Script for show and tell for Postgres Advisory Locks

advisory_locks.rb

require 'active_record'
 
class ObtainerOfLocks
  class << self
    def lock_it_up
      initiate_useless_connection
 
      2.times do
        fork do
          exclusive { puts 'Lock obtained.' }
        end
      end
 
      Process.waitall
    end
 
    private
 
    def exclusive
      if obtained_lock?
        yield
        sleep 0.5
        release_lock
      end
    end
 
    def obtained_lock?
      connection.select_value('select pg_try_advisory_lock(1);') == 't'
    end
 
    def release_lock
      connection.execute 'select pg_advisory_unlock(1);'
    end
 
    def connection
      ActiveRecord::Base.connection
    end
 
    def initiate_useless_connection
      ActiveRecord::Base.establish_connection({
        adapter: 'postgresql',
        encoding: 'unicode',
        database: 'your_db',
        pool: 5,
        timeout: 5000,
        username: 'username'
      })
    end
  end
end
 
ObtainerOfLocks.lock_it_up