From: Pit Capitain <pit@...>
Date: 2002-06-09T06:50:03+09:00
Subject: Re: 1-second events

On 8 Jun 2002, at 0:58, Dave Thomas wrote:

> Here's a version that corrects for the execution time of the body:
> 
>      def every(period)
>        base = last = Time.now.to_f
>        count = 0
> 
>        loop do
>          now = Time.now.to_f
>          actual_secs = now - base
>          expected_secs = period * count
>          correction = expected_secs - actual_secs
>          correction = -period if correction < -period
>          select(nil, nil, nil, period + correction)
>          now = Time.now
>          last = now.to_f
>          count += 1
>          yield(now)
>        end
>      end
> 
>      every(1.0) do |now|
>        puts "#{now.tv_sec}.#{now.tv_usec}"
> 
>        # the sleep below simuates doing some arbitrary amount of work
>        # that takes up to 1 second
> 
>        sleep(rand())
>      end
> 
You can get it even simpler with the original code and a method 
sleep_until:

def sleep_until( end_time )
  duration = end_time - Time.now
  sleep( duration ) if duration > 0
end

def periodically( seconds, *args )
  next_time = Time.now
  loop do
    sleeper = Thread.new { sleep_until( next_time += seconds )}
    yield( *args )
    sleeper.join
  end
end

periodically( 1.0 ) do
  puts "#{Time.now.tv_sec}.#{Time.now.tv_usec}"
  sleep( rand * 1.3 )
end


Just as Dave's code (I suppose), this should also handle work 
times longer than 1 second, as long as the average work time is 
less than one second. This is simulated by "rand * 1.3" in the code 
above and shown in the following sequence:

1023572512.226000
1023572513.217000
1023572514.219000
1023572515.220000
1023572516.222000
1023572517.453000  # work longer than a second
1023572518.515000  # work longer than a second
1023572519.216000  # back to normal
1023572520.217000
1023572521.219000
1023572522.220000
1023572523.222000
1023572524.223000
1023572525.225000
1023572526.226000
1023572527.217000
1023572528.259000  # work longer than a second
1023572529.220000  # back to normal
1023572530.222000
1023572531.223000

Regards,
Pit