Concurrent "Hello, world" with Celluloid, an actor library for Ruby

1_Note.md

The premise of this exercise is contained in Daniel Himelein's quote:

"The first thing I always do when playing around with a new software platform is to write a concurrent "Hello World" program. The program works as follows: One active entity (e.g. thread, Erlang process, Goroutine) has to print "Hello " and another one "World!\n" with the two active entities synchronizing with each other so that the output always is "Hello World!\n". Here is the concurrent Hello World program in Go, Erlang and in C++ using the Mindroid framework."

Original post

Here is a Hello World example in Ruby/Celluloid. Five, actually.

base.rb

require 'celluloid'                                                                                                                                         
                                                                                                                                                            
class Greeter                                                                                                                                               
                                                                                                                                                            
  def initialize(msg)                                                                                                                                       
    @msg = msg                                                                                                                                              
  end                                                                                                                                                       
                                                                                                                                                            
  def greet                                                                                                                                                 
    @msg                                                                                                                                                    
  end                                                                                                                                                       
end                                                                                                                                                         
                                                                                                                                                            
class Hello < Greeter                                                                                                                                       
  include Celluloid                                                                                                                                         
end                                                                                                                                                         
                                                                                                                                                            
class World < Greeter                                                                                                                                       
  include Celluloid                                                                                                                                         
                                                                                                                                                            
  def initialize(msg)                                                                                                                                       
    super                                                                                                                                                   
    wait_for_hello!                                                                                                                                         
  end                                                                                                                                                       
                                                                                                                                                            
  def wait_for_hello                                                                                                                                        
    loop do                                                                                                                                                 
      receive { |msg| puts "#{msg} #{greet}" }                                                                                                              
    end                                                                                                                                                     
  end                                                                                                                                                       
                                                                                                                                                            
end                           

example_1.rb

                                                                                                                                                
hello = Hello.new "hello"                                                                                                                                                            
world = World.new "world"                                                                                                                                                           
                                                                                                                                                                              
100.times do               
  world.mailbox << hello.greet                                                                                                                                            
end                                                                                                                                                                           
                                                                                                                                                                              

example_2.rb

hello = Hello.new "hello"                                                                                                                                                            
world = World.new "world"                                                                                                                                                           
                                                                                                                                                                                                                
futures = []                                                                                                                                                                                                    
100.times do                                                                                                                                                                                                    
  futures << hello.future.greet                                                                                                                                                                             
end                                                                                                                                                                                                             
futures.each { |future| world.mailbox << future.value }                                                                                                                                                         
                                                                                                                                                                                                                
sleep 1                                                                                                                                                                                                         
exit                                                                                                                                                                                                            
                                                                                                                                                                                                                

example_3.rb

hello = Hello.new "hello"                                                                                                                                                            
world = World.new "world"                                                                                                                                                           
                                                                                                                                                                                                                       
futures = []                                                                                                                                                                                                           
100.times do                                                                                                                                                                                                           
  futures << Celluloid::Future.new { world.mailbox << hello.greet }                                                                                                                                                
end                                                                                                                                                                                                                    
futures.each { |future| future.value } 

example_4.rb

                                                                                                                                                                         
class Runner                                                                                                                                                                                                           
  include Celluloid                                                                                                                                                                                                    
  def initialize                                                                                                                                                                                                       
    @hello = Actor[:hello]                                                                                                                                                                                             
    @world = Actor[:world]                                                                                                                                                                                             
    run!                                                                                                                                                                                                               
  end                                                                                                                                                                                                                  
                                                                                                                                                                                                                       
  def run                                                                                                                                                                                                              
    futures = []                                                                                                                                                                                                       
    100.times do                                                                                                                                                                                                       
      futures << @hello.future.greet                                                                                                                                                                               
    end                                                                                                                                                                                                                
    futures.each { |future| @world.mailbox << future.value }                                                                                                                                                           
 end                                                                                                                                                                                                                   
                                                                                                                                                                                                                       
end                                                                                                                                                                                                                    
                                                                                                                                                                                                                       
class MyGroup < Celluloid::SupervisionGroup                                                                                                                                                                            
  supervise Hello, :as => :hello, :args => ["hello"]                                                                                                                                                                                       
  supervise World, :as => :world, :args => ["world"]                                                                                                                                                                                       
  supervise Runner                                                                                                                                                                                                     
end                                                                                                                                                                                                                    
                                                                                                                                                                                                                       
MyGroup.run!                                                                                                                                                                                                           
sleep 1                                                                                                                                                                                                                
exit                                                                                                                                                                                                                   
                                                                                                                                                                                                                       

example_5.rb

## if we change the Hello greeter to this

class Hello < Greeter                                                                                                                                                             
  include Celluloid                                                                                                                                                               
                                                                                                                                                                                  
  def initialize(msg)                                                                                                                                                             
    super                                                                                                                                                                         
    @world = Actor[:world]                                                                                                                                                        
  end                                                                                                                                                                             
  def sync                                                                                                                                                                        
     @world.mailbox << greet                                                                                                                                                      
  end                                                                                                                                                                             
                                                                                                                                                                                  
end        
## We can then write this:

world = World.new "world"                                                                                                                                                         
Celluloid::Actor[:world] = world                                                                                                                                                  
hello = Hello.new "hello"                                                                                                                                                         
100.times do                                                                                                                                                                      
  hello.async.sync                                                                                                                                                                
end