locky

locky.rb

coups = Coupon.all.sample
coups.lock! # no other users can read this coupon, they have to wait until the lock is released
coups.save! # lock is released, other users can now read this 


# Get a coupon
@coupon = Coupon.all.sample
@coupon.with_lock do
  @coupon.balance += 5
  @coupon.save!
end

# Try this
@coupon = Coupon.first
# Make the two processes, access the same instance
sleep 10
@coupon.with_lock do
  @coupon.balance += 5
  @coupon.save!
end

module Locky
  module_function

  def unsafe(coupon, val = 1)
    sleep 8
    puts coupon.balance
    sleep 2
    coupon.balance += val
    coupon.save!
    puts "Final: #{coupon.balance}"
  end

  def safe(coupon, val = 1)
    sleep 8
    coupon.with_lock do
      puts coupon.balance
      sleep 2
      coupon.balance += val
      coupon.save!
      puts "Final: #{coupon.balance}"
    end
  end
end