Evented Ruby, yo

Kalon Hinds

http://github.com/hkal

@_hkal

$('.btn').click(function() {
    $(this).remove();
});

In the beginning,

there were batch processing systems

• non-interactive jobs
• jobs could be stored and executed later
• once a job began it continued until completion or an error occurred

However, as systems became larger and more complex people realized that...

Structured Design

Edward Yourdon, Larry L. Constantine

"Design Patterns" → Object-oriented programming

"Structured Design" → Structured programming

Transaction Analysis

Transaction Center

• get transactions
• analyze each transaction to determine its type
• dispatch on type of transaction
• complete the processing of each transaction

loop do
    # wait for user input
    input = gets.chomp
    
    if input == "1"
        # do whatever pressing "1" does
    elsif input == "k"
        # do whatever pressing "k" does
    elsif input == "q"
        # clean-up and exit application
    else
        # raise exception for unhandled event type or ignore
    end
end

Yeah, that's right, pretty much everyone has written a transaction center

Let's modernize and simplify

• stream of data called events (transactions)
• a dispatcher (transaction center)
• a set of subroutines called event handlers

Event-driven Programming

• Application control flow is determined by events
• has an event loop and various event handlers

but, what are events anyway?

Events are...

a significant change in state

Shoes

• GUI toolkit
• a Ruby DSL built upon jruby and SWT
• Originally created by _why

Shoes.app(title: "See this? It's a shoes app") do
  # make GUI things in here
  # P.S... nobody knows shoes
end

Observer Pattern

• One object notifies a set of third-party objects
• One-to-many relationship
• Used in MVC
• Decouples models from views
• Model → Observerable; View  → Observer

Reactor Pattern

• Calls handlers upon events
• Allows events from multiple sources
• Single threaded process
• Non-block IO

Constraints

• Synchronous event dispatching
• Code must be written in a non-blocking manner

http://www.dre.vanderbilt.edu/~schmidt/PDF/reactor-siemens.pdf

http://www.cs.vu.nl/~eliens/online/oo/I/2/events.html

http://www.slideshare.net/autonomous/ruby-concurrency-and-eventmachine

http://en.wikipedia.org/wiki/Event-driven_programming

http://iweb.dl.sourceforge.net/project/eventdrivenpgm/ event_driven_programming.pdf