From: Macario Ortega <macarui@...>
Date: 2009-08-08T14:40:11+09:00
Subject: Soft realtime with EventMachine and timer resolution



Hi, I trying to do music livecoding with Ruby but I am having problems
with event scheduling, I shold have known before.

My question is how to increse timer resolution for EventMachine timer.

Thing is I have a more or less precise timer (apparently a jitter of
10ms in rithmic patterns is not percieivable) but is kind of expensive
in terms of computation.

It looks somewhat like this:

   class Ticker
        attr_reader :tick

        def initialize tempo
            @tempo       = tempo
            @interval    = 60.0 / @tempo
            @sleep_time  = @interval / 100
            @tick        = 0
        end

        def run
            @thread = Thread.new do
                @next = Time.now.to_f
                loop do
                    @next += @interval
                    @tick += 1
                    Thread.new do
                        tick
                    end
                    sleep @sleep_time until Time.now.to_f >= @next
                end
            end
        end

        def tick
        end
    end

I've never used EventMachine and I don't understand much of it but I
made a timer. First thing I was surprised on how light on the processor
it is, but no matter how low is the number I pass to add_periodic_timer
I get jitter of average 50ms and If I create too much timers the jitter
regulary increases eventually reaching seconds.

Is there any way to increase timer quatum from Ruby?

I found this C line somewhere:
    evma_set_timer_quantum(16/*msec*/);      // roughly 60Hz

Any advice?

Thanks
Macario
btw, heres my code:



require 'rubygems'
require 'eventmachine'

class Ticker
    attr_reader :tick

    def initialize tempo
        @tempo       = tempo
        @interval    = 60.0 / @tempo
        @tick        = 0
    end

    def bang
        puts Time.now.to_f - @expected
        @expected   = @next
    end

    def run
        @expected = Time.now.to_f
        @next     = Time.now.to_f
        @thread   = Thread.new do
            EventMachine.run do
                EM.add_periodic_timer do
                    if Time.now.to_f >= @next
                        @next += @interval
                        @tick += 1
                        bang
                    end
                end
            end
        end
    end
end

10.times do
    Ticker.new(120*4).run
end

sleep 10
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