# Background tasks + multi processing

**URL:** <https://www.ruby-forum.com/t/background-tasks-multi-processing/165904>\
**Category:** Rails\
**Created:** [April 19, 2009, 3:13pm UTC](https://www.ruby-forum.com/t/background-tasks-multi-processing/165904 "2009-04-19T15:13:07Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![petrjanda](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ee7513/32.png) [@petrjanda](https://www.ruby-forum.com/u/petrjanda)\
**Post date:** [April 19, 2009, 3:13pm UTC](https://www.ruby-forum.com/t/background-tasks-multi-processing/165904/1 "2009-04-19T15:13:07Z")

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Hi all,

Ive recently been trying to figure out a way to make a long running  
background task scale accross all CPUs in Ruby on Rails, since  
multi-processing (not multi-threading) seems like the way to go.

A theoretical example would be:

# code in controller

def do\_something  
@mydata = Hash.new

```
   # Start 4 background processes
   # and start adding data to @mydata
   # Page loads while the processes are working, displaying
   # something like "We are currently processing your data"

```

end

Question is how to handle reading/writing to @mydata safely because 4  
processes would be trying to read/write to it? What is the best way to  
approach this problem?

Thanks,  
Petr

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<div class="post-metadata">

**Author:** ![petrjanda](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ee7513/32.png) [@petrjanda](https://www.ruby-forum.com/u/petrjanda)\
**Post date:** [April 19, 2009, 3:47pm UTC](https://www.ruby-forum.com/t/background-tasks-multi-processing/165904/2 "2009-04-19T15:47:36Z")

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I wouldn’t run a long running process directly from your controller,  
since rails first renders all stuff that should be sent to the client  
(html/xml/js/etc) before it actually sends it. This means that the  
complete controller action should be finished to show something in your  
browser.  
I think that the best way to go is to use something that is able to  
spawn background processes (like Starling).

---

<div class="post-metadata">

**Author:** ![petrjanda](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ee7513/32.png) [@petrjanda](https://www.ruby-forum.com/u/petrjanda)\
**Post date:** [April 19, 2009, 4:03pm UTC](https://www.ruby-forum.com/t/background-tasks-multi-processing/165904/3 "2009-04-19T16:03:51Z")

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I don’t think multiple processes can access the same Hash. Multiple  
threads should be able to do this. Maybe a dirty solution is to use the  
database for this and do pessimistic locking on a record.

---

<div class="post-metadata">

**Author:** ![petrjanda](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/ee7513/32.png) [@petrjanda](https://www.ruby-forum.com/u/petrjanda)\
**Post date:** [April 19, 2009, 3:56pm UTC](https://www.ruby-forum.com/t/background-tasks-multi-processing/165904/4 "2009-04-19T15:56:10Z")

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Wouter de Bie wrote:

> I wouldn’t run a long running process directly from your controller,  
> since rails first renders all stuff that should be sent to the client  
> (html/xml/js/etc) before it actually sends it. This means that the  
> complete controller action should be finished to show something in your  
> browser.  
> I think that the best way to go is to use something that is able to  
> spawn background processes (like Starling).

I’m aware of different solutions to run a background job. However, the  
problem is how to make 4 background jobs MPSAFE, all of them working on  
the same Hash. Any ideas?

Petr