Ruby's sleep is not very accurate and Eventmachine's timer is also not very good. So, If you need to process one periodic job with some interval, this approach might be helpful. There is a compensation for sleep and you just need to define your process.

Ruby - Periodic Process

class Service  
   def initialize  
     @interval = 1.0  
     @start_time = Time.now   
   end  
   def start   
     # Update the start-time  
     @start_time = Time.now   
     # run loop  
     loop do  
       t_start = Time.now  
       # process the job  
       process  
       elapsed = Time.now - t_start  
       if elapsed > @interval  
         puts "Error: Job is bigger than Interval.. #{elapsed}"  
       end  
       # apply some compensation.   
       compensation = (Time.now - @start_time) % @interval  
       sleep (@interval - compensation)  
     end  
   end  
   def process  
     raise NotImplementedError  
   end  
 end


And then, define your jobs in process method. 

 class MyService < Service   
   def initialize  
     super  
     @interval = 2.0  
   end  
   def process  
     puts "time: #{Time.now.to_f.round(3)}"  
     # do the random job .. it takes upto 1.5 seconds.   
     sleep rand(150) * 0.01  
   end  
 end  

Try to run it.. 

 service = MyService.new  
 service.start  

And you will get a very accurate intervals

time: 1298615010.271  
time: 1298615011.271  
time: 1298615012.271  
time: 1298615013.271  
time: 1298615014.271  
time: 1298615015.271  
time: 1298615016.271  
time: 1298615017.271  
time: 1298615018.271  
time: 1298615019.271  
time: 1298615020.271  
time: 1298615021.271  
time: 1298615022.271  
time: 1298615023.271  
time: 1298615024.271  
time: 1298615025.271  
time: 1298615026.271  
time: 1298615027.271


http://soohwan.blogspot.com/2011/02/ruby-periodic-process.html