From: Macario Ortega <macarui@...>
Date: 2009-08-09T06:47:48+09:00
Subject: Re: Soft realtime with EventMachine and timer resolution

Bill Kelly wrote:
> From: "Macario Ortega" <macarui@gmail.com>
>>    evma_set_timer_quantum(16/*msec*/);      // roughly 60Hz
> Hehe, i thought that looked familiar... it appears to be from an email
> I posted on the eventmachine-talk mailing list in 2006.  :)
> 
> But yes: these days the set_timer_quantum API is available from ruby.
> 
>   EventMachine.set_timer_quantum(10);
> 
> Note: Internally, EventMachine places limits on the min/max allowed
> values for quantum:  (in em.cpp)
> 
>   /* We get a timer-quantum expressed in milliseconds.
>    * Don't set a quantum smaller than 5 or larger than 2500.
>    */
> 
>   if ((interval < 5) || (interval > 2500))
>     throw std::runtime_error ("invalid timer-quantum");
> 
> 
> Hope this helps,
> 
> Bill


Thanks for your reply, it was useful!

I found the cheapest is to exclusivelly use add_periodic_timer with my 
desired interval but it increasingly drifted.

This is my timer loop:

def run
    @next   = Time.now.to_f
    @thread = Thread.new do
      EventMachine.run do
        @start = Time.now.to_f
        EM.set_quantum 5
        EM.add_periodic_timer @interval / 30 do
          if Time.now.to_f >= @next
            bang
            @tick += 1
            @next  = @tick * @interval + @start
          end
        end
      end
    end
    self
  end

EventMachine doesn't seem to warranty the accuracy of the periodic 
timers.
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