activerecord.rb

### A quick dirty fix.
## Current version ActiveRecord 4.2.0
## Jruby 9.0.5.0

## Avoid some Mutex lock. Reference issue ->  https://github.com/rails/rails/pull/14938.
## Why we need this.
## Since we cant upgrade to 5.2.stable because the JDBC driver support are still not mature and the 5.0.x is causing some strange
## error (which I seem is fixed only in 5.2.stable)

class Handler
  attr_accessor :conn
  def initialize
  end

 def start
   begin
    ## May be timeout in checkout process can help avoid the mutex hold propogating to all thread waiting to checkout a connection.
    Timeout::timeout(0.3) do
      ## activeRecord connection pool size is n
      ## connect_timeout : 0.25
      self.conn = ActiveRecord::Base.connection_pool.checkout
      ## there can be a slight a slight problem,where connection can become orphan i.e the driver created a connection but before
      ## self.conn was set the timeout happened.
    end
   rescue Timeout::Error
     logger.error "Bail out"   
   end
   ## get reserved connection
   reserved_connection = ActiveRecord::Base.connection_pool.instance_variable_get(:'@reserved_connections')
   reserved_connection[Thread.current.object_id] ||= conn
   
   ## do stuff A with DB
   ## do stuff B with DB
   
   ensure
    release_connection if self.conn
 end
 
 def release_connection
    ActiveRecord::Base.connection_pool.checkin(conn)
 end
end

class Puller
  def start
    loop do 
       ## A Celluloid Actor ThreadPool of size n 
       ThreadPool.schedule {
          Handler.new().start
       }
    end
  end
end