Time based loop limiting

ruby-talk
1

I'm trying to write a loop that will only run a certain number of times
per second. For instance, in Ruby-Processing, you would use
"frame_rate(30)" to make the main loop execute no more than 30 evenly
spaced frames per second. How might I go about doing something like
that?

I could try calling sleep with a float that represents the difference
between the next time I want the loop to run and the current time. That
seems clunky, though.

I also thought about using the Observer pattern to have a timer alert
the simulation each time it should update. That also seems wrong.

I feel like I must be overlooking something simple. Any ideas?

···

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2

I think your first method is the one I've seen the most in game loops.
You calculate how long you should sleep based on what time it is now
and what time you want to wake up, being careful that your last frame
could have taken over 1/30th of a second.

You also use the elapsed time in your physics, so the physics engine
is not tied to your frame rate.

···

On Tue, Sep 8, 2009 at 5:38 PM, Michael Tomer<michael.tomer@fnis.com> wrote:

I'm trying to write a loop that will only run a certain number of times
per second. For instance, in Ruby-Processing, you would use
"frame_rate(30)" to make the main loop execute no more than 30 evenly
spaced frames per second. How might I go about doing something like
that?

I could try calling sleep with a float that represents the difference
between the next time I want the loop to run and the current time. That
seems clunky, though.

I also thought about using the Observer pattern to have a timer alert
the simulation each time it should update. That also seems wrong.

I feel like I must be overlooking something simple. Any ideas?
--
Posted via http://www.ruby-forum.com/\.

--
Paul Smith
http://www.nomadicfun.co.uk

paul@pollyandpaul.co.uk

3

Hi,

I'm trying to write a loop that will only run a certain number of times
per second.

The proper way to do this is to call the setitimer(2) function
that will send SIGALRM periodically to the process. It has been
discussed a long time ago:

  http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/130989

Still I cannot find a setitimer mapping in the Ruby interpreter.
So I wrote my own:

  http://bertram-scharpf.homelinux.com:8808/doc_root/itimer-1.0/rdoc/index.html

Bertram

···

Am Mittwoch, 09. Sep 2009, 01:38:33 +0900 schrieb Michael Tomer:

--
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-scharpf.de

4

Thanks, Paul. I feel better knowing that my first guess was right, even
though it initially struck me as wrong. I guess that'll teach me to
second guess myself.

···

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5

Took a shot with FFI:

require 'ffi'

module LibC
  extend FFI::Library

  class Timeval < FFI::Struct
    layout :tv_sec, :long,
           :tv_usec, :long
  end

  class Itimerval < FFI::Struct
    layout :it_interval, Timeval,
           :it_value, Timeval
  end

  attach_function :getitimer, [:int, :pointer], :int
  attach_function :setitimer, [:int, :pointer, :pointer], :int
end

Signal.trap("SIGALRM") do
  puts "SIGALRM: #{Time.now}"
end

tv = LibC::Timeval.new
tv[:tv_sec] = 2
tv[:tv_usec] = 0

puts Time.now
LibC::setitimer(0, tv, nil)
sleep 15
puts Time.now

#=>
# Wed Sep 09 02:57:18 +0000 2009
# SIGALRM: Wed Sep 09 02:57:20 +0000 2009
# SIGALRM: Wed Sep 09 02:57:22 +0000 2009
# SIGALRM: Wed Sep 09 02:57:24 +0000 2009
# SIGALRM: Wed Sep 09 02:57:26 +0000 2009
# SIGALRM: Wed Sep 09 02:57:28 +0000 2009
# SIGALRM: Wed Sep 09 02:57:30 +0000 2009
# SIGALRM: Wed Sep 09 02:57:32 +0000 2009
# SIGALRM: Wed Sep 09 02:57:33 +0000 2009
# Wed Sep 09 02:57:33 +0000 2009

···

On Tue, Sep 8, 2009 at 6:14 PM, Bertram Scharpf<lists@bertram-scharpf.de> wrote:

Am Mittwoch, 09. Sep 2009, 01:38:33 +0900 schrieb Michael Tomer:

I'm trying to write a loop that will only run a certain number of times
per second.

The proper way to do this is to call the setitimer(2) function
that will send SIGALRM periodically to the process. It has been
discussed a long time ago:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/130989

Still I cannot find a setitimer mapping in the Ruby interpreter.
So I wrote my own:

http://bertram-scharpf.homelinux.com:8808/doc_root/itimer-1.0/rdoc/index.html

6

How would one make use of this?

···

On Sep 8, 2:14 pm, Bertram Scharpf <li...@bertram-scharpf.de> wrote:

Hi,

Am Mittwoch, 09. Sep 2009, 01:38:33 +0900 schrieb Michael Tomer:

> I'm trying to write a loop that will only run a certain number of times
> per second.

The proper way to do this is to call the setitimer(2) function
that will send SIGALRM periodically to the process. It has been
discussed a long time ago:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/130989

Still I cannot find a setitimer mapping in the Ruby interpreter.
So I wrote my own:

http://bertram-scharpf.homelinux.com:8808/doc_root/itimer-1.0/rdoc/in\.\.\.

Bertram

--
Bertram Scharpf
Stuttgart, Deutschland/Germanyhttp://www.bertram-scharpf.de

7

Hi,

>
> > I'm trying to write a loop that will only run a certain number of times
> > per second.
>
> Still I cannot find a setitimer mapping in the Ruby interpreter.
> So I wrote my own:
>
> http://bertram-scharpf.homelinux.com:8808/doc_root/itimer-1.0/rdoc/in\.\.\.

How would one make use of this?

Argh. I wonder how that could happen. The link is of course:
  
  http://bertram-scharpf.homelinux.com:8808/doc_root/itimer-1.0/rdoc/index.html

Install the gem. You can also use this gem source:

  http://gems.bertram-scharpf.de

Then (untested)

  require "itimer"
  trap "SIGALRM" do puts Time.now end
  Process.setitimer 2

This puts out the time every two seconds.

Bertram

···

Am Mittwoch, 09. Sep 2009, 13:05:27 +0900 schrieb Mike Barsalou:

On Sep 8, 2:14 pm, Bertram Scharpf <li...@bertram-scharpf.de> wrote:
> Am Mittwoch, 09. Sep 2009, 01:38:33 +0900 schrieb Michael Tomer:

--
Bertram Scharpf
Stuttgart, Deutschland/Germany
http://www.bertram-scharpf.de

8

Wow, thanks for the SIGALRM binding. That should do quite nicely!

···

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