Rails - Oct 2005 - Process meter

When processing an action which takes a long period of time, I would like to
update the user as to the progress of the transaction.  How can I do this in
Rails?  Since I can only render once in an action, I don''t see how I
can send
updates.  After the end of the process, I am sending the generated file, e.g.,

  def print_report
    record_list = Record.find (...) # long list of records
    pdf = PDF::Writer.new
    for record in record_list
       # do processing which adds to the PDF
       ...
       # ideally update the user periodically with status
       # (e.g., record x of y or %complete)
    end
 
    send_data(pdf.render, :filename => "report.pdf", :type =>
"application/pdf")
  end

I tried implementing such an update via AJAX using the remote update function
but I couldn''t figure out how to get the record number from the
print_report
action to the action being called remotely to update the user''s page.

Can anyone post an example (or a link to one) or send me an email with an
example?

I prefer not to have these long-running transactions take place
synchronously.  I load up the relevant data into a queue in the
database, and a Ruby runner script processes the queue, sleeps for a
few seconds, then loops. This way, I don''t tie up my limited and
memory intensive cgi processes with user waiting time.  When an item
is ready, I fire off an email to the user to inform him.

In line with this, you could also use periodically_call_remote to poll
the queue.   The queue processing script periodically writes back to
the queue an estimate of the percent finished.

If you don''t feel that this is responsive enough, you could have
multiple queue processing scripts running at once.  If you have 3
running, the first one handles queue rows with id % 3 == 0, the second
id % 3 == 1, etc.

On 10/11/05, cvoltz <cjunk-cTAGtEdy3/s@public.gmane.org>
wrote:
> When processing an action which takes a long period of time, I would like
to
> update the user as to the progress of the transaction.  How can I do this
in
> Rails?  Since I can only render once in an action, I don''t see how
I can send
> updates.  After the end of the process, I am sending the generated file,
e.g.,
>
>   def print_report
>     record_list = Record.find (...) # long list of records
>     pdf = PDF::Writer.new
>     for record in record_list
>        # do processing which adds to the PDF
>        ...
>        # ideally update the user periodically with status
>        # (e.g., record x of y or %complete)
>     end
>
>     send_data(pdf.render, :filename => "report.pdf", :type
=> "application/pdf")
>   end
>
> I tried implementing such an update via AJAX using the remote update
function
> but I couldn''t figure out how to get the record number from the
print_report
> action to the action being called remotely to update the user''s
page.
>
> Can anyone post an example (or a link to one) or send me an email with an
> example?
>
>
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>

Kyle Maxwell wrote:
> I prefer not to have these long-running transactions take place
> synchronously.  I load up the relevant data into a queue in the
[snip]

Me too.. but.
>>  def print_report
>>    record_list = Record.find (...) # long list of records
>>    pdf = PDF::Writer.new
>>    for record in record_list
>>       # do processing which adds to the PDF
>>       ...
>>       # ideally update the user periodically with status
>>       # (e.g., record x of y or %complete)
>>    end
>>
>>    send_data(pdf.render, :filename => "report.pdf", :type
=> "application/pdf")
>>  end
You could create another action called "print_report_status", meant to
run in parallel with "print_report", and call it via XHR to
dynamically
update a status bar in the browser.

This requires a JavaScript enabled client, of course.

--Steve