/ruby/alertsdaemons/eventmachine/libexec/eventmachine-daemon.rb:17:in `block in <top (required)>'
from /Volumes/External/Projects/ruby/alertsdaemons/eventmachine/libexec/eventmachine-daemon.rb:15:in `loop'
from /Volumes/External/Projects/ruby/alertsdaemons/eventmachine/libexec/eventmachine-daemon.rb:15:in `<top (required)>'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.7/lib/active_support/dependencies.rb:239:in `require'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.7/lib/active_support/dependencies.rb:239:in `block in require'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.7/lib/active_support/dependencies.rb:225:in `block in load_dependency'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.7/lib/active_support/dependencies.rb:596:in `new_constants_in'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.7/lib/active_support/dependencies.rb:225:in `load_dependency'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/activesupport-3.0.7/lib/active_support/dependencies.rb:239:in `require'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/daemon-kit-0.1.8.2/lib/daemon_kit/application.rb:38:in `run'
from /Users/lfaus/.rvm/gems/ruby-1.9.2-p180/gems/daemon-kit-0.1.8.2/lib/daemon_kit/application.rb:21:in `exec'
from /Volumes/External/Projects/ruby/alertsdaemons/eventmachine/bin/eventmachine:12:in `<top (required)>'
from -e:1:in `load'
from -e:1:in `<main>'
code for creating the object:
# Sample loop to show process
loop do
DaemonKit.logger.info "I'm running"
message = Message.create({
:first_name => 'Lee',
:last_name => 'Faus'
})
puts message.inspect
puts message.count
sleep 5
end
I had read that I could fork mongomapper to make the http calls async, but these errors seem to be coming from the mongodb ruby driver. any help is greatly appreciated.

Answer 1

It is tough to say what is really happening here, but I have a suspicion that I'd like you to investigate please.
Ensure you are establishing your Mongo connection in a POST-daemonize config, instead of a PRE-daemonize config. DaemonKit forks after the PRE-initializers and the mongo connection will need to be re-established at this point in time. This goes for any IO of any kind, after forking they all need to be re-opened.
The same logic holds true for ActiveRecord in a daemonized project. If this was ActiveRecord you could do something like this:
config/pre-daemonize/database.rb
ActiveRecord::Base.establish_connection(:foo => 'bar')
config/post-daemonize/database.rb
ActiveRecord::Base.verify_active_connections!
I'm not a mongomapper user, so I don't know how to translate the above example.
My best advise is to "ping" mongo in PRE-daemonization phase and error out if it failed, so the daemon doesn't even start, and the properly setup the connection in a post-daemonize configuration.