SdbLock

Poor man's distributed lock using SimpleDB. It is useful when you don't want to maintain distributed lock server by yourself.

Installation

Add this line to your application's Gemfile:

gem 'sdb_lock'

And then execute:

$ bundle

Or install it yourself as:

$ gem install sdb_lock

Usage

require 'sdb_lock'

lock = SdbLock.new(
  'my_app_lock_domain',  # SimpleDB domain name to use
  create_domain: true,   # At the first time, you will need to create domain. Note it might take long time.

  # Other hash members will be passed to AWS::SimpleDB#new as is.
  # You can set credential by other ways including environmental variables.
  # See https://github.com/amazonwebservices/aws-sdk-for-ruby

  # see http://docs.amazonwebservices.com/general/latest/gr/rande.html#sdb_region
  simple_db_endpoint: "sdb.ap-northeast-1.amazonaws.com",
  access_key_id: YOUR_AWS_ACCESS_KEY,
  secret_access_key: YOUR_AWS_SECRET
)

locked = lock.try_lock("a1") do
  # do some work
end

# if you want to block until gain lock, then use #lock
# WARN There is no way to wake up others. It is slow with high contention
#   because it does polling internally.
lock.lock("a1") do
  # do some work
end

# List locked resource names
lock.locked_resources

# Some times lock might remain because of network failure. Then we'll need
# a way to unlock these.
#
# Unlock older than 10 secs.
lock.unlock_old(10)

Test

AWS_REGION environmental variable is required to run tests.

$ AWS_REGION=ap-northeast-1 bundle exec rake

Limitation

Lock might remain by network failure or other reason. See #unlock_old.
Number of domains are limited by SimpleDB.
Each Lock is represented by an item in SimpleDB. Number of items are limited by SimpleDB.

Contributing

Fork it
Create your feature branch (git checkout -b my-new-feature)
Commit your changes (git commit -am 'Added some feature')
Push to the branch (git push origin my-new-feature)
Create new Pull Request

sdb_lock