# How to get a backgroundrb worker to delete itself?

**URL:** <https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567>\
**Category:** Rails\
**Created:** [April 10, 2007, 3:43pm UTC](https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567 "2007-04-10T15:43:04Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![simon1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@simon1](https://www.ruby-forum.com/u/simon1)\
**Post date:** [April 10, 2007, 3:43pm UTC](https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567/1 "2007-04-10T15:43:04Z")

</div>

Hi,

I am trying to get a worker instance to delete itself at the end of  
its do\_work method. I have my main rails app creating these workers  
upon certain incoming http requests to parse some XML files, and once  
the parsing is complete, I would like the worker to delete itself, so  
that I don’t need to try and manage several workers within the main  
rails app.

I was trying to accomplish this with the following  
line: ::BackgrounDRb::MiddleMan.instance.delete\_worker @\_job\_key.  
However, when I tried this, I get the following errer:

20070405-13:15:15 (19653) In do work  
20070405-13:15:18 (19653) You have a nil object when you didn’t expect  
it!  
The error occured while evaluating nil.shutdown - (NoMethodError)

It seems that perhaps this method of trying to access the job key of  
the current instance is not working. Has anybody else done something  
similar, or have any suggestions for a different method to accomplish  
this?

Thanks,

Simon

---

<div class="post-metadata">

**Author:** ![simon1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@simon1](https://www.ruby-forum.com/u/simon1)\
**Post date:** [April 10, 2007, 4:09pm UTC](https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567/2 "2007-04-10T16:09:16Z")

</div>

On a similar note, is there any way to monitor the number of worker  
instances that are running? What I am after is to ensure that worker  
instances are being deleted, and so I would like to be able to keep an  
eye on when new instances are created, and when they are deleted.

Thanks again,

Simon

---

<div class="post-metadata">

**Author:** ![simon1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@simon1](https://www.ruby-forum.com/u/simon1)\
**Post date:** [April 14, 2007, 2:04am UTC](https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567/3 "2007-04-14T02:04:37Z")

</div>

Hi Simon !

Well, I’m, at the moment , trying to do the same think !!  
Looks like calling self.delete at the end of the do\_work method of a  
worker is a bad idea …  
In fact, a worker cannot delete itself, looks like.  
What I’m thinking right now would be a sort of … worker that would  
act has a cleaner …

Let say, you have a worker that do some email check.

Step1 -\> an entry is created in a jobs table with job.cmd = “command  
to run the email check”, job.key\_job = " unique id for this job" and  
job.status = “Waiting”  
Step2 -\> you have a schedule worker that every 30 minutes, for  
example, look at the jobs table, and create worker that have the  
waiting status … ( so 1 row in the jobs table becomes a worker soon  
or later)  
Step3 -\> every “waiting” worker that are now running can then update  
the “jobs” table to say “hey I’m finish” so job.status = “finished”  
Step4 -\> the cleaner (the schedule worker that wakes up every 30  
minutes) re-check for “Waiting jobs” but also look for “finished jobs”  
and clean them … 'cos a woker can clean another one …

Don’t know if that make sence … it is just an “idea” that i’m having  
right now … (and it’s 2h00 - not 14h00 !- over here in France 😉 )

Anyway, I might try to implement such a “job cleaner” tomorrow and  
have a try …

PS : BUT IF SOMEONE’S GOT AN IDEA ON HOW A WORKER CAN KILL HIMSELF …  
I WOULD RATHER TAKE IT !

Jules

---

<div class="post-metadata">

**Author:** ![simon1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@simon1](https://www.ruby-forum.com/u/simon1)\
**Post date:** [April 14, 2007, 3:26pm UTC](https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567/4 "2007-04-14T15:26:28Z")

</div>

Hi Jules,

> In fact, a worker cannot delete itself, looks like.

It definitely can. I use the following two lines to do it. The first  
makes  
sure the database connection doesn’t hang around. The second line looks  
just like Simon’s and it works.

ActiveRecord::Base.connection.disconnect!  
::BackgrounDRb::MiddleMan.instance.delete\_worker @\_job\_key

Hi Simon,

Simon wrote:

> > I was trying to accomplish this with the following  
> > line: ::BackgrounDRb::MiddleMan.instance.delete\_worker @\_job\_key.

That looks correct.

> > However, when I tried this, I get the following errer:
> > 
> > 20070405-13:15:15 (19653) In do work  
> > 20070405-13:15:18 (19653) You have a nil object when you didn’t expect  
> > it!  
> > The error occured while evaluating nil.shutdown - (NoMethodError)

The error says you’re calling a ‘shutdown’ method on an object that  
doesn’t  
exist. Maybe you could show us some code?

Bill

---

<div class="post-metadata">

**Author:** ![simon1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@simon1](https://www.ruby-forum.com/u/simon1)\
**Post date:** [April 16, 2007, 1:20am UTC](https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567/5 "2007-04-16T01:20:23Z")

</div>

Hi Bill,

Thanks for the reply.  
I tried the  
"::BackgrounDRb::MiddleMan.instance.delete\_worker @\_job\_key " but I  
get the same error as Simon :  
“The error occured while evaluating nil.shutdown”

now here is the worker :

\*\*\*\*\*\*\*\*\* worker code starts here \*\*\*\*\*\*\*\*\*\*\*\*\*\*

class ProgressWorker \< BackgrounDRb::Worker::RailsBase

attr\_accessor :temp\_key

def do\_work(args)

```
cmdoutput = []
results[:worker_status] = false.to_s

filefrom = "video.mov"
fileto = "video.flv"

encode_cmd='ffmpeg -i '+filefrom+' -b 600k -r 24 -ar 22050 -ab 96

```

'+fileto

```
IO.popen(encode_cmd).each do |line|
 cmdoutput << line
 results[:worker_result] = cmdoutput
end

results[:worker_status] = true.to_s
ActiveRecord::Base.connection.disconnect!
::BackgrounDRb::MiddleMan.instance.delete_worker @_job_key

```

end  
end

ProgressWorker.register

\*\*\*\*\*\*\*\*\* worker code ends here \*\*\*\*\*\*\*\*\*\*\*\*\*\*

control calls this worker with :

::MiddleMan.new\_worker(:class =\> :progress\_worker)

Now, I’m trying to understand what is going … :

Is this worker properly registered ??? ( I have  
ProgressWorker.register after (at the end, end 😉 ) the class  
declaration in ProgressWorker.rb …)  
@\_job\_key is an instance variable but … is not defined anywhere ? is  
@\_job\_key automatically created when a worker is called ? if so … may  
be I should specify a :job\_key when creating it ?

Thanks for all your help !

Julien

---

<div class="post-metadata">

**Author:** ![simon1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@simon1](https://www.ruby-forum.com/u/simon1)\
**Post date:** [April 16, 2007, 1:38am UTC](https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567/6 "2007-04-16T01:38:24Z")

</div>

yo !

Some improuvment … but not yet finished …

when I logged the @\_job\_key I receive … an error complaining about  
nil string …  
I looked in the worker.rb code and found … @jobkey … so I gave it  
a try and tada !

when i do :  
logger.error(@jobkey) { "Job Key called with @jobkey : "+@jobkey }  
I get  
20070416-01:34:00 (1269) Job Key called with @jobkey :  
34b21fe088389b080578fd83dc1b47ea

but when I do :  
logger.error(@jobkey) { "Job Key called with @jobkey : "+@\_job\_key }  
I get  
20070416-01:34:00 (1269) can’t convert nil into String - (TypeError)

So sounds liek @\_job\_key does not exists … but @jobkey does …

(But sorry simon, yhis does not resolve the .shutdown nil for the  
moment … I keep seraching …)

jules

---

<div class="post-metadata">

**Author:** ![simon1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@simon1](https://www.ruby-forum.com/u/simon1)\
**Post date:** [April 16, 2007, 2:29am UTC](https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567/7 "2007-04-16T02:29:27Z")

</div>

Me again … more testing going on …

in the worker, I do :  
logger.error(@jobkey) { ::BackgrounDRb::MiddleMan.instance.jobs}

when I look at the log I see :

backgroundrb\_logger#Slave:0x24caef8backgroundrb\_results#\<Slave:  
0x24b6318\>

Looks like the only workers available are the logger and the  
result … where is my worker ???  
I understand now why we get :

You have a nil object when you didn’t expect it!  
The error occurred while evaluating nil.shutdown - (NoMethodError)

-\> there no job with my job\_key !

I’m lost …

---

<div class="post-metadata">

**Author:** ![simon1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@simon1](https://www.ruby-forum.com/u/simon1)\
**Post date:** [April 16, 2007, 5:34am UTC](https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567/8 "2007-04-16T05:34:36Z")

</div>

Hi Jules

Jules wrote:

> Now, I’m trying to understand what is going … :
> 
> Is this worker properly registered ??? ( I have  
> ProgressWorker.register after (at the end, end 😉 ) the class  
> declaration in ProgressWorker.rb …)  
> @\_job\_key is an instance variable but … is not defined anywhere ? is  
> @\_job\_key automatically created when a worker is called ? if so … may  
> be I should specify a :job\_key when creating it ?

I start the worker with:  
session[:job\_key] = MiddleMan.new\_worker(…

Maybe that’s it?

hth,  
Bill

---

<div class="post-metadata">

**Author:** ![simon1](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/fbc32d/32.png) [@simon1](https://www.ruby-forum.com/u/simon1)\
**Post date:** [April 16, 2007, 12:23pm UTC](https://www.ruby-forum.com/t/how-to-get-a-backgroundrb-worker-to-delete-itself/91567/9 "2007-04-16T12:23:11Z")

</div>

Hi Bill,

I will have a try with the session[:job\_key] but …

Looks lile self.delete in the do\_work method do the job …  
Here is a test to confirm this :

At the end of the do\_work method I put this :

results[:worker\_status] = true  
logger.error(@jobkey) { "Worker status :  
"+results[:worker\_status].to\_s }

And, in return I’ve got in the log : Worker status : true  
Now … if I call this instead :

results[:worker\_status] = true  
self.delete  
logger.error(@jobkey) { "Worker status :  
"+results[:worker\_status].to\_s }

I’ve got nothing in my log … why ?  
Simply because results for worker are kept until worker is deleted.  
So, if i cannot this "Worker status : true " in the log it is because  
the worker has been deleted …

So, my conclusion is : self.delete works 😉

PS : please let me know if you think that this test does not confirm  
the fact that calling self.delete, really kill the worker 😉