mega_mutex

A distributed mutex for Ruby.

Why

Sometimes I need to do this:

unless enough_things?
  make_more_things
end

If I'm running several processes in parallel, I can get a race condition that means two of the processes both think there are not enough things. So we go and make some more, even though we don't need to.

How

Suppose you have a ThingMaker:

class ThingMaker
  include MegaMutex

  def ensure_just_enough_things  
    with_distributed_mutex("ThingMaker Mutex ID") do
      unless enough_things?
        make_more_things
      end
    end
  end
end

Now, thanks to the magic of MegaMutex, you can be sure that all processes trying to run this code will wait their turn, so each one will have the chance to make exactly the right number of things, without anyone else poking their nose in.

Install

sudo gem install mega_mutex

Configure

MegaMutex uses memcache-client to store the mutex, so your infrastructure must be set up to use memcache servers.

By default, MegaMutex will attempt to connect to a memcache on the local machine, but you can configure any number of servers like so:

MegaMutex.configure do |config|
  config.memcache_servers = ['mc1', 'mc2']
end

Help

MegaMutex was built by the Songkick.com development team. Come chat to us on #songkick on freenode.net.

Copyright

Copyright (c) 2009 Songkick.com. See LICENSE for details.