Celluloid Promise

A promise / deferred implementation for Celluloid inspired by AngularJS / Kris Kowal’s Q.

From the perspective of dealing with error handling, deferred and promise apis are to asynchronous programing what try, catch and throw keywords are to synchronous programming.

require 'rubygems'
require 'celluloid-promise'

def asyncGreet(name)
	deferred = Celluloid::Q.defer
	
	Thread.new do
		sleep 10
		deferred.resolve("Hello #{name}")
	end
	
	deferred.promise
end


asyncGreet('Robin Hood').then(proc { |greeting|
	p "Success: #{greeting}"
}, proc { |reason|
	p "Failed: #{reason}"
})

asyncGreet('The Dude').then do |greeting|
	p "Jeff '#{greeting}' Lebowski"
end

As that example is pretty terrible here is a decent write up on the uses for promises

1. Read the Documentation
2. Then gem install celluloid-promise

Celluloid provides a toolkit for building concurrent applications however coordinating complex chains of concurrent events can be difficult.
Celluloid-Promise provides the following:

• allows you to track a mash up of events across Actors
• guarantees serial execution of callbacks
• callback chains are spread across multiple threads
  • So multiple promise chains can be executed concurrently

Of course passing blocks around is a fairly dangerous exercise, so do the following and you’ll be safe

• use Celluloid-Promise for flow control
• resolve and reject promises with locally scoped variables
• call Actor methods to change state or instance variables