Re: [Mongrel] Requests that make calls from XMLRPC::Client tie up Mongrel

[Jonathan Rochkind]

Cool, glad you solved it. Threading in ruby has all sorts of gotchas. 
Although I can't possibly explain why your new way works, it seems odd 
to me, although it does seem to confirm that _something_ about threading 
is what was causing you problems.  Out of curiosity, what was 
RpcTask.run defined as before?  Did it involve threads already?

Might be interesting to try your code under Passenger instead of Mongrel 
and see if the same problem occurs. I am trying to switch all my stuff 
out of mongrel to passenger, mongrel's continued development seems... 
not something I am confident in.

Jonathan

Thomas Allen wrote:
Thanks for suggesting that the problem may be related to threading. At
least on this Debian box, changing RpcTask.run to the following seems
to do the trick:

def run(task, task_params = {})
  Thread.new {
    server = XMLRPC::Client.new2('http://localhost:9192/')
    server.call(task,task_params)
  }.value
end

Thomas

On Wed, Nov 18, 2009 at 2:13 PM, Thomas Allen
<thomas.al...@litsoftinc.com> wrote:
  
Hi Jonathan,

I thought that maybe using 'call_async' rather than simply 'call'
might improve the situation but the behavior is the same with either
call.

Thomas Allen

On Wed, Nov 18, 2009 at 12:53 PM, Jonathan Rochkind <rochk...@jhu.edu> wrote:
    
Do the RpcTask task methods end up using ruby threads to do their work?
That call_async  method definitely sounds suspiciously like it might.

I've found that ruby threads under mongrel (although I don't think it's
neccesarily an issue specific to mongrel) sometimes block when you don't
think they ought to be, or end up in wait state for long periods when it
doesn't seem like they ought to be.

When I have actual control over my ruby threads, I've found that explicitly
setting the thread priority of 'background' threads to be lower than 0
generally frees things up.   If RpcTask is creating threads and you don't
want to hack it's code to set thread priorities...  is there a synchronous
method you can use instead of call_async to make your rpc?

Jonathan

Thomas Allen wrote:
      
Hi Everyone,

I'm running a Rails site on Mongrel and I can't figure out why a
particular type of request ties up Mongrel easily. The requests that
tie up Mongrel call an XML-RPC server like so:

# In the controller
def site_start
 if params[:id]
   @site = Site.find(params[:id])
   @site.site_start
   render :json=>{:success=>true}
 end
end

# In the model
def site_start
 RpcTask.manage(self, 'start')
end

# In RpcTask
def manage(site, task)
 run('manage_task', {
   :site => site.name,
   :site_id => site.id,
   :task => task
 })
end

# which calls
def run(task, task_params = {})
 begin
   server = XMLRPC::Client.new2('http://localhost:9192/')
   result = server.call_async(task,task_params)
   return result
 rescue XMLRPC::FaultException => err
   logger = ActiveRecord::Base.logger
   logger.error(err.faultCode)
   logger.error(err.faultString)
   logger.error(result)
 end
 false
end

If I call the model method directly from the console, the RPC side
responds very quickly:


        
start = Time.now; Site.first.site_start; (Time.now - start).to_s

            
=> "0.493253"

Removing the body of RpcTask.run results in comparable performance.
Also, by switching from a single mongrel to a four-mongrel cluster, I
was able to get the these actions to perform acceptably but I imagine
that I'm doing something very wrong here to require so much power. Any
ideas?

Thanks,
Thomas Allen
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