h1. Celluloid Promise

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A promise / deferred implementation for Celluloid inspired by "AngularJS":http://docs.angularjs.org/api/ng.$q / "Kris Kowal's Q.":https://github.com/kriskowal/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":http://blog.jcoglan.com/2013/03/30/callbacks-are-imperative-promises-are-functional-nodes-biggest-missed-opportunity/

h2. Start using it now

Read the "Documentation":http://rubydoc.info/gems/celluloid-promise/Celluloid/Promise

Then @gem install celluloid-promise@

h2. Use case

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":https://github.com/celluloid/celluloid/wiki/Blocks#proposal-for-fixing-blocks, 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