thread safety

thread-save.rb

class Inventory
  def initialize(stock_levels)
    @stock = stock_levels
  end

  def decrease(item)
    @stock[item] -= 1
  end

  def [](item)
    @stock[item]
  end
end


#4000.times do
#  inventory.decrease(:hats)
#end
#
#puts inventory[:hats]

inventory = Inventory.new(:hats => 4000)
threads = Array.new
40.times do
  threads << Thread.new do
    100.times do
      inventory.decrease(:hats)
    end
  end
end
threads.each(&:join)
puts inventory[:hats]


inventory = Inventory.new(:hats => 4000)
threads = Array.new
lock = Mutex.new

400.times do
  threads << Thread.new do
    lock.synchronize do
      10.times do
        inventory.decrease(:hats)
      end
    end
  end
end
threads.each(&:join)
puts inventory[:hats]