ruby variable and blocks

gistfile1.rb

def pr(n)
  puts n
  sleep 1
  puts n
end

# outputs 1 2 1 2
a = 1
Thread.new{pr(a)}
sleep 0.2
a=2
Thread.new{pr(a)}
sleep 2

# outputs 1 2 2 2 because a is shared between blocks / threads
a = 1
Thread.new{puts a; sleep 1; puts a}
sleep 0.2
a=2
Thread.new{puts a; sleep 1; puts a}
sleep 2