Proof of concept Redis cache, which blocks fiber if required on access

fiber_cache.rb

require 'eventmachine'
require 'em-hiredis'
require 'fiber'

class Cache
  include EM::Deferrable
  
  def initialize(key)
    $redis.get(key) { |v|
      @value = v
      succeed
    }
  end
  
  def value
    if @value
      puts "Returning cached value"
      @value
    else
      puts "Blocking the current fiber till result"
      start = Time.now
      f = Fiber.current
      callback {
        puts "Fiber blocked for #{Time.now - start}s"
        f.resume(@value)
      }
      return Fiber.yield
    end
  end
end

EM.run {
  $redis = EM::Hiredis.connect
  
  Fiber.new {
    $redis.set('foo', 'hello folks')
    
    c = Cache.new('foo')
    p c.value # Not populated yet - will block fiber
    
    EM.add_timer(1) {
      p c.value # Will return from cache
    }
  }.resume
}