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

[Jonathan Rochkind]

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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