From: Ken Ghosh <meetme2meat@...>
Date: 2010-10-22T16:48:24+09:00
Subject: EventMachine::Defer + Weird issue

I been Using EventMachine for quite a while a know and I really found it
great as It Manage show much more me that i didn't have to worry for
anything.But recently I just found this weird issue which i just fail to
understand

Here what is just telling

 I have Eventmachine loop Which look like this



>  EventMachine::run {
>       EventMachine::add_periodic_timer(10)
>   do
>         EventMachine::defer(@operation_block,@callback_block)
> end    }


here my operation block look like(Code below use of amqp using carrot
gem)

>     @operation_block = Proc.new {
                  begin
>                   puts "Initiating the queue"
>                   @carrot ||= Carrot.new(:host => localhost)
>                   @queue ||= @carrot.queue("my_queue")
>                   puts "The Queue is Poping the message"

>                   if @queue.pop
                      [MY LOGIC HERE]
                      $input_to_callback = "SUCCESS" ## IF LOGIC GET
EVALUATED WITHOUT ERROR ELSE WILL SET TO FAIL
                    else
                      $input_to_callback = "NOTHING TO PROCESSES"
                    end
                 rescue
                    puts e
                    retry!
                 end
                 $input_to_callback
>
>               }


Here my callback block look like

         @callback_block = Proc.new {|operation_block_output|
             if operation_block_output == "SUCCESS"
                puts "YAHOOOOOOOOO SUCCESS"
             elsif operation_block_output == "NOTHING TO PROCESSES"
                puts "BOO Nothing to processes"
              else
               puts "FAIL ALARM"
             end
          }


 Now Here come the Trouble
 The Code Though Work the way it should until something bad happen
 Here what i meant

 Now suppose I running this Above Code

 I have a queue set name "my_queue" or it will create one if it doesn't
exists the queue is initially empty

here the output that I get on console

>   Initiating the queue

>   The Queue is Poping the Message

>   BOO Nothing to processes


 As I message built the output Change in console accordingly based

Now the trouble

  If I momentarily shutdown my AMQP server Here the output(to show what
i meant)



> Initiating the queue
>
>   Broken Pipe  => Error That Caught in
> begin rescue block in operation block


  Now Start AMQP Server

  The Code just never seem move ahead from line where it currently got
error
  that means I never Seem to print the line

  The Queue is Poping the message

  not only the current defer for which is retry  happened but also the
new defer operation block that get initiated after the  Timer time just
elapsed
    i.e means of the subsequent call to operation block
    never seem to move ahead and do processing and always print the
following
    output only

    Initiating the queue

  Just never seem to move ahead(stuck) and do Processing that it meant
to i.e fetch the message from the queue do the processing accordingly
and all the other stuff(as the AMQP server is running now)




  Thanks

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