Rails - Dec 2007 - BackgroundRb and blocking analysis of progress.

Hi,

I''m using the BackgroundRb scheduler (http://
backgroundrb.rubyforge.org/172) w/ rails (I''m using the older version
-- not the 1.0 release announced yesterday).

My understanding of BackgroundRb is that it creates a separate thread
(divorced from http request/response) that can run a long-running
process (LRP).

The idea is to allow a rails application to periodically check on the
status of the LRP and (potentially) provide updates on a web-page to a
user.

There is a bit of sample-code for BackgroundRb (http://www.infoq.com/
articles/BackgrounDRb) that demonstrates how the status of a LRP can
be checked.

Here is sample-code from a worker class described in the link shown
above:

class FooWorker < BackgrounDRb::Rails
 attr_reader :progress
 def do_work(args)
 @progress = 0
 calculate_the_meaning_of_life(args)
 end
 def calculate_the_meaning_of_life(args)
 while @progress < 100
 # calculations here
 @progress += 1
 end
 end
 end

FooWorker functions properly in my hands (i.e. a sample web-page will
gradually show an increase in the value of @progress up to 100%).

The problem, however, happens when I change the code in the method
called calculate_the_meaning_of_life(args) found within FooWorker to
have it write a large file.  The idea is to have rails/the-web-page
check on the status of the file-writing until it is completely done.

The problem is that the file-writing method seems to lock the
@progress variable and I can''t access @progress via my controller/
periodical-updater until the entire
method (calculate_the_meaning_of_life(args)) is complete.

The method shown below (where I write a file) doesn''t give me access
to @progress until the file is completely written & closed.

This is part of my new FooWorker class file
1   def calculate_the_meaning_of_life(args)
2     e = Event.find_all_by_id(best, :limit => 500000)
3     @progress = 0.0
4     @file_name = "#{args[:user_name]}.csv"
5     open("/e1/public/csvs/#{@file_name}", "w")
6       e.each_with_index do |row, i|
7         f.puts((columns.map {|c| row.send(c[:accessor])}).join("$"))
8         @progress = 100.0 * (i.to_f / e.size.to_f)
9       end
10    end
11    @progress = 100
12  end
13  FooWorker.register

if I delete lines 5 and 10 (i.e. I remove the file-writing commands,
then I have access to the @progress variable even while I''m iterating
through the result set (e.each_with_index {|blah| blah blah }), but
lines 5 and 10 block access.

Clearly, I''m doing something wrong (perhaps using the wrong file i/o
method), but I''m not sure of how to fix the problem.

Any suggestions or explanations as to what I''m doing wrong are much
appreciated.



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figured it out.

f.flush is needed.

On Dec 11, 2:38 pm,
"thebusy...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org"
<thebusy...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hi,
>
> I''m using the BackgroundRb scheduler (http://
> backgroundrb.rubyforge.org/172) w/ rails (I''m using the older
version
> -- not the 1.0 release announced yesterday).
>
> My understanding of BackgroundRb is that it creates a separate thread
> (divorced from http request/response) that can run a long-running
> process (LRP).
>
> The idea is to allow a rails application to periodically check on the
> status of the LRP and (potentially) provide updates on a web-page to a
> user.
>
> There is a bit of sample-code for BackgroundRb (http://www.infoq.com/
> articles/BackgrounDRb) that demonstrates how the status of a LRP can
> be checked.
>
> Here is sample-code from a worker class described in the link shown
> above:
>
> class FooWorker < BackgrounDRb::Rails
>  attr_reader :progress
>  def do_work(args)
>  @progress = 0
>  calculate_the_meaning_of_life(args)
>  end
>  def calculate_the_meaning_of_life(args)
>  while @progress < 100
>  # calculations here
>  @progress += 1
>  end
>  end
>  end
>
> FooWorker functions properly in my hands (i.e. a sample web-page will
> gradually show an increase in the value of @progress up to 100%).
>
> The problem, however, happens when I change the code in the method
> called calculate_the_meaning_of_life(args) found within FooWorker to
> have it write a large file.  The idea is to have rails/the-web-page
> check on the status of the file-writing until it is completely done.
>
> The problem is that the file-writing method seems to lock the
> @progress variable and I can''t access @progress via my controller/
> periodical-updater until the entire
> method (calculate_the_meaning_of_life(args)) is complete.
>
> The method shown below (where I write a file) doesn''t give me
access
> to @progress until the file is completely written & closed.
>
> This is part of my new FooWorker class file
> 1   def calculate_the_meaning_of_life(args)
> 2     e = Event.find_all_by_id(best, :limit => 500000)
> 3     @progress = 0.0
> 4     @file_name = "#{args[:user_name]}.csv"
> 5     open("/e1/public/csvs/#{@file_name}", "w")
> 6       e.each_with_index do |row, i|
> 7         f.puts((columns.map {|c|
row.send(c[:accessor])}).join("$"))
> 8         @progress = 100.0 * (i.to_f / e.size.to_f)
> 9       end
> 10    end
> 11    @progress = 100
> 12  end
> 13  FooWorker.register
>
> if I delete lines 5 and 10 (i.e. I remove the file-writing commands,
> then I have access to the @progress variable even while I''m
iterating
> through the result set (e.each_with_index {|blah| blah blah }), but
> lines 5 and 10 block access.
>
> Clearly, I''m doing something wrong (perhaps using the wrong file
i/o
> method), but I''m not sure of how to fix the problem.
>
> Any suggestions or explanations as to what I''m doing wrong are
much
> appreciated.
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