# Rails hook for post-processing after page is rendered?

**URL:** <https://www.ruby-forum.com/t/rails-hook-for-post-processing-after-page-is-rendered/148723>\
**Category:** Rails\
**Created:** [September 16, 2008, 4:47pm UTC](https://www.ruby-forum.com/t/rails-hook-for-post-processing-after-page-is-rendered/148723 "2008-09-16T16:47:41Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![colinkelley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/3ec8ea/32.png) [@colinkelley](https://www.ruby-forum.com/u/colinkelley)\
**Post date:** [September 16, 2008, 4:47pm UTC](https://www.ruby-forum.com/t/rails-hook-for-post-processing-after-page-is-rendered/148723/1 "2008-09-16T16:47:41Z")

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We’re starting to notice a pattern in our Rails app that there are  
asynchronous actions we’d like to take after the response is rendered  
and shipped to the browser. Examples including queuing email and  
writing statistics to the database.

It would be cool if there were a hook in Rails that would allow us to  
throw this work onto a queue and have it done in the same process but  
just after the response is sent back to the browser.

Anyone know of a hook like this, or a plugin that creates one?

-Colin

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<div class="post-metadata">

**Author:** ![colinkelley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/3ec8ea/32.png) [@colinkelley](https://www.ruby-forum.com/u/colinkelley)\
**Post date:** [September 16, 2008, 5:20pm UTC](https://www.ruby-forum.com/t/rails-hook-for-post-processing-after-page-is-rendered/148723/2 "2008-09-16T17:20:05Z")

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Hi Colin,

Colin Kelley wrote:

> Anyone know of a hook like this, or a plugin that creates one?  
> If I understand your question correctly, you’re looking for a  
> distributed  
> Ruby library / plugin. The standard library includes dRuby. The  
> choices  
> re: plugins includes BackgrounDRb which was the standard choice for  
> quite a  
> while. There are other options available today which may suit your  
> needs  
> better, depending. Google ‘distributed ruby plugins’.

WRT doing the work in the same process that handled the request, the  
Rails  
architecture pretty much precludes that, at least as a ‘best practice.’

HTH,  
Bill

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<div class="post-metadata">

**Author:** ![colinkelley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/3ec8ea/32.png) [@colinkelley](https://www.ruby-forum.com/u/colinkelley)\
**Post date:** [September 17, 2008, 3:40pm UTC](https://www.ruby-forum.com/t/rails-hook-for-post-processing-after-page-is-rendered/148723/3 "2008-09-17T15:40:26Z")

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Colin Kelley wrote:

> Thanks Bill for the quick response.
> 
> Distributed Ruby is pretty heavyweight for what I have in mind. It has  
> a lot of moving parts. I was thinking lightweight that would just allow  
> me to time shift a few operations that can take a second or two so that  
> the page is returned first and then those operations are then performed.  
> (Example: queue an email.) I’d like to have access to the full cached  
> model when those post\_processing operations run.

BackgrounDRb gives you access to your app’s models. I haven’t used any  
of  
the available alternatives, but I’d expect them to do the same.

> end  
> @@background\_tasks.)
> 
> The timers supervision is to preclude them taking too much time away  
> from serving the next pages. And it would be best to not allow more  
> than one post\_processing mongrel at a time for the same session (or  
> possibly IP:port), lest a runaway Ajax loop consume all the mongrels for  
> example.
> 
> Does this sound feasible? Anyone know of some work along these lines  
> already?

I would absolutely recommend against thsi approach. You’re adding at  
least  
three levels of complexity when one would do. And the one’s you’re  
contemplating are dangerous. Using a distributed process like  
BackgrounDRb  
solves your problem with a tested and supported solution. I was using  
the  
‘old’ one, primarily because it also ran on Windows. And I didn’t find  
it  
‘heavyweight’ at all. I’d strongly recommend you try out the existing  
solutions to this very common problem before you go hacking Rails’ core.

Best regards,  
Bill

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<div class="post-metadata">

**Author:** ![colinkelley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/3ec8ea/32.png) [@colinkelley](https://www.ruby-forum.com/u/colinkelley)\
**Post date:** [September 17, 2008, 8:42pm UTC](https://www.ruby-forum.com/t/rails-hook-for-post-processing-after-page-is-rendered/148723/4 "2008-09-17T20:42:31Z")

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Bill W. wrote:

> BackgrounDRb gives you access to your app’s models.

Excellent–I wasn’t aware of that.

> I’d strongly recommend you try out the existing  
> solutions to this very common problem before you go hacking Rails’ core.

I will follow your advice and try out BackgrounDRb and perhaps one of  
the alternatives as well.

Thanks again,

-Colin

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<div class="post-metadata">

**Author:** ![colinkelley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/3ec8ea/32.png) [@colinkelley](https://www.ruby-forum.com/u/colinkelley)\
**Post date:** [September 17, 2008, 7:18am UTC](https://www.ruby-forum.com/t/rails-hook-for-post-processing-after-page-is-rendered/148723/5 "2008-09-17T07:18:10Z")

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Bill W. wrote:

> If I understand your question correctly, you’re looking for a  
> distributed  
> Ruby library / plugin. The standard library includes dRuby.  
> …  
> WRT doing the work in the same process that handled the request, the  
> Rails  
> architecture pretty much precludes that, at least as a ‘best practice.’

Thanks Bill for the quick response.

Distributed Ruby is pretty heavyweight for what I have in mind. It has  
a lot of moving parts. I was thinking lightweight that would just allow  
me to time shift a few operations that can take a second or two so that  
the page is returned first and then those operations are then performed.  
(Example: queue an email.) I’d like to have access to the full cached  
model when those post\_processing operations run.

I poked around the source a little today and it seems feasible to patch  
in at the RailsHandler::process(request, response) level. That method  
could be aliased and replaced with a new process method:

alias :old\_process :process

def process(request, response)  
old\_process(request, response)  
post\_process  
end

where post\_process was something like

within\_timer\_block do  
while task = @@background\_tasks.shift  
task.call  
end  
end

(The controllers would queue their slow operations onto  
@@background\_tasks.)

The timers supervision is to preclude them taking too much time away  
from serving the next pages. And it would be best to not allow more  
than one post\_processing mongrel at a time for the same session (or  
possibly IP:port), lest a runaway Ajax loop consume all the mongrels for  
example.

Does this sound feasible? Anyone know of some work along these lines  
already?

---

<div class="post-metadata">

**Author:** ![colinkelley](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/3ec8ea/32.png) [@colinkelley](https://www.ruby-forum.com/u/colinkelley)\
**Post date:** [September 17, 2008, 10:41pm UTC](https://www.ruby-forum.com/t/rails-hook-for-post-processing-after-page-is-rendered/148723/6 "2008-09-17T22:41:58Z")

</div>

The Rails Wiki lists all possibilities -  
[http://wiki.rubyonrails.org/rails/pages/HowToRunBackgroundJobsInRails](http://wiki.rubyonrails.org/rails/pages/HowToRunBackgroundJobsInRails)

The most simple (and low-level) solution I found was to use script/  
runner  
(from  
[http://www.ahabman.com/blog/2008/05/rails-background-process-simple-fast-easy/](http://www.ahabman.com/blog/2008/05/rails-background-process-simple-fast-easy/))

My\_Controller

def in\_background  
# your normal code here

```
system " RAILS_ENV=#{RAILS_ENV} ruby #{RAILS_ROOT}/script/

```

runner ‘MyModel.some\_method\_to\_run\_in\_background’ & ”

end

end